APPENDIX B—RECOMMENDATIONS FOR DESIGN AND …



AGENDA ITEM 650-554

TITLE: Bottom Underside Corrosion Mitigation (prevention)

Date: July, 2007

Handled By: Alan Watson

A.R. Watson USA

4016 E Maryland St.

Bellingham, WA 98226

Cell phone: 251-751-7732

Fax: 360-752-1779

E-Mail: arwatson@

Purpose: To revisit Appendix “B” Recommendations for Design and Construction of Foundations for Aboveground Oil Storage Tanks with bottom underside corrosion mitigation (prevention) in mind

Source: EEMUA Publication No 183: 1999 “Guide for the Prevention of Bottom Leakage from Vertical, Cylindrical, Steel Storage Tanks”

Alan Watson 25 years experience with lifting aboveground storage tanks and has seen what has caused bottom underside corrosion from faulty foundations

Input from aboveground storage tanks terminal operators.

Industry Impact: Clarifications to existing text with an end result of extending the tank bottom life from underside corrosion.

Acknowledgements: I wish to thank the Engineering Equipment and Materials Users Association and the British Standards Institution for allowing various diagrams from their respective publications to be reproduced in this document

Edit Legend: Red is additions

APPENDIX B—RECOMMENDATIONS FOR DESIGN AND CONSTRUCTION OF FOUNDATIONS FOR ABOVEGROUND OIL STORAGE TANKS

B.1 Scope

B.1.1 This appendix provides important considerations for the design and construction of foundations for aboveground steel oil storage tanks. Recommendations are offered to outline good practice and to point out some pre-cautions that should be considered in the design and construction of storage tank foundations and to assist in minimizing soilside corrosion to tank bottoms

B.1.2 Since there are a wide variety of surface, subsurface and climatic conditions, it is not practical to establish design data to cover all situations. However it is common practice to build tanks on the following foundation types:

a. Earth foundation (Fig. B-1)

b. Earth foundation with a concrete ringwall (Fig. B-2)

c. Earth foundation with crushed stone ringwall (Fig. B-3)

d. Concrete slab foundation, plain (Fig. B-4)

e. Concrete slab foundation, piled (Fig. B-4)

The allowable soil loading and the exact type of subsurface construction to be used must be decided for each individual case after careful consideration. The same rules and precautions shall be used in selecting foundation sites as would be applicable in designing and constructing foundations for other structures of comparable magnitude.

B.2 Subsurface Investigation and Construction

B.2.1 At any tank site, the subsurface conditions must be known to estimate the soil bearing capacity and settlement that will be experienced. This information is generally obtained from soil borings, load tests, sampling, laboratory testing and analysis by an experienced geotechnical engineer familiar with the history of similar structures in the vicinity. The subgrade must be capable of supporting the load of the tank and its contents. The total settlement must not strain connecting piping or produce gauging inaccuracies, and the settlement should not continue to a point at which the tank bottom is below the surrounding ground surface. The estimated settlement shall be within the acceptable tolerances for the tank shell and bottom.

Common methods of site investigation include Cone Penetration Tests (CPTs), boreholes, and in-situ and laboratory testing. The purpose of the investigation is to determine the physical, mechanical and chemical properties of the underlying strata. The required number of CPTs or borings depends on the diameter of the proposed tank and the variation of the subsoil layers.

The recommended minimum number of CPTs or borings is;

a. 5, for tanks up to 12m (40ft) diameter

b. 9, for tanks larger than 12m (40ft) and up to 40m (130ft) diameter

c. 13, for tanks larger than 40m (130ft) diameter

The CPTs or borings shall be carried out on the tank foundation circumference at approximately 10m (32ft) center to center and one close to the center of the tank foundation, together with one or more borings.

B.2.2 When actual experience with similar tanks and foundations at a particular site is not available, the following ranges for factors of safety should be considered for use in the foundation design criteria for determining the allowable soil bearing pressures. (The owner or geotechnical engineer responsible for the project may use factors of safety outside these ranges.)

a. From 2.0 to 3.0 against ultimate bearing failure for normal operating conditions.

b. From 1.5 to 2.25 against ultimate bearing failure during hydrostatic testing.

c. From 1.5 to 2.25 against ultimate bearing failure for operating conditions plus the maximum effect of wind or seismic loads.

B.2.3 Some of the many conditions that require special engineering consideration are as follows:

a. Sites on hillsides, where part of a tank may be on undisturbed ground or muck and part may be on till or another construction or where the depth of required fill is variable.

b. Sites on swampy or filled ground, where layers of muck or compressible vegetation are at or below the surface or where unstable or corrosive materials may have been deposited as fill.

c. Sites underlain by soils, such as layers of plastic clay or organic clays that may support heavy loads temporarily but settle excessively over long periods of time.

d. Sites adjacent to water courses or deep excavations, where the lateral stability of the ground is questionable.

e. Sites immediately adjacent to heavy structures that distribute some of their load to the subsoil under the tank sites. There by reducing the subsoil’s capacity to carry additional loads without excessive settlement.

f. Sites where tanks may be exposed to flood waters, possibly resulting in uplift, displacement, or scour.

g. Sites in regions of high seismicity that may be susceptible to liquefaction.

h. Sites with thin layers of soft clay soils that are directly beneath the tank bottom and that can cause lateral ground stability problems.

i. Sites where tanks, buildings or existing piles have been removed causing the ground under the new tank having differential compaction.

