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Preparing Tank Bottoms forHot Work

API PUBLICATION 2207FOURTH EDITION, SEPTEMBER 1991

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*b”Strategies for Today~

Environmental Purtnersbip

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@i#”Stratq+es forToday~

Envtronme;taI-Partnership

One of the most significant long-term trends affecting the future vitality of the petroleumindustry is the public’s concerns about the environment. Recognizing this trend, API mem-

ber companies have developed a positive, forward looking strategy called STEP: Strategiesfor Today’s Environmental Partnership. This program aims to address public concerns byimproving industry’s environmental, health and safety performance; documenting perfor-mance improvements; and communicating them to the public. The foundation of STEP isthe API Environmental Mission and Guiding Environmental Principles. API standards, bypromoting the use of sound engineering and operational practices, are an important means

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Preparing Tank Bottoms forHot Work

Safety and Fire Protection Department

A~l PUBLICATION 2207FOURTH EDITION, SEPTEMBER 1991

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AmericanPetroleumInstitute

SPECIAL NOTES

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FACTURERS, OR SUPPLIERS TO WARN AND PROPERLY TRAIN AND EQUIPTHEIR EMPLOYEES, AND OTHERS EXPOSED, CONCERNING HEALTH AND

SAFETY RISKS AND PRECAUTIONS, NOR UNDERTAKING THEIR OBLIGATIONSUNDER LOCAL, STATE, OR FEDERAL LAWS.

3. INFORMATION CONCERNING SAFETY AND HEALTH RISKS AND PROPERPRECAUTIONS WITH RESPECT TO PARTICULAR MATERIALS AND CONDI-

TIONS SHOULD BE OBTAINED FROM THE EMPLOYER, THE MANUFACTUREROR SUPPLIER OF THAT MATERIAL, OR THE MATERIAL SAFETY DATA SHEET.

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GRANTING ANY RIGHT, BY IMPLICATION OR OTHERWISE, FOR THE MANU-

FACTURE, SALE, OR USE OF ANY METHOD, APPARATUS, OR PRODUCT COV-ERED BY LETTERS PATENT. NEITHER SHOULD ANYTHING CONTAINED IN

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Copyright @ 1991 American Perroleum Institute

w

This publication outlines safety precautions for preventing accidental fires and explo-sions when hot work is performed on tank bottoms.

API publications may be used by anyone desiring to do so. Every effort has been madeby the Institute to assure the accuracy and reliability of the data contained in them, however,the Institute makes no representation, warranty, or guarantee in connection with this pub-lication and hereby expressly disclaims any liability or responsibility for loss or darnage re-

sulting from its use or for the violation of any federal, state, or municipal regulation withwhich this publication may conflict.

Suggested revisions are invited and should be submitted to the director of the Safety andFire Protection Department, American Petroleum Institute, 1220 L Street, N.W., Washing-ton. D.C. 20005.

— CONTENTS

sEcTIoN i---0ENERAL1.1 Introduction and Scope ................................................ ....................................1.2 Referenced Publications ............. .....................................................................

SECTION 2—PRECAUTIONS2.1 General Precautions .. ......................................................................................

2.2 Specific Precautions ..... ...................................................................... .............

SECTION 3—INSPECTION PROCEDURES3.1 General Procedures ................................... ............ ..........................................

3.2 Specific Procedures ... ................................................ ............. ............ .............

SECTION 4-SAFE WORK PROCEDURES4.14.2

4.34.4

4.54.6

General .................. ....... ......................................... ............................. .............

Minor Repairs .............. ...................................................................... .............Major Repairs ...... ......... .................................. ................................................-

Perimeter Repairs ......... ........................................................................ ...........

Double-Bottom Installation ................................................................ .............

Sectional Repairs ....... ... ...................................................................................

.Figure

l—Preparing a Tank for Repairs ............................... .......................... ... .............

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— Preparing Tank Bottoms for Hot

SECTION l-GENERAL

1.1 Introduction and Scope

This publication outlines safety precautions for preventingaccidental fires and explosions when hot work is performed

on tank bottoms. The term hot work, as used in this publica-tion, is defined as an operation that can produce a spark orflame hot enough to ignite flammable vapors.

Tanks that have contained flammable or combustible liq-uids, regardless of their age and type of construction, mustbe considered unsafe for hot work until safety inspections

prove otherwise. These inspections include gas testing to de-termine if the oxygen content of each tank is between 19.5and 22.5 percent. Special techniques are required in the per-

formance of hot work on tank bottoms to prevent the ignitionof flammable vapors that may be trapped under the tank.

Although each repair of tank bottoms must receive careful

consideration, the safety procedures described in this publi-cation provide various methods for preparing tank bottomsfor hot work. These procedures will apply to most situations.

1.2 Referenced Publications

The most recent editions of the following standards,codes, and specifications are cited in this publication.

