DEP SPECIFICATION
INSTALL ATION OF ON-LINE INSTRUMENT INSTRUMENTS S e l a s e r r o f t o N . l l e h S m o r f e s n e c i l t u o h t i w d e t t i m r e p g n i k r o w t e n r o n o i t c u d o r p e r o N . s e i n a p m o C f o p u o r G l l e h S t h g i r y p o C
DEP 32.37.10.11-Gen. September 2012 ECCN EAR99
DESIGN AND ENGINEERING PRACTICE
© 2012 Shell Group of companies All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, published or transmitted, in any form or by any means, without the prior written permission of the copyright owner or Shell Global Solutions International BV. This document contains information that is classified as EAR99 and, as a consequence, can neither be exported nor re-exported to any country which is under an embargo of the U.S. government pursuant to Part 746 of the Export Administration Regulations (15 C.F R. Part 746) nor can be made available to any national of such country. In addition, the information in this document cannot be exported nor re-exported to an end-user or for an end-use that is prohibited by Part 744 of the Export Administration Regulations (15 C.F.R. Part 744).
ECCN EAR99
DEP 32.37.10.11-Gen. September 2012 Page 2
PREFACE DEP (Design and Engineering Practice) publications reflect the views, at the time of publication, of Shell Global Solutions International B.V. (Shell GSI) and, in some cases, of other Shell Companies. These views are based on the experience acquired during involvement with the design, construction, operation and maintenance of processing units and facilities. Where deemed appropriate DEPs are based on, or reference international, regional, national and industry standards. The objective is to set the standard for good design and engineering practice to be applied by Shell companies in oil and gas production, oil refining, gas handling, gasification, chemical processing, or any other such facility, and thereby to help achieve maximum technical and economic benefit from standardization. The information set forth in these publications is provided to Shell companies for their consideration and decision to implement. This is of particular importance where DEPs may not cover every requirement or diversity of condition at each locality. The system of DEPs is expected to be sufficiently flexible to allow individual Operating Units to adapt the information set forth in DEPs to their own environment and requirements. When Contractors or Manufacturers/Suppliers use DEPs, they shall be solely responsible for such use, including the quality of their work and the attainment of the required design and engineering standards. In particular, for those requirements not specifically covered, the Principal will typically expect them to follow those design and engineering practices that will achieve at least the same level of integrity as reflected in the DEPs. If in doubt, the Contractor or Manufacturer/Supplier shall, shall, without detracting from his own respons bility, consult the Principal. The right to obtain and to use DEPs is restricted, and is typically granted by Shell GSI (and in some cases by other Shell Companies) under a Service Agreement or a License Agreement. This right is granted primarily to Shell companies and other companies receiving technical advice and services from Shell GSI or another Shell Company. Consequently, three categories of users of DEPs can be distinguished: 1)
Operating Units having a Service Agreement with Shell GSI or another Shell Company. The use of DEPs by these Operating Units is subject in all respects to the terms and conditions of the relevant Service Agreement.
2)
Other parties who are authorised to use DEPs subject to appropriate contractual arrangements (whether as part of a Service Agreement or otherwise).
3)
Contractors/subcontractors Contractors/subcontrac tors and Manufacturers/Suppliers Manufacturers/Suppliers under a contract with users referred to under 1) or 2) which requires that tenders for projects, materials supplied or - generally - work performed on behalf of the said users comply with the relevant standards.
Subject to any particular terms and conditions as may be set forth in specific agreements with users, Shell GSI disclaims any liability of whatsoever nature for any damage (including injury or death) suffered by any company or person whomsoever as a result of or in connection with the use, application or implementation of any DEP, combination of DEPs or any part thereof, even if it is wholly or partly caused by negligence on the part of Shell GSI or other Shell Company. The benefit of this disclaimer shall inure in all respects t o Shell GSI and/or any Shell Company, or companies affiliated to these companies, that may issue DEPs or advise or require the use of DEPs. Without prejudice to any specific terms in respect of confidentiality under relevant contractual arrangements, DEPs shall not, without the prior written consent of Shell GSI, be disclosed by users to any company or person whomsoever and the DEPs shall be used exclusively for the purpose for which they have been provided to t he user. They shall be returned after use, including any copies which shall only be made by users with the express prior written consent of Shell GSI. The copyright of DEPs vests in Shell Group of companies. Users shall arrange for DEPs to be held in safe custody and Shell GSI may at any time require information satisfactory to them in order to ascertain how users implement this requirement. requirement. All administrative administrative queries should be directed directed to the DEP Administrator Administrator in Shell Shell GSI.
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DEP 32.37.10.11-Gen. September 2012 Page 3 TABLE OF CONTENTS
1. 1.1 1.2 1.3 1.4 1.5 1.6 1.7
INTRODUCTION ................................................... ........................................................................................................ ..................................................... 5 SCOPE........................................................................................................................ ........................................................................................................................ 5 DISTRIBUTION, INTENDED USE AND REGULATORY CONSIDERATIONS ......... 5 DEFINITIONS ....................................................... ............................................................................................................. ...................................................... 5 CROSS-REFERENCES ............................................................. ............................................................................................. ................................ 7 SUMMARY OF MAIN CHANGES ........................................................... ............................................................................... .................... 7 COMMENTS ON THIS DEP ........................................................................... ....................................................................................... ............ 7 DUAL UNITS .................................................................................................. ............................................................................................................... ............. 8
2. 2.1 2.2 2.3
GENERAL ................................................... ................................................................................................................ ................................................................ ...9 INTRODUCTION ................................................... ........................................................................................................ ..................................................... 9 DESIGN CONCEPTS ............................................................................................... ................................................................................................. .. 9 MAINTENANCE AND TESTING............................................................ TESTING............................................................................... ................... 12
3. 3.1 3.2
INSTRUMENT PROCESS CONNECTIONS FOR ON-LINE ON- LINE INSTRUMENTS ........ 13 GENERAL ............................................................. ................................................................................................................. ....................................................13 INSTRUMENT PROCESS CONNECTIONS FOR THE REMOTE MOUNTING CONCEPT................................................................................................................. ................................................................................................................. 14 INSTRUMENT PROCESS CONNECTIONS FOR THE DIRECT MOUNTING CONCEPT................................................................................................................. ................................................................................................................. 14
3.3 4. 4.1 4.2 4.3 4.4 4.5
GENERAL SPECIFICATION FOR IMPULSE LINES .............................................. 15 SPECIFICATION OF COMPONENTS ..................................................................... 15 MOUNTING ARRANGEMENTS ............................................................................... ............................................................................... 16 FILLING, FLUSHING, VENTING AND DRAINING ................................................... 18 PAINTING AND COATING ....................................................................................... ....................................................................................... 18 TESTING................................................................................................................... ................................................................................................................... 19
5. 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8
5.9 5.10 5.11
SPECIAL APPLICATIONS AND CONSIDERATIONS FOR IMPULSE L INES ...... ...... 19 GENERAL ............................................................. ................................................................................................................. ....................................................19 STEAM SERVICE ..................................................................................................... ..................................................................................................... 19 OXYGEN SERVICE .................................................................................................. .................................................................................................. 20 HYDROGEN FLUORIDE (HF) SERVICE ......................................................... ................................................................. ........ 20 FLUIDS WITH HIGH POUR POINTS OR HYDRATE FORMATION RISK .............. .............. 20 FLUIDS CONTAINING SUSPENDED SOLIDS ........................................................ 20 FOULING AND WAXY SERVICE .......................................................... ............................................................................. ................... 21 SUSCEPTIBILITY OF LOW RANGE GAS MEASUREMENTS TO LIQUID SLUGS ....................................................... .................................................................................................................... ............................................................... ..21 LOW TEMPERATURE SERVICE .......................................................... ............................................................................. ................... 21 VERY TOXIC SERVICE ........................................................................................... 21 ‘SOUR’ OR ‘WET H2S’ SERVICE ............................................................................ ............................................................................ 22
6. 6.1 6.2 6.3 6.4 6.5
SEAL ING AND PURGING ....................................................................................... ....................................................................................... 22 LIQUID SEAL ............................................................................................................ ............................................................................................................ 22 LIQUID SEAL AND HOOK-UP OF WET LEG LEVEL APPLICATIONS ..................23 DIAPHRAGM SEALS ..................................................................................... ................................................................................................ ........... 25 EXTERNAL PURGING ............................................................................................. 26 SELF-PURGING .................................................... ....................................................................................................... ...................................................26
7. 7.1 7.2 7.3 7.4
WINTERISATION, WINTERISAT ION, HEAT TRACING AND INSUL ATION ........................................27 GENERAL ............................................................. ................................................................................................................. ....................................................27 STEAM HEATING .......................................................................................... ..................................................................................................... ........... 29 ELECTRICAL TRACING ................................................................................. ........................................................................................... .......... 29 INSULATION.................................................................................................. INSULATION..................................... ........................................................................ ........... 29
8.
REFERENCES ..................................................... ......................................................................................................... .................................................... 30
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DEP 32.37.10.11-Gen. September 2012 Page 4 APPENDICES APPENDICE S
APPENDIX 1
PRESSURE AND A ND TEMPERATURE TEMPERATU RE LIMIT ATIONS OF SS TUB ING AND PACK INGS ...................................................................................................... ...................................................................................................... 32
APPENDIX 2
EXAMPL E OF CAL CUL ATIONS OF THE EFFECT EFF ECT OF PROCESS VARIAB LE CHANGES ON dP LEVEL MEASUREMENTS ........... ................ ........... ........... .....33
ECCN EAR99
1.