J Rerouting existing drainage ditches, water courses and underground water courses

B.2.4 If the subgrade is inadequate to carry the load of the filled tank without excessive settlement, shallow or superficial construction under the tank bottom will not improve the support conditions. One or more of the following general methods should be considered to improve the support conditions:

a. Removing the objectionable material and replacing it with suitable, compacted material.

b. Compacting the soft material with short piles.

c. Compacting the soft material by preloading the area with an overburden of soil. Strip or sand drains may be used in conjunction with this method.

d. Stabilizing the soft material by chemical methods or injection of cement grout.

e. Transferring the load to a more stable material underneath the subgrade by driving piles or constructing foundation piers. This involves constructing a reinforced concrete slab on the piles to distribute the load of the tank bottom.

f. Constructing a slab foundation that will distribute the load over a sufficiently large area of the soft material so that the load intensity will be within allowable limits and excessive settlement will not occur.

g. Improving soil properties by vibrocompaction, vibro-replacement, or deep dynamic compaction.

h. Slow and controlled filling of the tank during hydrostatic testing. When this method is used, the integrity of the tank may be compromised by excessive settlements of the shell or bottom. For this reason, the settlements of the tank shall be closely monitored. In the event of settlements beyond established ranges, the test may have to be stopped and the tank releveled.

B.2.5 The fill material used to replace muck or other objectionable material or to build up the grade to a suitable height above the existing ground level shall be adequate for the support of the tank and product after the material has been compacted. It is very important that the fill material shall be fine and uniform and free of vegetation, organic matter, cinders, lumps of clay, rocks, paper, plastic, wood, welding electrodes etc. and any material that will cause corrosion of the tank bottom. If large particle sizes are used, differential aeration corrosion may result at points where the large particles or debris contact the steel tank bottom. In this case, cathodic protection will not be effective in eliminating the pitting.

B.2.6 The chemistry of native soil and fill material shall consider in the foundation design. Osmosis and/or periodic flooding can cause corrosive material such as chloride salts and sulfates to migrate up to the tank bottom and increase the risk of corrosion.

B.2.7 Soil resistivity provides valuable information about the corrosivity of the material used under and around a tank. A general resistivity classification is given in Table 1. There are several techniques for measuring soil resistivity. A common method is described in ASTM G 57.

Table 1—General Classification of Resistivity

|Resistivity Range (ohm-cm) |Potential Corrosion Activity |

|10,000 |Progressively less corrosive |

B.2.8 The resistivity of the pad material may be higher than the existing surrounding soil. Corrosive soil beneath the higher resistivity pad material may contaminate the pad fill by capillary action. Thus, resistivity of surrounding soil may be used to determine the probability of corrosion on the tank bottom. The results of soil resistivity surveys can be used to determine the need for cathodic protection. However, other properties of the soil (see B.3.2c) f, g, h, I, j and k) should also be considered.

B.2.9 In coastal areas, salt spray on tank surfaces will be washed down the sides of the tank by rain and may flow beneath the tank to contaminate the tank pad. This also can occur in areas where fertilizers or chemicals may be in the atmosphere either from spraying or industrial operations. The tank pad also can become contaminated by wicking action that can draw contaminates such as chlorides up from the water table. Cathodic protection is usually necessary for corrosion prevention in these situations.

B.2.10 If a leak occurs in a tank bottom, the leaking material can also influence corrosion on the external side. If water leaks from the tank, the environment under the tank may become more corrosive, if product leaks from the tank, it could create corrosion cells that did not previously exist or adversely affect the effectiveness of cathodic protection. A leak may wash away part of the pad material and eliminate the contact of the tank bottom with the ground in some areas. Cathodic protection will not be effective in such areas. Additionally, the drainage properties of the pad material may be deteriorated by a leak and allow water and contaminates to remain in contact with the tank bottom.

B.2.11 The grade and type of fill material shall be capable of being compacted with standard industry compaction techniques to a density sufficient to provide appropriate bearing capacity and acceptable settlements. The placement of the fill material shall be in accordance with the project specifications prepared by a qualified geotechnical engineer.

B.3 Tank Pads

B.3.1 In wet climates the grade or surface on which the lowest point of a tank bottom will rest should be constructed preferably 450 mm (18 in) or more above the surrounding ground surface. This will provide suitable drainage, help keep the tank bottom dry and compensate for some small settlement that is likely to occur. If a large settlement is expected, the tank bottom elevation shall be raised so that the final elevation above grade will be a minimum of 450 mm (18 in.) after settlement.

In dry climates the grade or surface on which the lowest point of a tank bottom will rest can be reduced to 150 mm (6 in) above the surrounding ground surface.

In lieu of elevating the tank foundation, consideration can be given to have adequate sump volume in the dike for the worst case storm or snowmelt to keep moisture away from the tank bottom

Consideration shall be given in the design of a new tank foundation in the event that the difference between the expected settlement at the center of the tank and the shell is greater than 30% of the maximum expected settlement See B.2.4.h

B.3.2 There are several different materials that can be used for the grade or surface on which the tank bottom will rest. To minimize future corrosion problems and maximize the effect of corrosion prevention systems such as cathodic protection, the material in contact with the tank bottom should be fine and uniform. Precautions shall be taken during installation of the grade material and erection of the tank to prevent contamination of the grade material.

The following material including but not limited to can be readily shaped to the bottom contour of the tank to provide maximum contact area and will protect the tank bottom from coming into contact with large particles and debris.

a. Bitumen-sand (cold patch asphalt) mix 50 mm (2 in) thick laid on top of the foundation under the tank steel bottom

Note; Bitumen-sand layers under steel tank bottoms inhibit cathodic protection current.

Bitumen-sand layers can be affected by welding resulting in porosity or cracks in welds and producing smoke discomfort to welders

b. Oil sand mixture consists of approximately 90 liter (18 gal) of heavy base petroleum oil per cu meter (per cu yd). The sand has the correct amount of oil when it can be formed into a ball without dripping oil. Sand should be coated but not running with excess oil.

c. Clean washed sand (see API Recommended Practice 651 section 5.3.2.1)

f. Electrical resistivity of the sand material is a commonly used method for determining its corrosivity because it is relatively easy to measure. The resistivity of a soil depends on its chemical properties, moisture content, and temperature. The resistivity of the sand material may be determined in accordance with ASTM (157, or equivalent. The results of the testing shall be forwarded to the cathodic protection designer.

g. Measuring pH indicates the hydrogen ion content of a soil. Corrosion of steel is fairly independent of pH when it is in the range of 5.0 to 8.0. The rate of corrosion increases appreciably when pH is < 5.0 and decreases when pH is> 8.0. pH may be determined in accordance with ASTM G 51 or equivalent.

