tank8.pdf

100 Overview of Tank Design Abstract This section covers the basic design requirements for atmospheric pressure and internal pressure (up to 2.5 psig) tanks. Company and industry specifications are discussed and the data required before sizing and designing a new tank are listed. Information on tank sizing is given, including procedures for determining safe operational height (SOH)and low level alarms. High level alarms and high-high level shutdowns on tanks are briefly discussed. For design of low pressure (up to 15 psig) and fiberglass tanks, see Section 1200.

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Contents

Page

110

Phases of Tank Engineering

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120

General Considerations

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121

Atmospheric Pressure Tanks

122

Internal Pressure Tanks

130

Basic Data

131

Service-related Data

132

Site-related Data

140

Tank Sizing

141

Factors Limiting Tank Dimensions

142

Diameter versus Height

143

Safe Operational Height and Low Level Alarm Determination

150

Tank Overfill Protection

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160

Industry Codes and Practices

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110 Phases of Tank Engineering The design and construction of a tank involves the following primary phases of engineering work before work can begin: 1.

Compiling the basic data (Section 130 and Appendix B)

2.

Sizing the tank (Section 140)

3.

Selecting type of bottom and roof (Sections 200 and 400)

4.

Designing the tank (Sections 200, 300, 400, and 500), and

5.

Selecting appurtenances (Sections 600, 700 and Appendix A).

6.

Considering site layout (Sections 700 and 800).

Sections 200 and 400 discuss and illustrate the types of bottoms and roofs. Advantages and disadvantages of the various designs are also given. Be sure to refer to Section 160 for information about industry codes and practices that apply to tank engineering.

120 General Considerations This section covers the basic design requirements for atmospheric pressure and internal pressure (up to 2.5 psig) tanks. Use of the company and industry specifications is discussed. Design considerations for low pressure (up to 15 psig) and fiberglass tanks are covered in Section 1200.

121 Atmospheric Pressure Tanks General Requirements Tanks designed for atmospheric pressure usually have cylindrical shells with flat bottoms. For such a tank, the primary stress on the shell is developed by the product hydrostatic pressure at the design fill height called “hoop stress.” The hydrostatic pressure develops a significant stress in a flat tank bottom only around the outer edge where it is joined to the shell. A ring of butt welded annular plates, with a thickness greater than the lap welded bottom plates, is required under certain conditions. Tank roofs are designed for the dead load weight of the roof plus a live load of not less than 25 psf. A stiffening ring (top angle) on the shell is required at the junction of a fixed roof with the shell to support the lateral force (discontinuity stress) applied to the shell by combined load on the roof. The top angles are not there to support lateral forces. A stiffening ring (wind girder) on the shell is also required on all open top tanks.

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100 Overview of Tank Design

API 650 Requirements For most flat bottom, vertical cylindrical storage tanks, API 650 is the standard of choice. •

Using API 650 for water tanks retains the possibility of converting the water tank into a hydrocarbon tank in the future, providing flexibility in a long term capital asset.

•

Use Appendix A gives simplified rules for the design and construction of small tanks that have shell thicknesses not exceeding ½ inch.

•

Use Appendix J gives simplified rules for the design and fabrication of tanks not exceeding 20 feet in diameter that can be completely shop fabricated.

Tanks built to Appendices A and J can be obtained at lower cost, but the simplified design requirements and construction details should be carefully reviewed with regard to reliability required for the tank’s service conditions. Company Specifications and API 650. Large tanks constructed in accordance with API 650 and Company Specifications (TAM-MS-967 Welded Storage Tanks, Fixed Roof or Open Top and TAM-MS-968 Floating Roofs and Internal Floating Covers) are highly reliable as long as service conditions are no more severe than the design allows. These specifications significantly increase reliability by: 1.

Requiring use of materials that resist brittle fracture at the design temperature.

2.

Limiting welding procedures to those that are known to produce high quality welds.

3.

Increasing the extent of radiographic inspection, and requiring magnetic particle inspection to assure a high quality of fabrication.

4.

Requiring hardness testing of production welds for critical service conditions when stress-corrosion cracking can occur, and requiring ultrasonic inspection in addition to radiography.

5.

Requiring more conservative design in seismically active locations.

This high reliability is especially important in environmentally sensitive and populous areas, and areas where a tank failure could cause a major property loss or safety hazard.

