atmospheric storage tank specification (api 650) vesta002-0600

June 2000

Process Industry PracticesVessels

PIP VESTA002Atmospheric Storage Tank Specification(in Accordance with API Standard 650)

PURPOSE AND USE OF PROCESS INDUSTRY PRACTICES

In an effort to minimize the cost of process industry facilities, this Practice hasbeen prepared from the technical requirements in the existing standards of majorindustrial users, contractors, or standards organizations. By harmonizing thesetechnical requirements into a single set of Practices, administrative, application, andengineering costs to both the purchaser and the manufacturer should be reduced. Whilethis Practice is expected to incorporate the majority of requirements of most users,individual applications may involve requirements that will be appended to and takeprecedence over this Practice. Determinations concerning fitness for purpose andparticular matters or application of the Practice to particular project or engineeringsituations should not be made solely on information contained in these materials. Theuse of trade names from time to time should not be viewed as an expression ofpreference but rather recognized as normal usage in the trade. Other brands having thesame specifications are equally correct and may be substituted for those named. AllPractices or guidelines are intended to be consistent with applicable laws andregulations including OSHA requirements. To the extent these Practices or guidelinesshould conflict with OSHA or other applicable laws or regulations, such laws orregulations must be followed. Consult an appropriate professional before applying oracting on any material contained in or suggested by the Practice.

This Practice is subject to revision at any time by the responsible Function Team andwill be reviewed every 5 years. This Practice will be revised, reaffirmed, orwithdrawn. Information on whether this Practice has been revised may be found athttp://www.pipdocs.org.

© Process Industry Practices (PIP), Construction Industry Institute, TheUniversity of Texas at Austin, 3208 Red River Street, Suite 300, Austin,Texas 78705. PIP member companies and subscribers may copy this Practicefor their internal use.

Not printed with State funds

June 2000

Process Industry Practices Page 1 of 39

Process Industry PracticesVessels

PIP VESTA002Atmospheric Storage Tank Specification(in Accordance with API Standard 650)

Table of Contents

1. Scope...........................................21.1 General .............................................. 21.2 Compliance........................................ 21.3 Referenced Publications.................... 31.4 Definitions .......................................... 51.5 Document Submittals and Review..... 5

2. Materials....................................102.1 General ............................................ 102.2 Plates............................................... 102.7 Bolting.............................................. 102.9 Gaskets............................................ 10

3. Design .......................................113.1 Joints ............................................... 113.2 Design Considerations..................... 123.3 Special Considerations .................... 123.4 Bottom Plates .................................. 133.6 Shell Design..................................... 143.7 Shell Openings ................................ 143.8 Shell Attachments and Tank

Appurtenances................................. 153.9 Top and Intermediate Wind Girders 163.10 Roofs ............................................... 17

4. Fabrication................................ 174.1 General ............................................ 174.2 Shop Inspection ............................... 18

5. Erection..................................... 185.1 General ............................................ 185.2 Details of Welding............................ 195.3 Inspection, Testing, and Repairs ..... 195.5 Dimensional Tolerances .................. 22

6. Methods of Inspecting Joints.. 23

Appendices .................................... 24

Appendix C..................................... 25

Appendix E..................................... 36

Appendix H..................................... 37

PIP VESTA002 June 2000Atmospheric Storage Tank Specification

Page 2 of 39 Process Industry Practices

1. Scope

1.1 General

Aboveground, atmospheric storage tanks shall be constructed per this Practice,PIP VEDTA003, Atmospheric Storage Tank Data Sheet and Instructions (inAccordance with API Standard 650), and API Standard 650 (hereafter referred to asAPI 650). The data sheet portion of PIP VEDTA003 will hereafter be referred to asthe Data Sheet.

A. This Practice establishes minimum construction requirements for thematerials, design, fabrication, erection (if applicable), inspection, and testingof aboveground, non-refrigerated storage tanks fabricated of carbon steel oraustenitic stainless steel. When neither API 650 nor this Practice addressesmaterial requirements for miscellaneous items and appurtenances, thePurchaser and/or the Manufacturer shall supply additional materialrequirements within a supplement to the Data Sheet. Design internalpressures of 2.5 psig or less (see API 650, Appendix F) and designtemperatures of up to 500°F (see API 650, Appendix M) are permissibleunder this Practice.

B. In addition to this Practice, all tanks and appurtenances shall comply withthe Data Sheet and all attachments thereto.

C. This Practice shall supplement, but not supersede, API 650 and anyapplicable jurisdictional requirements. Pressure boundary materials otherthan those listed or otherwise permitted in API 650 may be specified at thediscretion and the responsibility of the Purchaser. In such case, the markingand certification of API 650 shall not be applied by the Manufacturer.

