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200 Bottom Selection and Design

AbstractThis section of the manual discusses the design requirements and Company and

industry specifications for atmospheric storage tank bottoms. It provides data

required to determine the most cost-effective new tank bottom and/or replacement

or repair for existing tanks. The advantages and disadvantages of the different types

of new designs are addressed. Included is a cost benefit methodology for deter-

mining the most cost-effective bottom for a particular site. Leak detection and

containment are also discussed.

Contents Page

210 Bottom Selection 200-3

211 Single Bottom vs. Double Bottom Characteristic Differences

220 Bottom Design 200-5

221 Bottom Plate Thickness

222 Shell-to-Bottom Joint

223 Reinforcing Pads

230 Bottom Construction 200-9

231 Bottoms for New Tanks

240 Bottom Repair or Replacement 200-10

241 Philosophy

242 Repair Alternatives

243 Bottom Replacement

244 Bottom Replacement Requirements

250 Leak Detection and Containment 200-17

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200 Bottom Selection and Design Tank Manual

255 Miscellaneous Design Considerations

256 Design Variations260 Membrane Design and Selection 200-27

261 Introduction

262 Elastomeric Liner

263 Membrane Materials for Tank Secondary Containment

264 Design and Construction

265 Inspection

266 Approved Manufacturers and Installers

270 References 200-32

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Tank Manual 200 Bottom Selection and Design

210 Bottom Selection

Tank Bottom Selection

If the tank is to store petroleum crude or products and if water is present in the

contents, then a means for removing the water must be provided. How the water is

removed determines the type of bottom. Small tanks where water drawing is not a

problem have flat bottoms. Flat bottoms are inexpensive to build and may be

supported on a concrete ring or flat pad-type foundation.

Larger tanks usually have a cone up or cone down bottom. The cone up bottom is

the more common and is the less expensive of the two. The cone up bottom permitsthe use of a bottom outlet or waterdraw basin at the edge of the tank. The primary

disadvantage of the cone up bottom is that water tends to stand along the edge of the

bottom rather than drain to the waterdraw outlet. The standing water can cause

severe corrosion on the bottom near the edge and the lower two to three inches of

the shell.

The cone down bottom offers better drainage and removal of water since the bottom

slopes toward the center of the tank, but installing piping to center of tank is costlyand could be difficult. This type of design is not recommended.

Single-slope bottoms are used on tanks where the ability to draw water and clean

the tank is important and where the center sump is not practical.

Figure 200-1 summarizes basic configurations for tank bottoms and arrangements

for piping and drain connections. The advantages and disadvantages of the different

designs are listed. The designs shown deal only with tank structureand do not

show any means for corrosion prevention or leak detection such as linings, double

bottoms, cathodic protection, etc. See Sections600and250for information on

corrosion prevention and leak detection.

Note Figure 200-1 appears at the end of this section.

Choice of bottom is influenced by: 1) operating requirements for the product to be

stored, 2) maintenance considerations, and 3) characteristics of the support soil

(unless a piled foundation is to be used). Typical operating requirements include:

Keeping a layer of water on the bottom in some services.

Removing water frequently to keep the contents of the tank dry. This can be

important for quality control or when the tank feeds an operating unit.

Changing service or specifications. In this case, you would want a design that

would enable you to completely drain the product in the tank.
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211 Single Bottom vs. Double Bottom Characteristic Differences

Exemptions for Double Bottom Tanks

The following are examples of exemptions on the Use of Double Bottoms for

aboveground storage tanks (ASTs).

Characteristic Single Bottom Double Bottom

Mean life 25 years Approximately 35 years (a 40-50%

increase over single bottoms)

Costs Initial installation costs are lower

than double bottoms

Higher inspection costs

Potential for high environmental

clean up costs

Lower operating factor. Repair scope

is less.

Lower total cost of ownership

Reduced by longer in-service run

time intervals

Lower material costs due to a smaller

safety factor against leaks (bottom

thickness can be less)

Reduced inspection costs by

reducing inspection frequency

Minimal environmental cleanup costs

(Secondary benefits) Can retrofit

slopes, coating, etc., for improved

product integrity

Leak detection Leaks often not detectable and go on for

years resulting in future cleanups

Leaks are detected early and results in

minimal, if any, environmental damage

Corrosion Most serious from underside of tank

bottom because of:

Variable soil conditions and chemistry

Moisture and oxygen variation

Salts, dirt, debris, scale

Underside attack reduced substantially

by changing underside conditions

Elevated aboveground so less mois-

ture

Clean uniform contact with concrete

Concrete is a corrosion inhibitor

Reduces the variance of oxygen

concentration, moisture and electro-

lytes because they provide a uniform

surface, elevating the new steel

bottom out of the mud and dirt

Concrete is itself a corrosion inhib-

itor and reduces underside corrosion

rates

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Exemptions based on OPCO. All Production tanks are exempt from requirements

to apply double bottoms or RPBs.

Exemptions based on liquids stored. The following tanks do not need to be

considered for implementation of double bottoms:

Chemical tanks less than 100 feet in diameter

Lubricants

Asphalt tanks

Exemptions based on site. Certain sites such as the Pascagoula Refinery havesettling or shifting soil conditions which weigh against the use of a double bottom

tank or a release prevention barrier. In this case, the entire refinery is exempt from

using double bottom tanks. However, for new tanks or tanks which will be

retrofitted with double bottoms, consideration should be given to installation of

RPBs. In order to determine whether a site is exempt, an engineering analysis

should be performed, documenting the considerations which weigh against the use

of the double bottom practice. The use of double bottoms should also be evaluated

in areas of high humidity and/or low water table.

Exemptions based on analysis. Any tank may be exempted from the requirement

of a double bottom provided that:

an analysis is documented which shows why the tank does not need to

have a double bottom, or

the benefits of the double bottom are so marginal as to not justify the costs

of the double bottom.

Tanks which may not be exempted. Any tank which stores motor fuels or fuels

with MTBE or TAME or pure oxygenates shall be put onto a schedule which

implements an RPB or a double bottom.

220 Bottom Design

Refer to Section 210for the selection of bottom configuration, andSection 300for

foundation design.

The design of bottoms for cylindrical storage tanks at atmospheric pressure does not

involve a direct consideration of the hydrostatic pressure for the design fill height at

the bottom of the tank. The weight of the liquid contained in the tank is assumed to

be supported by the foundation upon which the bottom rests, and no significant

stress is developed in the bottom plates attributable to the hydrostatic pressure. In

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This section is a briefing of why we have several different double bottom designs.

Although there are several different designs, they are all functionally equivalent.