API 12 Series Tanks The API 12 series production tanks are usually found only at production facilities. These tanks provide the production industry with standard size tanks of adequate safety and reasonable economy. The economy is achieved by limiting the material specifications for plates and other components and allowing safe but lower standards for welding, inspections and, in some instances, testing. Similar to Appendix J of API 650, the API 12 rules for design and construction are relatively simple, and tanks designed to these codes are relatively inexpensive. Capacity is limited to 10,000 bbl maximum, and the tanks cannot be considered to

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be as reliable as API 650 tanks. They are most suitable for remote production sites, where the highest reliability is not required and anticipated service life is relatively short. API 12B is for field assembled tanks of bolted construction and is very useful for the installation of tanks at sites where hot work (welding) cannot be safely performed, or at remote locations where properly qualified welders are not available. API 12D and F are for field welded and shop welded tanks respectively. Company Specification. TAM-MS-4813, Small Production Tanks, supplements API 12B, D and F primarily in the material requirements for fabrication.

122 Internal Pressure Tanks Several API codes cover design of closed top (fixed roof) internal pressure tanks where temperature is below 200°F: •

For atmospheric tanks use API 650.

•

For higher pressure, not exceeding 2.5 psi, use Appendix F to API 650.

•

For low internal pressures between 2.5 - 15 psi, use API Standard 620.

•

For internal pressures higher than 15 psi use ASME Pressure Vessel Code, Section VIII, which is covered in the Pressure Vessel Manual.

Frangible roof joint calculations will be the same for tanks with internal pressures up to 2.5 psi. The emergency venting calculations are the same with the exception that the vents are changed to hold pressure before opening. This will help prevent rupture and release of contents in the event of overpressure. It is recommended that both emergency venting and a frangible roof joint be provided, whenever possible. Furthermore, either the uplift at the base of the shell resulting from the internal pressure must be less than the total weight of the shell plus the roof, or anchoring to a ring wall must be provided along with some other restrictions that limit the tanks to relatively small sizes. This limits the frangible roofs to tanks larger than 20 - 40 feet. Tanks designed for low pressures, up to 15 psi, according to API 620 tend to have (on larger tanks) more complex geometries compared to cylindrical flat bottom tanks for atmospheric pressure. Low pressure tanks are covered in Section 1200 of this manual.

130 Basic Data This section discusses the data required to size and design a new tank. It briefly discusses use of the Company Data Sheets TAM-DS-967 and TAM-DS-968 located in the specification section of this manual. Construction of a new tank should begin by careful consideration of operational needs, maintenance requirements, and jurisdictional regulations. The following

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information is needed for optimizing the economics of tank design and construction, including tank sizing and site use:

Service-related Data • • • • • • •

Overfill protection Planned and potential service Required operating capacity Liquid properties Anticipated corrosion rates Required hydraulic head Fill and drain rates

Site-related Data • • • •

Air and ground water quality regulations (now and near future) Local earthquake and weather conditions Site conditions Fire protection requirements

131 Service-related Data Planned and Potential Service Future service sometimes dictates tank selection rather than the liquid properties and required capacity of the first stock to be stored. Service most often will affect choice of roof type. For example, finished jet fuel may need to be stored in a cone roof tank equipped with an internal floating roof, to maintain product specifications with respect to water content. Also, crude storage tanks at refineries normally have floating roofs so the tanks can accept many types of crude oil in the future.

Required Operating Capacity Often a comparison of processing unit capacity versus ability to ship product is important in order to get an accurate fix on required storage capacity. An error in determining the amount of storage required can result in unnecessary and costly plant slowdowns or shutdowns. Tank capacity is defined three ways: 1) nominal capacity is the total volume of the tank to the top of the shell expressed in round numbers; 2) gross capacity is the same volume accurately stated; and 3) operating capacity is usable volume from low level alarms to SOH. The difference between 2) and 3) represents storage which is unavailable because of limitations on both the maximum fill height and the low pump out. The designer should always assume that the capacity given to him for determining tank dimensions is the operating capacity unless it is clearly stated otherwise. Unavailable inventory should be held to a minimum and must not be overlooked in sizing a tank.

