Rp 581 Inspection Effectiveness

DATE: 2-20-2012

API RP 581 Committee Meeting

API Ballot Proposal: Removal of most of the language and all of the tables regarding inspection effectiveness from the main body of Part 1 and Part 2 of API RP 581. Reassembly of this information in a new annex of Part 2 that will discuss inspection effectiveness and provide the tables per API RBI damage mechanism as examples for the user to adapt and adopt to their specific knowledge and skills. Technical Basis: This will provide a good platform that emphasizes the user responsibility to understand and apply RBI principles. In particular, it will consider: a) b) c) d)

Philosophy behind the new tables and how to use them; Owner-User responsibility of adoption/adaptation; Methodology to account for confidence in inspection Application to PoF

Proposed By: API RBI Software User Group: Inspection Effectiveness Review Sub-Committee

API RP 581 RISK-BASED INSPECTION TECHNOLOGY

PART 1 INSPECTION PLANNING USING API RBI TECHNOLOGY

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API RP 581 RISK-BASED INSPECTION TECHNOLOGY

PART CONTENTS 1 2 3 4

5

6

7

8

SCOPE ........................................................................................................................................... 4 REFERENCES ............................................................................................................................... 4 DEFINITIONS ................................................................................................................................. 4 API RBI CONCEPTS ..................................................................................................................... 4 4.1 Probability of Failure ............................................................................................................ 4 4.2 Consequence of Failure ....................................................................................................... 4 4.3 Risk Analysis ........................................................................................................................ 4 4.4 Inspection Planning Based on Risk Analysis .................................................................... 4 4.4.1 Overview ........................................................................................................................ 4 4.4.2 Risk Target .................................................................................................................... 4 4.4.3 Inspection Effectiveness – The Value of Inspection ................................................. 4 4.4.4 Inspection Effectiveness – Example ........................................................................... 5 4.4.5 Inspection Planning ...................................................................................................... 5 4.5 Nomenclature ........................................................................................................................ 6 4.6 Tables..................................................................................................................................... 6 4.7 Figures ................................................................................................................................... 7 PRESSURE VESSELS AND PIPING ............................................................................................ 8 5.1 Probability of Failure ............................................................................................................ 8 5.2 Consequence of Failure ....................................................................................................... 8 5.3 Risk Analysis ........................................................................................................................ 8 5.4 Inspection Planning Based on Risk Analysis .................................................................... 8 ATMOSPHERIC STORAGE TANKS ............................................................................................. 9 6.1 Probability of Failure ............................................................................................................ 9 6.2 Consequence of Failure ....................................................................................................... 9 6.3 Risk Analysis ........................................................................................................................ 9 6.4 Inspection Planning Based on Risk Analysis .................................................................... 9 PRESSURE RELIEF DEVICES ................................................................................................... 10 7.1 General................................................................................................................................. 10 7.2 Probability of Failure .......................................................................................................... 10 7.2.1 Definition ..................................................................................................................... 10 7.2.2 Calculation of Probability of Failure to Open .......................................................... 10 7.2.3 PRD Demand Rate ...................................................................................................... 10 7.2.4 PRD Probability of Failure on Demand ..................................................................... 10 7.2.5 Protected Equipment Failure Frequency as a Function of Overpressure ............ 11 7.2.6 Calculation Procedure ................................................................................................ 11 7.2.7 Overview ...................................................................................................................... 11 7.2.8 Calculation of Probability of Leakage....................................................................... 11 7.2.9 Calculation Procedure ................................................................................................ 11 7.3 Consequence of PRD Failure to Open .............................................................................. 11 7.4 Consequence of Leakage .................................................................................................. 11 7.5 Risk Analysis ...................................................................................................................... 11 7.6 Inspection Planning Based on Risk Analysis .................................................................. 11 7.7 Nomenclature ...................................................................................................................... 11 7.8 Tables................................................................................................................................... 12 7.9 Figures ................................................................................................................................. 12 HEAT EXCHANGER TUBE BUNDLES ...................................................................................... 13 8.1 General................................................................................................................................. 13 8.2 Methodology Overview ...................................................................................................... 13 8.3 Probability of Failure .......................................................................................................... 13 8.4 Consequence of Failure ..................................................................................................... 13 8.5 Risk Analysis ...................................................................................................................... 13 8.6 Inspection Planning Based on Risk Analysis .................................................................. 13 8.6.1 Use of Risk Target in Inspection Planning ............................................................... 13 8.6.2 Example ....................................................................................................................... 13

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API RP 581 RISK-BASED INSPECTION TECHNOLOGY

8.6.3 Inspection Planning Without Inspection History (First Inspection Date) ............. 13 8.6.4 Inspection Planning with Inspection History ........................................................... 13 8.6.5 Effects of Bundle Life Extension Efforts .................................................................. 14 8.6.6 Future Inspection Recommendation ........................................................................ 14 8.7 Bundle Inspect/Replacement Decisions using Cost Benefit Analysis ......................... 14 8.8 Nomenclature ...................................................................................................................... 14 8.9 Tables................................................................................................................................... 14

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1

SCOPE

2

REFERENCES

3

DEFINITIONS

4

API RBI CONCEPTS

4.1

Probability of Failure

4.2

Consequence of Failure

4.3

Risk Analysis

4.4

Inspection Planning Based on Risk Analysis

4.4.1

Overview

4.4.2

Risk Target

4.4.3 Inspection Effectiveness – The Value of Inspection An estimate of the probability of failure for a component is dependent on how well the independent variables of the limit state are known [10]. Using guidelines for inspection effectiveness given in API RBI, Part 2, Annex B.2 aIn the models used for calculating the probability of failure, the flaw size (e.g. metal loss for thinning or crack size for environmental cracking) may have significant uncertainty especially when these parameters need to be projected into the future. An inspection program may be implemented in order to obtain a better estimate of the damage rate and associated flaw size. An inspection program is the combination of NDE methods (i.e. visual, ultrasonic, radiographic etc.), frequency of inspection, and the location and coverage of an inspection in order to find a specific or set of damage mechanisms. Inspection programs vary in their effectiveness for locating and sizing damage, and thus for determining damage rates. Once the likely damage mechanisms have been identified, the inspection program should must be evaluated in order to determine the effectiveness in finding the identified mechanisms. The effectiveness of an inspection program may be limited by: a) Lack of coverage of an area subject to deterioration, b) Inherent limitations of some inspection methods to detect and quantify certain types of deterioration, c) Selection of inappropriate inspection methods and tools, d) Application of methods and tools by inadequately trained inspection personnel, e) Inadequate inspection procedures, f) The damage rate under some conditions (e.g. start-up, shut-down, or process upsets) may increase the likelihood or probability that failure may occur within a very short time; even if damage is not found during an inspection, failure may still occur as a result of a change or upset in conditions, g) Inaccurate analysis of results leading to inaccurate trending of individual components, (problem with a statistical approach to trending), and h) Probability of detection of the applied NDE technique for a given component type, metallurgy, temperature and geometry . It is important to evaluate the benefits of multiple inspections and to also recognize that the most recent inspection may best reflect the current state of the component under the current operating conditions. If the operating conditions have changed, damage rates based on inspection data from the previous operating conditions may not be valid. Determination of inspection effectiveness should consider the following: a) Equipment or component type,

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API RP 581 RISK-BASED INSPECTION TECHNOLOGY

a) Active and credible damage mechanism(s), b) Susceptibility to and rate of damage, c) NDE methods, coverage and frequency, and d) Accessibility to expected deterioration areas. Inspection effectiveness may be introduced into the probability of failure calculation by using Bayesian analysis or more directly by modifying the model for the independent variables, the distribution function, and/or the distribution function parameters. For example, if the model for metal loss is determined to be a lognormal distribution, the distribution parameters, mean and coefficient of variation, may be changed based on the NDE method and coverage used during an inspection. Extending this concept further, a series of standard inspection categories may be defined, and the distribution parameters adjusted based on the NDE method and coverage defined for each standard category. In API RBI, examples of the inspection effectiveness categories for various damage mechanisms and the associated inspections recommended (i.e. NDE technique and coverage) for each damage mechanism are provided in Part 2, Annex 2.C. These are provided as examples to the user and represent minimally acceptable inspections per damage mechanism, corresponding to various inspection effectiveness ratings. The user should adopt and modify similar tables according to specific risk management plans and experience-based inspection programs. In addition, the rules for combining the benefits of multiple inspections are also provided in Part 2. By identifying credible damage mechanisms, determining the damage rate, and selecting an inspection effectiveness category based on a defined level of inspection, a probability of failure and associated risk may be determined using Equations (1.8) or (1.9). The probability of failure and risk may be determined using these equations for future time periods or conditions as well as current conditions by projecting the damage rate and associated flaw size into the futurean inspection program will become more effective. 4.4.4 Inspection Effectiveness – Example In API RBI, the inspection effectiveness is graded A through E, with an A inspection providing the most effective inspection available (90% effective) and E representing no inspection. A description of the inspection effective levels for general thinning damage is provided in Part 2, Table 5.5. To illustrate the method in which different inspection levels effect the damage factor and probability of failure, consider the example of the general thinning damage mechanism (procedures for modifying damage factors based on inspection effectiveness are provided in API 581 for all damage mechanisms). For general thinning, API RBI utilizes an approach based on a metal loss parameter, Art . The damage factor is calculated as a function of this parameter and is based on the premise that as a pressure vessel or piping wall corrodes below the construction Code minimum wall thickness plus the specified corrosion allowance, the damage factor will increase. An inspection program for general thinning will result in a reduction of the damage factor based on the effectiveness of the inspection to quantify the corrosion rate. As an example, the general thinning damage factor,

D thin f , for a component with an Art equal to 0.5 is 1200 if there is no inspection (i.e. Inspection

Effectiveness is E) as shown in Part 2, Table 5.5. If a B level inspection is performed, the damage factor is reduced to 600. If two B level inspections have been completed, the damage factor is further reduced to 200. When these damage factors are substituted into Equation (1.1), it becomes apparent that an effective inspection program can reduce the probability of failure of a component and the risk of loss of containment. 4.4.54.4.4 Inspection Planning In planning inspections using API RBI, a plan date is typically chosen far enough out into the future to include a time period covering one or several future maintenance turnarounds. Within this period, three cases are possible based on predicted risk and the specified risk target. a) Case 1 – Risk target is exceeded at a point in the future prior to the inspection plan date – This is the classical case and is represented in Figure 4.3. In this case, the results of an inspection plan will be the number of inspections required, as well as the type or inspection effectiveness required, to reduce the risk at the future plan date down below the risk target. The target date is the date where the risk target is expected to be reached and is the date of the recommended inspection.