INTRODUCTION
1.1
SCOPE
DEP 32.37.10.11-Gen. September 2012 Page 5
This DEP specifies requirements and gives recommendations for the installation of on-line instruments. This DEP is a revision of the DEP of the same number, dated February 2011; see (1.5) regarding the changes. 1.2
DISTRIBUTION, INTENDED USE AND REGULATORY CONSIDERATIONS Unless otherwise authorised by Shell GSI, the distribution of this DEP is confined to Shell companies and, where necessary, to Contractors and Manufacturers/Suppliers nominated by them. Any authorised access to DEPs does not for that reason constitute an authorisation to any documents, data or information to which the DEPs may refer. This DEP is intended for use in facilities related to oil and gas production, gas handling, oil refining, chemical processing, gasification, distribution and supply/marketing. This DEP may also be applied in other similar facilities. When DEPs are applied, a Management of Change (MOC) process shall be implemented; this is of particular importance when existing facilities are to be modified. If national and/or local regulations exist in which some of the requirements could be more stringent than in this DEP, the Contractor shall determine by careful scrutiny which of the requirements are the more stringent and which combination of requirements will be acceptable with regards to the safety, environmental, economic and legal aspects. In all cases, the Contractor shall inform the Principal of any deviation from the requirements of this DEP which is considered to be necessary in order to comply with national and/or local regulations. The Principal may then negotiate with the Authorities concerned, the objective being to obtain agreement to follow this DEP as closely as possible.
1.3
DEFINITIONS
1.3.1 1.3.1
General defin iti ons
The Contractor is the party that carries out all or part of the design, engineering, procurement, construction, commissioning or management of a project or operation of a facility. The Principal may undertake all or part of the duties of the Contractor. The Manufacturer/Supplier is the party that manufactures or supplies equipment and services to perform the duties specified by the Contractor. The Principal is the party that initiates the project and ultimately pays for it. The Principal may also include an agent or consultant authorised to act for, and on behalf of, the Principal. The word shall indicates a requirement. The word should indicates a recommendation. 1.3. 1.3.2 2
Specific definitio ns Terms Direct Mounting
Definitions
A mounting concept, whereby an on-line instrument (with or without manifold) is mounted directly on and supported by the process connection(s). NOTE:
This mounting concept is sometimes referred to as ‘close coupled’. This term is, however, also used in the literal sense for instruments mounted on a separate stand in the direct vicinity of the process connection(s). To avoid confusion, the term ‘close coupled’ is no longer used in this DEP.
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DEP 32.37.10.11-Gen. September 2012 Page 6
Terms
Definitions
Electrical Engineering
Term used in this DEP to identify activities or devices/components which are considered outside the responsibility of the typical Instrument Engineering discipline serving a project. It is not intended to preclude a particular project from reassigning responsibilities, but primarily to identify areas which may otherwise be overlooked.
Impulse Lin e(s)
Components used to connect an on-line instrument to its process connection. It includes but is not limited to tubing, fittings and manifold blocks plus components for filling, flushing, sealing, purging, heating, insulation, venting, draining, mounting and supporting.
Mechanical Engineering
Term used in various parts of this DEP to identify activities or devices/components that are considered outside the responsibility of the typical Instrument Engineering discipline serving a project. It is not intended to preclude a particular project from reassigning responsibilities, but primarily to identify areas that may otherwise be overlooked.
On-Line Instrument
Instruments connected to process and utility lines or equipment via small [maximum DN 50 (NPS 2)] block valves. They are subjected to the pressures of the piping systems or equipment on which they are installed. The block valves are referred to as primary isolation valves in the context of this DEP. Instruments with diaphragm seals are also considered to be on-line instruments, if they are connected to process and utility lines or equipment via primary isolation valves of any size.
1.3.3
Remote Mounting
A modular mounting concept, whereby an on-line instrument (with or without manifold) is installed on a dedicated instrument mounting support and connected with the process connection via tubing, capillary or pipe.
Very Very Toxic
See definition in DEP 00.00.01.30-Gen.
Abbreviations Terms
Definitions
HF
Hydrofluoric Acid
IPF
Instrument Protective Function
LRV
Lower Range Value; the lowest quantity that a device is adjusted to measure
MTBF
Mean Time Between Failure
MVC
Measurement Validation and Comparison
NPT
Nominal Pipe Thread
SCE
Safety Critical Element
SS
Stainless Steel
TCoO
Total Cost of Ownership
UNS
Unified Numbering System
URV
Upper Range Value; the highest quantity that a device is adjusted to measure
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1.4
DEP 32.37.10.11-Gen. September 2012 Page 7
CROSS-REFERENCES Where cross-references to other parts of this DEP are made, the referenced section number is shown in brackets ( ). Other documents referenced by this DEP are listed in (8).
1.5
SUMMARY OF MAIN CHANGES This DEP is a revision of the DEP of the same number, February 2011. The following are the main, non-editorial changes. Old section
1.6
New section
Change
2.3
Addition of Maintenance and Testing from DEP Feedback Comments.
3.
3.
Updated (3.1) and (3.2). Brought in line with Standard Drawing S 37.001.
4.1
4.1
Brought in line with S 37.001.
4.2.1
4.2.1
Updated section with PEARL Feedback.
5.1
5.1
Addition of a “General Section” and associated statements for Special Applications from DEP Feedback Comments. All sections have been moved up one number.
5.2
5.2
Added additional requirements for steam.
5.9
5.10
Change of two (2) ‘should’ statements to ‘shall’ and removed manifold interlock.
6.1
6.1
Added statement to evaluate pad transmitters or remote seal.
6.2
6.2
Updated section and brought in line with Standard Drawing S 37.001.
6.3.2.2
6.3.2.2
Removed the equalising line requirements.
7.
7.
Appended section name from “Heating and Insulation” to “Winterisation heat tracing and insulation” and harmonized with local standards. Inclusion of new sub sections (7.1.3), (7.1.4), (7.1.5), (7.1.6).
8.
8.
Update references.
COMMENTS ON THIS DEP Comments on this DEP may be submitted to the Administrator using the DEP Feedback Form by: •
•
•
Entering comments directly in the DEP Feedback System on the Technical Standards Portal http://sww.shell.com/standards (mandatory for users with access to Shell Wide Web); Clicking on the DEP Feedback Form button on the DEPs DEPs DVD-ROM main page page (for users without access to Shell Wide Web); Requesting a copy of the DEP Feedback Form from the the Administrator at
[email protected] (for users without access to Shell Wide Web).
For the last two options, the completed DEP Feedback Form can be attached to an email and submitted to the Administrator at
[email protected] [email protected].. Only feedback that is entered into the Feedback Form will be considered.
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1.7
DEP 32.37.10.11-Gen. September 2012 Page 8
DUAL UNITS This DEP contains both the International System (SI) units, as well as the corresponding US Customary (USC) units, which are given following the SI units in brackets. When agreed by the Principal, the indicated USC values/units may be used.
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2.
GENERAL
2.1
INTRODUCTION This DEP should be used in conjunction with DEP 32.31.00.32-Gen. The best hook-up arrangement for each on-line instrument shall be determined on the basis of the specifications given in (4) and (5) and the additional requirements of (6) and (7) on sealing, purging, heating and insulation. The selected hook-up shall guarantee proper measurement at all normal and abnormal process operating and climatic conditions. Instrument sealing and purging shall only be used if alternative hook-ups arrangements are less attractive from a TCoO, measurement accuracy or maintenance point of view. To obtain acceptable response times, the kinematic viscosity of liquids in impulse lines shall 2
be kept below 200 mm /s (200 cSt) under all normal and abnormal conditions for remote mounted instruments. Instruments installed with remote seals and capillary type filled lines are not subject to this requirement due to the response of the instrument and sealed fluid being acceptable (as designed and recommended by the instrument Manufacturer). In locations where freezing may occur, the water-filled parts of sensing lines and the instrument shall be winterised (i.e., heated and insulated), see (7). For access requirements and guidance on selecting the location of instruments and instrument process connections, refer to DEP 32.31.00.32-Gen. Impulse lines for sample take-off and transport for on-line process stream analysis are covered by DEP 32.31.50.10-Gen. 2.2
DESIGN CONCEPTS This DEP covers the requirements for two distinct design concepts: •
Remote mounting concept, as example given in Figure 1.
•
Direct mounting concept, as example given in Figure 2.
Figure 1
Example of remote mount ing concept
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DEP 32.37.10.11-Gen. September 2012 Page 10
Figure 2
2.2. 2.2.1 1
Example Example of direct moun ting concept
Remote Remote mount ing concept
The process is connected to the manifold and instrument through tubing with compression fittings. Maintenance requirements have dominated the design of the remote mounting concept. The concept is based on a need for permanent access and includes facilities for in situ testing and calibration. Typical hook-up arrangements with MESC-coded component listings are available for liquid, gas and steam applications as given in Standard Drawings S 37.001. Metric tubing (10 mm OD) and compression fittings should be used for new projects. The application of US Customary Custom ary sized tubing t ubing (1/2 in OD for USA and 3/8 in for f or Canada) and related compression fittings should be restricted to locations that have standardised on US Customary sizes, and may only be applied if approved by the Principal. The reliable and proven use of compression fittings requires that: •
•
all compression fittings in new projects, including those supplied with equipment packages, shall be of the same size, make and type. Requirements for the size, make and type will be provided by the Principal. The fittings and tubing shall be installed by skilled personnel, strictly in accordance with the Manufacturer's instructions; the impulse lines shall be pressure tested after installation, see (4.5).
2.2. 2.2.2 2
Direct mount ing concept
2.2.2.1
General In the direct mounting concept, the on-line instrument and its manifold are mounted directly on and supported by the process connection(s). These are only acceptable when DEP piping specifications are followed.