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Unused Storage Volume—Top of Tank. Most operating organizations have standards which specify the safe overflow or damage height for new tanks, and these standards will fix the unused storage volume at the top of the tank. For cone roof tanks, this storage will generally be 6 to 12 inches below shell height. A value of 6 inches below rafter connections or any shell opening is recommended when the specific standard is not known. In a floating roof tank, the seal and centering mechanisms set the highest roof position because of 1) concern for mechanical damage should they rise above the top angle of the tank and 2) the need to maintain a constant seal to meet air quality regulations. Individual tank vendor’s seal designs should be examined to establish the highest allowable roof elevation. This elevation should be used in determining maximum usable tank volume. The value of any additional storage available in a particular design should be taken into account when evaluating vendor proposals. For tanks located in earthquake Zones 3 and 4, consideration should be given to increasing the unused volume at the top of the tank to allow for sloshing of the contents that may occur during an earthquake thus avoiding stock spillage and damage to the roof and upper shell. Generally, a freeboard of 2 feet will be sufficient. In considering whether to provide this freeboard, the probability of occurrence of an earthquake with a full tank and the probable loss due to sloshing if freeboard is not provided should be weighed against the value of the unused storage capacity. Normally, freeboard for sloshing may be justified for tanks which are full or nearly so for extended periods of time, such as for seasonal storage, but is not justified for tanks which are almost continually being drawn down and refilled. Generally, the secondary seal design requires greater reduction of SOH than does sloshing. Unavailable Inventory—Bottom of Tank. The portion of the tank height that should be allocated to unavailable inventory at the bottom is set by a combination of conditions, many of which are within the designer’s control. In the final design, every reasonable and economic consideration should be given to minimizing this inventory. Crude oil tanks, where more unavailable inventory is needed to accumulate water, are an exception. The minimum operating level for a cone roof must satisfy the suction requirements of the withdrawal pumps. For tanks with a cone down bottom and center sump, or a cone up bottom with bottom nozzle, the unavailable inventory can be reduced to nearly zero in some cases. The minimum operating level of a floating roof is limited by internal appurtenances such as mixers and suction and fill lines or by the landed roof position. The most economical minimum roof level can be achieved by weighing the cost to modify internal appurtenances against the value of any additional inventory obtained by the modification. Roof legs should also be factored into the design. Section 143 gives procedures for determining SOH including high and low level alarms.

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Liquid Properties Data on the following liquid properties is required for both tank selection and design: • • • • •

Specific gravity True vapor pressure, psia Corrosiveness Flash point Viscosity

Knowing the vapor pressure and flash point of the stock is very important in choosing type of roof. Some stock may require pressurized storage. If your stock does, the design process for pressurized storage is covered in Section 1200. Some stock such as high-viscosity or high-pour-point crudes have special requirements such as heated, insulated storage to make the stock pumpable. Another characteristic of heavier oils is their tendency to stratify or layer out when uncirculated. To provide a uniform mixture within a storage vessel it is sometimes desirable to install mechanical mixers. These devices are often found on tanks in gasoline service where additives are slugged into the tank and require thorough mixing into the product.

Anticipated Corrosion Rates Corrosion rates can be determined from the following sources: •

Inspection data for similar services at that location

•

Data collected in Section 300 of this manual and Section 700 of the Corrosion Prevention and Metallurgy Manual

•

Consultation with the CRTC Materials and Equipment Engineering Unit

Required Hydraulic Head Hydraulic head requirements from upstream and downstream facilities can impact tank location and elevation, tank height, and possible pumping requirements. The engineer must work closely with operations or engineers in these facilities to determine these requirements. Examples are: • • •

Feed pump suction pressure requirements for process plants Discharge pressure of product pumps Ship loading or discharge pressures and rates

Fill and Drain Rates The short-range process or shipping requirements should be analyzed so that an accurate fill/drain rate can be determined. Fill/drain rates determine breathing and venting requirements. These requirements are especially important for cone roof tanks installed with special vent devices. These devices relieve the pressure or vacuum which may be generated during the fill/drain operation. Since the vents

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installed on a cone roof tank are a purchased item, overdesign of venting requirements will result in unnecessary cost. Also, an over-sized breathing valve may “chatter” and become damaged. On the other hand, a low estimate of venting requirements could result in a shell failure caused by overpressuring (when filling) or pulling a vacuum (when emptying).

132 Site-related Data The following site-related data must be gathered before sizing and designing a new tank:

Air and Groundwater Quality Regulations Government regulations impact almost every aspect of tank location and design. It is critical that the engineer understand all of the federal, state or local regulatory requirements which affect the project.