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b)

Case 2 – Risk already exceeds the risk target at the time the RBI analysis is performed – This case is shown in Figure 4.4 and indicates that the current risk at the time of the RBI analysis exceeds the risk target. An immediate inspection will be recommended at a level sufficient to reduce the risk at the future plan date down below the risk target. c) Case 3 – Risk at the future plan date does not exceed the risk target – This case is shown in Figure 4.5 and indicates that the predicted future risk at the plan date will not exceed the risk target and therefore, no inspection is recommended during the plan period. In this case, the inspection due date for inspection scheduling purposes should be adjusted to the plan date indicating that an evaluation of the equipment for Inspection or re-analysis of risk should be performed by the plan end date. The concept of how the different inspection techniques with different effectiveness levels can reduce risk is shown in Figure 4.3. In the example shown, a B Level inspection was recommended at the target date. This inspection level was sufficient since the risk predicted after the inspection was performed was determined to be below the risk target at the plan date. Note that in Figure 4.3, a D Level inspection at the target date would not have been sufficient to satisfy the risk target criteria. The projected risk at the plan date would have exceeded the risk target. 4.5

Nomenclature

4.6

Tables

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4.7

Figures

Risk

Total Risk without Inspection at the Risk Target Date D Risk Target C

B

Total Risk with Inspection at the Risk Target Date

A

time Installation Date

RBI Date

Target Date, Inspection Performed

Plan Date

Figure 4.3 – Case 1: Inspection Planning When the Risk Target is Exceeded Between the RBI Date and the Plan Date and the Impact of Inspection at Various Levels of Effectiveness

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API RP 581 RISK-BASED INSPECTION TECHNOLOGY

5

PRESSURE VESSELS AND PIPING

5.1

Probability of Failure

5.2

Consequence of Failure

5.3

Risk Analysis

5.4 Inspection Planning Based on Risk Analysis The procedure to determine an inspection plan is provided in paragraph 4.4 and is supplemented by Annex 2.C. This procedure may be used to determine both the time and type of inspection to be performed based on the process fluid and design conditions, component type and materials of construction, and the active damage mechanisms.

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API RP 581 RISK-BASED INSPECTION TECHNOLOGY

6

ATMOSPHERIC STORAGE TANKS

6.1

Probability of Failure

6.2

Consequence of Failure

6.3

Risk Analysis

6.4 Inspection Planning Based on Risk Analysis The procedure to determine an inspection plan is provided in paragraph 4.4 and is supplemented by Annex 2.C. This procedure may be used to determine both the time and type of inspection to be performed based on the process fluid and design conditions, component type and materials of construction, and the active damage mechanisms.

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API RP 581 RISK-BASED INSPECTION TECHNOLOGY

7

PRESSURE RELIEF DEVICES

7.1

General

7.2

Probability of Failure

7.2.1

Definition

7.2.2

Calculation of Probability of Failure to Open

7.2.3

PRD Demand Rate

7.2.4 PRD Probability of Failure on Demand a) General b) Categories of Service Severity c) Default Probability of Failure on Demand vs Time in Service d) Default Data for Balanced Bellows Pressure Relief Valves e) Default Weibull Parameters for Pilot-Operated Pressure Relief Valves f) Default Weibull Parameters for Rupture Disks g) Adjustment for Conventional PRVs Discharging to Closed System h) Adjustment for Overpressures Higher than Set Pressure i) Adjustment for Environmental Factors j) Presence of an Upstream Rupture Disk k) Use of Plant Specific Failure Data l) Modification of Failure on Demand Based on PRD Specific Testing Data 1) Tracking Historical Inspection and Testing Data 2) Determine the Effectiveness of Inspection Programs in Confirming Failure Rates Inspection programs vary in their effectiveness for determining failure rates. The definitions for inspection effectiveness used by API RBI are provided in Table 7.7. The inspection’s effectiveness is based on the inspection’s ability to adequately predict the failure (or pass) state of the PRD being inspected. Limitations in the ability of a program to improve confidence in the failure rate result from the inability of some test methods to detect and quantify damage.For pressure relief devices, Aan inspection and testing program should track the effectiveness of the inspection and the testing performed for each pressure relief device. The concept of inspection effectiveness is similar to the concept that is described in paragraph 4.4.3 Annex 2.C of this document for fixed equipment. With For inspection effectiveness for pressure relief devices, a measure of confidence in the Pass/Fail/Leak result of the inspection effort is obtainedutilized. For a full discussion of inspection effectiveness as related to pressure relief devices, refer to Annex 2.C. Default confidence values, based on expert opinion, are provided in Table 7.8, indicating the level of confidence each of the three levels of inspection effectiveness will accurately represent actual PRD performance in an overpressure demand case. For example, the 90% effectiveness associated with passing a “highly effective” bench test means that there is a 90% probability the valve would have opened upon demand in its installed service. Therefore, it also carries a 10% probability that the PRD would have failed upon demand during operation. The values shown in Table 7.8 are called conditional probabilities. The conditional probabilities listed reflect the confidence that an inspection result will predict the device’s performance upon demand. For passing PRDs, the highest confidence is assigned when the PRD is bench tested without any prior cleaning (i.e. as-received condition.) Bench testing where the devices are cleaned prior to testing, in-situ testing, and visual inspections provide some information about PRD performance, but are not considered as reliable as the as-received bench test.

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API RP 581 RISK-BASED INSPECTION TECHNOLOGY

The philosophy is different for PRDs that fail an inspection. In the case of a “highly effective” bench test failure, the 95% confidence translates to a 95% chance that the PRD would have failed upon demand in actual service. Unlike the passing test case, the “usually effective” in-situ test, or bench test where the valve has been steamed out prior to testing, is assumed to have the same 95% confidence for failure upon demand in actual service. An ineffective test does not provide any information to predict PRD performance upon demand and therefore the PRD does not receive any credit for the test/inspection date. The inspection still will get some credit if an overhaul was performed in that the valve is assumed to be returned to service in likenew condition, and the in-service duration is calculated from the ineffective inspection date. 3) Inspection Updating 4) Example – Bayesian Updating Calculation 5) Updating Failure Rates after Modification to the Design of the PRD 7.2.5

Protected Equipment Failure Frequency as a Function of Overpressure

7.2.6

Calculation Procedure

7.2.7

Overview

7.2.8

Calculation of Probability of Leakage

7.2.9

Calculation Procedure

7.3

Consequence of PRD Failure to Open

7.4

Consequence of Leakage

7.5

Risk Analysis

7.6

Inspection Planning Based on Risk Analysis

7.7

Nomenclature

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API RP 581 RISK-BASED INSPECTION TECHNOLOGY

7.8

Tables

Table 7.7 – Inspection and Testing Effectiveness Inspection Effectiveness

Highly Effective

Component Type

Pressure Relief Device

A Rupture Disk

Usually Effective

Description of Inspection A bench test has been performed on the PRV in the asreceived condition from the unit and the initial leak pressure, opening pressure and the reseat pressure has been documented on the test form. The inlet and outlet piping has been examined for signs of excessive plugging or fouling. None Available. •

A bench test has been performed, however, the PRD was cleaned or steamed out prior to the bench test. Additionally, a visual inspection has been performed where detailed documentation of the condition of the PRD internal components was made.

•

An in-situ test has been performed using the actual process fluid to pressurize the system.

Pressure Relief Device

B

Rupture Disk

Pressure Relief Device Fairly Effective C

Rupture Disk

Ineffective

Pressure Relief Device

D

Rupture Disk

The rupture disk is removed and visually inspected for damage or deformations. •

A visual inspection has been performed without a pop test, where detailed documentation of the condition of the PRD internal components was made.

•

A trevitest or in-situ test has been performed where the actual process fluid was not used to pressurize the system.

The space between the disk and the PRV is monitored for leakage in accordance with the ASME Code and API RP 520 Part 2. No pop test was conducted. No details of the internal component were documented.