That is, they perform the function of secondary leak detection and containment. Allof these designs have the following functional components in them:

Concrete Spacer

While sand, steel or other media may be used Chevron has chosen concrete as

the spacer material upon which to install the new or second bottom. This mate-

rial gives good control over the slope of the tank bottom allowing for better

water drainage and reduced corrosion due to stagnant water in the tank bottom.

The main reason for the selection of concrete, however, is that it is alkaline andit actually reduced corrosion from the underside. In many inspections, we have

found the concrete to extend the life of the tank bottom by a factor of 25 to 50

percent due to reduced underside corrosion attack.

Corner Lock Design

In the original El Segundo Design, the liner is simply spread out and trimmed at

the inside diameter of the tank. A caulk bead is then applied between the dead

shell and the liner to seal the double bottom space and create leak containment.However, Chevron has recognized that the integrity of the system could be

improved by making a continuous bathtub out of the HDPE liner. To do this we

have used the CBI PROPRIETARYcorner lock method is described as

follows.

This design uses a perforated angle iron. To this angle iron is attached a short

segment of HDPE liner. This is extruded into the angle so that the flap can be

used to heat weld the basic liner to the angle. This provides the same bathtub

effect that the Chevron In-house design does.

Chevron In-House Design (Batten Strip Design)

In this design we use a steel batten strip to seal the liner to the dead shell. This

involves using stud welding to bolt the batten strip to the shell. By using this

technique a bathtub is created by heat seaming all seams up to the point at the

top of the batten strip. In this system we do not depend on caulking to provide a

tight joint.

All of these systems are of the open design. We do have a few closed systems which

are described below.

Open vs. Closed System

Chevron does not support the use of a closed double bottom system in general

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Reasons for not using closed design:

1. Making a weld that would actually seal the space is difficult if not impossible.In most cases there is inadequate room to make the weld. It is therefore of poor

quality and would not keep water out and leaks in.

2. Due to the difficulty of making this weld and due to the nature of fillet welds it

is prone to having cracks and flaws. As this is the most highly stressed region

in the tank, it makes the possibility of a catastrophic failure much more likely.

From the principle of fracture mechanics, crack growth or sudden propagation

occurs in the presence of flaws and stress. Both are likely with this weld.

It is for this reason that API Standard 650 makes such stringent non-destructive

examination requirements for the topside fillet welds in this highly stressed

area. It would be basically impossible to verify the integrity of the underside

weld at this location.

3. It was originally thought that water and thus corrosion could be minimized on

the underside of tank bottoms to reduce underside attack. However, due to the

large size of the tank double bottom space and the humidity of the air, if the

bottom is sealed into a closed system, water will actually condense on theunderside of the tank bottom plates, causing accelerated corrosion. This is

similar to the crawl space of a house in which moisture will damage the

flooring unless adequate ventilation is provided. For this reason, the open

system is superior in that it allows for this ventilation to occur, removing any

moisture that does enter the space. Even if the bottom could be perfectly sealed

and constructed with no moisture, the concrete itself has moisture which evapo-

rates from it and would create a humid corrosive environment were the space

not allowed to breathe.

4. The closed system also defeats the purpose of leak detection. By closing the

system, a leak cannot be viewed as soon as it occurs. Since leaks tend to start

very slowly and increase with time, the best way to protect the environment is

to detect leaks as early as possible.

221 Bottom Plate Thickness

The minimum thickness for bottom plates required by API 650 is inch exclusiveof any corrosion allowance that may be required (API 650, Paragraph 3.4.1). Single-

welded lap joints with full-fillet welds are normally used for bottom plates;

however, single-welded butt joints with backing plates are an acceptable alternative

(API 650, Paragraph 3.1.5.4 through 3.1.5.7) as shown in Figure 200-2. It is

preferred that bottom plates over 3/8-inch thick be butt welded.

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Butt welds with full penetration and complete fusion are required to join the plates

that form the annular ring. However, the butt welded plates in the annular ring can

be lap welded to the bottom plates. The required thickness of the plates for the

annular ring is determined by the hydrostatic stress and thickness of the lowest shell

course (API 650, Paragraph 3.5.3), as given in Table 3.1 of API 650.

Width of annular rings must be able to support the column of liquid above it at

design fill height, in the event of foundation settlement. The minimum widthallowed is 24 inches. However, a greater width may be needed as calculated by the

formula given in Paragraph 3.5.2 of API 650. In addition, seismic design requires

checking the thickness of the annular ring, as discussed in Section 530.

222 Shell-to-Bottom Joint

API Standard 650 requires double fillet welds for the shell-to-bottom joint (API

650, Paragraph 3.1.5.7), as illustrated in Figure 200-3. The stress in this joint isdependent on the hydrostatic pressure at the design fill height and the diameter of

the tank. The minimum size of the fillet welds required by API 650 is based upon

the thickness of the lowest shell course, as given in API 650, Paragraph 3.1.5.7. In

this manner, the size of the fillet welds is increased in proportion to the hydrostatic

pressure acting on the shell-to-bottom joint, without making separate design

calculations.

Fig. 200-2 Bottom Plate Welds (From API 650, Figure 3-3A.) Courtesy of the AmericanPetroleum Institute

Fig. 200-3 Bottom-to-shell Joint (From API 650, Figure 3-3A.) Courtesy of the AmericanPetroleum Institute

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223 Reinforcing Pads

Pads, at least 3/8 inch thick, should be provided under columns that support fixedroofs and under the legs for floating roofs. The pads for floating roof legs should be

wide enough to accommodate the maximum horizontal roof movement. Pads at

least inch thick should be installed to serve as wear plates under mixers and inlet

nozzles and under any bottom-mounted appurtenances, including gauge wells. The

pads prevent high local loads from developing in the bottom plates and tend to

minimize localized corrosion of the bottom plates. All pads should be welded to the

bottom plates with continuous inch fillet welds. SeeSection 700for additional

appurtenance design guidelines.

230 Bottom Construction

This section covers field installation of steel bottoms.

231 Bottoms for New Tanks

Bottoms Not Requiring Annular Rings

The new bottom sheets are tacked into place, then welded. Watch for excessive

overlapping of plates and grinding down of the upper plate to hide a less-than-full

fillet weld. Before welding, check that enough plate extends beyond the outside

edge of the shell radius to meet the specified overlap

Fig. 200-4 Configuration of Lap-welded Bottom Plates Under Shell (From API 650, Figure 3-3B.) Courtesy of the American Petroleum Institute

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ring, the bottom plate is tack welded in place and then welded. The plates should

shingle toward the low point, i.e., the outside row of plates should be installed first

with the higher center plate row installed last.

