Welded Steel Tanks for

Welded Steel Tanks for Oil Storage

1 Scope

1.1 GENERAL

1.1.1

This standard covers material, design, fabrication,

erection, and testing requirements for vertical, cylindrical,

aboveground, closed- and open-top, welded steel storage

tanks in various sizes and capacities for internal pressures

approximating atmospheric pressure (internal pressures not

exceeding the weight of the roof plates), but a higher internal

pressure is permitted when additional requirements are met

(see 1.1.10). This standard applies only to tanks whose entire

bottom is uniformly supported and to tanks in nonrefrigerated

service that have a maximum design temperature of 93°C

(200°F) (see 1.1.17) or less.

1.1.2

This standard is designed to provide the petroleum

industry with tanks of adequate safety and reasonable economy

for use in the storage of petroleum, petroleum products,

and other liquid products commonly handled and stored by

the various branches of the industry. This standard does not

present or establish a fixed series of allowable tank sizes;

instead, it is intended to permit the purchaser to select whatever

size tank may best meet his needs. This standard is

intended to help purchasers and manufacturers in ordering,

fabricating, and erecting tanks; it is not intended to prohibit

purchasers and manufacturers from purchasing or fabricating

tanks that meet specifications other than those contained in

this standard.

Note: A bullet (

•) at the beginning of a paragraph indicates that there

is an expressed decision or action required of the purchaser. The purchaser’s

responsibility is not limited to these decisions or actions

alone. When such decisions and actions are taken, they are to be

specified in documents such as requisitions, change orders, data

sheets, and drawings.

1.1.3

This standard has requirements given in two alternate

systems of units. The requirements are similar but not identical.

These minor differences are due to issues such as numerical

rounding and material supply. When applying the

requirements of this standard to a given tank, the manufacturer

shall either comply with all of the requirements given in SI

units or shall comply with all of the requirements given in US

Customary units. The selection of which set of requirements

(SI or US Customary) shall apply to a given tank shall be by

mutual agreement between the manufacturer and purchaser.

1.1.4

The appendices of this standard provide a number of

design options requiring decisions by the purchaser, standard

requirements, recommendations, and information that supplements

the basic standard. An appendix becomes a requirement

only when the purchaser specifies an option covered by

that appendix. See Table 1-1 for the status of each appendix.

1.1.5

Appendix A provides alternative simplified design

requirements for tanks where the stressed components, such

as shell plates and reinforcing plates, are limited to a maximum

nominal thickness of 12.5 mm (

1/2 in.), including any

corrosion allowance, and whose design metal temperature

exceeds the minimums stated in the appendix.

1.1.6

Appendix B provides recommendations for the

design and construction of foundations for flat-bottom oil

storage tanks.

1.1.7

Appendix C provides minimum requirements for

pan-type, pontoon-type, and double-deck-type external floating

roofs.

1.1.8

Appendix D provides requirements for submission of

technical inquiries on this standard.

1.1.9

Appendix E provides minimum requirements for

tanks subject to seismic loading. An alternative or supplemental

design may be mutually agreed upon by the manufacturer

and purchaser.

1.1.10

Appendix F provides requirements for the design of

tanks subject to a small internal pressure.

1.1.11

Appendix G provides requirements for an optional

aluminum dome roof.

1.1.12

Appendix H provides minimum requirements that

apply to an internal floating roof in a tank with a fixed roof at

the top of the tank shell.

1.1.13

Appendix I provides acceptable construction details

that may be specified by the purchaser for design and construction

of tank and foundation systems that provide leak

detection and subgrade protection in the event of tank bottom

leakage, and provides for tanks supported by grillage.

1.1.14

Appendix J provides requirements covering the

complete shop assembly of tanks that do not exceed 6 m (20

ft) in diameter.

1.1.15

Appendix K provides a sample application of the

variable-design-point method to determine shell-plate thicknesses.