7.97.8 Figures

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API RP 581 RISK-BASED INSPECTION TECHNOLOGY

8

HEAT EXCHANGER TUBE BUNDLES

8.1

General

8.2

Methodology Overview

8.3

Probability of Failure

8.4

Consequence of Failure

8.5

Risk Analysis

8.6

Inspection Planning Based on Risk Analysis

8.6.1

Use of Risk Target in Inspection Planning

8.6.2

Example

8.6.3

Inspection Planning Without Inspection History (First Inspection Date)

8.6.4

Inspection Planning with Inspection History

a)

b)

Effect of Inspection on Probability of Failure The information gained from an inspection of the tube bundle can be used to assess the actual condition of the bundle and to make adjustments to the probability of failure rate curves as necessary. An inspection provides two things: 1) Reduction in uncertainty due to the effectiveness of the inspection resulting in the use of a more accurate failure rate curve, e.g. moving from a 50% AU curve (no inspection history) to a curve 20% AU curve (Usually Effective Inspection), see paragraph 8.6.4.b for a discussion of inspection effectiveness. 2) Knowledge of the true condition of the bundle. This can result in a shift of the failure rate curve to the right or to the left. The current condition of the bundle could either be quantified by remaining wall thickness data or by an estimate of the remaining life that comes directly from an actual inspection, see paragraph 8.6.4.c. Reduction in Uncertainty Due to Inspection Effectiveness If the tube bundle has been inspected, the uncertainty is reduced (probability of failure curve moves to the right) and the probability of failure at any time decreases. In this way, the API RBI methodology allows inspection knowledge to reduce probability of failure and the calculated risk. At this point the concept of inspection effectiveness is introduced, similar to the methodology used in other modules of API RBI. Table 8.5 provides the recommended default values for the uncertainty applied to the failure rate curve as a function of inspection effectiveness. As improved inspection techniques are used, the amount of uncertainty decreases and the Weibull plot shifts to the right. Using this concept will result in more rigorous inspection techniques being implemented as the bundle reaches end of life. In the example bundle problem, the impact of more rigorous inspection techniques can be seen by evaluating the predicted duration as a function of inspection effectiveness in Table 8.5. The discussion of inspection effectiveness is continued in Annex 2.C.

c) d) e)

Shift of POF Curve Due to Knowledge of True Bundle Condition Predicted Future Failure Date Based on Estimated Remaining Life Adjustment to Failure Rate Curve Based on Actual Condition of Bundle

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8.6.5

Effects of Bundle Life Extension Efforts

8.6.6

Future Inspection Recommendation

8.7

Bundle Inspect/Replacement Decisions using Cost Benefit Analysis

8.8

Nomenclature

8.9

Tables Table 8.1 – Basic Data for Exchanger Bundle Risk Analysis Inspection Effectiveness

A, B, C, D or E per Table 8.5

No

Table 8.5 – Inspection Effectiveness and Uncertainty Inspection Effectiveness

Inspection Cost ($)

Uncertainty (%)

E – Ineffective

0

50

D – Usually Not Effective

1,000

30

C –Moderately Effective

2,000

20

B – Usually Effective

3,000

10

A – Highly Effective

5,000

5

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PART 2 DETERMINATION OF PROBABILITY OF FAILURE IN AN API RBI ASSESSMENT

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1 2 3 4

5

6 7

8

PART CONTENTS SCOPE ........................................................................................................................................... 8 REFERENCES ............................................................................................................................... 8 DEFINTIONS .................................................................................................................................. 8 PROBABILITY OF FAILURE CALCULATIONS ........................................................................... 8 4.1 Overview ................................................................................................................................ 8 4.2 Calculation of Probability of Failure ................................................................................... 8 4.3 Generic Failure Frequency .................................................................................................. 8 4.4 Damage Factor ...................................................................................................................... 8 4.4.1 Overview ........................................................................................................................ 8 4.4.2 Damage Factor Combination for Multiple Damage Mechanisms ............................ 8 4.4.3 Inspection Effectiveness Category ............................................................................. 8 4.5 Management Systems Factor .............................................................................................. 8 4.5.1 General ........................................................................................................................... 8 4.5.2 Overview ........................................................................................................................ 8 4.5.3 Auditing Technique ...................................................................................................... 8 4.5.4 Calculation of the Management Systems Factor ....................................................... 8 4.6 Nomenclature ........................................................................................................................ 8 4.7 Tables..................................................................................................................................... 9 THINNING DAMAGE FACTOR ................................................................................................... 10 5.1 Scope ................................................................................................................................... 10 5.2 Screening Criteria ............................................................................................................... 10 5.3 Required Data ..................................................................................................................... 10 5.4 Basic Assumptions ............................................................................................................ 10 5.5 Determination of the Damage Factor ................................................................................ 10 5.5.1 Overview ...................................................................................................................... 10 5.5.2 Inspection Effectiveness ............................................................................................ 10 5.5.3 Calculation of the Damage Factor ............................................................................. 10 5.6 Nomenclature ...................................................................................................................... 10 5.7 Tables................................................................................................................................... 10 COMPONENT LINING DAMAGE FACTOR ................................................................................ 15 SCC DAMAGE FACTOR – CAUSTIC CRACKING .................................................................... 16 7.1 Scope ................................................................................................................................... 16 7.2 Description of Damage....................................................................................................... 16 7.3 Screening Criteria ............................................................................................................... 16 7.4 Required Data ..................................................................................................................... 16 7.5 Basic Assumptions ............................................................................................................ 16 7.6 Determination of the Damage Factor ................................................................................ 16 7.6.1 Overview ...................................................................................................................... 16 7.6.2 Inspection Effectiveness ............................................................................................ 16 7.6.3 Calculation of the Damage Factor ............................................................................. 16 7.7 Nomenclature ...................................................................................................................... 16 7.8 References .......................................................................................................................... 16 7.9 Tables................................................................................................................................... 16 SCC DAMAGE FACTOR – AMINE CRACKING ......................................................................... 18 8.1 Scope ................................................................................................................................... 18 8.2 Description of Damage....................................................................................................... 18 8.3 Screening Criteria ............................................................................................................... 18 8.4 Required Data ..................................................................................................................... 18 8.5 Basic Assumptions ............................................................................................................ 18 8.6 Determination of the Damage Factor ................................................................................ 18 8.6.1 Overview ...................................................................................................................... 18 8.6.2 Inspection Effectiveness ............................................................................................ 18 8.6.3 Calculation of the Damage Factor ............................................................................. 18

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9

10

11

12

13

8.7 Nomenclature ...................................................................................................................... 18 8.8 References .......................................................................................................................... 18 8.9 Tables................................................................................................................................... 18 SCC DAMAGE FACTOR – SULFIDE STRESS CRACKING ..................................................... 20 9.1 Scope ................................................................................................................................... 20 9.2 Description of Damage....................................................................................................... 20 9.3 Screening Criteria ............................................................................................................... 20 9.4 Required Data ..................................................................................................................... 20 9.5 Basic Assumptions ............................................................................................................ 20 9.6 Determination of the Damage Factor ................................................................................ 20 9.6.1 Overview ...................................................................................................................... 20 9.6.2 Inspection Effectiveness ............................................................................................ 20 9.6.3 Calculation of the Damage Factor ............................................................................. 20 9.7 Nomenclature ...................................................................................................................... 20 9.8 References .......................................................................................................................... 20 9.9 Tables................................................................................................................................... 20 SCC DAMAGE FACTOR – HIC/SOHIC-H 2 S .............................................................................. 22 10.1 Scope ................................................................................................................................... 22 10.2 Description of Damage....................................................................................................... 22 10.3 Screening Criteria ............................................................................................................... 22 10.4 Required Data ..................................................................................................................... 22 10.5 Basic Assumptions ............................................................................................................ 22 10.6 Determination of the Damage Factor ................................................................................ 22 10.6.1 Overview ...................................................................................................................... 22 10.6.2 Inspection Effectiveness ............................................................................................ 22 10.6.3 Calculation of the Damage Factor ............................................................................. 22 10.7 Nomenclature ...................................................................................................................... 22 10.8 References .......................................................................................................................... 22 10.9 Tables................................................................................................................................... 22 SCC DAMAGE FACTOR – CARBONATE CRACKING ............................................................. 24 11.1 Scope ................................................................................................................................... 24 11.2 Description of Damage....................................................................................................... 24 11.3 Screening Criteria ............................................................................................................... 24 11.4 Required Data ..................................................................................................................... 24 11.5 Basic Assumptions ............................................................................................................ 24 11.6 Determination of the Damage Factor ................................................................................ 24 11.6.1 Overview ...................................................................................................................... 24 11.6.2 Inspection Effectiveness ............................................................................................ 24 11.6.3 Calculation of the Damage Factor ............................................................................. 24 11.7 Nomenclature ...................................................................................................................... 24 11.8 References .......................................................................................................................... 24 11.9 Tables................................................................................................................................... 24 SCC DAMAGE FACTOR – PTA CRACKING ............................................................................. 26 12.1 Scope ................................................................................................................................... 26 12.2 Description of Damage....................................................................................................... 26 12.3 Screening Criteria ............................................................................................................... 26 12.4 Required Data ..................................................................................................................... 26 12.5 Basic Assumptions ............................................................................................................ 26 12.6 Determination of the Damage Factor ................................................................................ 26 12.6.1 Overview ...................................................................................................................... 26 12.6.2 Inspection Effectiveness ............................................................................................ 26 12.6.3 Calculation of the Damage Factor ............................................................................. 26 12.7 Nomenclature ...................................................................................................................... 26 12.8 References .......................................................................................................................... 26 12.9 Tables................................................................................................................................... 26 SCC DAMAGE FACTOR – CLSCC ............................................................................................ 28