D. This Practice generally parallels the order of API 650, Tenth Edition, to thesubsection level. For example, roofs are the subject matter of Sections 3.10in both API 650 and this Practice. Occasionally, this parallelism descends toan additional level.

E. Field-erected tanks shall be furnished completely erected, tested, and readyto place into service, unless specified otherwise.

F. Shop-fabricated tanks shall be furnished-tested and ready for installation.

1.2 Compliance

A. The Manufacturer shall be responsible for design, fabrication, erection (non-shop-built), certification of materials, quality of workmanship, andcompliance with this Practice, its references, the Purchaser’s supplementalspecifications, and all other data or instructions associated with the PurchaseOrder. The Manufacturer shall also communicate all Purchaser’srequirements to all subcontractors or suppliers working at the request of theManufacturer.

June 2000 PIP VESTA002Atmospheric Storage Tank Specification


B. The Purchaser shall provide any jurisdictional site permits that may berequired to erect the tank(s). The Manufacturer shall provide all otherpermits that may be required to complete or transport the tank.

C. Unless otherwise specified in the Purchase Order, the Manufacturer shallfurnish all labor, tools, equipment, supplies, materials, utilities, storage, andpersonnel services necessary for, and reasonably incidental to, the deliveryof materials to the site, the construction of the tank(s), and the removal ofsurplus and scrap materials from the job site. The Purchaser shall furnish anddispose of the water for hydrotesting the tank from the tie-in points asdesignated on the Data Sheet, Line 14.

D. The Purchaser retains the right to provide personnel to observe all shop andjob site work (including testing and inspection). Such individuals shall beafforded full and free access for these purposes.

E. In this Practice, language indicating that the Purchaser accepts, agrees,reviews, or approves a Manufacturer’s design, work process, manufacturingaction, etc., shall not limit or relieve the Manufacturer’s responsibility toconform to applicable industry design and safety standards and codes,project specifications and drawings, and professional workmanship.

F. If a conflict occurs between this Practice and any drawings or otherdocuments, it shall be the Manufacturer’s responsibility to advise thePurchaser of the conflict and request clarification.

G. Required foundation and grade work shall be supplied by others, unlessotherwise specified in the Purchase Order. The Manufacturer shall inspectand check level tolerances and contour before starting work, and shall notifythe Purchaser of any deficiency that might affect the quality of the finishedwork.

H. During construction of the tank(s), the Manufacturer shall avoidcontaminating the grade with any foreign material that may contribute toaccelerated bottom corrosion. The Manufacturer shall maintain the grade intrue profile and free of foreign materials such as clay, coal, cinders, metalscraps, or animal or vegetable matter of any sort. The Manufacturer shallrepair any damage to either the foundation or grade surface caused by theManufacturer’s operations.

I. In this Practice, language indicating that any particular issue is subject toagreement between the Purchaser and the Manufacturer shall be interpretedto require any such agreement to be expressly identified in writing.

1.3 Referenced Publications

To the extent referenced herein, the publications listed below form part of thisPractice. Each publication shall be the latest edition and addendum in effect on thedate of the Purchase Order. Short titles will be used herein when appropriate.

A. Process Industry Practices (PIP)

– PIP STF05501 - Fixed Ladders and Cages

– PIP STF05520 - Pipe Railing for Walking and Working Surface Details



– PIP STF05521 - Angle Railing for Walking and Working Surfaces

– PIP VEDTA003 - Atmospheric Storage Tank Data Sheet andInstructions (in Accordance with API Standard 650)

– PIP VEFTA100 - Tank Standard Details Index

VEFTA108 - Tank; Ground (In Progress)

– PIP VEFV1100 - Vessel/S&T Heat Exchanger Standard Details

VEFV1116 - Vessel: Manway HingesVEFV1117 - Vessel: Manway Vertical Davit

B. Industry Codes and Standards

• American Petroleum Institute (API)

– API Standard 650 - Welded Steel Tanks for Oil Storage

– API Standard 653 - Tank Inspection, Repair, Alteration, andReconstruction

– API Standard 2000 - Venting Atmospheric and Low-Pressure StorageTanks Nonrefrigerated and Refrigerated

– API MPMS 19.2 - Manual of Petroleum Measurement Standards

Chapter 19 - Evaporative Loss Measurement

Section 2 - Evaporative Loss from Floating-Roof Tanks

• American Society of Civil Engineers (ASCE)

– ASCE 7 - Minimum Design Loads for Buildings and Other Structures

• American Society of Mechanical Engineers (ASME)