1.1.16

Appendix L provides data sheets listing required

information to be used by the purchaser in ordering a storage

tank and by the manufacturer upon completion of construction

of the tank.

1.1.17

Appendix M provides requirements for tanks with a

maximum design temperature exceeding 93°C (200°F) but

not exceeding 260°C (500°F).

05

98

●

03

98

98

●

98

●

05

00

1-2 API S

TANDARD 650

1.1.18

Appendix N provides requirements for the use of

new or unused plate and pipe materials that are not completely

identified as complying with any listed specification

for use in accordance with this standard.

1.1.19

Appendix O provides recommendations for the

design and construction of under-bottom connections for storage

tanks.

1.1.20

Appendix P provides minimum recommendations

for design of shell openings that conform to Table 3-6 that

are subject to external piping loads. An alternative or supplemental

design may be agreed upon by the purchaser or

manufacturer.

1.1.21

Appendix R provides a description of the load

combinations used for the design equations appearing in

this standard.

1.1.22

Appendix S provides requirements for stainless

steel tanks.

1.1.23

Appendix T summarizes the requirements for

inspection by method of examination and the reference sections

within the standard. The acceptance standards, examiner

qualifications, and procedure requirements are also provided.

This appendix is not intended to be used alone to determine

the inspection requirements within this standard. The specific

requirements listed within each applicable section shall be

followed in all cases.

1.1.24

Appendix U provides detailed rules for the use of

the ultrasonic examination (UT) method for the examination

of tank seams.

1.1.25

Appendix V provides additional requirements for

tanks that are designed to operate under external pressure

(vacuum) conditions.

1.2 LIMITATIONS

The rules of this standard are not applicable beyond the following

limits of piping connected internally or externally to the roof,

shell, or bottom of tanks constructed according to this standard:

a. The face of the first flange in bolted flanged connections,

unless covers or blinds are provided as permitted in this standard.

b. The first sealing surface for proprietary connections or

fittings.

c. The first threaded joint on the pipe in a threaded connection

to the tank wall.

Table 1-1—Status of Appendixes to API Standard 650

Appendix Title Status

A Optional design basis for small tanks Purchaser’s Option

B Recommendations for design and construction of foundations

for aboveground oil storage tanks

Recommendations

C External floating roofs Purchaser’s Option

D Technical inquiries Required Procedures

E Seismic design of storage tanks Purchaser’s option

F Design of tanks for small internal pressures Requirements

G Structurally supported aluminum dome roofs Purchaser’s Option

H Internal floating roofs Purchaser’s Option

I Undertank leak detection and subgrade protection Purchaser’s option

J Shop-assembled storage tanks Requirements

K Sample application of the variable-design-point method to

determine shell-plate thickness

Information

L API Standard 650 storage tank data sheets Requirements

M Requirements for tanks operating at elevated temperatures Requirements

N Use of new materials that are not identified Requirements

O Recommendation for under-bottom connections Purchaser’s option

P Allowable external load on tank shell openings Purchaser’s option

V Design of Storage Tanks for External Pressure Purchaser’s option

R Load Combinations Requirements

S Austenitic stainless steel storage tanks Requirements

Definitions:

Mandatory: Required sections of the standard become mandatory if the standard has

been adopted by a Legal Jurisdiction or if the purchaser and the manufacturer

choose to make reference to this standard on the nameplate or in the

manufacturer’s certification.

Requirement: The outlined design criteria must be used unless the purchaser and manufacturer

agree upon a more stringent alternative design.

Recommendation: The outlined criteria provides a good acceptable design and may be used at

the option of the purchaser and manufacturer.

Purchaser’s Option: When the purchaser specifies an option covered by an appendix, the appendix

then becomes a requirement.

98

●

98

●

98

●

●

05

98

98

●

●

●

98

05

01

01

03

05

00

W

ELDED STEEL TANKS FOR OIL STORAGE 1-3

d. The first circumferential joint in welding-end pipe connections

if not welded to a flange.