Local Earthquake and Weather Conditions Refer to Section 100 of the Civil and Structural Manual for the seismic and wind classifications of your area. Section 500 of the same manual gives rainfall quantities in many of the key areas of the Company. Consult your local weather bureau if your area is not included in these tables.

Site Conditions Know your site conditions. The allowable soil bearing pressure may be the controlling factor in selecting tank height. Nonuniformity of soil conditions may also limit tank height. Some differential settlement between the tank periphery and the center of the tank normally can be accommodated, and uniform settlement over the entire area is seldom a problem except in the design of tank lines. However, very little differential settlement around the periphery of the tank can be tolerated, particularly for floating roof tanks where binding of the roof may occur. Refer to Section 350 for specific recommendations on permissible settlements. In seismically active areas, the site should be investigated to determine the potential for liquefaction during an earthquake. Tanks should not be located on sites subject to liquefaction, or such sites should be stabilized through densification of the underlying soils, if feasible. Similarly, where appropriate, sites in seismically active areas should be investigated for landslides or tsunamis. For the design of tanks to resist earthquakes, see Section 530. Other site conditions may affect tank dimensions:

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The amount of land available often sets diameter restrictions on the tanks to be installed. Also, how near the proposed tank can safely be put to adjacent structures and tanks often limits its size. (See Section 800.)

•

Topography and required earthwork may limit tank diameter and thus increase tank height.

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Prevailing height in an established tank field may dictate tank height, to maintain uniform access between tanks and general appearance of the group.

•

Topography will also have a major impact on the drainage and impounding system design.

•

Local regulations often affect maximum tank height.

Fire Protection Requirements Section 800 lists requirements that affect tank dimensions, site selection, location and spacing. These requirements include: •

Spacing between tanks and minimum distance from property lines. (Refer to NFPA 30.)

•

Type of roof required for certain services. For example, floating roofs are required on tanks with stock having a flash point lower than 100°F, unless vapor recovery or padded gas/inert systems are used. The padded gas/inert system requires additional maintenance.

140 Tank Sizing This section helps the engineer determine the most practical and economical dimensions for the required capacity. It discusses factors which may limit the dimensions. It contains procedures for determining SOH and low level alarms.

141 Factors Limiting Tank Dimensions Site Limitations A specific number of tanks may be required in an area of limited available land space, especially in multiple service areas where different stocks are stored for separate process streams. Available land space can, therefore, limit the diameter of a tank and favor increasing its height to obtain the required capacity. Consideration should also be given to leaving land space available for future tank construction, and to providing adequate space for piping and sufficient access for maintenance equipment. It is desirable to have overhead walkways connect multiple, relatively small tanks that are close together to facilitate gauging. Therefore, it is most convenient to design all of the small interconnected tanks the same height and obtain the required capacity by adjusting tank diameter. Also evaluate the hazards that tanks and adjacent equipment or property present to each other, to assure the most efficient use of available site space. This evaluation should emphasize personnel safety. Consideration should be given to fire danger, chemical contamination, odor nuisance, and noise emission. Section 820 discusses location and spacing in more detail.

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Economic Considerations Economic factors can influence the choice made between diameter and height for the design capacity of a tank. Both the initial investment and long-term operating and maintenance costs should be considered. Let the vendor propose the costs for the Company to evaluate. Some general trends are discussed below, but they may not always hold true. Plant locations, tank design, and type of service can change the relative magnitudes of the economic factors. Therefore, individual plants should make a separate economic analysis for each category of tank. Costly real estate would favor reducing the diameter and increasing the height, despite the availability of sufficient land space for a larger diameter and the possible disadvantages of greater height noted above. Furthermore, larger diameter tanks require thicker shell plates, which may increase materials and construction costs. Also, some steel mills may not stock the thicker (more than about 1.25 inch) plate. Smaller diameter tanks usually have a lower foundation cost for the same tank capacity, because of the smaller circumference ringwall and area of compacted fill under the bottom. Insulation and coating or painting costs are generally higher for larger diameter tanks, due to the greater surface area of the shell.