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14

15

16

17

13.1 Scope ................................................................................................................................... 28 13.2 Description of Damage....................................................................................................... 28 13.3 Screening Criteria ............................................................................................................... 28 13.4 Required Data ..................................................................................................................... 28 13.5 Basic Assumptions ............................................................................................................ 28 13.6 Determination of the Damage Factor ................................................................................ 28 13.6.1 Overview ...................................................................................................................... 28 13.6.2 Inspection Effectiveness ............................................................................................ 28 13.6.3 Calculation of the Damage Factor ............................................................................. 28 13.7 Nomenclature ...................................................................................................................... 28 13.8 References .......................................................................................................................... 28 13.9 Tables................................................................................................................................... 28 SCC DAMAGE FACTOR – HSC-HF ........................................................................................... 30 14.1 Scope ................................................................................................................................... 30 14.2 Description of Damage....................................................................................................... 30 14.3 Screening Criteria ............................................................................................................... 30 14.4 Required Data ..................................................................................................................... 30 14.5 Basic Assumptions ............................................................................................................ 30 14.6 Determination of the Damage Factor ................................................................................ 30 14.6.1 Overview ...................................................................................................................... 30 14.6.2 Inspection Effectiveness ............................................................................................ 30 14.6.3 Calculation of the Damage Factor ............................................................................. 30 14.7 Nomenclature ...................................................................................................................... 30 14.8 References .......................................................................................................................... 30 14.9 Tables................................................................................................................................... 30 SCC DAMAGE FACTOR – HIC/SOHIC-HF ................................................................................ 32 15.1 Scope ................................................................................................................................... 32 15.2 Description of Damage....................................................................................................... 32 15.3 Screening Criteria ............................................................................................................... 32 15.4 Required Data ..................................................................................................................... 32 15.5 Basic Assumptions ............................................................................................................ 32 15.6 Determination of the Damage Factor ................................................................................ 32 15.6.1 Overview ...................................................................................................................... 32 15.6.2 Inspection Effectiveness ............................................................................................ 32 15.6.3 Calculation of the Damage Factor ............................................................................. 32 15.7 Nomenclature ...................................................................................................................... 32 15.8 References .......................................................................................................................... 32 15.9 Tables................................................................................................................................... 32 EXTERNAL CORROSION DAMAGE FACTOR – FERRITIC COMPONENT ............................ 34 16.1 Scope ................................................................................................................................... 34 16.2 Description of Damage....................................................................................................... 34 16.3 Screening Criteria ............................................................................................................... 34 16.4 Required Data ..................................................................................................................... 34 16.5 Basic Assumption .............................................................................................................. 34 16.6 Determination of the Damage Factor ................................................................................ 34 16.6.1 Overview ...................................................................................................................... 34 16.6.2 Inspection Effectiveness ............................................................................................ 34 16.6.3 Calculation of the Damage Factor ............................................................................. 34 16.7 Nomenclature ...................................................................................................................... 34 16.8 Tables................................................................................................................................... 34 CUI DAMAGE FACTOR – FERRITIC COMPONENT ................................................................. 36

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API RP 581 RISK-BASED INSPECTION TECHNOLOGY

18

19

20

21

17.1 Scope ................................................................................................................................... 36 17.2 Description of Damage....................................................................................................... 36 17.3 Screening Criteria ............................................................................................................... 36 17.4 Required Data ..................................................................................................................... 36 17.5 Basic Assumption .............................................................................................................. 36 17.6 Determination of the Damage Factor ................................................................................ 36 17.6.1 Overview ...................................................................................................................... 36 17.6.2 Inspection Effectiveness ............................................................................................ 36 17.6.3 Calculation of the Damage Factor ............................................................................. 36 17.7 Nomenclature ...................................................................................................................... 36 17.8 Tables................................................................................................................................... 36 EXTERNAL CLSCC DAMAGE FACTOR – AUSTENITIC COMPONENT ................................. 39 18.1 Scope ................................................................................................................................... 39 18.2 Description of Damage....................................................................................................... 39 18.3 Required Data ..................................................................................................................... 39 18.4 Basic Assumption .............................................................................................................. 39 18.5 Determination of the Damage Factor ................................................................................ 39 18.5.1 Overview ...................................................................................................................... 39 18.5.2 Inspection Effectiveness ............................................................................................ 39 18.5.3 Calculation of the Damage Factor ............................................................................. 39 18.6 Nomenclature ...................................................................................................................... 39 18.7 Tables................................................................................................................................... 39 EXTERNAL CUI CLSCC DAMAGE FACTOR – AUSTENITIC COMPONENT .......................... 41 19.1 Scope ................................................................................................................................... 41 19.2 Description of Damage....................................................................................................... 41 19.3 Screening Criteria ............................................................................................................... 41 19.4 Required Data ..................................................................................................................... 41 19.5 Basic Assumption .............................................................................................................. 41 19.6 Determination of the Damage Factor ................................................................................ 41 19.6.1 Overview ...................................................................................................................... 41 19.6.2 Inspection Effectiveness ............................................................................................ 41 19.6.3 Calculation of the Damage Factor ............................................................................. 41 19.7 Nomenclature ...................................................................................................................... 41 19.8 Tables................................................................................................................................... 41 HTHA DAMAGE FACTOR........................................................................................................... 43 20.1 Scope ................................................................................................................................... 43 20.2 Description of Damage....................................................................................................... 43 20.3 Screening Criteria ............................................................................................................... 43 20.4 Required Data ..................................................................................................................... 43 20.5 Basic Assumption .............................................................................................................. 43 20.6 Determination of the Damage Factor ................................................................................ 43 20.6.1 Overview ...................................................................................................................... 43 20.6.2 Inspection Effectiveness ............................................................................................ 43 20.6.3 Calculation of the Damage Factor ............................................................................. 43 20.7 Nomenclature ...................................................................................................................... 43 20.8 Tables................................................................................................................................... 43 BRITTLE FACTURE DAMAGE FACTOR ................................................................................... 45 21.1 Scope ................................................................................................................................... 45 21.2 Description of Damage....................................................................................................... 45 21.3 Screening Criteria ............................................................................................................... 45 21.4 Required Data ..................................................................................................................... 45 21.5 Basic Assumption .............................................................................................................. 45 21.6 Determination of the Damage Factor ................................................................................ 45 21.6.1 Overview ...................................................................................................................... 45 21.6.2 Inspection Effectiveness ............................................................................................ 45 21.6.3 Calculation of the Damage Factor ............................................................................. 45

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API RP 581 RISK-BASED INSPECTION TECHNOLOGY

22

23

24

25

21.7 Nomenclature ...................................................................................................................... 45 21.8 Tables................................................................................................................................... 45 TEMPER EMBRITTLEMENT DAMAGE FACTOR...................................................................... 46 22.1 Scope ................................................................................................................................... 46 22.2 Description of Damage....................................................................................................... 46 22.3 Screening Criteria ............................................................................................................... 46 22.4 Required Data ..................................................................................................................... 46 22.5 Basic Assumption .............................................................................................................. 46 22.6 Determination of the Damage Factor ................................................................................ 46 22.6.1 Overview ...................................................................................................................... 46 22.6.2 Inspection Effectiveness ............................................................................................ 46 22.6.3 Calculation of the Damage Factor ............................................................................. 46 22.7 Nomenclature ...................................................................................................................... 46 22.8 References .......................................................................................................................... 46 22.9 Tables................................................................................................................................... 46 885 EMBRITTLEMENT DAMAGE FACTOR............................................................................... 47 23.1 Scope ................................................................................................................................... 47 23.2 Description of Damage....................................................................................................... 47 23.3 Screening Criteria ............................................................................................................... 47 23.4 Required Data ..................................................................................................................... 47 23.5 Basic Assumption .............................................................................................................. 47 23.6 Determination of the Damage Factor ................................................................................ 47 23.6.1 Overview ...................................................................................................................... 47 23.6.2 Inspection Effectiveness ............................................................................................ 47 23.6.3 Calculation of the Damage Factor ............................................................................. 47 23.7 Nomenclature ...................................................................................................................... 47 23.8 References .......................................................................................................................... 47 23.9 Tables................................................................................................................................... 47 SIGMA PHASE EMBRITTLEMENT DAMAGE FACTOR ........................................................... 48 24.1 Scope ................................................................................................................................... 48 24.2 Description of Damage....................................................................................................... 48 24.3 Screening Criteria ............................................................................................................... 48 24.4 Required Data ..................................................................................................................... 48 24.5 Basic Assumption .............................................................................................................. 48 24.6 Determination of the Damage Factor ................................................................................ 48 24.6.1 Overview ...................................................................................................................... 48 24.6.2 Inspection Effectiveness ............................................................................................ 48 24.6.3 Calculation of the Damage Factor ............................................................................. 48 24.7 Nomenclature ...................................................................................................................... 48 24.8 References .......................................................................................................................... 48 24.9 Tables................................................................................................................................... 48 PIPING MECHANICAL FATIGUE DAMAGE FACTOR .............................................................. 49 25.1 Scope ................................................................................................................................... 49 25.2 Description of Damage....................................................................................................... 49 25.3 Screening Criteria ............................................................................................................... 49 25.4 Required Data ..................................................................................................................... 49 25.5 Basic Assumption .............................................................................................................. 49 25.6 Determination of the Damage Factor ................................................................................ 49 25.6.1 Overview ...................................................................................................................... 49 25.6.2 Inspection Effectiveness ............................................................................................ 49 25.6.3 Calculation of the Damage Factor ............................................................................. 50 25.7 Nomenclature ...................................................................................................................... 50 25.8 Tables................................................................................................................................... 50

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API RP 581 RISK-BASED INSPECTION TECHNOLOGY