h. Chlorides will affect the resistivity of soil, and act as a depolarizing agent which will increase the current requirement for cathodic protection of steel. Pitting corrosion on steel can begin at chloride levels of 10 ppm. Chloride content may be determined in accordance with ASTM D 512 or equivalent. There is currently no industry consensus on an acceptable range for chloride levels; therefore the tank owner/operator should specify the acceptable chloride level. There are practical and possible economic limitations in achieving minimum levels of chloride content.

i. Sulfate levels >200 ppm frequently indicate high concentrations of organic matter. Sulfate content may be determined in accordance with ASTM D 516 or equivalent. There is currently no industry consensus on an acceptable range for sulfate levels, therefore the tank owner/operator should specify the acceptable sulfate level. There are practical and possible economic limitations in achieving minimum levels of sulfate content.

j. Sulfide levels> 0.10 ppm, may indicate that sulfates have been reduced by bacteria. Sulfide content may be determined in accordance with EPA 0376.1 or equivalent. There is currently no industry consensus on an acceptable range for sulfide levels, therefore the tank owner/operator should specify the acceptable sulfide level. There are practical and possible economic limitations in achieving minimum levels of sulfide content.

k. Random testing of the sand material should be conducted at the supply source to determine if the electrical resistivity and chemical properties are at acceptable levels. Sand samples used to determine the properties of the material should be taken from the actual material that is to be used during construction. If test results do not meet owner/operator specified levels then additional steps such as rewashing and/or adding Portland cement or lime, or secure another source of sand, may need to be taken.

If cathodic protection is to be utilized the clean washed sand layer should be increased to a minimum of 150 mm (6 in).

B.3.3 During construction, the movement of equipment and materials across the grade will damage the graded surface and possibly bring in native soil (e.g. mud or lumps of clay) into the grade material. These irregularities should be corrected before bottom plates are placed for welding.

B.3.4 The bottom side of each steel plate to be used for tank bottom construction should be inspected immediately before placement onto the pad to ensure that any contaminating debris that is adhered to it (e.g., mud) is removed and that the plate surface is clean.

B.3.5 Mechanical vibratory compaction and rolling is suggested to be done for each layer to achieve compaction to 95% of the maximum dry density per ASTM D 1557 or equivalent

B.3.6 Adequate provisions, such as making size gradients in sub- layers progressively smaller from bottom to top, or the use of synthetic membrane or geotextile fabric liners should be made to prevent the fine material from leaching down into the larger material, thus negating the effect of using the fine material as a final layer. This is particularly important for the top of a crushed rock ringwall.

CAUTION: Compaction by water flooding is not recommended because the water used to flood the sand pad may cause contamination and deterioration of the original chemical properties of the sand material. Additionally, flooding can cause bulking of the pad and subsequent adverse settlement when loaded, possibly causing damage to the tank bottom, attached piping or other appurtenances.

B.3.7. Unless otherwise specified by the owner, the finished tank grade shall be crowned from its outer periphery to its center at a slope of one inch in ten feet. The crown will partly compensate for settlement which is likely to be 30% greater at the center than the tank shell. It will also facilitate cleaning and the removal of water and sludge through openings in the shell or from sumps situated near the shell. Because crowning will affect the lengths of roof-supporting columns, it is essential that the tank manufacturer be fully informed of this feature sufficiently in advance. (For an alternative to this paragraph. see B.3.4.)

Note: There are specific advantages and disadvantages of each type of foundation and fill material regarding the risk of corrosion and the effectiveness of corrosion prevention techniques, such as cathodic protection. Tank bottom corrosion and corrosion prevention practice that relates to the foundation of a tank are addressed in API Recommended Practice 651. These practices shall be considered in the design and installation of the tank foundation and grade materials and in the erection of the tank.

B.3.8. As an alternative to B.3.7 the tank bottom may be sloped toward a sump. The tank manufacturer must be advised as required in B.3.7

B.4 Typical Foundation Types

Many satisfactory foundation designs are possible when sound engineering judgment is used in there development. Seven design examples are given to illustrate various options and advantages or disadvantages of each type and are not meant to exclude other designs from being used. Some examples show sand bitumen mix and flexible membrane liners. The sand bitumen materials will preclude the use of cathodic protection in the future since it is highly resistant to CP currents. The membrane liner will restrict the options for cathodic protection to only the installation of anodes between the liner and the tank bottom by directional drilling. Precautions addressed in API 651 shall be considered in the selection of tank bottom design.

B.4.1 Earth Foundation (Fig. B-1)

B. 4.1.1 When an engineering evaluation of subsurface conditions that is based on experience and/or exploratory work has shown that the subgrade has adequate bearing capacity and that tank settlements will be acceptable, satisfactory foundations may be constructed from earth materials. The performance requirements for earth foundations are identical to those for more extensive foundations. Specifically, an earth foundation should accomplish the following:

a. Provide a stable plane for the support of the tank.

b. Limit overall settlement of the tank grade to values compatible with the allowances used in the design of the connecting piping.

c. Provide adequate drainage.

d. Not settle excessively at the perimeter due to the weight of the shell wall.

B.4.1.2 Earth foundations can consist of compacted crushed stone, screenings, fine gravel, clean sand, or similar material placed directly on virgin soil. Any unstable material must be removed, and any replacement material must be thoroughly compacted.

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B.4.2. Earth Foundation with a Concrete Ring Wall (Fig. B-2)

B.4.2.1 Large tanks, tanks with heavy or tall shells and/ or self-supported roofs impose a substantial load on the foundation under the shell. This is particularly important with regard to shell distortion in floating-roof tanks. When there is some doubt whether a foundation will be able to carry the shell load directly, a concrete ringwall foundation should be used. As an alternative to the concrete ringwall noted in this section, a crushed stone ringwall (see B.4.3) may be used. A foundation with a concrete ringwall has the following advantages:

a. It provides better distribution of the concentrated load of the shell to produce a more nearly uniform soil loading under the tank.

b. It provides a level, solid starting plane for construction of the shell.

c. It provides a better means of leveling the tank grade, and it is capable of preserving its contour during construction.

d. It retains the fill under the tank bottom and prevents loss of material as a result of erosion.

e. It contributes to limiting moisture under the tank if adequately sealed

A disadvantage of concrete ringwalls is that they may not smoothly conform to differential settlements. This disadvantage may lead to high bending stresses in the bottom plates adjacent to the ringwall.