Seismic Design Limitations In seismically active areas, earthquake design criteria may limit tanks to heights below what would otherwise be economical. For small tanks (under about 4000-bbl capacity) greater height-to-diameter ratios can be used by anchoring the tank. However, anchoring is generally not recommended because the anchors impose large local loading on the tank shell. Figure 100-1 gives the maximum height-todiameter ratio for tanks in four seismic zones, described in Section 100 of the Civil and Structural Manual. Do not use the height-to-diameter ratios listed for assessing existing tanks. Refer to Section 530 of this manual for more detailed information on seismic and wind design. Normally, seismic requirements will govern design limitations. Fig. 100-1

Tank Height-to-Diameter Ratio, by Seismic Zone

Seismic Zone

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Maximum Tank Height-to-Diameter Ratio

1

2.4:1

2

1.25:1

3

0.67:1

4

0.5:1 (Small tanks, soft soil)

4

0.6:1 (Large tanks, firm soil)

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Mechanical Design Limitations Maximum size can be restricted by one or both of the following: 1.

Thickness of the bottom course or ring, which is restricted by API 650 to a maximum of 1¾ inch.

2.

Load bearing capabilities of the soil supporting a tank, or the cost of a piled foundation.

142 Diameter versus Height Choosing the optimum diameter/height combination involves tradeoffs. Consider the following:

Higher, Thinner Tanks Technical factors favoring reduced diameter and increased height are: Minimized unavailable stock. The tank must always remain filled above the low level alarms during operation, which is a fixed distance above the bottom of the tank (see Section 143) regardless of the diameter. Therefore, a smaller diameter reduces the amount of unavailable stock. Maximized head in tank. Increased height of stock level above the low level alarms increases the head available to assist with the transfer of stock out of the tank. Reduced cost of floating roof. The cost of a floating roof is proportionally higher than that of the shell, for a given tank capacity. Increased mixing efficiency. Mixing energy dissipates across large diameter tanks. Easier removal of sediment and easier cleaning. Outside wash and siphon hoses can function across entire bottom of small diameter tanks. Better water draw. Reduced bottom surface area and shorter maximum distance to sump minimizes formation of “birdbaths.” Reduced vapor space in fixed roof tanks. The volume above the top of the shell under the roof increases with increasing diameter. Higher foundation loads. Affect size and cost of foundation. Lower foundation loads. Affect size and cost of foundation.

Shorter, Wider Tanks Technical factors favoring increased diameter and reduced height are: Better resistance to overturning during earthquake. A larger overturning moment is developed in tanks with a large height-to-diameter ratio.

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Reduced floating roof maintenance. The speed and distance of floating roof movement, when filling or emptying, is reduced by increasing the diameter, which reduces wear on the seal assembly. Reduced depth of sediment. The same volume of sediment is distributed over a greater surface area in a larger diameter tank.

Guidelines The information in this section gives rough guidelines for initially choosing height, assuming that other factors do not limit you. With few exceptions, tank height is a multiple of 6 or 8 feet. (A multiple of 10 feet is one acceptable exception.) Tank fabricators generally prefer the larger multiple since it reduces the number of field circumferential welds. Figure 100-2 may be helpful in selecting the preliminary size. Fixed Roof Tanks. Fixed roof tanks are available in many sizes. For fixed roof tank capacities less than 25,000 bbl, the economical height is generally 40 feet or less. In the capacity range of 25,000 to 100,000 bbl, the economical height will generally be 48 feet. In this range, there is little difference in steel cost between 40-foot and 48foot tanks. Usually, 48 - 52 or 60 feet can be economical. Check with vendor for price information. Floating Roof Tanks. The economical height for floating roof tank capacities up to 200,000 bbl will generally be one course (8 feet) higher than for a fixed roof tank of the same capacity. This is due to the higher unit cost of the floating roof in comparison to the shell costs. For capacities over 200,000 bbl, the economical height will generally be 56 to 64 feet. Tanks with Internal Floating Roof. The economical height of a fixed roof tank in which an internal floating roof will be used generally will be the same as for a floating roof tank of the same capacity.

143 Safe Operational Height and Low Level Alarm Determination As discussed in Section 130, many factors affect the SOH and low level alarms of the tank. It is the engineer’s responsibility to work closely with operations to develop SOH and low level alarms which will permit safe operation of the tank while minimizing the unavailable space in the tank. These dimensions should be recalculated any time work done on a tank could affect the SOH or low level alarm.

Safe Operational Height For new tanks or tanks not limited by shell strength (see Section 630), the SOH shall be limited to the lowest value determined among the following factors:

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Six inches below the top angle.

•

Six inches below the bottom of the lowest opening in the tank shell through which oil might overflow.