1

SCOPE

2

REFERENCES

3

DEFINTIONS

4

PROBABILITY OF FAILURE CALCULATIONS

4.1

Overview

4.2

Calculation of Probability of Failure

4.3

Generic Failure Frequency

4.4

Damage Factor

4.4.1

Overview

4.4.2

Damage Factor Combination for Multiple Damage Mechanisms

4.4.3 Inspection Effectiveness Category Damage factors are determined as a function of inspection effectiveness. Inspection effectiveness discussion and example tables are provided in Annex 2.C of this document. The five inspection effectiveness categories used in API RBI are shown in Table 4.3. The inspection effectiveness categories presented are meant to be examples and in order to provide a guideline for the user infor assigning actual inspection effectiveness. The actual effectiveness of any inspection technique depends on many factors such as the skill and training of inspectors, and the level of expertise used in selecting inspection locations. Inspections are ranked according to their expected effectiveness at detecting damage and correctly predicting the rate of damage. The actual effectiveness of a given inspection technique depends on the characteristics of the damage mechanism. The effectiveness of each inspection performed within the designated time period is characterized for each damage mechanism. The number of highest effectiveness inspections will be used to determine the damage factor. If multiple inspections of a lower effectiveness have been conducted during the designated time period, they can be approximated to an equivalent higher effectiveness inspection in accordance with the following relationships: a) 2 Usually Effective (B) Inspections = 1 Highly Effective (A) Inspection, or 2B = 1A b) 2 Fairly Effective (C) Inspections = 1 Usually Effective (B) inspection, or 2C = 1B c) 2 Poorly Effective (D) Inspections = 1 Fairly Effective (C) inspection, or 2D = 1C Note that these equivalent higher inspection rules shall not be applied to No Inspections (E). 4.5

Management Systems Factor

4.5.1

General

4.5.2

Overview

4.5.3

Auditing Technique

4.5.4

Calculation of the Management Systems Factor

4.6

Nomenclature

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API RP 581 RISK-BASED INSPECTION TECHNOLOGY

4.7

Tables Table 4.3 – Inspection Effectiveness Categories

Qualitative Inspection Effectiveness Category

Description

Highly Effective

The inspection methods will correctly identify the true damage state in nearly every case (or 80–100% confidence).

Usually Effective

The inspection methods will correctly identify the true damage state most of the time (or 60–80% confidence).

Fairly Effective

The inspection methods will correctly identify the true damage state about half of the time (or 40–60% confidence).

Poorly Effective

The inspection methods will provide little information to correctly identify the true damage state (or 20–40% confidence).

Ineffective

The inspection method will provide no or almost no information that will correctly identify the true damage state and are considered ineffective for detecting the specific damage mechanism (less than 20% confidence).

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API RP 581 RISK-BASED INSPECTION TECHNOLOGY

5

THINNING DAMAGE FACTOR

5.1

Scope

5.2

Screening Criteria

5.3

Required Data

5.4

Basic Assumptions

5.5

Determination of the Damage Factor

5.5.1

Overview

5.5.2 Inspection Effectiveness Inspections are ranked according to their expected effectiveness at detecting thinning and correctly predicting the rate of thinning. The actual effectiveness of a given inspection technique depends on the characteristics of the thinning mechanism, (i.e., whether it is general or localized). Examples of inspection activities for general and localized thinning, respectively, that are both intrusive (requires entry into the equipment), non-intrusive (can be performed externally), and buried components are provided in Annex 2.C, Tables 5.57.1, 7.2, and 7.3 through 5.7, respectively. Examples of inspection activities for general and localized thinning, regarding tank shell courses and bottoms are provided in Annex 2.C, Tables 7.4 to 7.6. Note that the effectiveness category assigned to the inspection activity differs depending on whether the thinning is general or localized. For localized thinning, selection of locations for examination must be based on a thorough understanding of the damage mechanism in the specific process. The effectiveness of each inspection performed within the designated time period must be characterized in accordance a manner similar to with the examples provided in Annex 2.C, Tables 5.57.1 through 5.107.6, as applicable. The number and category of the highest effective inspection will be used to determine the damage factor. If multiple inspections of a lower effectiveness have been conducted during the designated time period, they can be equated to an equivalent higher effectiveness inspection in accordance with paragraph 4.4.3. Note that for tank bottoms, credit is given for only one inspection. 5.5.3

Calculation of the Damage Factor

5.6

Nomenclature

5.7

Tables Table 5.5 – Guidelines for Assigning Inspection Effectiveness – General Thinning

Inspection Category

Inspection Effectiveness Category

A

Highly Effective

50 to 100% examination of the surface (partial internals removed), and accompanied by thickness measurements

50 to 100% ultrasonic scanning coverage (automated or manual) or profile radiography

B

Usually Effective

Nominally 20% examination (no internals removed), and spot external ultrasonic thickness measurements

Nominally 20% ultrasonic scanning coverage (automated or manual), or profile radiography, or external spot thickness (statistically validated)

Intrusive Inspection Example

2-10

Non-intrusive Inspection Example

API RP 581 RISK-BASED INSPECTION TECHNOLOGY

C

Fairly Effective

D

Poorly Effective

E

Ineffective

Visual examination with thickness measurements

2 to 3% examination, spot external ultrasonic thickness measurements, and little or no internal visual examination

Visual examination

Several thickness measurements, and a documented inspection planning system

No inspection

Several thickness measurements taken only externally, and a poorly documented inspection planning system

Table 5.6 – Guidelines for Assigning Inspection Effectiveness – Local Thinning Inspection Category

Inspection Effectiveness Category

A

Highly Effective

B

Usually Effective

C

Fairly Effective

D

Poorly Effective

E

Ineffective

Intrusive Inspection Example

Non-intrusive Inspection Example

100% visual examination (with removal of internal packing, trays, etc.) and thickness measurements

50 to 100% coverage using automated ultrasonic scanning, or profile radiography in areas specified by a corrosion engineer or other knowledgeable specialist.

100% visual examination (with partial removal of the internals) including manways, nozzles, etc. and thickness measurements.

20% coverage using automated ultrasonic scanning, or 50% manual ultrasonic scanning, or 50% profile radiography in areas specified by a corrosion engineer or other knowledgeable specialist.

Nominally 50% visual examination and spot ultrasonic thickness measurements

Nominally 20% coverage using automated or manual ultrasonic scanning, or profile radiography, and spot thickness measurements at areas specified by a corrosion engineer or other knowledgeable specialist.

Nominally 20% visual examination and spot ultrasonic thickness measurements

Spot ultrasonic thickness measurements or profile radiography without areas being specified by a corrosion engineer or other knowledgeable specialist.

No inspection

Spot ultrasonic thickness measurements without areas being specified by a corrosion engineer or other knowledgeable specialist.

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API RP 581 RISK-BASED INSPECTION TECHNOLOGY

Table 5.7 – Guidelines for Assigning Inspection Effectiveness – Buried Components Inspection Category

A

Inspection Effectivenes s Category

Highly Effective

Intrusive Inspection Example

Non-intrusive Inspection Example

Non-intrusive Inspection Example

100% internal inspection via state-of-the-art pigging and in-line inspection technologies (UT, MFL, internal rotary UT, etc.)

Complete excavation, 100% external visual inspection, and 100% inspection with NDE technologies (UT thickness measurement such as handheld devices at close-interval grid locations, UT B-scan, automated ultrasonic scanning, guided-wave UT global search, crawler with circumferential inspection technology such as MFL or lambwave UT, digital radiography in more than one direction)

a. Cathodic Protection (CP) System maintained and managed by NACE certified personnel and complying with NACE SP0169 [14]– includes Stray current surveys on a regular basis b. Close Interval Survey (at excavation sites) to assess the performance of the CP system locally c.a. Sample soil and water resistivity and chemistry measurements along entire structure a. CP System maintained and managed by NACE certified personnel and complying with NACE SP0169 [14] – includes Stray current surveys on a regular basis b. Close Interval Survey (at excavation sites) to assess the performance of the CP system locally c. Sample soil and water resistivity and chemistry measurements along entire structure d.a. DC Voltage Gradient (DCVG) to determine coating damage

100% external inspection of equipment that is only partially buried using an NDE crawler with circumferential inspection technology (MFL, lambwave UT)

Internal inspection via pigging and in-line inspection technologies (UT, MFL, internal rotary UT, etc.) of selected areas / sections, combined with statistical analysis or extreme value analysis (EVA). B

Usually Effective

C

Fairly Effective

D

Poorly Effective

E

Ineffective

External inspection of equipment that is only partially buried using an NDE crawler with circumferential inspection technology (MFL, lambwave UT) on selected areas / sections, combined with statistical analysis or extreme value analysis (EVA). Partly inspection by internal smart pig or specialized crawler device, including a representative portion of the buried pipe. (95% external visual inspection prior to removal of insulation Remove >90% of insulation at suspect locations, OR >90% pulse eddy current inspection. Visual inspection of the exposed surface area with follow-up by UT or pit gauge as required. Non-Insulated - >95% visual inspection of the exposed surface area with follow-up by UT or pit gauge as required. Insulated – >95% external visual inspection prior to removal of insulation Remove >30% of insulation at suspect locations, OR >30% pulse eddy current inspection. Visual inspection of the exposed surface area with follow-up by UT or pit gauge as required. Non-Insulated - >50% visual inspection of the exposed surface area with follow-up by UT or pit gauge as required. Insulated – >95% external visual inspection prior to removal of insulation Remove >10% of insulation at suspect locations, OR >10% pulse eddy current inspection. Visual inspection of the exposed surface area with follow-up by UT or pit gauge as required. Non-Insulated - >25% visual inspection of the exposed surface area with follow-up by UT or pit gauge as required. Insulated – >95% external visual inspection prior to removal of insulation Remove >5% of insulation at suspect locations, OR >5% pulse eddy current inspection. Visual inspection of the exposed surface area with follow-up by UT or pit gauge as required. Non-Insulated - >10% visual inspection of the exposed surface area with follow-up by UT or pit gauge as required.