B.4.2.2 When a concrete ringwall is designed. it shall be proportioned so that the allowable soil bearing is not exceeded. The ringwall shall not be less than 300mm (12 in.) thick. The centerline diameter of the ringwall should equal the nominal diameter of the tank: however, the ringwall centerline may vary if required to facilitate the placement of anchor bolts or to satisfy soil bearing limits for seismic loads or excessive uplift forces. The depth of the wall will depend on local conditions, but the depth must be sufficient to place the bottom of the ringwall below the anticipated frost penetration and within the specified bearing strata. As a minimum, the bottom of the ringwall, if founded on soil, shall be located 0.6 m (2 ft) below the lowest adjacent finish grade. Tank foundations must be constructed within the tolerances specified in 5.5.5. Recesses shall be provided in the wall for flush- type cleanouts, drawoff sumps and any other appurtenances that require recesses.

B.4.2.3 A ringwall should be reinforced against temperature changes and shrinkage and reinforced to resist the lateral pressure of the confined fill with its surcharge from product loads. ACI 318 is recommended for design stress values, material specifications, and rebar development and cover. It is recommended that concrete be measured, mixed, transported and placed in accordance with ACI 304R. The following items concerning a ringwall shall be considered:

a. The ringwall shall be reinforced to resist the direct hoop tension resulting from the lateral earth pressure on the ringwalls inside face. Unless substantiated by proper geotechnical analysis, the lateral earth pressure shall be assumed to be at least 50% of the vertical pressure due to fluid and soil weight. If a granular backfill is used, a lateral earth pressure coefficient of 30% may be used.

b. The ringwall shall be reinforced to resist the bending moment resulting from the uniform moment load. The uniform moment load shall account for the eccentricities of the applied shell and pressure loads relative to the centroid of the resulting soil pressure. The pressure load is due to the fluid pressure on the horizontal projection of the ringwall inside the shell.

c. The ringwall shall be reinforced to resist the bending and torsion moments resulting from lateral, wind, or seismic loads applied eccentrically to it. A rational analysis, which includes the effect of the foundation stiffness, shall be used to determine these moments and soil pressure distributions.

d. The total hoop steel area required to resist the loads noted above shall not be less than the area required for temperature changes and shrinkage. The hoop steel area required for temperature changes and shrinkage is 0.0025 times the vertical cross-sectional area of the ringwall or the minimum reinforcement for walls called for in ACI 318, Chapter 14.

e. For ringwalls, the vertical steel area required for temperature changes and shrinkage is 0.0015 times the horizontal cross-sectional area of the ringwall or the minimum reinforcement for walls called for in ACI 318, Chapter 14. Additional vertical steel may be required for uplift or tensional resistance. If the ring foundation is wider than its depth, the design shall consider its behavior as an annular slab with flexure in the radial direction. Temperature and shrinkage reinforcement shall meet the ACI 318 provisions for slabs. (See ACI 318, Chapter 7.)

f. When the ringwall width exceeds 460 mm (18 in.), using a spread footing beneath the wall should be considered. Footings may also be useful for resistance to uplift forces.

g. Structural backfill within and adjacent to concrete ring- walls and around items such as vaults, undertank piping, and sumps requires close field control to maintain settlement tolerances. Backfill should be granular material compacted to the density and compacting as specified in the foundation construction specifications. For other backfill materials, sufficient tests shall he conducted to verify that the material has adequate strength and will undergo minimal settlement.

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B.4.3. Earth Foundation with a Crushed Stone and Gravel Ringwall (Fig. B-3)

B.4.3.1 A crushed stone or gravel ringwall will provide adequate support for high loads imposed by a shell. A foundation with a crushed stone or gravel ringwall has the following advantages:

a. It provides better distribution of the concentrated load of the shell to produce a more nearly uniform soil loading under the tank.

b. It provides a means of leveling the tank grade, and it is capable of preserving its contour during construction.

c. It retains the fill under the tank bottom and prevents loss of material as a result of erosion.

d. It can more smoothly accommodate differential settlement because of its flexibility.

A disadvantage of the crushed stone or gravel ringwall is that it is more difficult to construct it to close tolerances and achieve a flat, level plane for construction of the tank shell.

B.4.3.2. For crushed stone or gravel ringwalls, careful selection of design details is necessary to ensure satisfactory performance.

The type of foundation suggested is shown in Figure B-3, Significant details include the following:

a. The 0.9 m (3 ft) shoulder and berm shall be protected from erosion by being constructed of crushed stone or covered with a permanent paving material.

b. Care shall be taken during construction to prepare and maintain a smooth, level surface for the tank bottom plates.

c. The tank grade shall be constructed to provide adequate drainage away from the tank foundation.

d. The tank foundation must be true to the specified plane within the tolerances specified in API 650 5.5.5.

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B.4.4 Concrete Slab Foundation (Fig. B.4)

B.4.4.1 When the soil bearing loads must be distributed over an area larger than the tank area or when it is specified by the owner, a reinforced concrete slab shall be used. Piles beneath the slab may be required for proper tank support.

B.4.4.2 The structural design of the slab, whether on grade or on piles, shall properly account for all loads imposed upon the slab by the tank. The reinforcement requirements and the design details of construction shall be in accordance with ACI 318.

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B.5 Tank Foundations for Leak Detection

API 650 Appendix “I” provides additional designs and recommendations on the construction of tank and foundation systems for the detection of leaks through the bottoms of storage tanks.