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Typical Sizes and Corresponding Nominal Capacities for Tanks with 96-inch Butt-welded Courses From API 650, Table A-7. Courtesy of the American Petroleum Institute

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•

Six inches below the lowest girder, rafter or other support which might restrict the flow of foam over the oil surface. Where the total reduction is more than 12 inches below the top angle, or other overflow point, the individual case should be analyzed.

•

Top edge of sealing strip on secondary seals (for tanks so equipped) must be no closer than six inches from the tank shell rim.

•

Any other special conditions (operational or mechanical) which govern, such as height at which a floating roof might hang up or otherwise fail to operate freely.

Form TAM-EF-880 gives a simplified procedure for calculating SOH. Again, this procedure assumes that the SOH is not limited by shell strength.

Low Level Alarms Low level alarms and or shutdowns should be determined using the following factors: Fixed Roof Tanks: •

Six inches above the level where the normal suction line on the tank would lose suction (this could be six inches for bottom drawoff nozzles).

•

Six inches above the top surface of the fill line deflector or suction line vortex breaker.

•

At any level acceptable to the operators with their acknowledgment of the potential cavitation and loss of suction.

Floating Roof Tanks: •

Six inches above the level where the mechanical vacuum breaker leg would contact the bottom. (The mechanical vacuum breaker leg should always hit before the legs of the roof.)

•

Six inches above the level where the floating roof operating legs would contact the bottom (or six inches above the level where the floating roof would land on its fixed supports).

150 Tank Overfill Protection Tank overfill protection system is a special application of high level alarms and high-high level shutdowns on tanks. As a result of two major fires at marketing terminals, NFPA revised its “Flammable and Combustible Liquids Code” (NFPA30) to provide a higher degree of safety for terminals receiving Class I liquids (flash point below 100°F and vapor pressure not more than 40 psia at 100°F) from mainline pipelines or marine vessels.

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Section 2-9 of NFPA-30 states the methods of protection, which are briefly summarized below: 1.

Frequent gauging by personnel continuously on the premises and in communication with the supplier.

2.

High level detection devices independent of tank gauging equipment. Alarms located where personnel can promptly arrange for flow stoppage or diversion.

3.

Independent high level detection system to shut down or divert flow.

Methods 2 and 3 require a tank overfill protection system. API Recommended Practice 2350, “Overfill Protection for Petroleum Storage Tanks,” gives information on equipment, installation, alarm level settings and procedures. Local ordinances may specify the overfill protection method(s). Since 1982, Chevron has installed many new overfill protection systems at Chevron USA Marketing Terminals. Most of these installations were engineered by CRTC. Detailed designs are available. Marketing has determined that tank overfills can create such dangerous hazards that it conducted a Safety Operational Analysis that resulted in adding an additional layer of protection for tanks (automated shutdown system). Click this link: CPL-Mkt Overfill Calculator to go to an example spreadsheet that Marketing and Chevron Pipeline has developed to help describe and calculate overfill alarm settings.

160 Industry Codes and Practices Company tanks are normally designed and fabricated according to one of the specifications or standards listed below. Refer to Section 120 for when to use API 650 and API 12 series specifications. The asterisked (*) documents are included in the manual. Copies of the other documents may be obtained from the addresses at the end of Section 160.

*API Specification 12B, Bolted Tanks for Storage of Production Liquids This specification covers material, design, fabrication, and testing requirements for vertical, cylindrical, aboveground, closed, and open-top bolted-steel storage tanks. Tanks are in standard sizes with nominal capacities of 100-10,000 bbl.

*API Specification 12D, Field Welded Tanks for Storage of Production Liquids This specification covers material, design, fabrication, and testing of vertical cylindrical aboveground, closed-top, field-welded storage tanks in nominal capacities of 500-10,000 bbl.

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*API Specification 12F, Shop Welded Tanks for Storage of Production Liquids This specification covers material, design, fabrication, and testing requirements for shop fabricated, vertical, cylindrical, aboveground, closed-top welded steel storage tanks in nominal capacities of 90-500 bbl.

*API Specification 12P, Fiberglass Reinforced Plastic Tanks Covers minimum requirements for material, design, fabrication and testing of fiberglass reinforced plastic tanks.

API Standard 620, Recommended Rules for Design and Construction of Large Welded, Low-Pressure Storage Tanks These rules cover the design and construction of large, welded, field-assembled storage tanks used for products operated at gas pressure of 15 psig or less. Storage temperatures may range from 200°F to minus 270°F.