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API RP 581 RISK-BASED INSPECTION TECHNOLOGY

a. E

Ineffective a.

Insulated – No visual inspection of insulation surface area or removal of insulation. Non-Insulated - 75% b. Adhesion test c.a. Scrape test a. Broom swept b. Effective supplementary light c. Visual 100% d. Pit depth gauge Coating or Liner: a. Sponge test 50 – 75% b. Adhesion test c.a. Scrape test a. Broom swept b. No effective supplementary lighting c. Visual 25-50% Coating or Liner: a. Sponge test 60% of the exposed surface area with follow-up by UT, RT or pit gauge as required.

C

Fairly Effective

Visual inspection of >30% of the exposed surface area with follow-up by UT, RT or pit gauge as required.

D

Poorly Effective

Visual inspection of >5% of the exposed surface area with follow-up by UT, RT or pit gauge as required.

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API RP 581 RISK-BASED INSPECTION TECHNOLOGY

E

Ineffective

Visual inspection of 95% of the insulation including suspect areas; AND

For the total surface area: 100% visual inspection AND 100% inspection with highly effective NDE technique (such as profile or real-time radiography or guided wave UT)

2-36

API RP 581 RISK-BASED INSPECTION TECHNOLOGY

B

C

D

Usually Effective

Fairly Effective

Poorly Effective

100% visual inspection of the exposed surface area with followup by UT, RT or pit gauge as required.

AND strip 100% of areas where NDE technique is not effective (e.g., fittings) AND 100% visual inspection of the exposed surface area with follow-up by UT, RT or pit gauge as required. or real-time radiography.

For the total surface area: >95% external visual inspection prior to removal of insulation; AND remove >60% of total surface area of insulation including suspect areas; AND visual inspection of the exposed surface area with follow-up by UT, RT or pit gauge as required.

For the total surface area: >95% visual inspection AND > 60% inspection with highly effective NDE technique (such as profile or real-time radiography or guided wave UT) including suspect areas AND strip > 60% of areas where NDE technique is not effective (e.g., fittings) AND 100% visual inspection of the exposed surface area with follow-up by UT, RT or pit gauge as required.

For the total surface area: >95% external visual inspection prior to removal of insulation; AND remove >30% of total surface area of insulation including suspect areas; AND visual inspection of the exposed surface area with follow-up by UT, RT or pit gauge as required.

For the total surface area: >95% visual inspection AND > 24% inspection with highly effective NDE technique (such as profile or real-time radiography or guided wave UT) including suspect areas AND strip > 24% of areas where NDE technique is not effective (e.g., fittings) AND 100% visual inspection of the exposed surface area with follow-up by UT, RT or pit gauge as required.

>95% external visual inspection prior to removal of insulation; AND remove >5% of total surface area of insulation including suspect areas. AND

For the total surface area: >95% visual inspection AND > 5% inspection with highly effective NDE technique (such as profile or real-time radiography or guided wave UT) including suspect

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API RP 581 RISK-BASED INSPECTION TECHNOLOGY

E

Ineffective

visual inspection of the exposed surface area with follow-up by UT, RT or pit gauge as required.

areas AND strip > 5% of areas where NDE technique is not effective (e.g., fittings) AND 100% visual inspection of the exposed surface area with follow-up by UT, RT or pit gauge as required.

90% of insulation at suspect locations, OR >90% pulse eddy current inspection.

Non-Insulated Tank Inspection 1 Example >95% visual inspection of the exposed surface area AND Follow-up by UT or pit gauge as required.

• Visual inspection of the exposed surface area with follow-up by UT or pit gauge as required. • >95% external visual inspection prior to removal of insulation

B

Usually Effective

• Remove >50% of insulation at suspect locations, OR >50% pulse eddy current inspection.

>50% visual inspection of the exposed surface area AND Follow-up by UT or pit gauge as required.

• Visual inspection of the exposed surface area with follow-up by UT or pit gauge as required. • >95% external visual inspection prior to removal of insulation

C

Fairly Effective

• Remove >30% of insulation at suspect locations, OR >30% pulse eddy current inspection.

>25% visual inspection of the exposed surface area AND Follow-up by UT or pit gauge as required.

• Visual inspection of the exposed surface area with follow-up by UT or pit gauge as required. • >95% external visual inspection prior to removal of insulation

D

Poorly Effective

• Remove >10% of insulation at suspect locations, OR >10% pulse eddy current inspection.

>10% visual inspection of the exposed surface area AND Follow-up by UT or pit gauge as required.

• Visual inspection of the exposed surface area with follow-up by UT or pit gauge as required.

E

Ineffective

No inspection, less than above recommendations or ineffective technique used.

C-17

No inspection, less than above recommendations or ineffective technique used.

Table 7.3 – LoIE Example for Tank Bottoms Inspection Category

Inspection Effectiveness Category

1

Soil Side Floor scan >90% AND UT follow-up

A

Highly Effective

NOTE • Include welds if warranted from the results on the plate scanning • Hand scan of the critical zone

Floor scan >50% AND

B

Usually Effective

UT follow-up OR EVA or other statistical method with Floor scan follow-up (if warranted by the result) Floor scan 5-10+% plates AND Supplement with scanning near shell AND

Fairly Effective

1

Bare Plate: • Commercial blast • Effective supplementary light • Visual 100% (API 653) • Pit depth gauge • 100% vacuum box testing of suspect welded joints Coating or Liner: • Sponge test 100% • Adhesion test • Scrape test Bare Plate: • Brush blast • Effective supplementary light • Visual 100% (API 653) • Pit depth gauge Coating or Liner: • Sponge test >75% • Adhesion test • Scrape test Bare Plate: • Broom swept • Effective supplementary light • Visual 100% • Pit depth gauge Coating or Liner: • Sponge test 50-75% • Adhesion test • Scrape test

UT follow-up

C

Product Side

OR Use a ‘Scan Circle-and-X’ pattern (progressively increase if damage found during scanning) Other Testing: • Helium/Argon test • Hammer test • Cut coupons Possible Testing: • Spot UT • Flood test

D

E

Poorly Effective

Ineffective

No inspection, less than above recommendations or ineffective technique used.

C-18

Bare Plate: • Broom swept • No effective supplementary lighting • Visual >50% Coating or Liner: • Sponge test 65% Visual inspection 100% automated or manual AND ultrasonic scanning. Usually >65% Holiday test Effective AND >65% UT or magnetic tester for disbonding for bonded liners. For the total surface area: For the total surface area: >35% Visual inspection >65% automated or manual OR ultrasonic scanning. Fairly Effective >35% Holiday test OR >35% UT or magnetic tester for disbonding for bonded liners. For the total surface area: For the total surface area: >5% Visual inspection >35% automated or manual OR ultrasonic scanning. Poorly >5% Holiday test Effective OR >5% UT or magnetic tester for disbonding for bonded liners. No inspection, less than above No inspection, less than above Ineffective recommendations or ineffective recommendations or ineffective technique used. technique used.

C-19

Table 7.5 – LoIE Example for Buried Components Inspection Category

Inspection Effectiveness Category

Intrusive Inspection 1 Example 100% internal inspection via state-of-the-art pigging and in-line inspection technologies (UT, MFL, internal rotary UT, etc.)

A

Highly Effective

Internal inspection via pigging and in-line inspection technologies (UT, MFL, internal rotary UT, etc.) of selected areas / sections, combined with statistical analysis or extreme value analysis (EVA).

B

C

D E

Usually Effective

Fairly Effective

Poorly Effective Ineffective

Partial inspection by internal smart pig or specialized crawler device, including a representative portion of the buried pipe. (50% visual examination (partial internals removed), AND >50% of the spot ultrasonic thickness measurements

For the total surface area: >25% visual examination AND >25% of the spot ultrasonic thickness measurements

For the total surface area: >5% visual examination AND >5% of the spot ultrasonic thickness measurements For the total surface area: 75% spot UT OR >5% UT scanning, automated or manual OR >5% profile radiography of the selected area(s)

For the total surface area: >50% spot UT or random UT scans (automated or manual) OR random profile radiography of the selected area(s) For the total surface area: >25% spot UT No inspection, less than above recommendations or ineffective technique used.

Table 8.2 – LoIE Example for Local Thinning Inspection Category

A

B

C

Inspection Effectiveness Category

Highly Effective

Usually Effective

Fairly Effective

D

Poorly Effective

E

Ineffective

1,5,6,7

Intrusive Inspection Example

For the total surface area: 100% visual examination (with removal of internal packing, trays, etc.) AND 100% follow-up at locally thinned areas For the total surface area: >75 % visual examination AND 100% follow-up at locally thinned areas For the total surface area: >50% visual examination AND 100% follow-up at locally thinned areas. For the total surface area: >20% visual examination AND 100% follow-up at locally thinned areas No inspection, less than above recommendations or ineffective technique used.

C-23

Non-intrusive Inspection 1,5,7,8 Example For the total suspect area: 100% coverage of the TML’s/CML’s using ultrasonic scanning or profile radiography

For the total suspect area: >75% coverage of the TML’s/CML’s using ultrasonic scanning or profile radiography For the total suspect area: >50% coverage of the TML’s/CML’s using ultrasonic scanning or profile radiography For the total suspect area: >20% coverage of the TML’s/CML’s using ultrasonic scanning or profile radiography No inspection, less than above recommendations or ineffective technique used.