1.3 COMPLIANCE

The manufacturer is responsible for complying with all

provisions of this standard. Inspection by the purchaser does

not negate the manufacturer’s obligation to provide quality

control and inspection necessary to ensure such compliance.

1.4 REFERENCED PUBLICATIONS

The following standards, codes, specifications, and publications

are cited in this standard. The most recent edition

shall be used unless otherwise specified.

API

Spec 5L

Specification for Line Pipe

Std 620

Design and Construction of Large, Welded,

Low-Pressure Storage Tanks

RP 651

Cathodic Protection of Aboveground Petroleum

Storage Tanks

RP 652

Lining of Aboveground Petroleum Storage Tank

Bottoms

Std 2000

Venting Atmospheric and Low-Pressure Storage

Tanks (Nonrefrigerated and Refrigerated)

RP 2003

Protection Against Ignitions Arising Out of

Static, Lightning, and Stray Currents

Publ 2026

Safe Access/Egress Involving Floating Roofs of

Storage Tanks in Petroleum Service

RP 2350

Overfill Protection for Storage Tanks in Petroleum

Facilities

AA

1

Aluminum Design Manual

Aluminum Standards and Data

Specifications for Aluminum Sheet Metal Work

in Building Construction

ACI

2

318

Building Code Requirements for Reinforced

Concrete

(ANSI/ACI 318)

350

Environmental Engineering Concrete Structures

AISC

3

Manual of Steel Construction, Allowable Stress

Design

AISI

4

T-192

Steel Plate Engineering Data Series—Useful

Information—Design of Plate Structures, Volumes

I & II

ASCE

5

ASCE 7

Minimum Design Loads for Buildings

and other Structures

ASME

6

B1.20.1

Pipe Threads, General Purpose (Inch)

(ANSI/ASME B1.20.1)

B16.1

Cast Iron Pipe Flanges and Flanged Fittings

(ANSI/ASME B16.1)

B16.5

Pipe Flanges and Flanged Fittings

(ANSI/ASME B16.5)

B16.47

Large Diameter Steel Flanges: NPS 26

Through NPS 60

(ANSI/ASME B16.47)

B96.1

Welded Aluminum-Alloy Storage Tanks

(ANSI/ASME B96.1)

Boiler & Pressure Vessel Code,

Section V,

“Nondestructive Examination”; Section

VIII, “Pressure Vessels,” Division 1; and

Section IX, “Welding and Brazing

Qualifications”

ASNT

7

CP-189

Standard for Qualification and Certification

of Nondestructive Testing

Personnel

RP SNT-TC-1A

Personnel Qualification and Certification

in Nondestructive Testing

ASTM

8

A 6M/A 6

General Requirements for Rolled Steel

Plates, Shapes, Sheet Piling, and Bars for

Structural Use

A 20M/A 20

General Requirements for Steel Plates

for Pressure Vessels

A 27M/A 27

Steel Castings, Carbon, for General

Application

A 36M/A 36

Structural Steel

1

The Aluminum Association Inc., 900 19th Street, N.W., Washington,

D.C. 20006, www.aluminum.org.

2

American Concrete Institute, P.O. Box 19150, Detroit, Michigan

48219-0150, www.aci-int.org.

3

American Institute of Steel Construction, One East Wacker Drive,

Suite 3100, Chicago, Illinois 60601-2001, www.aisc.org.

●

05

01

00

4

American Iron and Steel Institute, 1101 17th Street, N.W.,

Suite 1300, Washington, D.C. 20036-4700, www.steel.org.

5

American Society of Civil Engineers, 1801 Alexander Bell Drive,

Reston, VA 20191-4400, www.asce.org.

6

ASME International, 3 Park Avenue, New York, New York 10016-

5990, www.asme.org.

7

American Society for Nondestructive Testing, 1711 Arlingate Lane,

Columbus, Ohio 43228-0518, www.asnt.org.

8

ASTM, 100 Barr Harbor Drive, West Conshohocken, Pennsylvania

19428-2959, www.astm.org.