*API Standard 650, Welded Steel Tanks for Oil Storage This standard covers material, design, fabrication, erection, and testing requirements for vertical cylindrical, aboveground, closed, and open-top welded steel storage tanks in various sizes and capacities. API 650 tanks may be designed for an internal pressure not exceeding 2.5 psig. Standards for external and internal floating roofs are also included.

API Recommended Practice 651, Cathodic Protection of Above-Ground Petroleum Storage Tanks This RP starts the reader off with corrosion fundamentals, and progresses to discussions concerning how to determine the need for CP based on tank service, corrosion history, soil conditions, environmental regulations, etc. Effects on the reliability of CP by external forces such as foundation design and secondary containment are addressed. The advantages and disadvantages of sacrificial vs. impressed current anode systems, and deep well vs. shallow and ribbon anodes are also discussed.

API Recommended Practice 652, Lining of Above-Ground Petroleum Storage Tank Bottoms This RP deals with the need for linings based on tank service, corrosion history, location, environmental regulations, metal thickness requirements, etc. The RP discusses thin- and thick-film linings bases on epoxy, polyester, and glass-flake. Inspection procedures and equipment are discussed as are techniques for spot repair and relining.

API Standard 653, Tank Inspection, Repair, Alteration, and Reconstruction This standard provides requirements for maintaining the integrity of aboveground storage tanks after they have been placed in service. It covers maintenance, repair, alteration, relocation, and reconstruction of such tanks. In cases where this standard overlaps with API Standard 650 (for new tanks), this standard should be followed for tanks which have already been placed in service.

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API Recommended Practice 1615, Installation of Underground Petroleum Product Storage Systems This publication is a guide for the installation of underground tanks and piping typical of a service station. It covers all aspects of the installation process including materials and equipment, cathodic protection, leak detection and system inspection and testing.

API Recommended Practice 1631, Interior Lining of Underground Storage Tanks This publication recommends procedures for the interior lining of underground tanks used for the storage of petroleum-based motor fuels and middle distillates. In general, it outlines requirements, procedures and operating conditions to be followed by contractors, mechanics and engineers. Methods for gas-freeing tanks, removing sediment and cleaning interior surfaces of steel tanks are also included.

*API Standard 2000, Venting Atmospheric and Low-Pressure Storage Tanks (Non-refrigerated and Refrigerated) This standard covers the normal and emergency venting design requirements for aboveground liquid petroleum storage tanks and aboveground and below ground refrigerated storage tanks designed for operation at pressures from ½ oz. per sq. in. (22 millimeters water column) vacuum through 15 psig (1.034 bar gauge). The requirements of the standard do not apply to floating roof tanks.

API Recommended Practice 2003, Protection Against Ignitions Arising Out of Static, Lightning, and Stray Currents Described in this publication are some of the conditions which have resulted in oil fires ignited by electrical sparks and arcs from natural causes, as well as the methods that the petroleum industry currently is using to prevent ignitions from these sources.

API Publication 2015, Cleaning Petroleum Storage Tanks This publication describes precautions and procedures to clean non-portable, nonrefrigerated atmospheric and pressurized petroleum storage tanks. It includes the use of suitable mechanical equipment and protective clothing, use of proper cleaning methods, elimination of potential ignition hazards, and provision of a means of emergency exit. These procedures are essential for personnel safety and health and for preventing property damage.

API Publication 2027, Ignition Hazards Involved in Abrasive Blasting of Tanks in Service This publication identifies the ignition hazards involved in abrasive blasting of the exteriors of hydrocarbon storage tanks that are in service, including those whose vapor space contains a mixture that is flammable or that can become flammable when air is added. It provides operational guidelines that significantly reduce ignition risks during abrasive blasting.

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API Publication 2023, Guide for Safe Storage and Handling of Heated Petroleum Derived Asphalt Products and Crude Oil Residua The publication discusses precautions to be followed for the storage and handling of asphalt products in heated tanks.

API Publication 2207, Preparing Tank Bottom for Hot Work This publication outlines safety precautions for preventing accidental fires and explosions while making hot-work repairs to tank bottoms.

API Recommended Practice 2350, Overfill Protection for Petroleum Storage Tanks This recommended practice suggests methods of preventing petroleum storage tanks from being overfilled and covers manual and automatic systems that provide protection against tank overfills, as well as safety, environmental protection, optimization of the work place, maintenance, and installation and training.