Cone down Bottoms with Annular Rings

The preferred method of installing a new cone down bottom with annular ring is to

install the bottom deck plate first, shingled toward the center (i.e., the row of plates

running through the center is placed first). The annular ring is then placed on top of

the deck plate with its installation being the same as detailed above. Installing theannular ring first traps a small amount of liquid near the edge of the shell. The

finished fillet weld attaching the annular ring to the bottom deck plate should, as a

minimum, be equal to the bottom deck plate thickness. If the surface is to be coated,

the weld should be ground to a smooth radius.

240 Bottom Repair or Replacement

This section discusses the justification for replacing a bottom versus a less costlyrepair. It also gives guidance on the types of replacement bottoms along with the

repair methods available and where they are applicable.

241 Philosophy

Fig. 200-5 Details of Annular Ring Butt Weld and Backup Strip Installation

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Corrosion and pitting are localized to a specific area (i.e., annular ring

corrosion due to water standing around the inside edge of the shell).

Most of the pitting is underside, and external cathodic protection is being

installed to minimize this pitting.

242 Repair Alternatives

Weld Repair and Plate Patching. These methods are for repairing mechanical

damage and stockside pitting. Patching is also done to repair openings in the bottom

resulting from turning coupons. The following guidelines are suggested:

1. Repair holes by welding on patches, rather than by spot welding.

Fig. 200-6 Procedure for Determining the Remaining Life of a Tank Bottom

Step 1 Gauge bottom plate thickness in multiple locations where there is no bottom pitting observed on thestockside or indicated on the underside. Average the readings.

Average Reading: 0. inch

Step 2 Gauge the depth of the deepest stockside pitting not to be patched during the shutdown and record.

Deepest Pitting: 0. inch

Step 3 Gauge the depth of the deepest pit on the underside of the bottom by measuring turned coupons.

Deepest Pitting: 0. inch

Step 4 Determine whether the stockside bottom is to be protective coated. If it is, stockside pitting rate inStep 5 is zero.

Yes_____ No_____

Step 5 Determine the following rates:

General Corrosion Rate:

Stockside Pitting Rate:

Underside Pitting Rate:

0. inch/yr

0. inch/yr

0. inch/yr

Step 6 Perform the following calculation:Remaining bottom general thickness:

Less general bottom corrosion rate X years next operating run:Less deepest unrepaired stockside pitting:

Less deepest underside pitting:

Less stockside pitting rate X years next operating run:

Less underside pitting rate X years next operating run:

= 0.

= 0.= 0.

= 0.

= 0.

= 0.

If total is equal to or less than zero, the bottom should be replaced. Total

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3. Spot weld pits half way or more through the plate if the pit is not greater than

1 inch in diameter and is surrounded by substantially full thickness material.

Shallower pits may be filled with special epoxy compounds, if necessary, priorto the application of internal coatings.

4. Patch pitted areas of larger than 1 inch diameter with pieces of -inch plate full

fillet welded all around. Time can be saved by supplying patch material

consisting of random-sized square and rectangular pieces with dimensions from

12 to 30 inches sheared from scrap plate. Sheared patches must be small

enough to pass through the shell manway or existing opening.

Annular Ring Replacement. Water accumulating around the inside edge of theshell can cause accelerated corrosion on the bottom in this area. For tanks over

100 feet in diameter, it is often less costly to replace the annular ring than the entire

bottom. See Section 300and API 650 for annular ring design and installation.

Laminate Reinforced Coating. Section 640discusses the various internal coating

systems available for tanks. Company Specification COM-MS-4738 is a standard

specification to use for thin film, glass flake, or laminate-reinforced coatings.

Because properly applied laminates have some structural strength, they can be an

effective tool for prolonging the life of a tank bottom which has moderate underside

corrosion. However, they must be used cautiously.

Laminates should notbe used in the following situations:

Where a hole has worn through the bottom plate and it remains unrepaired

Where the bottom plate will hole through before the end of the next run and no

leakage can be allowed

Where general corrosion has caused loss of structural strength in the annular

ring area. A rule of thumb is not to coat the annular ring if there is a 20%

general reduction in plate thickness over any 2-square foot area of the

annular ring

Thin Film or Glass Flake Coatings. Thin film or glass flake coatings can be used

in conjunction with bottom repairs or a new bottom to prolong the life of the

bottom. They should not be put on over a bottom with severe internal or external

corrosion or pitting.

Section 640discusses the use of these coatings. Specification COM-MS-4738 speci-

fies the materials and application procedures. Section 100 of the Coatings Manual

discusses in more detail the factors that affect the type of coatings selected. Thin

film coating is most effective when used with internal cathodic protection. See

Specification TAM-MS-3
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An impermeable pavement will prevent the flow of cathodic protective current to

the bottom steel. Cathodic protection will be effective where there are permeable

areas or breaks in the pavement and will prevent moisture-caused corrosion at theselocations. However, cathodic protection cannot eliminate corrosion due to moisture

migrating under the tank from permeable to impermeable areas. Similarly, cathodic

protection cannot completely control corrosion caused by moisture penetration

beneath the tank from the periphery due to breathing. It is very difficult to

determine conclusively from short term field tests whether cathodic protection will

be helpful for a specific situation.Section 650and the Corrosion Prevention and

Metallurgy Manualdiscuss cathodic protection in more detail.

Bottom Repairs.New tank bottoms should be installed by cutting horizontal slots

in the shell above the existing bottom and slipping in new bottom plates. The new

bottom must be joined to the shell with a fillet weld on both the inside and outside.

The area between the new and old bottom must be filled with sand or concrete.

Refer to Specification TAM-MS-1, Tank Bottom Replacement and Membrane

Placement.

Bottom patch plates, when used, should have full fillet welds all around except

when they are butted together. Full penetration welds should join patch plates whenbutted together. When a patch plate is within 6" of the shell, the patch plate shall be

tombstone shaped. The sides of the patch plate shall intersect the shell-to-bottom

joint at approximately 90. When bottom patch plates are added directly below the

shell, the shell should be slotted immediately above the old bottom and the plate

inserted. Fillet weld the patch plate to the shell on both the inside and outside. A

continuous fillet weld should join the patch plate to the old bottom, including the

section under the shell. For additional information, consult API 653 Section 7.10.

243 Bottom Replacement

Specification. A bottom replacement specification, TAM-MS-1, is included in this

manual.

Types of Replacement Bottoms. The considerations in selecting a replacement

bottom are generally the same as for new construction. These are discussed in

Section 210.