A foundation which incorporates a Release Prevention Barrier (RPB) such as a flexible, impermeable membrane liner with leak detection piping, or a concrete slab, may be used under some conditions to increase the internal inspection interval for the tank. See API 653.6.4.3

A flexible, impermeable membrane liner will block groundwater from migrating upward into the foundation and serve to contain and channel leaks for detection. The liner material should be compatible with and impermeable to the stored substance, and be protected from the backfill and below by a geotextile fabric. The liner should slope from the center of the tank towards the tank edge, extending outside of the footprint of the tank.

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B.6 Tank Anchorage

When a tank is required to be anchored due to wind loading or seismic stress, see API 650 Section 3.11, and 3.12. API 650 Appendix E, API 650 Appendix F and Figure 1-11.

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Suitable Backfill Material

Geotextile Fabric.

45o

45o

600 mm (24 in)

Notes:

1. Geotextile fabric to be laid around crushed rock ringwall

2. Top of crushed rock ring wall under tank shell to be minimum of 600 mm (24 in) wide

3. Tank shoulder 1 m (3 ft) wide for tanks dia under 15 m (50 ft) and 1.5 m (5 ft) wide for tanks over 15 m (50 ft)

4. For tank with a cone down bottom, recommended foundation height is equal to the greater of 450 mm (18 in), or the dimension from the bottom of the tank shell to the bottom of the tank sump, plus the slope of the leak detection / drainage pipe from the center of the tank to terminate outside the foundation, plus 100 mm (4 in). The drainage pipe shall finish 100 mm (4 in) above the surrounding grade

5. Recommend laying sand or sand bitumen mix over backfill and under tank bottom as a corrosion mitigation barrier API 650 Appendix B.3.2. a and b

6. After the foundation shoulder has weathered, lay 25 mm (1in) hot sand bitumen mix or chip seal over the tank shoulder from grade to tank bottom edge, to protect the tank shoulder from erosion. Seal the bitumen to the tank bottom as a moisture barrier. If there is a liner, seal bitumen to the liner as well for proper leak containment and detection, and as a moisture barrier. Do not lay material over the tank chime

7. A flexible, impermeable membrane liner will block groundwater from migrating upward into the foundation and serve to contain and channel leaks for detection. The liner material should be compatible with and impermeable to the stored substance, and be protected from the backfill and below by a geotextile fabric. The liner should slope from the center of the tank towards the tank edge, extending outside of the footprint of the tank. Flexible membrane liner will preclude the future use of CP from anodes outside of the liner.

8. Recommended foundation height above surrounding ground is a minimum of 450 mm (18 in)

9. The flexible membrane liner can be used to increase the inspection interval of the tank bottom under API 653 6.4.3

10. The outside edge of the tank bottom should be sealed to prevent moisture from going under the tank Assure that sealing material at the bottom junction does not extend above top of tank bottom chime to form a water trap outside of the tank shell. After tank testing inspect this area and remove any sealing material or bitumen mix which extrudes out from beneath tank to form such a water trap. The tank bottom chime must be visible for inspection at all times.

11. Where a concrete ringwall is not provided, the foundation under the shell shall be level within ±3 mm (1/8 in.) in any 3 m (10 ft) of the circumference and within ±13 mm (1/2 in.) in the total circumference measured from the average elevation. API 650 5.5.5.2 b

12. Leak detection / drainage pipes API 650 Appendix B Fig B-5

13. Suitable backfill material API 650 Appendix B 2.5

Crushed Stone

Ground Level

Leak Detection / Drainage Pipes.

Figure B-2 Earth Foundation, with a Concrete Ringwall without Cathodic Protection

Beveled 50 mm (2 in)

Tank shell to be center of concrete ringwall

Notes:

1. Concrete ringwall is to be designed by a person experienced in tank foundation design

2. See B.4.2.3 for requirements for reinforcement.

3. The top of the concrete ringwall shall be smooth and level. The concrete strength shall be at least 20 MPa (3000 lbs/sqin) after 28 days. Reinforcement splices must be staggered and shall be lapped to develop full strength in the bond. If staggering of laps is not possible, refer to ACI 318 for additional development requirements.

4. Where a concrete ringwall is provided under the shell, the top of the ringwall shall be level within ±3 mm (1/8 in.) in any 9 m (30 ft) of the circumference and within ±6 mm (1/4 in.) in the total circumference measured from the average elevation. API 650 5.5.5.2 a

5. Concrete ringwalls shall not be built less than 300 mm (12 in) in width

6. Concrete ringwalls that exceed 300 mm (12 in.) in width shall have rebar distributed on both faces.

7. After concrete ringwall has been built, remove any unsuitable material from inside of the ringwall and replace with suitable thoroughly compacted fill material. Do not allow any water to run under the concrete ringwall.

8. The need for a spread footing should be evaluated when building concrete ring wall on soft ground.

9. When the ringwall width exceeds 460 mm (18 in) using a spread footing beneath the wall should be considered.

10. Tank anchorage bolts maybe required see Section 3.11.1, Appendix E, Appendix F

11. 50 mm (2 in) Sand Bitumen Mix laid on top of concrete ring wall will stop sand from eroding out from under the tank bottom, and will allow the annular plate backing strips from touching the concrete ring wall. This will prevent moisture from going under the tank bottom.

12. The flexible membrane liner slopes from the center of the tank and is bolted to the inside of the concrete ring wall. A flexible, impermeable membrane liner will block groundwater from migrating upward into the foundation and serve to contain and channel leaks for detection. The liner material should be compatible with and impermeable to the stored substance, and be protected from the backfill and below by a geotextile fabric. Flexible membrane liner will preclude the future use of CP from anodes outside of the liner.

13. The flexible membrane liner can be used to increase the inspection interval of the tank bottom under API 653 6.4.3

14. The outside edge of the tank bottom should be sealed to prevent moisture from going under the tank. Assure that sealing material at the bottom junction does not extend above top of tank bottom chime to form a water trap outside of the tank shell. After tank testing inspect this area and remove any sealing material or bitumen mix which extrudes out from beneath tank to form such a water trap. The tank bottom chime must be visible for inspection at all times.