ANSI’Z49. 1

API

Pub] 2009

Publ 2015

Publ 2202

Publ 2217

Publ 2217A

HTC2

Work

Safety in Cutting and Welding

Safe Welding and Cutting Practices in Re-fineries, Gasoline Plants, and Petrochem-ical PlantsCleaning Petroleum Storage TanksDismantling and Disposing of Steel From4boveground Leaded Gasoline StorageTanksGuidelines for Conjined Space Work in thePetroleum IndustrySidelines for Work in Inert Confined~paces in the Petroleum Industry

Safe Tank Cleaning, (audiovisual/workbook trainingprogram)

0SHA329 Code of Federal Regulations, Pti 1910

SECTION 2—PRECAUTIONS

2.1 General Precautions

2.1.1 The tank must be isolated, cleaned, ventilated, andtested for toxic and flammable vapors and oxygen defi-ciency. All tests should be performed in accordance with ap-

plicable national, state and local regulations and withrecognized industry practices (see OSHA Pm 1910 Regula-tions and API Publications 2015 and 2217).

2.1.2 A visual inspection of the hot-work area is neces-

sary. A competently mined or experienced person should beresponsible for authorizing the hot work and should desig-nate the safety precautions to be followed.

2.1.3 Adequate fmt aid and fire-fighting equipment, such

as fire extinguishers and water hose lines, should be avail-able and ready for instant use. Workers should be instructedin the proper use of this equipment.

2.2 Specific Precautions

2.2.1 The work permits for the job, tank entry, and hot workmust be properly signed and issued before the work is started.

1

2.2.2 An airmover rated for the appropriate electrical clas-sification should be in operation at all times during entry andhot work. The capacity of the air mover must be large enough

to provide enough fresh air for workers inside the tank.

2.2.3 Lines to and from the tank that have been discon-nected, blanked off, or otherwise isolated should not be dis-turbed during entry and hot work.

2.2.4 Tank surfaces that have been in contact with leadedgasoline should be scraped down to bare metal. On each sideof a line that might be heated excessively by welding orother operations, an area of at least 30 centimeters (12inches) should be scraped down to bare metal.

As an alternative to scraping down to bare metal, weldersshould use supplied-air respiratory equipment. If the area de-

]American National Standards Institute. 1430 Broadway, New York. NewYork 100182Howell Training Company, 5201 Langtleld Road, Houston, Texas 7704030ccupatiorsal Safety and Healrh Admiisrradon, U.S. Depamnem of Labor.The Code of Federal Reguloriom is available from the U.S. GovernmentPrinting Oftlce, Washington, D.C. 20402.

2 PUBLICATION2207

scribed above is not scraped down to bare metal and as long

as frequent air-quality tests during the hot work indicate asafe atmosphere, it may not be necessary for other personnelin the tank to wear air-supplied respiratory equipment (seeAPI Publication 2015).

2.2.5 Grounding leads from the welding machine should

be attached directly to a bared surface on the tank shell onwhich hot work is to be performed. Welding leads should be

carefully inspected for insulation abrasions, cuts, scuffs, or

breaks; any of these can cause shorting.

2.2.6 Compressed-gas cylinders used for cutting opera-

tions should be securely fastened in an upright position and

kept outside the tank at a safe distance from the open man- —holes. When not in use, cutting torches and hoses must be

shut off at the cylinder valves and kept outside the tank.

Compressed-gas supply hoses and hose comections shouldbe inspected for leaks before being taken inside the tank.

To prevent a possible flammable mixture with air from

forming in the tank, compressed-gas supply hoses must beprotected from damage outside the tank and from bums,

cuts, breaks, or other damage inside the tank.

2.2.7 While work is in progress, all work areas must bemonitored for oxygen deficiency and combustible and toxic

atmospheres.

SECTION 3-INSPECTION PROCEDURES

3.1 General Procedures

When repairs are planned, the tank bottom must be in-

spected, regardless of its suspected condition.

3.2 Specific Procedures

Appropriately sized small openings are sometimes made

in the tank bottom b} cold curnng or by drilling holes in eacharea where hot work is to be performed. These openings fa-cilitate visual ins+e-ction and freeing the interior from gas.When such openings are made, care must be taken to avoid

SECTION 4-SAFE

4.1 General

The work procedures adopted will depend on the condl-

tion of the tank bottom, the type and extent of the hot-workrepairs to be performed, and the results of the inspection.The safe work procedures described in 4.2 through 4.6 applyonly to those situations in which flammable liquids or vaporsare known or suspected to be present. These procedures arenot intended to coverall the different types of tank-bottom orhot-work repairs that may be encounter, they do, however,

describe a variety of situations in which these safety princi-ples can be applied. Safe work procedures should be written

and approved by a competent, trained or experienced person.

4.2 Minor Repairs

Minor repairs usually involve welding corrosion pits andpatches or other localized jobs, such as welding supports orbraces. If the bottom is not in good condition, the followingprocedure may be used

a source of ignition that could result in a fwe or explosionarising from flammable vapors or liquid that might be re-

leased from under the tank bottom. A coolant should be ap-plied to the cutting edge of tools to reduce the heat of

friction. The use of open-type electric drilling machines isnot recommended.