Secondary Containment and Leak Detection Bottoms. If future leakage cannot

be tolerated, then a retrofit bottom, which includes secondary containment and leak

detection, should be installed (see Standard Drawing GD-D1120, sheets 1 and 2). A

membrane (HDPE) liner is placed over the existing steel bottom and overlaid with a

concrete slab. The new steel bottom is then placed above the slab. This retrofit

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Non-leak Detection Bottoms. An important item to consider when secondary

containment and leak detection are not included is that the new steel bottom will be

anodic to the old steel bottom. This galvanic effect accelerates corrosion of the newbottom and has produced bottom failures in as little as four years. Therefore, it is

essential either to remove the old corroded bottom before putting in the new bottom,

or else to provide a good dielectric shield to stop current flow between the two.

An asphalt pad between the old and new bottoms provides a good dielectric shield,

but it may not entirely stop water migration to the tank bottom. However, in a

retrofit situation, there will be a semi-intact old bottom beneath the asphalt, and

most of the tank settling will have already occurred, so the chance for success of

asphalt is much greater than in the case of new construction. Therefore, if secondary

containment is not required, asphalt may be a viable alternative. See TAM-EF-364

for asphalt pad foundation design.

Replacement Bottom Installation. The replacement bottom plates should be

installed in accordance with API 653 and API 650. Generally, the replacement

sketch plates (bottom plates upon which the shell rests) or annular ring plates are

slid through a slot cut in the shell. The new bottom is continuously welded to the

shell, both inside and outside, using fillet welds on the top. Intermittent fillet weldsfor strength are made between the new bottom and the lower part of the old shell.

The weld size should be enough to develop the full strength of the bottom plates in

bending. Undercutting at the toe of the fillets should be avoided. Care must be taken

to be sure the new pad fully supports the new bottom next to the shell.

Annular ring plates are butt welded together using a 1/8 inch thick compatible

backing strip, 2 inches wide, under the joint where it passes through the shell.

Inside, the bottom plates are welded with a 1 inch lap and a full fillet lap weld as

for new API tanks. In either case, it is necessary to notch (rat hole) the shell overthis joint in the tank bottom to permit the welder to make a good weld through the

shell. See Figure 200-5for details of the annular ring installation in a replacement

bottom.

244 Bottom Replacement Requirements

For a complete description of the requirements for replacing tank bottoms, see the

commented version of Specification TAM-MS-1, Tank Bottom Replacement, andthe discussion above. Below is a summary of the procedure to follow for tank

bottom replacement for small and large tanks.

Small Tanks

Small tank bottom replacement is best done by lifting (or jacking up) the tank,

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Large Tanks

For replacing the bottoms of large tanks, follow the steps described below for each

of the replacement phases: preparation, bottom-to-shell welding, weld seam testing,and welding of pads and reinforcing plates to bottom.

Preparation Phase

To prepare the shell for bottom replacement follow these steps:

1. Remove internal appurtenances, supports, and brackets.

2. Cut horizontal slots in the shell. These slots are usually about 5 to 8 feet

long with 6 inches of shell left between the slots. The height of the slot should

be inch. The lower face of the slot should be relieved (notched out) for butt

welded annular ring backup strips. The bottom edge of the slot will act as a

form for the concrete spacer. SeeFigure 200-2.

3. Weld square C-shaped support clamps (or dogs) of heavy steel to the shell so

that the open area of the C allows the new bottom plate to slip through the

shell with the required overhang. SeeFigure 200-2.

4. Install membrane under roof supports. Form around fixed roof supports and

wrap floating roof legs as discussed in Specification TAM-MS-1.

5. Install the membrane liner as discussed inSection 260and shown on Drawing

GD-D1120.

6. Install the concrete spacer. Complete concrete around supports as discussed in

the specification.

7. Remove 6-inch spacers between slots, install annular ring through shell slotsand install bottom plate.

Relieving Shell over Bottom Plate Weld.A portion of the shell plate directly over

the field welded bottom lapped plate or butt welded annular ring joint should be

notched in order to permit completion of the weld under the tank shell. Each of the

lap welded bottom plates or butt welded annular ring joints under the shell should

be inspected before the notch can be welded up. Failure in this weld joint can

produce a bottom leak almost impossible to track down. SeeFigure 200-5.

Bottom-to-Shell Weld Seam

Minimum weld thickness is specified in API 650, Paragraph 3.1.5.7. There is no

increase in strength by exceeding the thinner plate thickness dimension with the

weld. However, since this particular weld is subject to considerable potential corro-

sion on cone up bottoms in particular some extra corrosion allowance in the weld

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stockside weld. It should be used wherever the bottom design does not include a

thick welded annular ring.

Bottoms equipped with annular rings cannot be welded this way. Making the stock-

side weld first causes the annular ring plate to rotate about the bottom edge of the

shell. For this reason, the outer weld must be made first and tested before the inner

weld is made.

Verify that all traces of diesel oil or penetrant are removed by detergent washing

from the opposite side prior to making the weld.

Replacement Bottoms. After the bottom-to-shell weld has been completed and

tested, the dogs supporting the shell are removed and the tank permitted to settle

down on the spacer pad.

Vacuum Testing of Weld Seams

Vacuum testing of weld seams is often done as the bottom seam welding progresses;however, this practice is not recommended. Sometimes slag inclusions occur in the

welds, particularly at stop and start weld points. Vacuum testing immediately after

welding does not give these inclusions enough time to open up. For this reason,

vacuum testing of bottom welds should be delayed for 4 or more days (if possible)

after welding. Failure due to hydrogen cracking should be evident after 1 day.

Fig. 200-7 Slot Configuration for Replacement Bottom

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250 Leak Detection and Containment

251 Background and Scope

Contamination of surface and subsurface waters by leaks and spills from storage

tanks can be prevented by the use of leak detection, leak containment, secondary

containment, cathodic protection and internal linings. In this section, leak detection

and leak containment are addressed. SeeSection 650for details of cathodic

protection. Refer to the Coatings Manualfor details of coatings and linings.

The Oil Pollution Act of 1990 required EPA to conduct a liner study to determineif leak detection and containment can be effectively implemented using liners in an

effort to address the problem of surface and subsurface contamination by

aboveground storage tank leaks and spills. The American Petroleum Institute has

responded to this call to safeguard the environment by issuing a new Appendix I to

API Standard 650,Undertank Leak Detection and Subgrade Protection. In addition,

because of various accidents, leaks and spills, the trend in the industry has been to

install systems aimed at reducing the chance for undetected leaks and spills. Many

states now have some form of regulation that requires undertank leak detection andleak containment.

Undertank leaks, especially small ones, can go undetected for years contaminating

the aquifer and accumulating liability for the owner. In large tanks, the threshold for

leak detection is about 350 gallons per hour by tank gauging methods. This is

considered unacceptable for leak detection. Leak detection methods, leak

containment methods, cathodic protection, and linings for new and existing storage

tanks should be considered where the bottom is being replaced.