2.2.2.2
Close mount concept Close mount concept utilises an instrument stand that is attached to the process pipe with short run of tubing to the transmitter (typically less than 1 m (3 ft)). f t)). The close m ount installation is used when it is acceptable to install an instrument stand on a pipe and the access meets the ”limited accessibility” criteria in DEP 32.31.00.32-Gen. If the pipe is insulated, then the design shall incorporate an “over the insulation design” or mount the transmitter remotely. It is not acceptable to break the barrier of the insulation due to corrosion under insulation (CUI). Additionally, some pipe is considered “critical” in terms of corrosion; instrument stands shall not be placed on uninsulated critical pipe.
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DEP 32.37.10.11-Gen. September 2012 Page 11
This installation has the advantages of the direct mounting installation (e.g., low cost, short impulse lines, reduced plugging, ability to rod out, minimal issues with filling the seal leg, reduced cost of tracing) without the issues of the direct mounting design. 2.2. 2.2.3 3
Comparison of design concepts
2.2.3.1
General It is essential to make the selection between the remote mounting and the direct mounting concept in an early project stage. This Section lists aspects to be considered.
2.2.3.2
Accessibility For maintenance purposes, permanent and easy access used to be the dominant factor in selecting the physical location of remote mounted instruments. Long impulse lines and additional ladders/platforms were the result. The location of a direct mounted instrument is fully determined by the physical location of the process connection, which typically provides limited freedom for positioning. Major improvements in MTBF, MVC techniques and remote diagnostics via ‘intelligent’ communication (e.g., Smart Instrumentation connection to an Instrument Asset Management System (IAMS) have drastically reduced the need for on-the-spot maintenance of modern field instruments. Minimum accessibility requirements are specified in DEP 32.31.00.32-Gen.
2.2.3.3
Performance and maintenance aspects The compactness of the direct mounting concept brings the sensor closer to the process which improves the measurement accuracy and makes the measurement less susceptible to the proper functioning of heating and insulation. Shorter runs and fewer fittings reduce vulnerability to damage and leaks.
2.2.3.4
Responsibilities, risks and construction timing The installation of a remote mounted transmitter (material delivery/erection/wiring/loop testing) is hardly affected by the progress of piping installation activities and, therefore, not time critical. Remote mounted transmitters (including the impulse lines) shall be preserved where the final connections cannot be completed due to outstanding completion. Most direct mounting concepts include the primary isolation valve (e.g., by using monoflanges), which requires additional coordination between the Mechanical and Instrument Engineering disciplines, as the concept should satisfy the requirements of both disciplines. The Manufacturer should be selected in an early project phase, as proprietary design details affect plant design. Furthermore, the primary isolation valve should be installed before pressure testing of equipment and process piping, which might not be the appropriate time for transmitter installation and associated instrumentation activities.
2.2.3.5
Variety control If the direct mounting concept is selected, it will not be suitable for all applications, so both concepts will be mixed on a specific project. This will increase the variety of components and Engineering effort.
2.2.3.6
Design aspects For the direct mounting concept, the following aspects need specific attention: •
•
•
To prevent too high stresses on the process nozzle, the length and weight of the instrument with its accessories shall be reviewed, especially in vibrating service and on small bore process piping. Direct mounting is is less less suitable for applications applications that that require rodding out of process process connections. The compactness compactness of of most direct direct mounting designs causes the instrument housing housing to operate close to the process operating temperature. The upper and lower temperature limits of sensor fill fluids/electronics of instruments restrict the use of
ECCN EAR99
DEP 32.37.10.11-Gen. September 2012 Page 12 the direct mounting concept in low and high temperature applications.
•
When the direct mounting of a differential pressure type flow meter is is considered, the transmitter/manifold shall be supported by only one of the tappings and connected by tubing to the second tapping. If the transmitter is supported by two tappings pointing in the same direction, as shown in Figure 3, a slight misalignment of the tapping points causes leakage and undue stress at the mounting bolts. Furthermore, the thickness of an orifice plate depends on the plate type and its nominal pipe size.
Figure 3
2.3
Incorrect direct mount ing of a dP flow transmitt er/manifol er/manifol d by supporting it from both tappings
MAINTENANCE AND TESTING On-Line Instrumentation design requirements shall provide suitable means to test and verify instrument performance for preventative and reactive maintenance. Such design requirements will be based on the technology chosen (i.e., can diagnostics be leveraged) and any further means that may be reasonable required to allow testing and maintenance. For the various selected technologies, the maintenance philosophy shall define the testing requirements and be approved by the Principal. Further details can be found in DEP 32.31.00.32-Gen.
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DEP 32.37.10.11-Gen. September 2012 Page 13
3.
INSTRUMENT PROCESS CONNECTIONS FOR ON-LINE ON-L INE INSTRUMENTS
3.1
GENERAL Process connections for on-line instruments shall have dedicated primary isolation valves to allow disconnection from the process (applicable for direct mounted pressure gauges as well). Only if a loop requires multiple instruments to cover the full operating range may the primary isolation valve(s) be shared, providing that secondary isolation is available for each instrument. NOTE:
In certain applications, a straight straight through type primary isolation isolation valve, e.g., gate, gate, ball or plug plug valve, valve, may be required to allow rodding out of plugged connections. connections.
The flange facing finishing of direct mounting components (e.g., gauge blocks) and lap joint tube adapters shall be in accordance with ASME B16.5. The number of connections shall be minimised. Where required, compression fittings and/or flanged connections are preferred. For certain applications, the Principal may specify threaded connections. The following factors shall be considered for threaded connection: •
Piping class,
•
Type of service,
•
The process pressure.
Parallel threaded connections with soft annealed metal sealing rings, as shown in Standard Drawings S 37.808 and S 37.809, have preference over tapered sealing connections for their leak tightness. The use of threaded connections shall conform to DEP 31.38.01.11-Gen. NOTE:
Instrument air is category D and NPT connections are acceptable.
NOTE:
Tapered threaded connections such as NPT require a thread sealant such as PTFE. See (Appendix 1) for temperature limitations.
Figure 4
Top tapping
Instrument process connections for gas applications on horizontal process lines shall be located at the top (vertically up or pointing upwards at an angle of up to 45 degrees from the vertical axis) to limit the blocking risk by solids, dirt or pipe scale, as shown in Figure 4. Differential pressure liquid flow measurement on horizontal lines shall have side tapping. If this is not feasible, tappings pointing downwards at an angle of up to 45 degrees from the horizontal axis are acceptable provided they are approved by the Principal. NOTE:
Downwards pointing taps are more susceptible to plugging.
Tappings off the top for liquid dP flow measurement shall only be used on cryogenic selfpurging applications, NOTE:
Gas can get get trapped trapped in the tubing causing a significant error for liquid differential flow measurement.
In all liquid applications, the impulse lines shall slope downwards to the instrument so that gas is automatically vented back into the process, as shown in Figure 5.
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DEP 32.37.10.11-Gen. September 2012 Page 14
For liquid pressure measurement, the preferred installation is tappings off the side with the impulse lines sloped downwards to the instrument so that gas is automatically vented back into the process, as shown in Figure 5. However, for pressure and differential pressure where the error due to trapped gas is not significant (e.g., less than 1 % of range), tappings off the top are acceptable. In all liquid applications, the impulse lines shall slope downwards to the instrument so that gas is automatically vented back into the process, as shown in Figure 5. For all installations, tappings off the bottom shall be the last alternative and shall be approved by the Principal. For differential flow applications containing liquid with vapours or dissolved gas, the process connection should be installed in a vertical line with the flow upwards.
Figure 5
3.2
Vapour Vapour or disso lved gas in liquid , instr ument below side tapping
INSTRUMENT PROCESS CONNECTIONS FOR THE REMOTE MOUNTING CONCEPT Process connections for on-line instruments shall terminate in a DN 15 (NPS ½) lap joint flange with lap joint joint tube adaptor or flange adaptor. If the orifice tappings are next to each other, the DN 15 (NPS ½) ½) flanges will interfere with the adjacent adjacent tap. Thus, the connection will include a process valve with buttweld both ends, a buttweld to cone and thread port, and cone to compression fitting per drawing S37.001 sheet 240.
3.3
INSTRUMENT PROCESS CONNECTIONS FOR THE DIRECT MOUNTING CONCEPT Some Manufacturers offer components that combine the primary isolation valve and instrument manifold in one housing, for instance, in a monoflange style. Such designs may be considered in consultation with Mechanical Engineering in the light of the issues identified in (2.2.3).
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DEP 32.37.10.11-Gen. September 2012 Page 15
4.
GENERAL SPECIFICATION FOR IMPULSE LINES
4.1
SPECIFICATION OF COMPONENTS The general rules for material selection of impulse line components are similar to those for wetted parts of instruments, as detailed in DEP 32.31.00.32-Gen. Material selection is subject to the Principal's approval. Where process conditions allow, the wetted instrument impulse line components (i.e., tubing, compression fittings, manifolds, etc.) shall be made of AISI 316 type stainless steel As a general rule, AISI 316 (or AISI 316L) will be suitable in systems with austenitic stainless steel or carbon steel equipment and piping. The stainless steel shall be resistant to intergranular corrosion in accordance with ASTM A262 Practice E. Stainless steel tubing and compression fittings shall be suitable for a maximum allowable working pressure of at least 413 bar (ga) (5995 psi) at temperatures between -200 °C (-330 °F) and +38 °C (100 (10 0 °F). For F or maximum allowable working pressures at higher temperatures, see (Appendix 1). NOTES:
1. The maximum maximum allowable allowable working pressure of at least 413 bar bar (ga) (5990 psi) applies applies to SS fittings only (see MESC specification 76/039). Lower maximum allowable working pressures apply to CS or brass fittings. 2. The maximum allowable allowable working pressure of the impulse impulse line components components shall equal or exceed exceed the upper design pressure of the process it serves.