Table 8.3 – LoIE Example for Amine Cracking Inspection Category

Inspection Effectiveness Category

A

Highly Effective

B

C

Usually Effective

Fairly Effective

D

Poorly Effective

E

Ineffective

1,8

Intrusive Inspection Example

1,8

Non-intrusive Inspection Example

For the total weld area: 100% WFMT/ACFM with UT followup of relevant indications.

For the total weld area: 100% automated or manual ultrasonic scanning.

For selected welds / weld area: >75% WFMT/ACFM with UT followup of all relevant indications.

For selected welds / weld area: >75% automated or manual ultrasonic scanning OR AE testing with 100% follow-up of relevant indications. For selected welds / weld area: >35% automated or manual ultrasonic scanning OR >35% radiographic testing. For selected welds / weld area: >10% automated or manual ultrasonic scanning OR >10% radiographic testing. No inspection, less than above recommendations or ineffective technique used.

For selected welds / weld area: >35% WFMT/ACFM with UT followup of all relevant indications.

For selected welds / weld area: >10% WFMT/ACFM with UT followup of all relevant indications or

No inspection, less than above recommendations or ineffective technique used.

C-24

Table 8.4 – LoIE Example for Carbonate Cracking Inspection Category

Inspection Effectiveness Category

A

Highly Effective

B

C

Usually Effective

Fairly Effective

D

Poorly Effective

E

Ineffective

1,8

Intrusive Inspection Example

1,8

Non-intrusive Inspection Example

For the total weld area: 100% WFMT/ACFM with UT followup of relevant indications.

For the total weld area: 100% automated or manual ultrasonic scanning.

For selected welds / weld area: >75% WFMT/ACFM with UT followup of all relevant indications.

For selected welds / weld area: >75% automated or manual ultrasonic scanning OR AE testing with 100% follow-up of relevant indications. For selected welds / weld area: >35% automated or manual ultrasonic scanning OR >35% radiographic testing. For selected welds / weld area: >10% automated or manual ultrasonic scanning OR >10% radiographic testing. No inspection, less than above recommendations or ineffective technique used.

For selected welds / weld area: >35% WFMT/ACFM with UT followup of all relevant indications.

For selected welds / weld area: >10% WFMT/ACFM with UT followup of all relevant indications or

No inspection, less than above recommendations or ineffective technique used.

C-25

Table 8.5 – LoIE Example for Caustic Cracking Inspection Category

Inspection Effectiveness Category

A

Highly Effective

B

C

Usually Effective

Fairly Effective

D

Poorly Effective

E

Ineffective

1,8,a

Intrusive Inspection Example

Non-intrusive Inspection 1,8,a Example

For the total weld area: 100% WFMT/ACFM with UT followup of relevant indications.

For the total weld area: 100% automated or manual ultrasonic scanning.

For selected welds / weld area: >75% WFMT/ACFM with UT followup of all relevant indications.

For selected welds / weld area: >75% automated or manual ultrasonic scanning OR AE testing with 100% follow-up of relevant indications. For selected welds / weld area: >35% automated or manual ultrasonic scanning OR >35% radiographic testing. For selected welds / weld area: >10% automated or manual ultrasonic scanning OR >10% radiographic testing. No inspection, less than above recommendations or ineffective technique used.

For selected welds / weld area: >35% WFMT/ACFM with UT followup of all relevant indications.

For selected welds / weld area: >10% WFMT/ACFM with UT followup of all relevant indications or

No inspection, less than above recommendations or ineffective technique used.

Additional Assumptions a) Cold bends may need inspection also for Caustic Cracking

C-26

Table 8.6 – LoIE Example for CLSCC Inspection Category

Inspection Effectiveness Category

A

Highly Effective

B

C

Usually Effective

Fairly Effective

D

Poorly Effective

E

Ineffective

1,8,a

Intrusive Inspection Example

Non-intrusive Inspection 1,8,a Example

For the total surface area: 100% Dye penetrant or eddy current test with UT follow-up of relevant indications.

No inspection techniques are yet available to meet the requirements for an ‘A’ level inspection.

For selected areas: >65% dye penetrant or eddy current testing with UT follow-up of all relevant indications.

For selected areas: 100% automated or manual ultrasonic scanning OR AE testing with 100% follow-up of relevant indications. For selected areas: >65% automated or manual ultrasonic scanning OR >65% radiographic testing. For selected areas: >35% automated or manual ultrasonic scanning OR >35% radiographic testing. No inspection, less than above recommendations or ineffective technique used.

For selected areas: >35% dye penetrant or eddy current testing with UT follow-up of all relevant indications. For selected areas: >10% dye penetrant or eddy current testing with UT follow-up of all relevant indications No inspection, less than above recommendations or ineffective technique used.

Additional Assumptions a) Internal stress corrosion cracking

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Table 8.7 – LoIE Example for PTA Cracking Inspection Category

Inspection Effectiveness Category

A

Highly Effective

1,8

Intrusive Inspection Example

For the total surface area: 100% Dye penetrant or eddy current test with UT follow-up of relevant indications. For selected areas: >65% dye penetrant or eddy current testing with UT follow-up of all relevant indications.

1,8

Non-intrusive Inspection Example

No inspection techniques are yet available to meet the requirements for an ‘A’ level inspection.

For selected areas: 100% automated or manual Usually ultrasonic scanning B OR Effective AE testing with 100% follow-up of relevant indications. For selected areas: For selected areas: >35% dye penetrant or eddy current >65% automated or manual C Fairly Effective testing with UT follow-up of all ultrasonic scanning OR relevant indications. >65% radiographic testing. For selected areas: For selected areas: >35% automated or manual >10% dye penetrant or eddy current Poorly D ultrasonic scanning testing with UT follow-up of all Effective OR relevant indications >35% radiographic testing. No inspection, less than above No inspection, less than above E Ineffective recommendations or ineffective recommendations or ineffective technique used. technique used. Note: There is no highly effective inspection without a minimum of partial insulation removal and external VT and PT.

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Table 8.8 – LoIE Example for Sulfide Stress Cracking Inspection Category

Inspection Effectiveness Category

A

Highly Effective

B

C

Usually Effective

Fairly Effective

D

Poorly Effective

E

Ineffective

1,8

Intrusive Inspection Example

1,8

Non-intrusive Inspection Example

For the total weld area: 100% WFMT/ACFM with UT followup of relevant indications.

For the total weld area: 100% automated or manual ultrasonic scanning.

For selected welds / weld area: >75% WFMT/ACFM with UT followup of all relevant indications.

For selected welds / weld area: >75% automated or manual ultrasonic scanning OR AE testing with 100% follow-up of relevant indications. For selected welds / weld area: >35% automated or manual ultrasonic scanning OR >35% radiographic testing. For selected welds / weld area: >10% automated or manual ultrasonic scanning OR >10% radiographic testing. No inspection, less than above recommendations or ineffective technique used.

For selected welds / weld area: >35% WFMT/ACFM with UT followup of all relevant indications.

For selected welds / weld area: >10% WFMT/ACFM with UT followup of all relevant indications or

No inspection, less than above recommendations or ineffective technique used.

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Table 8.9 – LoIE Example for HIC/SOHIC-H 2 S Cracking Inspection Category

A

B

C

Inspection Effectiveness Category

Highly Effective

Usually Effective

Fairly Effective

D

Poorly Effective

E

Ineffective

1,8,a

Intrusive Inspection Example

For the total surface area: • >95% A or C scan with straight beam • Followed by TOFD/Shear Wave • 100% Visual

For the total Surface area: • >75% A or C scan with straight beam • Followed by TOFD/Shear Wave • 100% Visual For the total Surface area: • >35% A or C scan with straight beam • Followed by TOFD/Shear Wave • 100% Visual OR • >50% WFMT/ACFM • UT follow-up of indications • 100% Visual of Total Surface area For the total Surface area: • >10% A or C scan with Shear Wave • 100% Visual OR • >25% WFMT/ACFM • UT follow-up of indications • 100% Visual of Total Surface area No inspection, less than above recommendations or ineffective technique used.

Non-intrusive Inspection 1,8,a Example For the total surface area: • SOHIC: • >90% C scan of the base metal using advanced UT • For the weld and HAZ 100% Shear Wave and TOFD AND 2 • HIC: Two 1-ft areas, C scan of the base metal using advanced UT on each plate and the heads. For the total surface area: • >65% C scan of the base metal using advanced UT AND 2 • HIC: Two 0.5-ft areas, C scan of the base metal using advanced UT on each plate and the heads. For the total surface area: • >35% C scan of the base metal using advanced UT AND 2 • HIC: One 1-ft area, C scan of the base metal using advanced UT on each plate and the heads.

For the total surface area: • >5% C scan of the base metal using advanced UT AND 2 • HIC: One 0.5-ft area, C scan of the base metal using advanced UT on each plate and the heads. No inspection, less than above recommendations or ineffective technique used.

Additional Assumptions a) Inspection Area: Welds and plates that are susceptible to the damage mechanism.

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Table 8.10 – LoIE Example for HSC-HF Cracking Inspection Category

Inspection Effectiveness Category

A

Highly Effective

B

C

Usually Effective

Fairly Effective

D

Poorly Effective

E

Ineffective

1,8

Intrusive Inspection Example

1,8

Non-intrusive Inspection Example

For the total weld area: 100% WFMT/ACFM with UT followup of relevant indications.