03

05

05

1-4 API S

TANDARD 650

A 53

Pipe, Steel, Black and Hot-Dipped, Zinc-

Coated Welded and Seamless

A 105M/A 105

Forgings, Carbon Steel, for Piping

Components

A 106

Seamless Carbon Steel Pipe for High-

Temperature Service

A 131M/A 131

Structural Steel for Ships

A 181M/A 181

Forgings, Carbon Steel, for General-Purpose

Piping

A 182M/A 182

Forged or Rolled Alloy-Steel Pipe

Flanges, Forged Fittings, and Valves and

Parts for High-Temperature Service

A 193M/A 193

Alloy-Steel and Stainless Steel Bolting

Materials for High-Temperature Service

A 194M/A 194

Carbon and Alloy Steel Nuts for Bolts for

High-Pressure and High-Temperature

Service

A 213M/A 213

Seamless Ferritic and Austenitic Alloy-

Steel Boiler, Superheater, and Heat-

Exchanger Tubes

A 216M/A 216

Standard Specifications for Steel Castings

for High-Temperature Service

A 234M/A 234

Piping Fittings of Wrought Carbon Steel

and Alloy Steel for Moderate and High-

Temperature Service

A 240M/A 240

Heat-Resisting Chromium and Chromium-

Nickel Stainless Steel Plate, Sheet, and

Strip for Pressure Vessels

A 276

Stainless Steel Bars and Shapes

A 283M/A 283

Low and Intermediate Tensile Strength

Carbon Steel Plates

A 285M/A 285

Pressure Vessel Plates, Carbon Steel, Lowand

Intermediate-Tensile Strength

A 307 Carbon Steel Bolts and Studs, 60,000 psi

Tensile Strength

A 312M/A 312

Seamless and Welded Austenitic Stainless

Steel Pipes

A 320M/A 320

Alloy Steel Bolting Materials for Low-Temperature

Service

A 333M/A 333

Seamless and Welded Steel Pipe for Low-

Temperature Service

A 334M/A 334

Seamless and Welded Carbon and Alloy-

Steel Tubes for Low-Temperature Service

A 350M/A 350

Forgings, Carbon and Low-Alloy Steel,

Requiring Notch Toughness Testing for

Piping Components

A 351M/A 351

Castings, Austenitic, Austenitic-Ferritic

(Duplex), for Pressure-Containing Parts

A 358M/A 358

Electric-Fusion-Welded Austenitic Chromium-

Nickel Alloy Steel Pipe for High-

Temperature Service

A 370

Test Methods and Definitions for Mechanical

Testing of Steel Products

A 380

Cleaning, Descaling, and Passivation of

Stainless Steel Parts, Equipment, and

Systems

A 403M/A 403

Wrought Austenitic Stainless Steel Piping

Fittings

A 420M/A 420

Piping Fittings of Wrought Carbon Steel

and Alloy Steel for Low-Temperature

Service

A 479M/A 479

Stainless Steel Bars and Shapes for Use in

Boilers and Other Pressure Vessels

A 480M/A 480

Flat-Rolled Stainless and Heat-Resisting

Steel Plate, Sheet, and Strip

A 516M/A 516

Pressure Vessel Plates, Carbon Steel, for

Moderate- and Lower-Temperature Service

A 524

Seamless Carbon Steel Pipe for Atmospheric

and Lower Temperatures

A 537M/A 537

Pressure Vessel Plates, Heat-Treated,

Carbon-Manganese-Silicon Steel

[Reference deleted.]