Austenitic stainless steel tubing (including insulated tubing) is vulnerable to chloride c hloride stress str ess corrosion if exposed to temperatures above 60 °C (140 °F) and salts or chlorides in combination of high temperature and moisture. Impulse and steam or electric electric tracer tubing installed under such conditions shall be constructed from any of the following materials: •
ASTM B423 alloy (UNS N08825) tubing, e.g., e.g., Incoloy® 825 or or Nicrofer® Nicrofer® 4221;
•
ASTM B668 alloy (UNS N08028) tubing, e.g., Sanicro® 28;
•
UNS S 312 254 SMO.
NOTES:
1. The three groups of of tubing materials, listed listed above, above, may be used in in conjunction conjunction with AISI AISI 316 316 type type stainless steel compression fittings. 2. The hardness of the high high nickel alloy alloy tubing shall be within the range of 77 HRB HRB to 83 HRB. 3. Chloride stress corrosion corrosion on the outside of the tubing tubing may be caused by chlorides present in rain rain water (especially in marine and coastal locations) and by water-soluble chlorides in insulation material. 4. Some Manufacturers offer offer pre-insulated tubing or tubing bundles (impulse and and tracer tubing plus insulation), including a wide range of dedicated sealing and installation accessories. If the Manufacturer’s instructions regarding installation and sealing are followed, such products may be considered in view of their commercial attractiveness and better ingress protection than field fabricated insulated bundles. If such products are chloride free (e.g., not containing any PVC) and if water tightness can be guaranteed during construction and plant operation, chloride stress corrosion will not occur and austenitic stainless stainless steel may be used.
In addition to Incoloy® 825, and for applications where AISI 316 stainless steel is not suitable, other materials such as Monel, Hastelloy, Tantalum or Titanium may be considered. The material selected shall be based on the process and external environment. Alternative ‘hook-up’ arrangements (e.g., diaphragm seals) or alternative measurement principles (e.g., in-line flow instruments or internal level measurements) should be considered as a first choice. Offshore applications shall use a minimum of Inconnel 625 tubing due to the sour process gas and the external affects for saline offshore environment. Where alternative material selection is identified and is a deviation from the site standard, these shall be clearly identified to ensure that cross contamination of materials does not occur.
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Stainless steel impulse line components may be selected on the basis of the MESC numbers given on the component list in the Standard Drawing S 37.001. The Standard Drawings S 37.001 can be used with the metric, USC units, or project specific component list as defined by the Principal. Stainless steel compression fittings shall conform to MESC specification 76/039 and stainless steel tubing to MESC specification 74/051 (for Incoloy® 825, refer to MESC SPE 74/052). Gauge blocks shall be provided with a 13 mm (1/2 in) female threaded gauge adapter to allow dial positioning. The type of thread for the pressure gauge shall be parallel G 13 mm (1/2 in)) unless 13 mm (1/2 in) NPT is specified by the Principal. Gauge blocks may be selected on the basis of MESC specification 60.98.55/201. 4.2
MOUNTING ARRANGEMENTS
4.2.1
General
Subject to environmental conditions, instruments may require protective shades or winterised enclosures (see (7) for enclosures or DEP 32.31.00.32-Gen.). When specified by the Principal for the site, electronic instruments exposed to direct sun radiation shall have a protective shade to limit zero/span shifts resulting from temperature changes/one-sided heating and to reduce instrument housing temperature variations between day and night. When specified by the Principal, shades shall also be provided for junction boxes and equipment boxes that contain electronic equipment, e.g., segment coupler boxes. Where instruments require shades which are not available as standard equipment or require specially made supports and brackets (e.g., in-line flow meters, displacer level instruments, tank gauges), these shall be shown on detailed construction drawings. The shade shall be fixed in a way allowing quick installation and removal. 4.2. 4.2.2 2
Mountin g aspects of the remote mount ing system
4.2.2.1
Instrument mounting supports In the remote mounting concept, instruments are installed on dedicated mounting supports. The use of instrument mounting supports mounted on the process line requires the approval of the Principal. They shall not be applied on: •
Process line sizes sizes smaller than DN 100 (NPS 4),
•
Insulated process piping (unless an over the insulation design is is used)
•
Vibrating service.
If instrument mounting supports are clamped around process piping of a different material, insulating barriers (e.g., tape or gasket material) shall be applied to prevent electrolytic corrosion. Instrument mounting supports shall not be fixed to grating, as this does not provide sufficient stiffness and does not allow the grating to be removed for painting. If instrument mounting supports have to be fixed to fireproofed plant structures, these supports shall be welded to the steel structure before the fireproofing is applied. Typical examples of instrument mounting supports are shown on Standard Drawing S 37.004. 4.2.2.2
Standardised mounting plates In the remote mounting concept, the instrument with its manifold is mounted on a standardised mounting plate. If required, the heating element with terminal box, insulating covers and protective shade are also installed on this plate. See Standard Drawings S 37.815 and S 37.816 for standardised mounting plates with and without protective shades respectively. These plates have facilities for installing nameplates
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in accordance with DEP 32.31.00.32-Gen. If approved by the Principal, the Supplier’s standard manifold mount may be used. 4.2.2.3
Instrument location and routing of impulse line tubing Impulse line tubing shall be as short as possible and the number of joints shall be kept to a minimum. ‘Horizontal’ lines shall slope downward between the transmitter and process connection at a ratio of approximately 1:5 for gas service and shall slope upward between transmitter and process connection for liquid services. For straight lengths up to a maximum of 1 m (3 ft) the tubing is self-supporting, for longer lengths, the tubing shall be supported at approximately 1 m (3 ft) intervals. Insulating spacer material shall be applied to separate the tubing from its supports to prevent galvanic corrosion. Impulse lines shall be grouped closely together. Heavy components such as seal pots shall be properly supported to prevent stress on or damage of compression fittings and tubing. For remote mounted instruments the impulse lines shall be so arranged that any movement will not exert excessive force on any connection. Such movement may be caused by thermal expansion (e.g., in steam or LNG service) or vibration of process pipes. Thermal expansion can be absorbed by expansion loops. Instruments connected to vibrating process pipes shall be installed on dedicated instrument mounting supports, with the tubing arranged sufficiently flexible to take up the vibration and to prevent the tubing from vibrating excessively. Typical examples of hook-ups for thermal expansion or vibrating service are shown on Standard Drawings S 37.001. NOTES:
1. Special attention shall be given to long long impulse impulse lines running horizontally. This type of installation installation shall be avoided to prevent mechanical damage or the formation of "pockets" which may result in false readings. 2. Where fittings are used used in parallel tubing tubing runs, their locations locations may require staggering staggering to provide proper access. 3. Flexible components components shall not be used to absorb movement by thermal expansion expansion or vibration.
4.2.2.4
Connections between differential pressure measuring instruments and manifolds For connections between differential pressure type measuring instruments and manifolds, one of the following connection types should be selected: •
•
4.2.2.5
Connections with standardised mating dimensions as specified in IEC 61518, type A (with an extended spigot) for a maximum allowable working pressure of 413 bar (ga) (5990 psi) at 38 °C (100 °F), with O-ring dimensions according to ISO 3601-1. Connections not standardised by an international body, such as coplanar type connections. The design is Manufacturer/Supplier dependent.
Line supported transmitters •
•
•
Designer shall work closely with the Manufacturer/Supplier who who will will supply the transmitter support system to ensure that the correct supports are used for all applications. All cable supports shall have metallised metallised finish finish and zinc plated carbon steel hardware for connecting individual parts. Type of support that is used shall conform to the following table:
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Type of Line
Line Temperature Temperature
Support Type
Uninsulated Carbon Steel
Less than 260 °C (500 °F)
1
260 °C (500 °F) to 450 °C (850 °F)
2
Insulated Carbon Steel
Less than 350 °F
3
175 °C (350 °F) to 260 °C (500 °F)
3
260 °C (500 °F) to 450 °C (850 °F)
3
Less than 260 °C (500 °F)
1
260 °C (500 °F) to 450 °C (850 °F)
2
Uninsulated Stainless Steel
Over 450 °C (850 °F) Insulated Stainless Steel
Support Type
Remote Mount
Less than 175 °C (350 °F)
3
175 °C (350 °F) to 260 °C (500 °F)
3
260 °C (500 °F) to 450 °C (850 °F)
3
Over 450 °C (850 °F)
3
Description
1
Zinc arc spray metallised carbon steel supports with galvanised cable and zinc plated washer, nuts and hardware.
2*
Stainless steel supports with stainless steel cable and stainless steel washers, nuts and hardware. *
3
Type 2 supports are approximately four to five five times as as expensive expensive as Type 1 and should be used only if required.
Remote mount (preferred) or Over the insulation support.
The above table applies only to the primary support components, and does not apply to components that are attached to the primary support components. For example, a zinc arc spray metallised carbon steel flag can be attached to a stainless steel support assembly using zinc plated u-bolts. 4.3
FILLING, FLUSHING, VENTING AND DRAINING The Principal shall be contacted about the policy on venting, draining and removal of (contaminated) seal and process fluids from impulse lines. Draining/venting is one option; disposal into the process by means of a mobile seal liquid refill pump unit is another frequently used option. The impulse line hook-up should include the necessary connections to connect such a pump unit. When the connectors are not in use, a compression-type plug shall be fitted and secured by a bead-type chain to the non-return valve. NOTE:
The design design of the mobile seal liquid refill pump unit requires the approval of the Principal. Principal.