– ASME Boiler and Pressure Vessel Code

Section VIII, Division 1 - Pressure Vessel Basic Coverage

– ASME B1.1 - Unified Inch Screw Threads (UN and UNR ThreadForm)

– ASME B16.5 - Pipe Flanges and Flanged Fittings NPS 1/2 throughNPS 24

– ASME B16.47 - Large Diameter Steel Flanges NPS 26 throughNPS 60

– ASME B18.2.1 - Square and Hex Bolts and Screws, Inch Series

– ASME B18.2.2 - Square and Hex Nuts (Inch Series)

• American Society of Testing and Materials (ASTM)

– ASTM A36 - Standard Specification for Carbon Structural Steel

– ASTM A193 - Specification for Alloy-Steel and Stainless Steel BoltingMaterial for High-Temperature Service

– ASTM A194 - Specification for Carbon and Alloy Steel Nuts for Boltsfor High-Pressure or High-Temperature Service, or Both



– ASTM A240 - Standard Specification for Heat-Resisting Chromiumand Chromium-Nickel Stainless Steel Plate, Sheet, and Strip forPressure Vessels

– ASTM A283 - Standard Specification for Low and IntermediateTensile Strength Carbon Steel Plates

• American Welding Society (AWS)

– ANSI/AWS A2.4 - Standard Symbols for Welding, Brazing, andNondestructive Examination

• National Fire Protection Association (NFPA)

– NFPA 11 - Standard for Low-Expansion Foam

– NFPA 780 - Standard for the Installation of Lightning ProtectionSystems

C. Government Regulations

• U. S. Department of Labor, Occupational Safety and HealthAdministration (OSHA)

– OSHA 29 CFR 1910 - Subpart D: Walking-Working Surfaces

1.4 Definitions

Centerline-stacked: The mid-thickness centerlines of plates in all shell coursescoincide

Design thickness: The thickness necessary to satisfy strength and stiffnessrequirements by stated expressions in API 650 or, in the absence of such expressions,by good and acceptable engineering practice for specified design conditions, withoutregard to constructability limitations or corrosion allowances

Floating suction line: Internal piping assembly that allows operator to withdrawproduct from the upper levels of the tank

Flush-stacked on the inside: The inside surfaces of plates in all shell coursescoincide

Inlet diffusers: Internal fill line piping with impingement plate, baffles, slots, orlateral openings to reduce the velocity of the flow entering a tank

Manufacturer: The fabricator and/or erector of the tank and/or floating roof

Purchase Order: The commercial instrument used to procure a tank(s), including allattachments

Purchaser: The owner or their designated agents, such as an engineering contractor

1.5 Document Submittals and Review

A. General

Technical documents listed below shall be submitted by the Manufacturerfor review by the Purchaser at specified times during a project. Additionaldocuments may be required and shall be a matter of agreement between the



Purchaser and the Manufacturer. Submittals and reviews shall be inaccordance with contractual schedule agreements. All documents shall be inreproducible form that permits microfilming without loss of clarity. Theunits of measure shall be U. S. Customary. If specified on the PurchaseOrder, alternate units of measure may be used. Minimum content of therequired technical documentation packages is described in Sections 1.5.Bthrough 1.5.E below. These include:

• Data Sheet with bid (see Section 1.5.B)

• Design review documents prior to construction (see Section 1.5.C)

• Construction documents during construction (see Section 1.5.D)

• As-built drawings and Manufacturer’s data book followingconstruction (see Section 1.5.E)

B. Quotation or Bid Document Package

1. All quotations shall be submitted in strict accordance with thisPractice. In addition, exceptions or alternates to these requirementsmay be quoted for Purchaser’s consideration provided the exceptionsor alternates are clearly marked as such and are completelydescribed in the bid.

2. The Manufacturer shall mark and return the Purchaser’s previouslyprepared Data Sheet. Each data entry space shall be marked as perPIP VEDTA003. Some entries will not be determined untilcompletion of negotiations and/or completion of the detailed design.Such entries may remain blank for this submittal.

C. Initial Review Document Packages

Unless specified otherwise, a Purchaser’s review of document packages andnegotiations are required before the order of materials (documents 1 and 2below) and start of fabrication (documents 3 through 7 below). Work maybegin following conclusion of any negotiations generated by the reviewprocess. A copy of the review packages with any annotations includingnozzle size, orientations, projections, placement and elevations of ladders,platforms, stairs, and attachments, etc., shall be returned to theManufacturer. The Manufacturer shall promptly revise/update the drawings,calculations, and information on the Data Sheet showing all review-generated changes and shall submit copies to the Purchaser. As a minimum,review documents shall consist of:

1. Manufacturer’s design calculations as described in Section 1.5.F andstructural loads for foundation design

2. General arrangement and detailed fabrication drawings with completematerial specification

3. Welding procedures, including weld hardness criteria to be used (ifapplicable). Review of duplicate weld procedures for multiple tanks isnot required when written permission is received from the Purchaser.