If tank-bottom-to-shell repairs are to be made, care must

be taken to remove any exterior insulation on the bottom of

the tank shell that could be oil soaked hot work conductedinternally could cause oil-soaked insulation to ignite. Beforethe insulation is removed, its type should be determined so

that it can be removed properly.

WORK PROCEDURES

a. Drill and tap a hole for a 13-millimeter (~-inch) pipe adja-

cent to the repair area.

b. Connect a supply of carbon dioxide or other inert gas tothe 13-millimeter (X-inch) tap, using metal tubing. A pres-

sure control valve with a flow indicator should be used toprevent overpressuring of the tank bottom.

c. Before beginning the hot work, establish a flow of inertgas under the tank bottom in the vicinity of any proposedwelding to ensure that any flammable vapors have been

swept away or diluted so that they cannot support combus-tion.

d. When using inert gas, continuously monitor the area to as-sure that the oxygen content remains between 19.5 and 22.5percent.

e. When the welding has been finished in a localized area,

stop the flow of inert gas, remove the tubing, plug the holewith a tapered pin or other device, and back weld promptly

before moving to another area.

PREPARINGTANKBo_rroMsFORHOT WORK 3

—4.3 Major Repairs

When repairs involve most of the tank bottom, it may be

desirable to displace the flammable liquids beneath the tankby water flooding. This may be done as follows:

a. Around the tank’s outer shell, construct an earthen dikehigher than the highest floor plate in the tank (see Figure 1).b. At the highest points in the tank bottom, drill and tap holesfor 13-millimeter (~-inch) pipe. These holes should be lo-cated to ensure that all flammable liquid or vapor under thetank will be displaced with water.

c. Install pipe nipples to be used as vents and check points.The height of the nipples should exceed that of the tempo-rary earthen dike.d. Fill the space under the tank with water until seepage oc-curs at each nipple. Continue the flow of water to maintain a

constant level within the dike to ensure that no voids developunder the tank.e. Watch for leaks inside the tank and plug them as neces-sary to keep the tank bottom dry.f. When repairs are completed, empty the water from the

dike to just below the nipples, remove the nipples, plug theholes with a tapered pin or other device, and back weld.

4.4 Perimeter Repairs.— Repairs around the perimeter of a tank bottom may be

made safely after the following preparations:

a. Excavate under the edge of the tank for a minimum of 30

centimeters (12 inches) beyond the point of any hot-workarea. The excavation should be large enough for a person towork in safety and comfort while excavating and applying a

liquid or vapor barrier. The area should be continuouslymonitored to assure the oxygen content is between 19.5 and22.5 percent.

b. Seal off all openings between the floor plates and the tankfoundation by packing them with mud or some other suit-able, noncorrosive material. The packing should be checked

periodically, and walking on the tank bottom should be re-

srncted to assure that the seal remains intact (see Figure 1).c. Use a vapor indicator to check the excavations and the

seals between the floor plates and the foundation.

d. Before starting hot work and while work is in progress,

monitor the surrounding area, including the excavations andthe tank interior, for the presence of airborne concentrationsof chemical contaminants.e. Ventilate the excavation, if necessary, with a portable airblower rated for the appropriate elecrncal classification.

Nole: When the repairs are completed. excavations should be promptly andcarefully refilled to prevent ttre possible failure of the rank foundations.

4.5 Doubl+Bottom Installation

When a tank double bottom is constructed, the followingprocedures may be used:

a. Place approximately 10 centimeters (4 inches) of sand or

other sealing material over the existing floor.b. Install a new bottom by welding.

Note: If vapors in the flammable range are not present under the originaltank bottom, hot work can be performed safely on the new tank bottom,even though the original tank bottom is resting on a foundation saturatedwith oil. In addition, hot work maybe pa-formed if there is no possibility ofoil penetrating the sand barrier and coming in contact with the new bottombeing welded.

4.6 Sectional Repairs

When sectional repairs are made on tank bottoms, the fol-lowing methods may be used:

a. Using a hand- or air-operated tool, coldcut the tank bot-tom to be replaced and remove it. A coolant should be ap-plied continuously to the cutting edge of the tool to reduce

the heat of friction.

b. Remove the earth from under the section to be replaced.Fill it with tamped sand, and seal the perimeter of the patcharea with mud or some other suitable, noncorrosive material.c. Continuously monitor the area for oxygen deficiency andcombustible or toxic atmospheres.d. When large sections of the bottom must be replaced and itis questionable whether the seal will remain effective, main-

tain an inefi area under the patch area while hot work is be-ing performed. While work is being performed in and aroundan area with an inert atmosphere, the area should be contin-uously monitored with an oxygen analyzer.

4 PUBLICATION2207

Crack in tank bottomto be welded

Steel tank

.

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TOP VIEW

Earthen dike12 inches from shell

Excavated12 inches beyondpoint of anyhot WO1’k

hhd pack6 inches thick

PERSPECTIVE VIEW

Figure I—Preparing a Tank for Repairs

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.

. l-110&9/91—1 4M (5A)1-0141+11/944 5C (3E) U

1-0832&l O/9WC (3E) CPR-0133G7/9&5C (IH) C

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