Vent and drain valves shall be provided with a device to prevent tampering. Approximately, 500 mm (19 in) tubing shall be fitted to vent or drain connections and directed downwards. 4.4
PAINTING AND COATING All supports, brackets, etc., shall be protected by a corrosion resistant paint or coating (e.g., galvanising) in accordance with the requirements of DEP 30.48.00.31-Gen. Surfaces that will be inaccessible after installation shall be treated before installation. Instruments and stainless steel components shall not be painted or coated. Painting shall not foul threaded connections or jeopardise the proper operation of moving parts such as valve handles.
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4.5
DEP 32.37.10.11-Gen. September 2012 Page 19
TESTING All on-line instruments and impulse line components shall be pressure tested to the pressure limit of the instrument or to a pressure of 1.5 times the upper design pressure of the process, whichever is lower. Primary isolation valves shall be closed during piping pressure testing and flushing, per the requirements of DEP 62.10.08.11-Gen. Instrument air, nitrogen or demineralised water shall be used for pressure testing. After pressure testing with water, the instrument and the impulse lines shall be carefully drained and blown out. If the process equipment or piping is tested with another medium than specified above, the primary isolation valves shall be closed to prevent it from entering the impulse lines.
5.
SPECIAL APPLICAT IONS AND CONSIDERATIONS CONSIDERATIONS FOR IMPULSE LINES
5.1
GENERAL For special applications that present additional risk and or exposure from a HSSE or environmental perspective, the use of impulse lines and the number of connections shall be minimised. It is preferable that alternative technologies such as in-line instrumentation or instruments with remote seals be installed to reduce exposure. Under all circumstances, suitable warning labels shall be installed indicating the service and application. For applications whereby remote seals have been installed, calibration and flushing rings shall be applied and be designed such that they have the same requirements as for manifolds (i.e., close vent/drain system).
5.2
STEAM SERVICE Impulse line(s) sizing and layout shall be designed so that any steam will condense before reaching the instrument. To assure steam will condense and cool sufficiently to prevent damage to the transmitter, the transmitter shall be mounted a minimum of 12 cm (5 in) below the highest elevation of the tubing. In freezing climates, steam/condensate steam/condensate impulse lines shall be winterised by tracing and insulation. For remote mounted instruments, seal pot(s) may be provided to establish a firm condensate reference point(s). The impulse line(s) shall slope downwards from the seal pot(s) to instrument process connection and to the instrument. For differential pressure type instruments, these condensate reference points shall be at the same elevation, as shown in Figure 6. The Principal's approval is required for seal pot installations in steam service. For direct mounted pressure instruments, a gauge block with integral siphon should be applied. The Manufacturer’s solutions for direct mounted, differential pressure type instruments may be acceptable, if a firm condensate reference point can be established.
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Figure 6
5.3
Steam Steam flow measurement measurement
OXYGEN SERVICE All components in oxygen service shall meet the requirements of DEP 31.10.11.31-Gen. NOTE:
5.4
Any medium medium containing containing more than 21 % oxygen by volume volume or a system system with air at at a pressure above 50 bar (ga) (725 psi) is to be considered as oxygen service.
HYDROGEN FLUORIDE (HF) SERVICE The material selection for wetted parts of instruments and components shall meet the requirements of DEP 31.38.01.11-Gen. Stainless steel type AISI 316 may, under certain conditions, be subject to pitting and/or stress cracking if exposed to process fluids containing HF. Impulse line tubing in HF service shall be constructed from ASTM B165, UNS NO4400 (Monel) with Monel compression fittings. Alternatively, Monel or carbon steel welded pipes may be applied (see DEP 31.38.01.11-Gen.). All valves shall be of Monel. NOTES:
1. Cold deformation deformation shall shall be minimised by the application application of the largest largest possible possible bending radius, limiting the extreme fibre deformation to 5 % maximum. In practice, this amounts to a minimum bending radius of 10 to 15 times the diameter for small bore piping (less than DN 25 (NPS 1)). 2. Before HF is put into the system, a careful check check of the tightness of compression compression joints and screwed connections shall be completed. Fluorides formed upon leakage will produce a very hard metal surface which will make re-tightening of the joint practically impossible. 3. The Principal shall be consulted for for the selection of impulse impulse line material material for HF service. 4. PTFE seals may be used used in valves in in HF service. service.
5.5
FLUIDS WITH HIGH POUR POINTS OR HYDRATE FORMATION RISK Liquids that solidify at ambient temperatures shall be prevented from entering process tappings, primary isolation valves and impulse lines, to prevent malfunctioning, blockage and/or damage. Applications whereby hydrates may form at low temperatures in gas services shall be reviewed on a case by case basis with the Principal. A liquid seal (6.1), diaphragm seal (6.3), external purging (6.4) or heating (7) may be applied to prevent solidification and hydrate formation.
5.6
FLUIDS CONTAINING SUSPENDED SOLIDS If process fluids contain suspended solids, these solids may settle in process tappings, primary isolation valves and impulse lines, and may ultimately cause complete blockage. Blockage may be prevented by sloping the process connections and (short) impulse lines downwards to the process at an angle of approximately 45°.
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For applications where the concentration of suspended solids is high diaphragm seal (6.3) is the preferred solution. Liquid seal (6.1) or external purging (6.4) may be applied with the Principal’s approval. 5.7
FOULING AND WAXY SERVICE Impulse lines in fouling/waxy service are likely to become plugged, even if heating is applied. In such cases, instruments with extended diaphragms or with remote diaphragm seals should be considered. In the latter case, additional purging may still be required to prevent plugging between the equipment/pipe wall and the remote seal. NOTE:
5.8
Vacuum Flashed Cracked Residue (VFCR) is known to be a non-stable non-stable liquid: liquid: delayed cracking will form coke, which plugs impulse lines. In such situations, remote seals with external purging have been successfully applied.
SUSCEPTIBILITY OF LOW RANGE GAS MEASUREMENTS TO LIQUID SLUGS Experience shows that standard 10 mm (3/8 in) OD impulse line tubing with an internal diameter of 7 mm (1/4 in) has a limited self-draining capability. If used in gas or vapour service, condensable formed, may not flow back into the process, not even in vertical lines. Droplets tend to cluster and slugs of liquids ‘hang’ in the impulse line. ‘Hanging slugs’ have a considerable impact on pressure or differential pressure sensing instruments with a relatively low adjusted range. For pressure and differential pressure sensing instruments with an adjusted range of 2 bar (30 psi) or below, one or more of the following remedial measures should be considered: •
apply heat heat tracing to keep the process fluid in the impulse lines in the vapour phase;
•
apply wet legs;
•
•
NOTE:
5.9
mount pressure sensing instruments in the direct direct vicinity vicinity of the the process connection, if feasible, to limit the tubing length and elevation difference between instrument and process connection; apply wide wide bore tubing/piping DN 15 (NPS ½) or DN 20 (NPS ¾)) instead of standard 10 mm (3/8 in) OD tubing to restore the self-draining capabilities. If very very long impulse lines are required for differential differential pressure sensing (e.g., differential differential pressure measurement across a high column or between columns), two independent pressure-sensing instruments may be installed, whereby the differential is determined by subtraction. For details and limitations of this alternative, see DEP 32.31.00.32-Gen.
LOW TEMPERATURE SERVICE Process liquids operating at temperatures below ambient that vaporise at ambient temperatures will evaporate upon entering the impulse lines before reaching the remote mounted instruments. The vapours formed will push the liquid back towards the process until an equilibrium is established. This self-purging phenomenon occurs for instance in cryogenic processes operating typically between -100 °C (-150 °F) to -170°C (-275 °F). Where required, heating shall be considered to assist self-purging (e.g., LPG applications). For details, see (6.4) and (6.5). Low temperature see (4.2.2.3).
5.10
services
require
expansion
loops
in their
impulse
line-tubing,
VERY TOXIC SERVICE For personnel protection and for environmental reasons, facilities shall be provided to dispel very toxic liquids from instrument impulse lines into the process equipment so that maintenance can be performed safely. A mobile seal liquid refill pump unit shall be used to displace very toxic liquids by safe liquids during operation. See also (4.3). For sites where the ‘vent and drain’ concept is still applied, the following shall apply to very toxic fluids:
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a) All vents vents from instruments/manifolds instruments/manifolds and seal pots shall be connected to flare; b) All drains shall be connected to a drain vessel or covered pit which is allocated for very toxic products and for which adequate disposal shall be arranged; c)
The required length of tubing for the vent and drain lines lines shall be added on the relevant hook-up drawing;
d) The instrument or the manifold shall be provided with filling/ filling/ flushing connector(s), if flushing and neutralising of the instrument and manifold is necessary before the instrument is disconnected. For details, see (4.3); e) The maximum allowable concentration of very toxic components in fluids which may be vented to atmosphere shall be approved by the Principal. 5.11
‘SOUR’ OR ‘WET H2S’ SERVICE ‘Sour’ or ‘Wet H2S’ service is defined in DEP 31.38.01.11-Gen. Materials that, under any process condition, are in contact with process water or aqueous condensate shall comply with ISO 15156 or NACE MR0103, as applicable, and the relevant piping class. If impulse line components cannot be obtained in accordance with these standards (e.g., the rolled thread of some male compression fittings), the Principal shall be consulted. Valve head spindles and/or parts of them in contact with sour fluids shall be constructed from 17-4 PH stainless steel, stellite-coated stainless steel, stellite or Hastelloy-C, complying with ISO 15156 or NACE MR0103, as applicable. NOTES:
1. ISO 15156 shall apply to oil and gas production facilities and natural natural gas sweetening sweetening plants. plants. NACE MR0175 is equivalent to ISO 15156. 2. NACE MR0103 shall apply to other applications (e.g., oil refineries, LNG plants and chemical plants). 3. The front ferrules of compression fittings are the second or third sealing sealing in the fitting and, since they need to have higher hardness in order to function properly, they may be exempted from the hardness limitations.