4. Weld assembly sequences (when requested by the Purchaser)

5. Heat treatment procedures (if required)

6. All required nondestructive examination (NDE) and planned testingprocedures

7. Description of proposed test gaskets (see Section 2.9), includingmaterial properties, dimensions, and design characteristics

D. Interim Documents During Construction

The Manufacturer shall promptly submit copies of any design changes to thePurchaser. Copies of Material Test Reports shall be forwarded to thePurchaser upon receipt of materials.

E. Post-Construction Document Package

Upon completion of construction and testing, copies of a Manufacturer’sdata book shall be supplied in the quantities specified on the PurchaseOrder. Each copy shall contain the documents listed below:

1. Final certified general arrangement and detail fabrication drawingsreflecting “as-built” dimensions and data, with complete materialsspecification and parts list

2. All design calculations

3. Certified Material Test Reports for all plate material. These certificatesshall be correlated with the actual tank plates, using formats such as cutsheets, weld maps, fabrication sequence sketches, or other meansselected by the Manufacturer.

4. Reports of the results of all tests including weld hardness (when weldhardness criteria are specified), nondestructive examinations (includingreport of radiographic examinations that includes a sketch of theposition and elevation of the radiographs), and the films

5. Results and duration of pressure test

6. Shell and bottom elevation measurements taken before, during, andafter hydrostatic test (unless waived by Purchaser as provided for inSection 5.3.6.A.5, and so indicated on the Data Sheet, Line 14)

7. Nameplate facsimile

8. Certificate of compliance with API 650, Figure 8-2

9. The Data Sheet reflecting as-built conditions

10. Allowable stresses (see API 650, Section 3.6.1.7)

11. Required thicknesses (design thickness plus any specified corrosion allowance) for all shell courses, roof, floor, annular ring, nozzle and manhole necks, custom flanges and covers for all design and pressure test conditions



12. Nominal thicknesses used for all components (see API 650, Section 3.6.1.7)

13. Handling criteria and rigging instructions for shop-built tanks

F. Manufacturer’s Calculations

All calculations shall include relevant API 650 formulas and sourceparagraphs, values used in the formulas, calculated results, and whereapplicable, comparisons with acceptable values. Where calculations arebased on other than API 650 formulas, the source of the formulas shall bereferenced. Where a computer program performs calculations, a programdescription shall be given, including name and version of the program. If theprogram is not commercially available to industry, the Manufacturer shallmaintain and provide program documentation upon request. As a minimum,these calculations shall address the following:

1. Determination of thicknesses for all pressure boundary elements tosatisfy all loading conditions, including, but not limited to, contents,pressure, partial vacuum, dead loads, live loads, snow loads, rain loads,roof flotation, dike or flood plain partial submergence, wind, andseismic activity

2. Overturning check and anchorage due to wind forces, seismic forces,and internal pressure, if applicable

3. Seismic design requirements (e.g., base shear, longitudinalcompression, sliding friction resistance checks, overturning momentchecks, and anchorage), if applicable

4. Shell stability checks to determine whether shell stiffeners or increasedshell course thicknesses will be required

5. Unless specified otherwise by the Purchaser, shell stiffness coefficients,maximum unrestrained radial deflection, angle of rotation of bottomcourse shell nozzles, and the nomographs for moments and forces thatthese nozzles can safely sustain from connected piping shall be inaccordance with provisions of API 650, Appendix P, whenever the tankdiameter exceeds 120 feet. The Purchaser shall provide the relevantpiping design loading. Alternate analysis techniques, such as the finiteelement method, may also be used to satisfy this requirement.