Examples of tanks with leak detection/containment are shown inFigure 200-8.

These examples are discussed in detail in Section 256.

Note Figure 200-8 is a foldout appearing at the end of this section.

252 Definitions

Leak Detection. Aside from product loss considerations, leaks in ASTs are unac-

ceptable because they may go on for years undetected while contaminating subsur-

face waters. Leak detection is the detection of leaks soon after they occur. In the

performance criteria outlined in API 650, Appendix I, a leak must be directed to the

perimeter of the tank where it shall be capable of detection by visual examination.

Other methods including sensors are acceptable but do not supplant the visual

method Also supplementary to the perimeter system of leak detection are all of the

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a tank from entering the groundwater system. Double bottom tanks and tanks with

liners that can contain a small fraction of the tank contents usually qualify as having

leak containment systems.

Secondary Containment. Secondary containment refers to impounding of the tank

contents. Most of the regulations such as NFPA 30 or SPCC require that the dikes

be sized to contain the largest AST volume plus some freeboard for rainwater.

Secondary containment is not covered in this section.

Cathodic Protection. External cathodic protection (CP) is becoming more and

more widespread throughout the industry, both as a means to meet federal and local

regulations regarding groundwater protection (some of which are already in placeand some of which are still being written), and as a cost-effective method of

prolonging the service life of tank bottoms between scheduled shutdowns. Internal

cathodic protection is common for corrosion protection of crude tank bottoms or

tanks containing water.

For smaller tanks (less than 50 feet in diameter), sacrificial zinc or magnesium

anodes are generally used for external CP, and require no maintenance. For larger

tanks it is more economical to use mixed metal oxide grids which require some

maintenance to keep them in working order. In either case, good tank bottomprotection can be had for as little as one to two dollars per square foot of steel

protected. External cathodic protection systems are covered by the new API

Recommended Practice 651.

Internal cathodic protection is usually provided by aluminum anodes attached to the

tank bottom. In order to work properly, the anodes must be submerged in a

conductive medium, such as the water layer at the bottom of a crude oil tank.

See Section 650for further discussion of cathodic protection.

253 Performance Criteria for Leak Detection and Leak Containment

In order to satisfy the requirements for leak detection outlined in API 650,

Appendix I the following criteria must be adhered to:

1. Leaks through the bottom must be directed to the perimeter where they are

visually detectable. If a leak does occur it must be collected.2. Electronic sensors and detectors may be used but they must be in addition to

the requirements for leak detection at the perimeter.

3. Materials used for leak detection must be compatible with the range of products

and the stockside temperature ranges and material in contact with the subgrade

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6. The installation of sumps and pipes below the tank bottom is acceptable;

however, the required leak detection and leak tightness shall be maintained.

254 Undertank and Double Bottom Spacer Material Considerations

When tank bottoms are replaced most of them are done by the shell slotting

method referenced to in API 653, 7.10.2.1.2 The details of this construction are

shown in Figure 200-9. Using this method requires that a spacer material be placed

between the old and the new bottom. Some options for this material are discussed

below.

Spacer Material for Double Bottoms

For double bottom designs a common question is whether concrete or sand shouldbe used. Although concrete is much more costly on a volumetric basis it has a

number of advantages. Concrete has essentially zero void space, whereas sand has a

void space of approximately 40 percent. This means that any leak that occurs will

come to the tell-tale holes at the perimeter faster with the concrete system than with

the sand system.

Fig. 200-9 Shell Slotting Removal of Existing Bottom

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specifications. It is easy to create an accurate surface with concrete. Sand, on the

other hand, is not easy to slope or control because it is too easily disturbed by men

and equipment pathways. The concrete acts as a rigid foundation and aids in theprocess of laying down and forming the bottom plates. This is especially true when

forming requires impacts, cutting, and welding operations. Sand is hard to keep out

of the weld joints and can contaminate welds. Dragging plates across the sand has

caused the plate to dive down through the sand and cut the liner on occasion. The

elastomeric liner under the sand can more easily be damaged during construction

than if placed under concrete.

Although the concrete system cannot accept a cathodic protection system, the

concrete itself is considered to be a factor in inhibiting corrosion since it is alkaline.

Sand should be considered where concrete may not be feasible. This occurs when

the tank is relatively large and the soil is subject to settlement. The settling concrete

can crack causing failure of the elastomeric liner.

Another problem with concrete can occur when settlement pockets introduced by

non-uniform settlement may cause pockets of water to form in the grooves under the

tank and accelerate corrosion.

Also, acoustic emissions testing companies claim that a concrete pad makes finding

leaks more difficult for them than does a sand pad or filler.

Undertank Materials

Concretehas most of the advantages that are listed above for double bottom fill

materials such as:

reduced corrosion

quicker bottom plate layout and installation

slope and flatness control

the ability to install leak detection grooves, and

low void space.

Sometimes, concrete is indispensable as a liner thus fulfilling the need for a leak

detection barrier when an elastomeric liner will not suffice. This is the case for hottanks. Since the liner should be designed for the stockside temperature which may

be well above any ordinary elastomeric liner design limits, the concrete, if

reinforced may be considered a liner.

Sand or soilas an undertank material has the advantage of reduced material costs.

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liner of the tank causing potential problems. It is recommended that a geotextile

fabric be installed between the clay and the liner because the effects of clay

shrinkage in direct contact with the liner on the integrity of the liner are not known.

A lot of experience does not exist for clay liners. Claymax bentonite liners which

have been used extensively for diking requirements are subject to changing perme-

ability when exposed to certain conditions of pH or chemistry. Some states do not

allow clay to be used as a liner because of its known expansion and contraction

problems affecting liner integrity. Clay is a poor conductor of electricity when dry

and therefore will have a variable effect on any cathodic protection systems that

must pass current through the clay. Also, it is hard to visualize a good method of

assuring a leak proof joint between the ringwall and the clay when shrinkagecontraction occurs.

255 Miscellaneous Design Considerations

Double Bottom Tanks

The design engineer should evaluate the condition of the dead shell that will exist

between the old bottom and the new bottom. In most cases, the dead shell is in goodcondition with little corrosion except at the very bottom. However, should it be

severely thinned or pitted the following may apply. A weakened dead shell may

not transfer the dead loads or seismic loads to the foundation. It may buckle or

warp. It also might not withstand a build up of hydrostatic pressure that could occur

should there be a severe leak in the new bottom.

A common error in the installation of new bottoms is to attempt to install the new

bottom inside the tank, fillet welding it to the interior surface of the shell as shown

in Figure 200-10. This is prohibited by API 653. This type of joint is subject to shell

rotation and will fail either on first filling or after fatigue of the new fillet weld.