6.
SEALING AND PURGING PURGING
6.1
LIQUID SEAL Guided Wave Radar, direct mounted pad transmitters, remote seal with capillary seals shall be used where possible. If the application cannot use a remote seal and a seal liquid design is required, then the following requirements for seal liquid shall apply. Seal liquids for use in impulse lines shall be selected in consultation with the party responsible for the process design, considering the following aspects: a) Effect of process fluid on seal liquid, i.e. the resistance/stability of the the seal liquid liquid in contact with the process fluids (polymerisation, disintegration, solubility of process fluid); Example: Some sealing liquids decay in sour service. H2S reacts for instance with silicon oil and causes polymerisation. b) Effect of seal liquid liquid on process fluid (process fluid contamination, poisoning of catalyst); c)
Seal liquid and the selected hook-up shall guarantee a low maintenance effort. A seal liquid that needs frequent replacement or replenishment for instance is not acceptable;
d) Seal liquid properties (temperature expansion coefficient, evaporation and freezing point, kinematic viscosity, handling safety, cost of purchase, tracing, disposal, etc.). This includes the following aspects:
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DEP 32.37.10.11-Gen. September 2012 Page 23 a.
the seal liquid liquid density in in the (traced) impulse line shall be higher than the density of any of the process fluid components to prevent gradual replacement of sealing liquid by components from the process fluid;
b.
the kinematic viscosity in in the impulse line shall not exceed 200 mm /s to obtain an acceptable response time;
c.
the seal liquid shall not evaporate under any operating condition at local ambient conditions;
d.
the seal liquid shall not freeze or shall be protected against freezing at local ambient conditions;
e.
the seal liquid shall not be very very toxic or flammable.
2
Three groups of seal liquids are listed below in order of preference: 1.
‘Familiar’ seal liquid: One of the heavy components, present in the process fluid, fluid, is selected as sealing liquid. If the process fluid contains water, water should be considered as a first choice, as it is attractive for its chemical and physical properties (non-toxic, non-flammable, non-viscous, immune to H2S, density higher than hydrocarbons, low temperature expansion coefficient), low cost, high availability, ease and safety of handling and disposal.
2.
‘Foreign’ seal liquid: A fluid not present in the process fluid. It shall not harm nor be harmed by the process fluid.
3.
Process liquid: liquid: The process liquid liquid is used as seal liquid. liquid.
NOTES:
1. The process process liquid liquid is only suitable as sealing sealing liquid, liquid, if it is self-condensing under any any normal normal and abnormal operating pressure at the highest ambient temperature. 2. If the process liquid is is a mixture of for instance instance hydrocarbons, the density density of process fluids fluids in wet legs may gradually drift away from the density in the associated equipment as a result of ‘stripping’. 3. If the composition of a process process liquid mixture in the equipment equipment changes gradually from light to heavy, self-condensing will replace the light components of the process fluid in the reference leg by heavier components, such as water. This will for instance happen in hydro-conversion plants, that are started up with a light feedstock and subsequently converted to heavier feedstock with a composition that changes gradually as a result of decaying catalyst activity. 4. Applications using ‘familiar’ and ‘foreign’ ‘foreign’ seal liquids liquids have the advantage advantage that the wet leg(s) can be filled prior to start-up and eventually zero checked. This will give a reasonable instrument reading at initial plant start. 5. Level applications using using process liquid in the wet reference leg require require a liquid level in the equipment above the lower nozzle elevation and sufficient pressure to fill the legs with process fluid at initial plant start.
Where seal liquids are used in impulse lines, a nameplate shall be installed near the instrument with information about the seal liquid, such as the seal liquid name. Additionally, the seal liquid density and the height of the wet leg(s) in mm (inches) shall be mentioned for pressure and dP type level/pressure measurements. 6.2
LIQUID SEAL AND HOOK-UP OF WET LEG LEVEL APPLICATIONS
6.2.1
Introduction
The selection of seal liquids and the hook-up arrangement for differential pressure type level instruments with wet legs is defined in global terms in DEP 32.31.00.32-Gen. This DEP section provides further guidance. NOTES:
1. Seal liquid liquid selection selection for the reference leg applications applications requires special attention, since the LRV calculation includes a term for elevation difference (upper nozzle < > transmitter) times density of the reference leg. The LRV shifts if the actual density in the reference leg differs from the one used for LRV calculation. 2. For transmitters mounted mounted just below the lower equipment nozzle nozzle (i.e., transmitters located less than 150 mm (6 in) below the lower equipment nozzle), only density changes in the reference leg affect the LRV. For transmitters mounted well below the lower equipment nozzle (i.e., transmitters located more than 150 mm (6 in) below the lower equipment nozzle), changes in density in the
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DEP 32.37.10.11-Gen. September 2012 Page 24 measurement leg will also affect the LRV and may justify the use of seal liquids in the measurement leg. 3. For transmitters mounted well below the lower equipment nozzle, changes changes in densities in the legs will partially counteract each other in their effect on LRV. The density drift in the measurement leg may however differ from the density change in the reference leg and even if they are equal, a density drift in the reference leg is only partially compensated by the same density drift in the measurement leg. 4. Apart from LRV errors resulting resulting from liquid density density changes, changes, the operating pressure pressure affects the measurement accuracy in two ways: −
−
The transmitter accuracy is affected by variations in operating pressure. This effect is however minor compared to other measurement errors; The LRV calculation includes a term for elevation difference (upper nozzle < > 0% level) times vapour density, which varies with operating pressure. This effect of vapour density on the LRV may be considerable for high pressure applications, as shown in (Appendix 2).
5. (Appendix 2) provides examples for the effect of changes in process variables variables on the measurements.
6.2.2 6.2.2
Hook-up selecti on
The table in Standard Drawing S 37.001 shall be used for hook-up selection of wet leg level measurements. NOTES:
1. If ‘familiar’ ‘familiar’ or ‘foreign’ seal liquid is used for the measurement leg, the the transmitter transmitter shall be mounted more than 150 mm (6 in) below the equipment nozzle to permit seal pot installation. 2. For the definition of ‘familiar’ and ‘foreign’ ‘foreign’ seal liquids, liquids, see (6.1). 3. For process equipment operating operating under partial or full vacuum vacuum conditions, filling filling of wet legs is cumbersome. For such applications, diaphragm seals or another level measurement principle should be considered as a first choice. 4. For standardization reasons, reasons, the Principal may decide to use only only a limited number number of the hook-up types. 5. Manifold valves ‘I-I-V-V’ means Isolate/Isolate/Vent/Vent Isolate/Isolate/Vent/Vent Isolate/Isolate/Equalise/Vent, Isolate/Isolate/Equalise/Vent, see Figure 7 and Figure 8.
and
‘I-I-E-V’
means
6. Hook-up requirements requirements are based based on the following following rationale: a) Seal pots with vent vent valves are provided provided as buffer volume volume for selected wet reference reference legs (optional for steam level measurement). The requirement for seal pot installation for level wet reference leg applications will be per the direction from the Principal. b) Seal pots with vent vent valves are provided provided as buffer volume volume in measurement legs legs if: •
the transmitter is mounted more than 150 mm (6 in) below the lower equipment nozzle and the measurement leg contains ‘familiar or ‘foreign’ liquid.
c) The vent valves on on the seal pots are required required for filling of the wet wet leg with process fluid. fluid. d) Manifolds for wet leg leg level measurements measurements shall only be provided with an equalising equalising valve valve (see Figure 8) if required to f ill the reference leg with process liquid, i.e., both legs contain process liquid and no equalising line is installed between the upper and lower equipment nozzle. In all other cases, the manifold shall be provided without equalising valve (Figure 7) to prevent mixture of measurement and reference leg liquids and/or partial loss of the wet reference leg.
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Figure 7
DEP 32.37.10.11-Gen. September 2012 Page 25
Double isolate/vent type manifold Valves provided I-I-V-V
6.3
DIAPHRAGM SEALS
6.3.1
Introduction
Figure 8
Double isolate/equalise/vent isolate/equalise/vent type manifold Valves provided I-I-E-V
Remote diaphragm seal applications and their installation (tracing/insulation) are covered by DEP 32.31.00.32-Gen. This DEP (6.3) provides additional requirements for installation and calibration of diaphragm seal type level transmitters. 6.3. 6.3.2 2
Remote Remote seals for level applications
6.3.2.1
Reducers For new installations, the equipment nozzle shall match the flange size of the diaphragm seal. If reducers are required to m atch the nozzle size of existing equipment ( e.g., DN 50 (NPS 2)) with the diaphragm seal size (e.g., DN 80 (NPS 3)), eccentric reducers shall be used and the bottom of the reducer shall be flush with the bottom of the primary isolation valve to prevent dirt from collecting/settling.
6.3.2.2
In situ calibration In situ zero and span calibration c alibration at the actual operating pressure should not be implemented. Apart from flushing/purge connections, vent connections are required for in situ zero calibration at atmospheric pressure (see Figure 9). For remote seals, drain/vent or flushing/purge connections shall be installed as required.
Figure 9
Hook-up diaphragm seal
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Flushing rings may be ordered with the diaphragm seals. Alternatively, butt-welded primary isolation valves may be used, provided with orifice flanges on the diaphragm seal side. 6.4
EXTERNAL PURGING External purging may be considered only if other methods to eliminate problems caused by condensation, vaporisation or plugging are not practicable. Its use however, should be avoided whenever possible since it could cause: •
false differentials;
•
installation costs are higher; and
•
more frequent maintenance is required.