A 573M/A 573

Structural Carbon Steel Plates of

Improved Toughness

A 633M/A 633

Normalized High-Strength Low-Alloy

Structural Steel

A 662M/A 662

Pressure Vessel Plates, Carbon-Manganese,

for Moderate and Lower

Temperature Service

A 671

Electric-Fusion-Welded Steel Pipe for

Atmospheric and Lower Temperatures

A 678M/A 678

Quenched and Tempered Carbon-Steel

and High-Strength Low-Alloy Steel Plates

for Structural Applications

A 737M/A 737

Pressure Vessel Plates, High-Strength,

Low-Alloy Steel

A 841M/A 841

Standard Specification for Steel Plates for

Pressure Vessels, Produced by the Thermo-

Mechanical Control Process (TMCP)

A 924M/A 924

General Requirements for Steel Sheet,

Metallic-Coated by the Hot-Dip Process

A 992M/A 992

Steel for Structural Shapes for Use in

Building Framing

98

03

01

W

ELDED STEEL TANKS FOR OIL STORAGE 1-5

A 1011M/A 1011

Standard Specification for Steel, Sheet

and Strip, Hot-rolled, Carbon, Structural,

High-strength Low-alloy and

High-strength Low-alloy with Improved

Formability

C 273

Method for Shear Test in Flatwise Plane

of Flat Sandwich Constructions or Sandwich

Cores

C 509

Cellular Elastomeric Preformed Gasket

and Sealing Material

D 1621

Test Method for Compressive Properties of

Rigid Cellular Plastics

D 1622

Test Method for Apparent Density of Rigid

Cellular Plastics

(ANSI/ASTM D1622)

D 2166

Standard Test Method for Unconfirmed Compressive

Strength of Cohesive Soil

D 2216

Standard Test Methods for Laboratory Determination

of Water (Moisture) Content of Soil

and Rock by Mass

D 2341

Rigid Urethane Foam

D 2850

Standard Test Method for Unconsolidated-

Undrained Triaxial Compression Test on

Cohesive Soils

D 2856

Test Method for Open Cell Content of Rigid

Cellular Plastics by the Air Pycnometer

D 3453

Flexible Cellular Materials—Urethane for

Furniture and Automotive Cushioning, Bedding,

and Similar Applications

D 4318

Standard Test Methods for Liquid Limit, Plastic

Limit, and Plasticity Index of Soils

E 84

Test Method for Surface Burning Characteristics

of Building Materials

E 96

Test Methods for Water Vapor Transmission of

Materials

AWS

9

A5.1

Specification for Carbon Steel Covered Arc-

Welding Electrodes

A5.5

Specification for Low-Alloy Steel Covered

Arc-Welding Electrodes

D1.2

Structural Welding Code—Aluminum

CSA

10

G40.21

Structural Quality Steels

Supplement to National Building Code of Canada

ISO

11

630

Structural Steels

NFPA

12

11 Standard for Low-Expansion Foam

30 Flammable and Combustible Liquids Code

U.S. Federal Specifications

13

TT-S-00230C

Sealing Compound Elastomeric Type, Single

Component for Caulking, Sealing, and

Glazing in Buildings and Other Structures

ZZ-R-765C

Rubber, Silicone (General Specification)

WRC

14

Bull 297

Local Stresses in Cylindrical Shells Due to

External Loadings—Supplement to WRC

Bulletin No. 107

03

9

American Welding Society, 550 N.W. LeJeune Road, Miami, Florida

33135, www.aws.org.

10

Canadian Standards Association, 178 Rexdale Boulevard,

Rexdale, Ontario M9W 1R3, www.csa.ca.

11

International Organization for Standardization. ISO publications

can be obtained from the American National Standards Institute

(ANSI) and national standards organizations such as the British

Standards Institute (BSI), Japanese Industrial Standards (JIS), and

Deutsches Institut fuer Normung [German Institute for Standardization

(DIN)], www.iso.ch.

12

NFPA International, 1 Batterymarch Park, Quincy, MA

02269-9101, www.nfpa.org.

13

Specifications Unit (WFSIS), 7th and D Streets, N.W., Washington,

D.C. 20407.

14

The Welding Research Council, 3 Park Avenue, 27th Floor, New

York, NY 10016-5902, www.forengineers.org.

05

01

03

03