A common question that arises with the design is whether to caulk or weld the

underside of the new bottom (See Figure 200-10). Unfortunately, this issue is far

from simple and involves a number of parameters.

API 650 Appendix I states that welding or caulking a double bottom under the new

bottom is required. However, the discussion in I.4.1 of the Appendix requires that

an analysis and evaluation be performed if the new double bottom is not uniformly

supported both inside and outside of the shell.

The intent of the caulk/weld is to seal out moisture which may enter by a number of

mechanisms. Rainfall may flow around the new chime and by capillary action

migrate into the leak containment space. If the foundation is in a flood area, the

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problem. To really do it right may require the welder to use mirrors, slowing down

the weld speed considerably. A proper weld should have a life expectancy

approximately equal to that of the service life of the tank. Whether or not this is

attained in practice is debatable. Most of our facilities do seal weld this juncture.

To reduce initial capital expenditures, an alternative to seal welding is to seal the

joint with caulking. If this choice is considered, Sherwin Williams Steelseam 920-

W-974 products are recommended.

Caulking probably does not have the life span of seal welding and is sensitive to

surface preparation, flexure of the joint, sunlight, chemical environment effects, etc.

However, it is probably cheaper to install on an initial cost basis compared to seal

welding the floor to the dead shell. Here are some comparisons between the twomethods of sealing this space:

Seal welding will have a longer life than caulking. The life of the caulking is

dependent on a number of factors as mentioned above. With a caulked joint the

position of the top shell and dead shell should be monitored periodically to

k t i th t th t k h ll i di tl t d b th f d ti th h

Fig. 200-10 Retrofitting an Existing Tank with a New Double Bottom

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Where high temperatures or varying temperatures of stored product are used,

caulking should not be considered because the caulking will tear away as the

shell grows radially outward. In this case seal welding would act to keep theupper and lower shells aligned.

Where large amounts of settlement are expected, caulking should not be used as

the seal will be broken.

After hydrostatic testing, and on first filling, the caulking should be checked for

its integrity against leaks.

The effect of uplift caused by seismic events on a welded joint versus caulked

joint is not really known. Further study is needed.

Triple Bottoms

In several refineries, not only have second bottoms been installed but additional

bottoms including up to as many as four bottoms have been installed. Although it is

certainly possible to add three or more bottoms, it should be realized that if the old

bottoms ever have to be removed the work will be more costly and difficult. As the

number of bottoms increases, the likelihood of having to relocate tank

appurtenances will increase and, of course, the usable volume of the tank is reduced.

Although the structural effects are not really understood, the proof that they do not

seem to be adverse is the large number of operating years experience with three or

more bottoms. One problem that has occurred is the oldest bottoms continue to

deteriorate, and since the void space is filled with sand it washes out. This causes

buckling of the dead shells and results in a very difficult repair job. If it is

determined that the second bottom is deteriorating and a new bottom required,

consideration should be given to more effective corrosion prevention techniques.

256 Design Variations

Leak detection/containment may be installed on new tanks or existing tanks.

Appendix I of API 650 applies to new installations since the standard is applicable

to new tank construction only. API 653, Tank Inspection, Repair, Alteration, and

Reconstruction, which applies only to tanks that have been in service makes only a

brief reference to leak detection/containment: If a tank bottom is to be replaced,

consideration should be given to installing a leak detection (tell-tale) system thatwill channel any leaks in the bottom to a location where it can be readily observed

from the outside of the tank (API 653 Paragraph 2.4.5Bottom Leak Detection). It

was the intent of the API Committee to allow the criteria from Appendix I of API

650 to be used for either new or existing construction.

C i h ll b i ll d bl b k i i

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Figure 200-8 shows most of the designs that are being used by various oil

companies today. The figure is divided into R figures, meant to cover the retrofit

designs where a new bottom is required because the old bottom must be replacedand N figures, meant to cover the designs that include leak detection for new

installations.

Chevron has used the Figure 1R and 1N in the vast majority of cases. These designs

are proven with over 10 to 12 years experience and have shown no special

problems. They are competitive with the other designs from a cost standpoint. This

manual also has detailed drawings and specifications that are based upon these

designs.

Because of the numerous factors and pros and cons associated with each of the

various designs, it is not a simple task to select the most optimal leak

detection/containment system for a given site. Probably the best way is to

coordinate the available knowledge by bringing in input from operations, tank

building contractors and Company experts.

Designs for New Installations

Design 1N. This design is shown in more detail as Foundation Type E, inStandard Drawing TAM-EF-364. It can be used on flat bottom or sloped bottom

tanks of any size.

The design incorporates ringwall foundations fitted with a grooved concrete slab.

The grooves act to direct the leak to the perimeter of the tank where it can be

observed. An 80-100 mil HDPE liner beneath the concrete slab acts to contain

the leak.

Since the concrete is slotted, there are strips of tank bottom underside which are notin contact with the concrete (it is doubtful that the areas adjacent to the bottom plate

fillet welds are in contact with the concrete either). It has been postulated that these

locations are more prone to corrosion from atmospheric moisture. In some samples

that were checked (in tanks with approximately seven years of service) in Richmond

this was not observed to be the case. What is far more of a potential problem is

backing up of condensing atmospheric moisture or of ground moisture that cannot

escape because the tell-tale holes are plugged. Debris either in the grooves of the

leak detection slab or plugged tell-tale holes can cause extremely acceleratedcorrosion rates on the bottom underside. The slab elevation should be high enough

so that the water table or flood level virtually never exceeds it.

One major drawback with this design is that if used on soft or uncompacted soils

subject to settlement, the concrete slab can crack. The cracked slab can damage, tear

or puncture the liner thus voiding the leak detection system So far this design has

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The choice of whether or not to construct a ringwall for a new foundation is best

decided on a location-by-location basis. In most locations, a compacted soil ringwall

will not withstand erosion from heavy rains and may allow too much settling of thebottom to assure the integrity of the leak detection system. In a few dry locations

with hard soils, going without a ringwall may be an alternative. A ringwall also

minimizes differential peripheral settlement which causes the need for repairs to be

made.

The question of whether or not to use a sacrificial anode system depends on cost.

Both systems can be installed in any tank. Using todays relative costs of zinc or

magnesium (for a sacrificial anode system) versus typical mixed-metal anodes (for

an impressed current system), the critical tank diameter size is about 35 feet. Tanksof less than about 35 feet diameter are constructed with a sacrificial anode system,

while tanks larger than this are generally constructed using an impressed current

system.

A definite advantage to designs 2N and 6N is that they incorporate not only leak

prevention (the cathodic protection system) but they have leak detection (the tell-

tale system).