Since the process fluid may enter part of the impulse line on purge failure, the selected impulse line materials shall be suitable for the process fluid. The purge fluid shall be free from solids, non-corrosive and in single phase at all operating temperatures and pressures. The purge fluid shall not interfere with the process nor react with the process fluid. Purge systems shall have a guaranteed source of supply at a pressure that is permanently higher than the maximum process pressure, but lower than the design pressure of the process equipment or piping. A low but constant flow rate shall be maintained. The fluid velocity at the process connection shall be approximately 0.06 m/s (2.5 in/s) for liquid purge and 0.6 m/s (25 in/s) for gas or steam purge. The purge injection point should be close to the process connection(s) to limit the effect of pressure drop caused by the purge flow in the impulse line(s). NOTES:
1. Purge gas gas injection injection near the instrument may cause cause considerable measurement errors in low pressure and vacuum applications due to relatively high pressure drop in t he impulse lines. 2. The purge injection point may be located located close to the instrument, if calculations calculations show that the pressure loss in the impulse line(s) has a negligible effect on the measurement accuracy.
A purge purg e assembly assem bly should consist of a filter, f ilter, soft-seated non-return valve(s) and vent valve with anti-tamper facilities. Purge blocks in accordance with these requirements shall be selected on the basis of MESC specification 60.98.70/201. A constant purge flow can be reached by one of the following methods: •
A restriction orifice orifice in the form of a purge orifice orifice nipple. A restriction orifice may be used, if the purge supply pressure is constant and high enough to guarantee a stable purge flow under all operating conditions. For gas and steam service, this is reached at critical flow across the restriction orifice, i.e., the purge flow rate is independent of variations in process operating pressure. For details on purge orifice nipples, see Standard Drawing S 37.805.
•
A constant flow device.
For side mounted m ounted purge pipes in equipment, se e Standard Drawings S 38.047 and S 38.048. Instruments with gas purging shall be mounted above the maximum liquid level and the impulse lines shall slope downwards from the instrument/manifold to the process connection(s). 6.5
SELF-PURGING
6.5. 6.5.1 1
Remote Remote moun ted instr uments
Where self-purging is applied, process connections should be located on the top or side of the equipment/process piping. For process connections at the side of the equipment/process piping, the impulse line(s) shall drop vertically downwards from the instrument and then continue horizontally with a
ECCN EAR99
DEP 32.37.10.11-Gen. September 2012 Page 27
slope of approximately 1:5 down to the primary isolating valve(s) at the process connection(s). To prevent measurement errors due to liquid static head if the self-purging is not operating properly, the vertical drop from the instrument shall be as short as possible, The first part of the impulse line(s) at the primary isolation valve side shall be insulated over a length of at least 300 mm (12 in) to reduce heat influx into the process. The remaining part shall have either: •
•
6.5. 6.5.2 2
an exposed, bare length of at least 300 mm (12 in) to enable evaporation of the process fluid by heat influx from the surrounding atmosphere. This arrangement shall be used if all process liquid components evaporate under all normal and abnormal operating pressures at the lowest ambient temperature; or a heated and insulated length length of at least 300 mm (12 in) to assist evaporation. This arrangement shall be used, if the liquid contains heavy components which will not evaporate under any of the normal or abnormal operating pressures at the lowest ambient temperature.
Direct mount ed instr uments
The currently available direct mounting products are less suitable for instruments in low temperature service, due to the requirement to reduce heat influx into the process and low temperature limits of instruments, see also (2.2.3). NOTE:
The lower temperature limit of instruments instruments depends on the applied sensor fluid and on limits for the electronics. The temperature drop between the process and a direct mounted instrument depends on the properties of the direct mount components, such as dimensions/exposed dimensions/exposed area/number and type of joints and materials materials of construction. construction.
7.
WINTERISATION, WINTERISATION, HEAT TRACING AND INSULATION
7.1
GENERAL The purpose of instrument winterisation, heat tracing and insulation is to: •
Prevent freezing of water;
•
Prevent hydrates;
•
Prevent condensation in gaseous streams;
•
Prevent abnormal fluid states
Failure to adequately winterise, heat trace or insulate instrumentation has the ability to interfere with the orderly and safe handling, and/or measurement or monitoring of the process fluids. The type of heating (steam heating, electrical tracing or other means) of instrumentation and impulse lines shall be established in consultation with the Principal and current site practices. Tracing temperatures shall be carefully selected to ensure appropriate material selection, and to prevent overheating. 7.1. 7.1.1 1
Remote Remote mount ed instr uments
Insulation for manifolds and transmitters shall be easily removable and reusable. Winterised instrumentation and manifolds shall be installed in insulated rigid enclosures. Where additional heating is required, the enclosure shall contain an integral heating system i.e., electric block heater, sized for the required temperature to be maintained. Where electric block heaters are used, they shall be cycled on/off by means of a thermostat located inside of the enclosure whose switching point is engineered for the desired maintain temperature. Irrespective of method used to maintain the temperature within an instrument enclosure, the enclosure shall be properly sealed around all penetrations such as the sensing line, in order to minimise heat loss.
ECCN EAR99
7.1. 7.1.2 2
DEP 32.37.10.11-Gen. September 2012 Page 28
Direct mount ed instr uments
If direct mounting of heated instruments is considered, the following aspects need specific attention: •
•
•
7.1. 7.1.3 3
interface with heating and insulation of the process piping or equipment; availability of prefabricated and readily removable enclosures with heating facilities and insulation for instruments within the selected direct mounting concept; length and additional weight weight resulting from heating and insulation insulation to prevent too high stress on process nozzles.
In line inst ruments
In-line instruments shall be traced in the same manner, i.e., part of the same zone as the corresponding piping. Control, relief, on/off valves, and certain flow meters installed installed in lines shall be insulated with removable blanket type insulation allowing for maintenance and suitable access, while still providing the required protection. All other in-line instruments that do not require maintenance or access shall be permanently insulated. 7.1. 7.1.4 4
Instrument criti cality
For instrumentation that is considered to be critical (i.e., Safety Critical Element), winterised, heat traced or insulated solutions shall be designed, engineered and maintainable to ensure that the reliability and availability of the measurement is not compromised. For applications including instrumentation that may be part of an IPF (as per DEP 32.80.10.10-Gen.), failure of the winterisation, heat tracing or insulation system shall not affect the availability and reliability of the instrument that could change the IPF’s overall Probability of Failure on Demand (PFD). Therefore the requirement for emergency electrical supply (in the event of electrical heat tracing) shall be investigated. 7.1. 7.1.5 5
Control and monit oring
During the design of the winterisation and heat tracing systems, the control requirements shall be approved by the Principal and be documented within the control narrative. The control requirements should consider integration to existing systems of the following topics: how information is shared/presented to operations, and how a system/operator will respond in the event of failure. No more than five instruments should be placed on a single ambient controller. Process temperature-maintain controllers shall be line sensed and turn on when either the impulse line or winterised enclosure interior temperatures drop below the process maintain setpoint. 7.1.6
Alarming
All alarming shall comply with DEP 32.80.10.14-Gen., based on the criticality associated with the winterised system. For instrumentation identified as being part of a Safety Critical Element (SCE) or an IPF, failure of a heat tracing circuit/winterisation system shall provide suitable alarming to operations to ensure timely response and or mitigation. For all other non-SCE or IPF application, an alarming philosophy shall be determined for winterisation systems. 7.1.7
Enclosures
The instrument winterisation enclosure may be of the totally enclosed type (all of the instrument within the enclosure) or of the exposed electronics type (with only manifold and transmitter wetted parts within the enclosure). Care shall be taken in selecting an enclosure type to ensure that the desired maintain temperature can be achieved under minimum ambient temperature conditions. Exposed electronics can sink too much heat to meet required maintain temperatures under minimum ambient conditions. Totally enclosed enclosures can expose the electronics to unacceptable temperatures. Care shall be taken in design to ensure that the enclosure selection can both meet the desired maintain temperature requirements and appropriately protect the electronics from temperatures above the instrument manufacturers specified limit.
ECCN EAR99
7.2
DEP 32.37.10.11-Gen. September 2012 Page 29
STEAM HEATING Steam heating systems shall comply with DEP 31.38.30.11-Gen. The steam supply and condensate return piping shall be short. The manifold and instrument body shall be heated by means of a tracer block. Special tubing (4.1) should be used to heat instrument impulse lines. Special tubing should also be used if impulse lines are winterised by steam heating. To prevent overheating, non-conducting spacers shall be fitted between the impulse and heater tubing at 400 mm (16 in) intervals. The arrangement shall be such that the instrument can be removed without disconnecting the tracer tubing and/or tracer block. If steam heating is applied for reasons of high fluid pour point, the heater tubing and the impulse line shall be clamped together. Clamping material shall be stainless steel. The total number of joints in the tracer tubing shall be kept to a minimum. NOTES:
1. Steam heating heating of in-line in-line instruments (e.g., control valves, vortex meters, turbine meters, positive displacement meters, etc.) shall be installed the same as the connected piping. 2. Hollow bolts bolts shall not not be applied for heating of instruments.