6. All calculations required to show compliance with API 650 and anyAppendices invoked

G. Manufacturer’s Drawing Contents

All Manufacturer’s drawings shall be thoroughly checked for accuracy andcompleteness before sending for Purchaser review. Manufacturer’sdrawing(s) shall show, as a minimum, the following information:

1. An updated list of drawings for each tank shall be resubmitted eachtime drawings are revised and reissued.

2. Identification of the storage tank as designated by the Purchaser



3. Reference to applicable practices, standards, specifications, details, andassociated drawings and sketches

4. Materials of construction, designated corrosion allowance(s), andgasket specifications

5. Extent of postweld heat treatments

6. Radiographic treatment (none, spot, or full coverage) to be applied tobottom, shell, and roof butt-welds

7. Joint efficiencies

8. Complete details and dimensions of the tank, including external andinternal attachments and appurtenances supplied by Manufacturer andsub-contractors

9. Bottom slope

10. As-specified nominal plate thicknesses for shell, roof, reinforcement, and floor

11. Location of all welded seams. All welds shall be either pictorially detailed or identified by use of the standard welding symbols of ANSI/AWS A2.4. Welding procedures shall be listed.

12. For flanges other than those conforming to ASME B16.5 or ASME B16.47, and marked accordingly, show all dimensions andfinish of flange face.

13. Facsimile of nameplate with data to be stamped thereon with location and details of fabrication of nameplate bracket

14. Tank pressure test outline (e.g., test water level, fill rate, imposed pneumatic pressure, hold times, drain rate, etc.)

15. Empty, operating, and test weight of tank, in pounds

16. Loads on foundation as also shown on the Data Sheet, Line 13

17. Foundation plans and construction details (if supplied by Manufacturer or sub-contractor)

18. Manufacturer’s drawings shall include the following notes if applicable:

a. Stainless steel tanks that will be exposed to any heat source,including welding and impingement fire, that could melt zincshall have the following note: “Zinc-coated (galvanized orpainted) components shall not be in contact with welded,bolted, or loose stainless steel parts of the tank.”

b. All tanks shall have the following note: “Substances thatcontain chlorine or that will decompose to hydrogen chloride(e.g., coatings to prevent adhesion of weld spatter) shall not beapplied to any part of the tank.”



2. Materials

2.1 General

A. Refer to the Data Sheet for material specifications.

B. Higher strength materials than those listed in API 650 that meet all otherrequirements of API 650 may be used if specifically approved by thePurchaser.

C. Rimmed or capped steels are not permitted.

D. Use of cast iron for any pressure part or any part attached to the tank bywelding is prohibited.

E. Cadmium-plated components shall not be used without the express consentof the Purchaser.

2.2 Plates

ASTM A283C shall not be used for shell, shell reinforcement, or tank bottom annularplates in thicknesses over 1/2 inch.

2.7 Bolting

A. Unless otherwise specified on the Data Sheet, Table 2, flange bolting shallconform to ASTM A193 B7 and the dimensions specified in ASME B18.2.1.Nuts shall conform to ASTM A194 Grade 2H and the dimensions specifiedin ASME B18.2.2. Both shall be heavy hex pattern. All bolts and nuts shallbe threaded in accordance with ASME B1.1, as follows:

1. Bolts up to and including 1 inch diameter: UNC Class 2A fit2. Nuts for bolts up to and including 1 inch diameter: UNC Class 2B fit3. Bolts 1.125 inch diameter and larger: 8N Class 2A fit4. Nuts for bolts 1.125 inch diameter and larger: 8N Class 2B fit

2.9 Gaskets

General

A. Unless otherwise specified by the Purchaser, gasket materials shall benon-asbestos.

B. Sheet gaskets shall be continuous. Metal gaskets made continuous bywelding are acceptable if the weld is ground-flush and finished the same asthe unwelded portion of the gasket. Rope or tape gaskets may haveoverlapped ends.

C. Each gasket shall have a means for positioning or centering the gasket duringjoint make-up.

D. No joint sealing compound, gasket adhesive, adhesive positioning tape, orlubricant shall be used on the sealing surfaces of gaskets unless specified bythe Purchaser.



Service

When service gaskets are designated to be furnished by the Manufacturer, thegaskets provided shall be as specified in the Data Sheet, Table 3.

Test

A. Test gaskets must have comparable dimensions and compressibilitycharacteristics as service gaskets. Descriptions of gaskets for temporary useonly as test gaskets shall be submitted for Purchaser’s approval.

B. For joints that will not be disassembled after testing, the test gasket must bethe specified service gasket. Spares are not required unless specified on DataSheet, Line 23.

3. Design

3.1 Joints

3.1.2 Weld Size

The following weld size instructions apply to all welding processes, whethermanual, semi-automatic, or automatic:

• Fillet welds or groove welds with legs or throat dimensions notexceeding 3/16 inch may be made in a single pass at theManufacturer’s option.

• Fillet welds or groove welds with legs or throat dimensions greaterthan 3/16 inch and not exceeding 5/16 inch shall be multi-pass if sospecified on the Data Sheet, Line 15.