15. Recommend laying sand or sand bitumen mix over backfill and under tank bottom as a corrosion mitigation barrier API 650 Appendix B.3.2. a and b

16. Leak detection / drainage pipes API 650 Appendix B Fig B-5

17. Suitable backfill material API 650 Appendix B 2.5

Concrete Ringwall

Slope 1: 1.5

Suitable Backfill Material

Compacted Crushed Stone sloping away from Concrete Ringwall 2 m (6ft 6in)

Leak Detection / Drainage Pipes

Optional

Flexible Membrane Liner.

Tank Bottom

Sand or Sand Bitumen Mix

Tank Shell

Beveled 25 mm (1 in)

Concrete Spread Footing

Notes:

1. Tank shoulder 1 m (3 ft) wide for tanks dia under 15 m (50 ft) and 1.5 m (5 ft) wide for tanks over 15 m (50 ft)

2. Tank with a cone up bottom, recommended foundation height at tank shell is 450 mm (18 in) above the surrounding ground elevation.

3. For tank with a cone down bottom, recommended foundation height is equal to the greater of 450 mm (18 in), or the dimension from the bottom of the tank shell to the bottom of the tank sump, plus the slope of the leak detection / drainage pipe from the center of the tank to terminate outside the foundation, plus 100 mm (4 in). The drainage pipe shall finish 100 mm (4 in) above the surrounding grade

4. Recommend laying sand or sand bitumen mix over backfill and under tank bottom as a corrosion mitigation barrier API 650 Appendix B.3.2. a and b

5. After the foundation shoulder has weathered, lay 25 mm (1in) hot sand bitumen mix or chip seal over the tank shoulder from grade to tank bottom edge, to protect the tank shoulder from erosion. Seal the bitumen to the tank bottom as a moisture barrier. If there is a liner, seal bitumen to the liner as well for proper leak containment and detection and as a moisture barrier. Do not lay material over the tank chime

6. A flexible, impermeable membrane liner will block groundwater from migrating upward into the foundation and serve to contain and channel leaks for detection. The liner material should be compatible with and impermeable to the stored substance, and be protected from the backfill and below by a geotextile fabric. The liner should slope from the center of the tank towards the tank edge, extending outside of the footprint of the tank. Flexible membrane liner will preclude the future use of CP from anodes outside of the liner

7. The flexible membrane liner can be used to increase the inspection interval of the tank bottom API 653 6.4.3

8. The outside edge of the tank bottom should be sealed to prevent moisture from going under the tank. Assure that sealing material at the bottom junction does not extend above top of tank bottom chime to form a water trap outside of the tank shell. After tank testing inspect this area and remove any sealing material or bitumen mix which extrudes out from beneath tank to form such a water trap. The tank bottom chime must be visible for inspection at all times.

9. Where a concrete ringwall is not provided, the foundation under the shell shall be level within ±3 mm (1/8 in.) in any 3 m (10 ft) of the circumference and within ±13 mm (1/2 in.) in the total circumference measured from the average elevation. API 650 5.5.5.2 b

10. Leak detection / drainage pipes API 650 Appendix B Fig B-5

11. Suitable backfill material API 650 Appendix B 2.5

Slope 1:10

Suitable Backfill Material

Ground Level

Leak Detection / Drainage Pipes

Optional

Flexible Membrane Liner.

Tank Bottom

Sand or Sand Bitumen Mix

Tank Shell

Slope 1:10

Figure B-1 Earth Foundation.

Optional

Flexible Membrane Liner.

Tank Bottom

Sand or Sand Bitumen

Tank Shell

Slope 1:10

Figure B-3 Foundation, with Crushed Stone Ringwall

Sand and Cathodic Protection

Figure B-3A Foundation, with Crushed Stone Ringwall and Cathodic Protection

Suitable backfill material

Geotextile Fabric.

45o

45o

600 mm (24 in)

Notes:

1. Geotextile fabric to be laid around crushed rock ringwall

2. Top of crushed rock ring wall under tank shell to be minimum of 600 mm (24 in) wide

3. Tank shoulder 1 m (3 ft) wide for tanks dia under 15 m (50 ft) and 1.5 m (5 ft) wide for tanks over 15 m (50 ft)

4. Each end of leak detection / drainage pipes to have screens installed

5. After the foundation shoulder has weathered, lay 25 mm (1in) hot sand bitumen mix or chip seal over the tank shoulder from grade to tank bottom edge, to protect the tank shoulder from erosion. Seal the bitumen to the tank bottom as a moisture barrier. If there is a liner, seal bitumen to the liner as well for proper leak containment and detection and as a moisture barrier. Do not lay material over the tank chime

6. Recommended foundation height above ground 450 mm (18 in)

7. 50 mm (2 in) Sand Bitumen Mix laid on top of crushed rock ringwall will stop sand from eroding out from under the tank bottom, This will allow the annular plate backing strips from touching the crushed rock ring wall and will stop the moisture from going under the tank.

8. Install cathode protection sand a minimum of 150 mm (6 in) deep and tie anode down to stop the anode from shorting out against the tank bottom. If Cathodic Protection is not installed sand depth can be reduced to 75mm (3 in)

9. The flexible membrane liner slopes from the center of the tank and extends outside of the footprint of the tank. A flexible, impermeable membrane liner will block groundwater from migrating upward into the foundation and serve to contain and channel leaks for detection. The liner material should be compatible with and impermeable to the stored substance, and be protected from the backfill and below by a geotextile fabric. Flexible membrane liner will preclude the future use of CP from anodes outside of the liner.

10. The flexible membrane liner can be used to increase the inspection interval of the tank bottom under API 653 6.4.3

11. The outside edge of the tank bottom should be sealed to prevent moisture from going under the tank. Assure that sealing material at the bottom junction does not extend above top of tank bottom chime to form a water trap outside of the tank shell. After tank testing inspect this area and remove any sealing material or bitumen mix which extrudes out from beneath tank to form such a water trap. The tank bottom chime must be visible for inspection at all times.