Each instrument shall have a dedicated steam supply and condensate return line with isolating valves, labelled with the instrument tag number. The steam supply to one instrument shall not be divided into parallel sections, i.e., for each instrument, a single continuous path is required from the steam-supply point, up to the steam trap. The steam flow in the tracer tubing shall be downwards and pockets in the tubing shall be avoided because build-up of condensate will prevent a continuous steam flow. Each tracer line shall terminate in a condensate return line via a steam trap. In applications requiring the use of pre-traced and pre-insulated tubing bundles, the bundles shall be selected in accordance with the process conditions such that the diameter, wall thickness meets minimum requirements. In addition, the outer jacket shall be selected based on the environmental conditions (inclusive of temperature, chemicals, UV, etc.). 7.3
ELECTRICAL TRACING The heating equipment shall satisfy the requirements for electrical safety in accordance with the area classification. NOTE :
Certain elements elements are certified only only when when installed in the manifold block. block. In such cases, cases, power power to the heating elements shall be switched on only when the elements are inserted in the manifold block.
The arrangement of the electric tracing shall be such that transmitters can be removed without disconnecting the electrical heating block. All electrical tr ace heating components (except the electrical heating block and/or electrical heater attached to the manifold) are covered in DEP 33.68.30.32-Gen. Electrical tracing shall not be applied in processes where the upper design temperature exceeds the temperature limit of the selected heating tape. If self-regulating tracing tape is used (e.g., for winterising), its ‘power off’ point shall be below the temperature at which the impulse line liquid starts to strip/evaporate. 7.4
INSULATION Traced impulse lines, traced instrument parts and all steam supply and condensate return lines shall be insulated. All couplings in the tracer tubing and the impulse lines shall be accessible without removing the complete insulation.
ECCN EAR99
8.
DEP 32.37.10.11-Gen. September 2012 Page 30
REFERENCES
In this DEP, reference is made to the following publications: NOTES:
1. Unless specifically specifically designated by date, the latest edition of of each publication shall be used, together with any amendments/supplements/revisions amendments/supplements/revisions thereto. 2. The DEPs and most referenced external external standards are available to Shell staff on the the SWW (Shell Wide Web) at http://sww.shell.com/standards/ http://sww.shell.com/standards/..
SHELL STANDARDS
Protective coatings for onshore facilities
DEP 30.48.00.31-Gen.
Gaseous oxygen systems
DEP 31.10.11.31-Gen.
Piping - general requirements
DEP 31.38.01.11-Gen.
Protective steam heating of piping systems (non-electrical)
DEP 31.38.30.11-Gen.
Instruments for measurement and control
DEP 32.31.00.32-Gen.
On-line process analyzers
DEP 32.31.50.10-Gen.
Instrumented protective functions (IPF)
DEP 32.80.10.10-Gen.
Alarm management
DEP 32.80.10.14-Gen.
Electrical trace heating
DEP 33.68.30.32-Gen.
Inspection and functional testing of instruments
DEP 62.10.08.11-Gen.
Compression type tube fittings
MESC SPE 76/039
Tubes, alloy steel, ASTM A269
MESC SPE 74/051
Tubes, Non-ferrous, ASTM B163
MESC SPE 74/052
Specification for instrument gauge blocks, isolate/vent
MESC SPE 60.98.55/201
Specification for instrument purge blocks, self venting
MESC SPE 60.98.70/201
STANDARD DRAWINGS
Instrument impulse lines
S 37.001
Instrument mounting supports
S 37.004
Purge orifice nipple
S 37.805
Parallel threaded connections
S 37.808
Parallel threaded connections, pressure transducers
S 37.809
Mounting plate type A2 (for protective shade without junction box)
S 37.815
Mounting plate type B2 (without protective shade without junction box)
S 37.816
Purge pipe for carbon steel and low-alloy steel equipment
S 38.047
Purge pipe for stainless steel and non-ferrous equipment
S 38.048
AMERICAN AMERIC AN STA NDARDS
Pipe flanges and flanged fittings, NPS 1/2 through NPS 24
ASME B16.5
Standard specification for seamless and welded austenitic stainless steel tubing for general service
ASTM A269
Standard specification of nickel-copper alloy (UNS N04400) seamless pipe and tube
ASTM B165
ECCN EAR99
Standard specification for nickel-iron-chromium-molybdenum-copper alloy (UNS N08825, N08221, and N06845) seamless pipe and tube
DEP 32.37.10.11-Gen. September 2012 Page 31
ASTM B423
Standard specification for UNS N08028 seamless pipe and tube
ASTM B668
Materials resistant to sulfide stress cracking in corrosive petroleum refining environments
NACE MR0103
Petroleum and natural gas industries — Materials for use in H2S-containing environments in oil and gas production
NACE MR0175
INTERNATIONAL STANDARDS
Mating dimensions between differential pressure (type) measuring instruments and flanged-on shut-off devices up to 413 bar (41,3 MPa)
IEC 61518
Fluid power systems - O-rings, Part 1: Inside diameters, crosssections, tolerances and size identification code
ISO 3601-1
Plain end steel tubes, welded and seamless - General tables of dimensions and masses per unit length
ISO 4200
Petroleum and natural gas industries — Materials for use in H2S-containing environments in oil and gas production
ISO 15156
ECCN EAR99
APPENDIX 1
DEP 32.37.10.11-Gen. September 2012 Page 32
PRESSURE AND A ND TEMPERATURE TEMPERATU RE LIMIT ATIONS OF SS TUB ING AND PACKINGS
Table 2
Pressure and temperature limitatio ns of SS tubin g and packing
Design temperature, °C (°F)
Maximum allowable working pr essure, barg barg (psig)
SS tubin g 10 mm OD wall thickness 1.5 mm
SS tubing 3/8 in OD wall thickness 0.065 in
SS components with grafoil packing
SS components with PTFE packing and PTFE tape
- 200 (-330)
413 (5990)
450 (6525)
413 (5990)
-
- 150 (-240)
413 (5990)
450 (6525)
413 (5990)
-
- 100 (-150)
413 (5990)
450 (6525)
413 (5990)
400 (5800)
-50 (-60)
413 (5990)
450 (6525)
413 (5990)
400 (5800)
+38 (100)
413 (5990)
450 (6525)
413 (5990)
400 (5800)
+50 (125)
413 (5990)
450 (6525)
399 (5787)
400 (5800)
+100 (210)
413 (5990)
450 (6525)
351 (5090)
350 (5075)
+150 (300)
411 (5961)
448 (6498)
320 (4641)
300 (4350)
+200 (390)
398 (5772)
434 (6295)
297 (4307)
200 (2900)
+250 (480)
372 (5395)
405 (5874)
276 (4003)
-
+300 (570)
357 (5178)
389 (5642)
260 (3770)
-
+350 (660)
342 ( 4960)
373 (5410)
245 (3553)
-
+400 (750)
332 (4815)
362 (5250)
235 (3408)
-
+450 (840)
325 (4713)
354 (5134)
200 (2900)
-
+500 (930)
319 (4627)
348 (5047)
-
-
+538 (1000)
316 (4583)
344 (4990)
-
-
NOTES :
1. The maximum allowable working pressures P for 10 mm OD x 1.5 mm wall thickness stainless steel tubing as per MESC specification 74/051 have been calculated using the formula:
in which: P
=
maximum allowable working pressure;
Sm
=
the maximum allowable stress in the material caused by internal pressure at the design temperature;
t
min
Do
=
max =
the minimum standard wall thickness; the standard maximum outside diameter.
2. The tolerances for metric sized tubing are in accordance with ISO 4200 and those for US Customary sized tubing are in accordance with ASTM A269.
ECCN EAR99
APPENDIX 2
DEP 32.37.10.11-Gen. September 2012 Page 33 EXAMPL E OF CAL CULATIONS CUL ATIONS OF THE T HE EFFECT OF PROCESS VA RIAB LE CHANGES ON dP LEVEL MEASUREMENTS
Figure 10
Effect of process variable changes on dP level measurement measurement
Table 3 below shows the importance of using operating process data when calculating the range of a level transmitter.
Ap pl ic abl e fo rm ul ae:
-5 LRV = 9.81 * 10 * [ (ELUN - EL0%)*dU
+ (ELo% - ELLN)*dL
-5 URV = 9.81 * 10 * [ (ELUN - EL100%)*dU
+ (EL100% - ELLN)*dL + (ELLN - ELTX)*dTX-H - (ELUN - ELTX)*dTX-L ]
Term T1
Term T2
+ (ELLN - ELTX)*dTX-
Term T3
- (ELUN - ELTX)*dTX-L ]
Term T4
ECCN EAR99
DEP 32.37.10.11-Gen. September 2012 Page 34
Table 3
Effect of process variable changes on dP level measurements measurements Scenarios Scenarios fo r process variable changes Ref. case
Process data
Higher P
Calibration at atm. Pressure
Lower MW
Higher t
Higher dL
Lower dTH
Combin -ed
Pressure
P
bar (abs)
181
190
1
181
181
181
181
190
Molecular Weight
MW
g/mol
28
28
28
22
28
28
28
22
Gas temperature
t
°C
20
20
20
20
35
20
20
35
Compressibility
Z
-
1
1
1
1
1
1
1
1
Process liquid density
dL
kg/m3
820
820
820
820
820
861
820
861
Measured leg density
dTX-H
kg/m3
1000
1000
1000
1000
1000
1000
990
990
Reference leg density
dTX-L
kg/m3
1000
1000
1000
1000
1000
1000
990
990
Gas density
dU
kg/m3
208.0
218.3
1.1
163.4
197.8
208.0
208.0
163.2
Lower Range value
LRV
mbar
-179.2
-177.0
-224.9
-189.1
-185.5
-178.2
-176.8
-185.7
Upper Range Value
URV
mbar
-59.2
-58.9
-64.2
-60.2
-59.4
-50.1
-56.7
-48.8
Calculated Calculated results
Measurement Measurement error s Shift in LRV
%
-
1.3
-25.5
-5.5
-1.2
0.6
1.4
-3.6
Shift in URV
%
-
0.4
-8.6
-1.8
-0.4
15.3
4.1
17.6