• Fillet welds or groove welds with legs or throat dimensions greaterthan 5/16 inch shall be multi-pass.

3.1.3 Restrictions on Joints

Intermittent welds shall not be used on tank exteriors unless specificallyapproved by the Purchaser.

3.1.5 Typical Joints

A. Spliced top angles and compression rings shall be butt-welded.

B. Shell courses on open top tanks and tanks with external or internalfloating roofs shall be flush-stacked on the inside. Shell courses onother tank types may be centerline-stacked or flush-stacked on theinside at the Manufacturer’s option.

C. Lap-welded bottom plates (see API 650, Figure 3-3B) shall be seal-welded on the outer periphery of their lapped edges.

D. Unless otherwise specified by the Purchaser, lap jointed floor plateson sloped bottoms shall be overlapped in a manner to reduce thetendency for liquid to puddle during draw down.



E. The top surfaces of floor welds (butt-welded annular plates, butt-welded sketch plates, or API 650 Figure 3-3B joints) shall beground-flush where they will contact the bottoms of the shell,extended insert plates, or reinforcement plates.

F. Joints for external attachments that are not otherwise welded (e.g.,wind girders, wind girder gussets, stairs, platforms, clip angles, etc.)shall be completely seal-welded at every juncture.

G. Permanent weld joint backing strips are permitted only with theapproval of the Purchaser.

3.2 Design Considerations

A. Unless otherwise specified, design for earthquakes shall be in accordancewith API 650, Appendix E.

B. Design for top and intermediate wind girders shall be in accordance withAPI 650.

C. Design for localized wind induced forces on roof components shall be amatter of agreement between the Purchaser and the Manufacturer.

D. The roof design load shall be the sum of the dead load plus the partialvacuum plus the greater of 25 PSF, the specified live load, or the snow loadof ASCE 7 (when no coincident live load is expected during a snow event).See Section 3.10.2.B for an exception.

E. Design for vacuum exceeding 1 inch of water column shall be a matter ofagreement between the Purchaser and the Manufacturer.

F. Design to resist flotation and attendant external fluid pressure shall be amatter of agreement between the Purchaser and the Manufacturer.

G. Localized loads resulting from items such as ladders, stairs, platforms, etc.,shall be considered.

H. For insulated tanks, means to prevent infiltration of water into the insulationshall be provided, especially around penetrations of the insulation and at theroof-to-shell junction.

3.3 Special Considerations

3.3.1 Foundations and Anchors

A. Foundation loading data shall be provided by the Manufacturer onthe Data Sheet, Line 13.

B. Adequate anchors and hold-downs to resist overturning momentsand/or uplift due to internal pressure shall be provided as required.Unless otherwise specified on the Data Sheet, Table 2, all anchorsshall be threaded, galvanized ASTM A36 round bar with galvanizedheavy hex nuts, doubled, or topped with appropriate jam nuts. Whenanchorage is required, the minimum number of anchors shall be four(4). Unless otherwise specified by API 650, Appendix F.7.4.b, theminimum anchor diameter shall be 1 inch.



C. Adequate sliding friction resistance shall be verified for unanchoredtanks subject to lateral wind and seismic loads.

3.3.2 Corrosion Allowance

Refer to the Data Sheet, Tables 1, 2, and 5, for the corrosion allowances.Corrosion allowances for shell, floor, supported roof, and structuralmembers shall be applied according to API 650. Corrosion allowances fornozzles, manholes, and self-supporting roofs shall be added to the designthickness. The resulting thickness shall in no case be less than the minimumnominal thickness required by API 650. Corrosion allowance on anchor boltsshall be applied to the nominal diameter. Corrosion allowance for anchorstraps shall be added to the required strap thickness. For internal structurals,the corrosion allowance shall be applied to each exposed surface unlessotherwise specified.

3.3.3 Service Conditions

Service conditions may require special metallurgical considerations in theselection of materials and the fabrication processes. These selections shall bea matter of agreement between the Purchaser and the Manufacturer basedupon the expected process conditions listed on the Data Sheet, Line 5.

3.3.4 Weld Hardness

Weld metal and Heat Affected Zone (HAZ) hardnesses shall comply with theH2S Supplemental Specification on the Data Sheet, Line 5, when specifiedby the Purchaser.

3.3.5 Grounding

The tank shall be grounded as per NFPA 780 and Section 3.8.11.C.

3.4 Bottom Plates

A. Unless otherwise specified on the Data Sheet, Line 12, tank bottomsrequiring sloping shall have a minimum slope of 1 inch per 10 feet.