12. Where a concrete ringwall is not provided, the foundation under the shell shall be level within ±3 mm (1/8 in.) in any 3 m (10 ft) of the circumference and within ±13 mm (1/2 in.) in the total circumference measured from the average elevation. API 650 5.5.5.2 b

13. Leak detection / drainage pipes API 650 Appendix B Fig B-5

14. Suitable backfill material API 650 Appendix B 2.5

Fig B-5 Leak Detection / Drainage Pipes

Notes:

1. The leak detection / drainage pipes should be made of non-corrosive material (e.g. PVC or fiberglass) and have slots in the pipe to maximize the opportunity to detect tank leaks

2. Recommend 50 mm (2 in) pipes

3. Each end of leak detection / drainage pipes to have screens installed

4. Underside of telltale pipes to be a minimum of 100 mm (4 in) above the surrounding bottom elevation.

At least 8 pipes with a max spacing of 10 m (32 ft) around the tank foundation

Pipes 3 m (10 ft) inside tank foundation

1 pipe to center of tank

Tank Foundation

Tank

Sand and Cathodic Protection

Figure B-2A Earth Foundation, with a Concrete Ringwall and Cathodic Protection

Beveled 50 mm (2 in)

Tank shell to be center of concrete ringwall

Notes:

1. Concrete ringwall is to be designed by a person experienced in tank foundation design

2. See B.4.2.3 for requirements for reinforcement.

3. The top of the concrete ringwall shall be smooth and level. The concrete strength shall be at least 20 MPa (3000 lbs/sqin) after 28 days. Reinforcement splices must be staggered and shall be lapped to develop full strength in the bond. If staggering of laps is not possible, refer to ACI 318 for additional development requirements.

4. Where a concrete ringwall is provided under the shell, the top of the ringwall shall be level within ±3 mm (1/8 in.) in any 9 m (30 ft) of the circumference and within ±6 mm (1/4 in.) in the total circumference measured from the average elevation. API 650 5.5.5.2 a

5. Concrete ringwalls shall not be built less than 300 mm (12 in) in width

6. Concrete ringwalls that exceed 300 mm (12 in.) in width shall have steel rebar distributed on both faces.

7. After concrete ringwall has been built, remove any unsuitable material from each side of the ringwall and replace with suitable thoroughly compacted fill material. Do not allow any water to run under the concrete ringwall.

8. The need for a spread footing should be evaluated when building concrete ring wall on soft ground.

9. When the ringwall width exceeds 460 mm (18 in) using a footing beneath the wall should be considered.

10. Tank anchorage bolts maybe required see Section 3.11.1, Appendix E, Appendix F

11. 50 mm (2 in) Sand Bitumen Mix laid on top of concrete ring wall will stop sand from eroding out from under the tank bottom, and will allow the annular plate backing strips from touching the concrete ring wall. This mix will prevent moisture from going under the tank bottom.

12. Install cathode protection sand minimum 150 mm (6 in) deep and tie anode down to stop the anode from shorting out against the tank bottom. If Cathodic Protection is not installed sand depth can be reduced to 75mm (3 in)

13. The flexible membrane liner slopes from the center of the tank and is bolted to the inside of the concrete ring wall. A flexible, impermeable membrane liner will block groundwater from migrating upward into the foundation and serve to contain and channel leaks for detection. The liner material should be compatible with and impermeable to the stored substance, and be protected from the backfill and below by a geotextile fabric. Flexible membrane liner will preclude the future use of CP from anodes outside of the liner.

14. The flexible membrane liner can be used to increase the inspection interval of the tank bottom under API 653 6.4.3

15. The outside edge of the tank bottom should be sealed to prevent moisture from going under the tank. Assure that sealing material at the bottom junction does not extend above top of tank bottom chime to form a water trap outside of the tank shell. After tank testing inspect this area and remove any sealing material or bitumen mix which extrudes out from beneath tank to form such a water trap. The tank bottom chime must be visible for inspection at all times.

16. Recommend laying sand over backfill and under tank bottom API 650 Appendix B.3.2. b

17. Leak detection / drainage pipes API 650 Appendix B Fig B-5

18. Suitable backfill material API 650 Appendix B 2.5

Concrete Ringwall

Crushed Stone

Ground Level

Leak Detection / Drainage Pipes.

Optional

Flexible Membrane Liner.

Tank Bottom

Tank Shell

Slope 1:10

Slope 1: 1.5

Tank shoulder

Suitable Backfill Material

Compacted Crushed stone sloping away from Concrete Ring Wall 2m (6 ft 6in)

Leak Detection / Drainage Pipes

Optional

Flexible Membrane Liner.

Tank Bottom

Sand Bitumen Mix

Tank Shell

Beveled 25 mm (1 in)

Concrete Spread Footing

Seal the edge around tank

Figure B-1A Earth Foundation, with Cathodic Protection

Figure B-4 Concrete Slab Foundation, Plain or Piled

Notes:

1. Concrete slab is to be designed by a person experienced in tank foundation design

2. The top of the concrete slab shall be smooth and level. The concrete strength shall be at least 20 MPa (3000 lbs/sqin) after 28 days. Reinforcement splices must be staggered and shall be lapped to develop full strength in the bond. If staggering of laps is not possible, refer to ACI 318 for additional development requirements.

3. Tank anchorage bolts maybe required see Section 3.11.1, Appendix E, Appendix F

4. Where a concrete slab foundation is provided, the first 0.3 m (1 ft) of the foundation (or width of the annular ring), measured from the outside of the tank radially towards the center, shall comply with the concrete ringwall requirement. The remainder of the foundation shall be within ±13 mm (1/2 in.) of the design shape. API 650 5.5.5.2.c

5. 50 mm (2 in) Sand Bitumen Mix laid on top of concrete slab will allow the annular plate backing strips from touching the concrete slab. This will prevent moisture from going under the tank bottom.

6. The outside edge of the tank bottom should be sealed to prevent moisture from going under the tank. Assure that sealing material at the bottom junction does not extend above top of tank bottom chime to form a water trap outside of the tank shell. After tank testing inspect this area and remove any sealing material or bitumen mix which extrudes out from beneath tank to form such a water trap. The tank bottom chime must be visible for inspection at all times.