For the total weld area: 100% automated or manual ultrasonic scanning.

For selected welds / weld area: >75% WFMT/ACFM with UT followup of all relevant indications.

For selected welds / weld area: >75% automated or manual ultrasonic scanning OR AE testing with 100% follow-up of relevant indications. For selected welds / weld area: >35% automated or manual ultrasonic scanning OR >65% radiographic testing. For selected welds / weld area: >10% automated or manual ultrasonic scanning OR >35% radiographic testing. No inspection, less than above recommendations or ineffective technique used.

For selected welds / weld area: >35% WFMT/ACFM with UT followup of all relevant indications.

For selected welds / weld area: >10% WFMT/ACFM with UT followup of all relevant indications or

No inspection, less than above recommendations or ineffective technique used.

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Table 8.11 – LoIE Example for HIC/SOHIC-HF Cracking Inspection Category

A

B

C

Inspection Effectiveness Category

Highly Effective

Usually Effective

Fairly Effective

D

Poorly Effective

E

Ineffective

1,2

Intrusive Inspection Example

For the total surface area: • 100% A or C scan with straight beam • Followed by TOFD/Shear Wave • 100% Visual

For the total Surface area: • >65% A or C scan with straight beam • Followed by TOFD/Shear Wave • 100% Visual For the total Surface area: • >35% A or C scan with straight beam • Followed by TOFD/Shear Wave • 100% Visual OR • >50% WFMT/ACFM • UT follow-up of indications • 100% Visual of Total Surface area For the total Surface area: • >10% A or C scan with Shear Wave • >50% Visual OR • >25% WFMT/ACFM • UT follow-up of indications • 100% Visual of Total Surface area No inspection, less than above recommendations or ineffective technique used.

1,2

Non-intrusive Inspection Example

For the total surface area: • SOHIC: • >90% C scan of the base metal using advanced UT • For the weld and HAZ 100% Shear Wave and TOFD AND 2 • HIC: Two 1-ft areas, C scan of the base metal using advanced UT on each plate and the heads. For the total surface area: • >65% C scan of the base metal using advanced UT AND 2 • HIC: Two 0.5-ft areas, C scan of the base metal using advanced UT on each plate and the heads. For the total surface area: • >35% C scan of the base metal using advanced UT AND 2 • HIC: One 1-ft area, C scan of the base metal using advanced UT on each plate and the heads.

For the total surface area: • >5% C scan of the base metal using advanced UT AND 2 • HIC: One 0.5-ft area, C scan of the base metal using advanced UT on each plate and the heads. No inspection, less than above recommendations or ineffective technique used.

Additional Assumptions a) Inspection Area: Welds and plates that are susceptible to the damage mechanism.

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Table 8.12 – LoIE Example for External Corrosion Inspection Category

Inspection Effectiveness Category

Inspection

A

Highly Effective

Visual inspection of >95% of the exposed surface area with follow-up by UT, RT or pit gauge as required.

B

Usually Effective

Visual inspection of >60% of the exposed surface area with follow-up by UT, RT or pit gauge as required.

C

Fairly Effective

Visual inspection of >30% of the exposed surface area with follow-up by UT, RT or pit gauge as required.

D

Poorly Effective

Visual inspection of >5% of the exposed surface area with follow-up by UT, RT or pit gauge as required.

E

Ineffective

1

No inspection, less than above recommendations or ineffective technique used.

Table 8.13 – LoIE Example for External CLSCC Cracking Inspection Category

Inspection Effectiveness Category

A

Highly Effective

For the suspected surface area: 100% dye penetrant or eddy current test with UT follow-up of relevant indications.

B

Usually Effective

For the suspected surface area: >60% dye penetrant or eddy current testing with UT follow-up of all relevant indications.

C

Fairly Effective

For the suspected surface area: >30% dye penetrant or eddy current testing with UT follow-up of all relevant indications.

D

Poorly Effective

For the suspected surface area: >5% dye penetrant or eddy current testing with UT follow-up of all relevant indications.

E

Ineffective

Inspection

1,8

No inspection, less than above recommendations or ineffective technique used.

Additional Assumptions a) Inspection Area: Welds and plates that are susceptible to the damage mechanism.

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Table 8.14 – LoIE Example for CUI Inspection Category

Inspection Effectiveness Category

A

Highly Effective

B

Usually Effective

C

Fairly Effective

D

Poorly Effective

E

Ineffective

Insulation Removed

1,8,a,b

For the total surface area: 100% external visual inspection prior to removal of insulation AND Remove 100% of the insulation for damaged or suspected areas. AND 100% visual inspection of the exposed surface area with UT, RT or pit gauge follow-up of the selected corroded areas. For the total surface area: 100% external visual inspection prior to removal of insulation AND Remove >50% of suspect areas AND Follow-up of corroded areas with 100% visual inspection of the exposed surface area with UT, RT or pit gauge For the total surface area: 100% external visual inspection prior to removal of insulation AND Remove >25% of suspect areas AND Follow-up of corroded areas with 100% visual inspection of the exposed surface area with UT, RT or pit gauge For the total surface area: 100% external visual inspection prior to removal of insulation AND Remove >5% of total surface area of insulation including suspect areas AND Follow-up of corroded areas with 100% visual inspection of the exposed surface area with UT, RT or pit gauge No inspection, less than above recommendations or ineffective technique used.

Insulation Not Removed

1,8,a,b

For the total surface area: 100% external visual inspection AND 100% profile or real-time radiography of damaged or suspect area AND Follow-up of corroded areas with 100% visual inspection of the exposed surface with UT, RT or pit gauge. For the total surface area: 100% external visual inspection AND Follow-up with profile or real time radiography of >65% of suspect areas AND Follow-up of corroded areas with 100% visual inspection of the exposed surface with UT, RT or pit gauge. For the total surface area: 100% external visual inspection AND Follow-up with profile or real time radiography of >35% of suspect areas AND Follow-up of corroded areas with 100% visual inspection of the exposed surface with UT, RT or pit gauge For the total surface area: 100% external visual inspection AND Follow-up with profile or real time radiography of >5% of total surface area of insulation including suspect areas AND Follow-up of corroded areas with 100% visual inspection of the exposed surface with UT, RT or pit gauge. No inspection, less than above recommendations or ineffective technique used.

Additional Assumptions: a) Suspect areas include damaged insulation, penetrations, terminations, etc. b) Surface preparation is sufficient to detect minimum wall for the NDE technique used to measure thickness.

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Table 8.15 – LoIE Example for CUI CLSCC Inspection Category

A

B

C

Inspection Effectiveness Category

Highly Effective

Usually Effective

Fairly Effective

D

Poorly Effective

E

Ineffective

Insulation Removed

1

Insulation Not Removed

1

For the suspected area: 100% external visual inspection prior to removal of insulation AND >100% dye penetrant or eddy current test with UT follow-up of relevant indications. For the suspected area: 100% external visual inspection prior to removal of insulation AND >60% dye penetrant or eddy current testing with UT follow-up of all relevant indications.

No inspection techniques are yet available to meet the requirements for an ‘A’ level inspection.

For the suspected area: 100% external visual inspection prior to removal of insulation AND >30% dye penetrant or eddy current testing with UT follow-up of all relevant indications.

No inspection techniques are yet available to meet the requirements for an ‘A’ level inspection.

For the suspected area: 100% external visual inspection prior to removal of insulation AND >5% dye penetrant or eddy current testing with UT follow-up of all relevant indications

No inspection techniques are yet available to meet the requirements for an ‘A’ level inspection.

No inspection, less than above recommendations or ineffective technique used.

No inspection, less than above recommendations or ineffective technique used.

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No inspection techniques are yet available to meet the requirements for an ‘A’ level inspection.

Table 8.16 – LoIE Example for HTHA Inspection Category

Inspection Effectiveness Category

Inspection

1,2,3,a,b

Inspect 100% of the susceptible areas with the following techniques:

A

Highly Effective

•

Advanced Ultrasonic Backscatter Technique (AUBT) for the base metal

•

Angle-beam Spectrum Analysis (ABSA) or ToFD techniques for the weld and heat affected zone Follow-up with Phased Array (external surface) and Field Metallography (internal surface)

•

Inspect >65% of the susceptible areas with the following techniques:

B

Usually Effective

•

Advanced Ultrasonic Backscatter Technique (AUBT) for the base metal

•

Angle-beam Spectrum Analysis (ABSA) or ToFD techniques for the weld and heat affected zone Follow-up with Phased Array (external surface) and/or Field Metallography (internal surface)

•

Inspect >30% of the susceptible areas with the following techniques:

C

Fairly Effective

•

Advanced Ultrasonic Backscatter Technique (AUBT) for the base metal

•

Angle-beam Spectrum Analysis (ABSA) or ToFD techniques for the weld and heat affected zone Follow-up with Phased Array (external surface) and/or Field Metallography (internal surface)

•

Inspect >10% of the susceptible areas with the following techniques:

D

Poorly Effective

•

Advanced Ultrasonic Backscatter Technique (AUBT) for the base metal

• •

Angle-beam Spectrum Analysis (ABSA) or ToFD techniques for the weld and heat affected zone Follow-up with Phased Array (external surface) or Field Metallography (internal surface)

•

Inspect >75% WFMPT of susceptible areas.

OR

E

Ineffective

No inspection, less than above recommendations or ineffective technique used.

Additional Assumptions: a) Selected areas are determined by individuals experienced in HTHA. b) See API 941 for additional guidance to HTHA damage.

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