Designs 3N and 5N. Designs 3N and 5N include clay as a form of liner beneath thetank bottom. These designs can be used for new tanks or for retrofits if the existing

tank soil is excavated first. Not very much experience on these designs is available.

Locations which might find this design suitable are locations with soft, moist soil

where settlement is a problem. Small chemical tank foundations might be able to

use these designs.

Design 7N. This design is a reinforced mat foundation extended at the perimeter to

act as a ring wall. The middle section relies on a liner and sand to support the

bottom.

Designs for Retrofitting Existing Tanks

Design 1R. This design has been used in many locations within Chevron. It is the

Standard Bottom Replacement for Existing Tanks, which is shown in more detail

on Standard Drawing GD-D1120.

The concept behind this design is to use the existing bottom four to six inches of the

tank as a form in which to pour concrete. A new bottom is then placed upon the

concrete producing a new tank that is reduced in height by approximately four to six

inches. The old bottom is generally in pretty bad shape. In order to satisfy the

requirements of leak detection/containment, an HDPE liner is placed over the old

bottom. The liner also acts to insulate the spacer concrete from infiltration of ground

moisture and to electrically insulate the new bottom from the old bottom It is

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mesh. In this application, the concrete is not designed for any structural

requirements but is simply a spacer.

After the concrete is hardened, leak detection grooves are sawcut into the slab in

radial patterns as applicable to the type of sloped bottom being used and dependent

on diameter. These patterns are shown on Standard Drawing GD-D-1120.

Design 2R. This design depends on grating, mesh, angles, I-beams, or other

structural steel shapes to form the spacer between the old and new bottoms. With

this design any leaks and spills should quickly flow to the leak detection points

located around the periphery of the tank. With this design hydrocarbon sensors can

presumably pick up vapors relatively quickly for sensing leaks.

However, this design has been installed in so few cases in the industry that there is

really no experience with it. It was created for relatively small diameter tanks only

on concrete foundations. If some moisture accumulates in the space between the

bottoms, it is not known if accelerated corrosion will be experienced at contact

points with the structural members due to galvanic action.

If this design is chosen, the filler material must be both structurally adequate in

itself and configured so as not to overstress any other component of the tank. It mustprovide the same characteristics as normal tank foundations, i.e., it must provide

uniform support to the new bottom as well as transfer the loads uniformly to the old

bottom and foundations. At least two potential problems must be addressed. First,

the material must have the ability to support the new bottom without buckling or

crushing due to the hydrostatic weight of the liquid above. Second, the bending

stresses in the new bottom must be limited to prevent cracking. Since lap welded

bottom plate construction is subject to failure where the welds are in excessive

bending, the bottom plates must be laid out such that the high bending stresses

caused by the hydrostatic head do not concentrate in long lengths of the bottom

fillet welds.

Designs 3R and 4R. These designs should be considered the backup design to 1R.

We have experience with them and they do not seem to present significant

problems. It is our opinion that the impressed current anodes are more effective at

delivering the required current to all sections of the tank bottom rather than

sacrificial anodes systems when the tank diameter exceeds about 35 feet.

If the anodes are covered with sand, they can be exposed or destroyed if the new

tank bottom plates are dragged across the sand.

Tank Bottom Selection Criteria

Figure 200-11lists a number of criteria as they apply to the various designs shown

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260 Membrane Design and Selection

261 Introduction

This section discusses the selection and installation of impermeable tank bottom

membranes used for secondary containment on both new tanks and old tanks

requiring new bottoms. The membranes are installed beneath supporting slabs (slabs

are covered in Section 310of this manual) as shown on Standard Drawings GF-

S1121, Standard Secondary Containment and Leak Detection Details for Storage

Tanks, and GF-D1120, Standard Bottom Replacement for Existing Cone-up and

Cone-down Bottom Tanks Including Secondary Containment and Leak Detection.The slabs are grooved on top to channel leaking fluid. The membrane provides the

impermeable layer to prevent the leaking fluid from reaching groundwater.

This section discusses only membranes appropriate for tank bottom secondary

containment. Refer to Section 600 of the Civil and Structural Manual, titled Ponds

and Basins, for a detailed and complete discussion of geomembranes for other

applications.

262 Elastomeric Liner

The primary function of this liner is to serve as a release prevention barrier. The

liner directs the leaks to the perimeter, serving as a leak detector while at the same

time, the liner prevents groundwater contamination. The liner is a backup system to

the original steel bottom, which also serves this function. In addition, the liner

functions to prevent galvanic corrosion between the new steel and old steel bottoms.

263 Membrane Materials for Tank Secondary Containment

HDPE

Company Standard Drawings GF-S1121 and GF-D1120 specify 80-100 mil thick

high density polyethylene (HDPE) as the appropriate membrane material for tank

secondary containment. This recommendation is based the tough physical properties

required of the membrane and on immersion testing of membrane materials in crude

oil and finished product by the CRTC Materials and Equipment Engineering Unit.(See References [1] through [5] in the Reference Section of this manual.)

California law requires that these membranes be at least 40 mil thick. This

requirement is based on the membrane being reinforced with a scrim (such as

Hytrel, described below). 80 to 100 mil HDPE is specified because HDPE is

200 B tt S l ti d D i T k M l

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Other Materials

Two other membrane materials, Fueltane and Hytrel, are considered good

alternatives and are preferred when design cannot eliminate potential installation

problems encountered with the thicker, stiffer HDPE. Fueltane (Seaman Corp.) is a

urethane-coated polyester membrane, and Hytrel (DuPont) is a polyester elastomer

membrane which has been used by the Company for service station piping

secondary containment

Fig. 200-11 Tank Bottom Selection Criteria

Design Number (See Fig. 500-11)

Criteria 1R 2R 3R 4R 1N 2N 3N 4N 5N 6N

Retrofit Design X X X X X X X

New Tank Design X X X X X X X

Cathodic Protection X X X X(1) X(1) X

Concrete Inhibits Corrosion X X

Leak Detection X X X X X X X X X

Reasonable Track Record X X X

Potential Hazardous Waste Disposal X X X X X X X

Moist Soil Conditions Required X X

Stable Soil/Foundation Required X X X X X

Cracking Concrete Can Cause Liner Failure X X

Foundation Washout Potential X

Relatively Small Diameter Only X X X

Releveling Difficult X X X X X X X

Releveling May Damage Leak Prevention X X X

High Number of Barriers to Leakage X X X

Sand Pumping Can Damage Liner or Tank

Bottom

X X X X X X

Leak Containment Space Reduces TankVolume

X X X X

Company Has Experience With This Design X X X

Quick Leak Detection Response X X X

(1) Deep-well cathodic protection possible


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264 Design and Construction

DesignThe membrane layout should be in a pattern that minimizes the number and length

of seams. Use the largest pieces that you can from HDPE rolls which come in 22-

foot widths and are several hundred feet long. Using odd-shaped, smaller pieces of

scrap results in a membrane that resembles a quilt. This patchworking is

unacceptable because it increases the number of seams and the total weld length,

and also results in weld intersections (often called weld Ts or Ys due to their

appearance) that are much more likely to leak or tear if stressed. On cone up and

cone down bottoms, the seams should be oriented down-slope to minimize stresses.