Concrete Slab

Tank shoulder

Tank shoulder

Compacted Crushed Stone sloping away from concrete slab 2 m (6ft 6in)

Seal the edge around tank

Piles

Tank Bottom

Sand or Sand Bitumen Mix

Tank Shell

Beveled 25 mm (1 in)

Seal the edge around tank

Seal the edge around tank

Sand and Cathodic Protection

Flexible Membrane Liner.

Seal the edge around tank

Slope 1: 1.5

Notes:

1. Tank shoulder 1 m (3 ft) wide for tanks dia under 15 m (50 ft) and 1.5 m (5 ft) wide for tanks over 15 m (50 ft)

2. Tank with a cone up bottom, recommended foundation height at tank shell is 450 mm (18 in) above the surrounding ground elevation.

3. For tank with a cone down bottom, recommended foundation height is equal to the greater of 450 mm (18 in), or the dimension from the bottom of the tank shell to the bottom of the tank sump, plus the slope of the leak detection / drainage pipe from the center of the tank to terminate outside the foundation, plus 100 mm (4 in). The drainage pipe shall finish 100 mm (4 in) above the surrounding grade

4. Recommend laying sand under tank bottom API 650 Appendix B.3.2. b

5. After the foundation shoulder has weathered, lay 25 mm (1in) hot sand bitumen mix or chip seal over the tank shoulder from grade to tank bottom edge, to protect the tank shoulder from erosion. Seal the bitumen to the tank bottom as a moisture barrier. If there is a liner, seal bitumen to the liner as well for proper leak containment and detection and as a moisture barrier. Do not lay material over the tank chime

6. A flexible, impermeable membrane liner will block groundwater from migrating upward into the foundation and serve to contain and channel leaks for detection. The liner material should be compatible with and impermeable to the stored substance, and be protected from the backfill and below by a geotextile fabric. The liner should slope from the center of the tank towards the tank edge, extending outside of the footprint of the tank. Flexible membrane liner will preclude the future use of CP from anodes outside of the liner

7. The flexible membrane liner can be used to increase the inspection interval of the tank bottom under API 653 6.4.3

8. The outside edge of the tank bottom should be sealed to prevent moisture from going under the tank. Assure that sealing material at the bottom junction does not extend above top of tank bottom chime to form a water trap outside of the tank shell. After tank testing inspect this area and remove any sealing material or bitumen mix which extrudes out from beneath tank to form such a water trap. The tank bottom plate must be visible for inspection at all times.

9. Where a concrete ringwall is not provided, the foundation under the shell shall be level within ±3 mm (1/8 in.) in any 3 m (10 ft) of the circumference and within ±13 mm (1/2 in.) in the total circumference measured from the average elevation. API 650 5.5.5.2 b

10. Leak detection / drainage pipes API 650 Appendix B Fig B-5

11. Suitable backfill material API 650 Appendix B 2.5

12. 50 mm (2 in) Sand Bitumen Mix laid under the shell will stop sand from eroding out from under the tank bottom

13. When installing Cathodic Protection sand minimum 150 mm (6 in) deep and tie anode down to stop the anode from shorting out against the tank bottom. If Cathodic Protection is not installed sand depth can be reduced to 75mm (3 in)

Suitable backfill material

Ground Level

Leak Detection / Drainage Pipes

Tank Bottom

Sand Bitumen

Tank Shell

Figure B-5 Tank Foundation Shoulder

Suitable Backfill Material

Leak Detection / Drainage Pipes

Optional

Flexible membrane Liner

Ground Level

Tank Bottom

Slope 1:1

Slope 1:1.5

Tank Shoulder

Notes:

1. Tank shoulder 1 m (3 ft) wide for tanks dia under 15 m (50 ft) and 1.5 m (5ft ) wide for tanks over 15 m (50 ft)

2. Tank with a cone up bottom, recommended foundation height at tank shell is 450 mm (18 in) above the surrounding ground elevation.

3. For tank with a cone down bottom, recommended foundation height is equal to the greater of 450 mm (18 in), or the dimension from the bottom of the tank shell to the bottom of the tank sump, plus the slope of the leak detection / drainage pipe from the center of the tank to terminate outside the foundation, plus 100 mm (4 in). The drainage pipe shall finish 100 mm (4 in) above the surrounding grade.

4. Recommend laying sand or sand bitumen mix over backfill and under tank bottom as a corrosion mitigation barrier (see B.3.2. a and b)

5. After the foundation shoulder has weathered, lay 25 mm (1in) hot sand bitumen mix or chip seal over the tank shoulder from grade to tank bottom edge, to protect the tank shoulder from erosion.

6. Seal the bitumen to the tank bottom as a moisture barrier. If there is a liner, seal bitumen to the liner as well for proper leak containment and detection and as a moisture barrier. Do not lay material over the tank chime

7. A flexible, impermeable membrane liner will block groundwater from migrating upward into the foundation and serve to contain and channel leaks for detection. The liner material should be compatible with and impermeable to the stored substance, and be protected from the backfill and below by a geotextile fabric. The liner should slope from the center of the tank towards the tank edge, extending outside of the footprint of the tank. Flexible membrane liner will preclude the future use of CP from anodes outside of the liner

8. The flexible membrane liner can be used to increase the inspection interval of the tank bottom under API 653 6.4.3

9. The outside edge of the tank bottom should be sealed to prevent moisture from going under the tank. Assure that sealing material at the bottom junction does not extend above top of tank bottom plate to form a water trap outside of the tank shell. After tank testing inspect this area and remove any sealing material or bitumen mix which extrudes out from beneath tank to form such a water trap. The tank bottom plate must be visible for inspection at all times.

10. Leak detection / drainage pipes API 650 Appendix B Fig B-5

11. Suitable backfill material API 650 Appendix B 2.5

Slope 1:10

Tank

Tank Shoulder

Slope 1: 1.5

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