B. If specified on the Data Sheet, Line 12, a foundation drip ring shall beprovided to prevent ingress of rainwater or condensation between the tankbottom and foundation. Unless the Purchaser specifies otherwise, the ringshall meet the following requirements:

1. Material shall be carbon steel, 1/8-inch minimum thickness.

2. All radial joints between sections of the drip rings, as well as betweenthe drip ring and the annular plate or bottom, shall be continuouslyseal-welded.

3. The drip ring shall extend at least 3 inches beyond the outer peripheryof the foundation.

4. The drip ring shall turn down at a 45 degree angle at its outer diameter.

5. The top of the drip ring and a 3-inch height of the tank shell shall bepainted with a 10-12 mil thick epoxy coating.



3.6 Shell Design

A. Shell plate thicknesses shall be in accordance with the design requirementsof API 650, except that the minimum nominal bottom shell course thicknessfor carbon steel shall be based upon nominal tank dimension tabulated in thetable below:

Nominal Tank Diameter D(feet)

Min. Nominal Carbon Steel Shell Thickness(inches)

D < 10.5 3/16

10.5 < D < 50 1/4

50 < D Per API 650, Section 3.6.1.1

B. Tank shell thickness shall be calculated by the “one-foot” method exceptwhere prohibited by API 650 or specifically declined on the Data Sheet,Line 10. Manufacturers may additionally propose an alternate shell thicknesscalculated by the “variable design point” method or “elastic analysis”method if a more economical design results.

C. Unless otherwise specified, the design liquid level for calculating shellthicknesses for non-floating roof tanks shall be to the top of the shell,irrespective of operating liquid levels.

D. Unless otherwise specified on the Data Sheet, Line 11, for fixed roof tanksequipped with full shell height insulation or jacketing and for internalfloating roof tanks, the horizontal leg of the top shell stiffener shall projectoutward. For other closed top tanks, the horizontal legs of the shell stiffenershall project inward when permitted by API 650.

E. For open top tanks and external floating roof tanks, all horizontal elementsof the top shell stiffener shall project outward.

3.7 Shell Openings

A. Reinforcing plates for manholes, nozzles, and other attachments shall be ofthe same nominal composition as the tank part to which they are attached.

B. If at all possible, nozzles and manholes shall not be placed in shell weldseams and reinforcement pads for nozzles and manholes shall not overlapplate seams (i.e., API 650, Figure 3-6, Details a, c, and e shall be avoided).These details may be used if there is no other feasible option and thePurchaser accepts the design.

C. If “Full Penetration on Openings” is marked “YES” on the Data Sheet,Table 3, full fusion and full penetration welds shall be used for attaching:

1. Nozzle necks, manhole necks, and flush-type shell nozzles, andcleanout fitting necks to the shell, to insert plates, to reinforcing pads,and to fabricated bolting flanges

2. Smaller nozzle necks through blind flanges or nozzle/manhole coverplates



D. Manhole or shell nozzle covers weighing 75 pounds or less shall have twohandles. Those weighing more than 75 pounds shall be equipped with eithera hinge or davit to facilitate the handling of the manhole cover plate (asshown in PIP VEFV1116 and PIP VEFV1117). The davit support arm shallbe welded to a structural member. If the structural member is of the sameweld group as the shell, it may be welded directly to the shell. Whenever thestructural member is not of the same weld group as the shell plate, anattachment plate of the same weld group as the shell shall be welded to theshell, and the structural member in turn welded to the attachment plate.

E. Unless otherwise specified, shell nozzle flanges in sizes NPS 1-1/2 throughNPS 20 and NPS 24 shall meet the requirements of ASME B16.5. For sizeslarger than NPS 24 but not greater than NPS 60, flanges shall meet therequirements of ASME B16.47, Series A or Series B. Series A and Series Bflanges are not compatible in all sizes and must be carefully selected tomatch the mating flange. If diameters, materials of construction, and flangestyles of ASME B16.47 are unavailable, fabricated flanges with drillingtemplate (bolt circle diameter, number of holes, and hole diameter) matchingSeries A or Series B shall be used. These fabricated flanges shall bedesigned in accordance with the ASME Boiler and Pressure Vessel Code,Section VIII, Division 1, Section UG-34 and Appendix 2. The allowablestresses for design shall be a matter of agreement between the Purchaser andthe Manufacturer.

F. Bolt holes shall straddle the vertical centerline of the flange.

G. The alternate thermal stress relief of API 650, Section 3.7.4.5, shall not beused.

3.8 Shell Attachments and Tank Appurtenances

3.8.5 Roof Nozzles

Normal venting nozzles shall be sized (or have their size verified) by theManufacturer in accordance with API 2000. The filling and emptying ratesare specified on the Data Sheet, Line 7. Bird screens shall protect all freevents. Venting devices shall be tabulated on the Data Sheet, Table 4.