Substrate

New Tanks. The Standard Drawing GF-S1121 for new tanks shows four inches of

sand or compacted fill as the membrane substrate. This substrate is ideal as it

separates the liner from the subgrade and helps protect it from any potential damage

if the foundation settles or shifts.

Existing Tanks. For retrofitting old tanks, the membrane is often installed over theold steel floor as shown in Standard Drawing GD-D1120. Most often, this provides

a good, stable substrate for the membrane. However, if the floor is badly corroded

and/or riveted, the possibility of puncturing the membrane increases. A high quality

10-to-16 ounce geotextile can be deployed under the liner to help protect the liner

from puncture and abrasion. The obvious burrs and edges should be ground flush

prior to the installation of the geotextile.

Floating roof tanks have internal support legs that sit on the tank floor if the fluid

level in the tank is low or empty. For existing tanks with the roof already in place,circular pieces of membrane, roughly two or three feet in diameter, are precut and

slid under the roof support legs while the roof is being temporarily supported. Then

the rest of the membrane is installed and welded to the circular pieces under the

stands.

Installation

Refer to the Engineering Specifications of this manual for bottom replacement

specification TAM-MS-1. This specification also includes membrane placement.The steps to be followed when installing a membrane are summarized below:

Preparation. Before deploying any membrane, remove all debris from the

supporting surface. The surface should also be dry.

C b d d l h f f h li A il


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should be hot air tack welded using a hot air gun (Liester). This will hold the

membrane in place until the seams are welded.

The ideal sequence is to install the liner in the afternoon when temperatures are thewarmest and the liner will be at its maximum expansion. This procedure will reduce

the problem of wrinkles. However, do not fasten the liner to the shell until it cools

down to prevent tearing due to shrinkage.

If the liner does wrinkle, it may become necessary to splice the liner and remove the

wrinkle. If this is done, repair the liner using an oversized patch that is at least six

inches larger than the cut at all locations. Merely welding the cut will not be

acceptable because it is impossible to obtain the minimum three inch overlaprequired by the specificationat the ends of the cut.

Seam Preparation. Bevel the top, overlying membrane edge at roughly 45 degrees.

This is necessary on thicker HDPE membranes (80 mil and up) to achieve a good

fusion weld. Just prior to extrudate welding, the seams should be lightly sanded or

ground to remove the thin layer of oxide that builds on the surface and then wiped

or air-blown to remove grindings, dust, or any other contaminants.

Weld Qualification. Prior to production seam welding, the installation technician

must weld a qualifying test strip. Two test specimens from separate points on the

test strip must be cut and pulled to failure in peel as shown inFigure 200-12.

To pass the peel test, the membrane material, not the weld, must fail. If the weld

breaks or if it peels off of the membrane, the test is a failure. The weld must bestronger than the membrane material.

Anchoring and Sealing

The liner is anchored with studs around the circumference of the liner near the tank

ll A l t i th li d t th b hi h th t d d l th

Fig. 200-12 Peel Test


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265 Inspection

Non-Destructive InspectionThe Company inspector should visually inspect the liner during and after

installation. He should verify that:

the seams are being lightly ground and cleaned prior to welding

the proper testing is being done

the liner is the correct thickness, and

sound construction practices are being enforced.

The installer must vacuum test the seams for pinhole leaks. The vacuum test

machine must pull at least 5 psi vacuum. Some installers prefer using a spark test,

which is also acceptable. Every inch of weld must be inspected by one of these

methods, including patches.

Destructive Inspection

Destructive samples are cut from the installed liner and tested in peel as described

above. The frequency of testing is usually one sample per seam. Often, two

destructive samples are also taken from the first 20 feet of seam welding to ensure

that the weld guns are operating properly. The holes are patched with a circular

piece of liner welded to the membrane.

266 Approved Manufacturers and Installers

Manufacturers

Company specifications should require testing of every roll of liner used to ensure

that we are getting only top quality material. Consult with the CRTC Materials and

Equipment Engineering unit for approved manufacturers.

Installers

The Company does not maintain an official list of approved installers because the

quality of the installation depends on the on-site crew installing the system and that

can vary widely within individual companies. Instead, we give guidance on the

experience level required for the site foreman and crew. On large pond projects, we

usually require two years experience in the specific position (field foreman, CQA

foreman, technician, etc.), a predetermined number of square feet installed, and job

references with contacts and phone numbers. For tanks, require a set number of tank

installations and ask for references with contacts and phone numbers.


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Standard Drawings

GF-S1121, Standard Secondary Containment and Leak Detection Details for

Storage Tanks.

GD-D1120, Standard Bottom Replacement for Existing Cone-up and Cone-down

Bottom Tanks Including Secondary Containment and Leak Detection.

270 References

1. Cummiskey, B. J.,Impoundment Liner Testing - Western Producing Oil

Cleaning Plant, June 30, 1983, Materials and Equipment Engineering Unit

File 25.6.

2. Klein, L. J., Storage Tank Containment Membrane TestsEl Segundo,

December 7, 1983, Materials and Equipment Engineering Unit File 6.85.

3. Stofanak, R. J., Storage Tank Containment Membrane TestsEl Segundo, April

3, 1985, Materials and Equipment Engineering Unit File 6.85.

4. Rippel, T. E., Permeability Testing Flexible Membrane Liners, February 28,

1986, Materials and Equipment Engineering Unit File 25.06.01.

5. Rippel, T. E.,Immersion Testing of Flexible Membrane Liners for Secondary

Containment, May 30, 1986, Materials and Equipment Engineering Unit

File 6.85.

6. Kmetz, J. H.,Adhesives Testing for Secondary Containment Membrane

Systems, December 3, 1987, Materials and Equipment Engineering Unit

File 56.1.

7. Environmental Protection Agency, Document EPA-600/2-88/052,Lining of

Waste Containment and Other Impoundment Facilities, Appendix K

Tank Manual 100 General I

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Chevron Corporation 200-33

Fig. 200-1 Bottom Designs for Storage Tanks

Tank Manual 100 General I

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Chevron Corporation 200-35

Fig. 200-8 Tank Bottoms with Secondary Containment, Leak Detection and Cathodic Protection (New or Retrofitted)

Documents

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