API Bulletin 2516, Evaporation Loss from Low-Pressure Tanks Breathing, working, and leakage losses encountered in low-pressure tanks (atmospheric to 15 psig) are discussed in this bulletin, which also provides equations for calculating these values.

API Publication 2517, Evaporation Loss from External Floating Roof Tanks A method of estimating total evaporative stock loss from volatile stocks stored in external floating roof storage tanks is presented along with a description of roofs and seals and details of loss analysis.

API Bulletin 2518, Evaporation Loss from Fixed Roof Tanks This bulletin contains the correlation and evaluation of test data for evaporation loss from fixed roof tanks. The information has been used to develop methods of estimating breathing and working losses from gasoline and crude oil tanks. Also included are a loss calculation summary and sample calculations.

API Publication 2519, Evaporation Loss from Internal Floating Roof Tanks This publication contains a method for estimating total evaporative losses and/or the equivalent atmospheric hydrocarbon emissions from freely vented internal floating roof tanks containing multi-component hydrocarbon mixtures, as well as single component stocks.

API Bulletin 2521, Use of Pressure-Vacuum Vent Valves for Atmospheric Pressure Tanks to Reduce Evaporation Loss This bulletin describes the use of pressure-vacuum vent valves to reduce evaporation loss of petroleum and petroleum products stored at essentially atmospheric pressure in aboveground fixed roof tanks and variable vapor-space systems. It also presents factors to be considered when selecting vent valves and serves to increase the awareness of operation and maintenance requirements.

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API Standard 2550 (ASTM D 1220-65), Measurement and Calibration of Upright Cylindrical Tanks Covers procedures for calibrating upright cylindrical tanks larger than a barrel or drum, including procedures for making necessary measurements to determine total and incremental tank volumes and the recommended procedure for computing volumes.

API Standard 2555 (ASTM D 1406-65), Liquid Calibration of Tanks Covers standard procedure for calibrating tanks, or portions of tanks, larger than a barrel or drum by introducing or withdrawing measured quantities of liquid.

Guide for Inspection of Refinery Equipment, Chapter XIII, Atmospheric and Low-Pressure Storage Tanks This chapter covers the inspection of atmospheric storage tanks that have been designed to operate at pressures from atmospheric through 0.5 psig, and of lowpressure storage tanks that have been designed to operate at pressures above 0.5 psig through, but not over, 15 psig. Such details as reasons for inspection, frequency and time of inspection, methods of inspection, and of repair, and records are included.

API Manual of Petroleum Measurement This booklet gives API Standards for tank calibration and gauging. See Chapter 2— Tank Calibration (by conventional strapping and optical methods) and Chapter 3— Manual and Automatic Tank Gauging.

ANSI/ASME Standard B96.1, Welded Aluminum-Alloy Storage Tanks This standard contains rules for the design, fabrication, and testing of aboveground welded aluminum storage tanks.

AWWA Standard D100, Welded Steel Elevated Tanks, Standpipes, and Reservoirs for Water Storage This American Water Works Association standard outlines the general requirements associated with design loads, earthquakes, allowable stress, and testing of tanks designed for water storage.

NFPA 30, Flammable and Combustible Liquids Code This National Fire Protection Association code discusses tank spacing, impoundage and drainage requirements and minimum fire protection facilities for tanks.

NFPA 78, Lightning Protection Code Chapter 6 of this document provides guidelines on lightning protection of aboveground tanks.

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UL 58, Steel Underground Tanks for Flammable and Combustible Liquids UL 142, Steel Aboveground Tanks for Flammable and Combustible Liquids These Underwriters’ Laboratories, Inc. (UL) standards cover the design, fabrication, and testing of shop welded horizontal or vertical tanks. The maximum capacity of UL tanks is approximately 1000 bbl.

Addresses Write to the following addresses to obtain copies of any of the above listed codes or standards. Note: All ASME, AWWA, NFPA, and UL standards can be ordered from ANSI. American Petroleum Institute (API) Publications and Distribution Section 1220 L Street Northwest Washington, D.C. 20005 (202) 682-8375 American National Standards Institute (ANSI) Publications Orders 1430 Broadway New York, NY 10016 (212) 642-4900 American Water Works Association Publications Orders 6666 W. Quincy Avenue Denver, CO 80235 National Fire Protection Association Batterymarch Park Quincy, MA 02269 Underwriters’ Laboratories, Inc. Publications Orders 1655 Scott Blvd. Santa Clara, CA 95050

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