3.8.10 Platforms, Walkways, and Stairways

A. As a minimum, platforms, walkways, ladders, and stairways shall bein accordance with API 650, Section 3.8.10, Tables 3-17, 3-18, and3-19, and OSHA 29 CFR 1910, Subpart D, or other applicablenational labor safety standard, except as noted in this Practice. Forexamples of acceptable details, see PIP STF05501, PIP STF05520,and PIP STF05521. For stainless steel tanks subject to externalimpingement fire, the use of galvanizing is not recommended (seeSection 1.5.G.18.a).

B. When provided, stairways shall have a minimum width of 28 inchesand shall extend from the bottom of the tank up to a roof edgelanding or gauger’s platform.



C. Unless declined on Data Sheet, Line 24, a roof edge landing orgauger’s platform shall be provided at the top of all tanks.

3.8.11 Other Appurtenances

A. Floating Suction Lines

Floating suction lines shall be provided when specified on the DataSheet, Table 4. Floating suction lines using rigid pipe shall bedesigned to prevent over-rotation beyond the vertical axis. Floatingsuction lines using articulated pipe shall be designed so that the tipof the suction line is always on the axial centerline of the tankthroughout its entire travel.

B. Inlet Diffusers

Inlet diffusers shall be provided for floating roof tank and for otherconfigurations if requested in the Other Tank Appurtenances sectionof the Data Sheet, Table 4.

C. Grounding Lugs

Grounding lugs in accordance with PIP VESTA108 shall be providedin the quantity specified on the Data Sheet, Table 4. Lugs shall beequally spaced around the base of the tank. Tanks in hydrocarbonservice shall be provided with a minimum of four lugs.

D. Miscellaneous Pads

All miscellaneous pads shall have rounded corners with a minimumradius of 2 inches. Pads that must cover shell seams shall beprovided with a 1/4-inch telltale hole (see Section 3.7.B).

3.9 Top and Intermediate Wind Girders

A. The structural stability check of wind girder stiffened shells in accordancewith API 650, Sections 3.9.6 and 3.9.7, shall be based upon nominaldimensions of the shell course and the wind girders irrespective of specifiedcorrosions allowance whenever the “No” option is selected for “CheckBuckling in Corroded Cond.?” on the Data Sheet, Line 9. Whenever the“Yes” option is selected, the check must be based upon the nominaldimensions minus the specified corrosion allowance.

B. A wind girder that also serves as a walkway shall be located 3 feet 6 inchesbelow the top of the shell of open top and external floating roof tanks.

C. Wind girders shall not retain standing water. Uninsulated tanks shall havegirders with small water shedding slopes and/or drain holes unless thePurchaser approves an alternate means of drainage. If drain holes areprovided, they shall be 1-1/2 inch diameter on 8-foot centers, as a minimum.Insulated tanks where the girders function as insulation closures shall haveno drain holes. Wind girders shall be checked for proper drainage duringtank test of Section 5.3.6.A.7 to demonstrate that water does not stand on thegirders. If water is retained, additional drainage shall be provided subject tothe Purchaser’s approval.



3.10 Roofs

3.10.2 General

A. The Manufacturer may supply any of the fixed roof configurationslisted in API 650, unless otherwise specified on the Data Sheet,Line 11.

B. Partial vacuums of 1-inch water pressure or less need not beconsidered as adding to the roof load for design purposes. Whenvacuums in excess of 1-inch water pressure are specified, the fullspecified partial vacuum must be added to any other roof operatingloads for design purposes. (See Section 3.2.D.)

C. For frangible roof tanks, where a corrosion allowance is specified,the design must have frangible characteristics in both the as-built(uncorroded) condition and the future (corroded) condition.

3.10.4 Supported Cone Roofs

A. Roof columns may be made from either pipe or structural shapes asselected on the Data Sheet, Line 11. Pipe type roof columns arepreferred for internal floating roof tanks. Pipe columns shall beprovided with openings or removable plugs at both the top and thebottom to allow for draining and cleaning of the columns even whennormally sealed during operation.

B. Column base plates and cap plates shall be continuously welded tothe column ends. However, welding of the baseplate to bearing plateis not allowed. Bearing plates shall be provided under all fixed roofsupport columns. The bearing plates shall be circular with a diameteras shown in the table below:

Bearing Plate Diameter shall be the largest of:

14 inches

or 2 x diameter of pipe column

or 2 x largest diagonal dimension ofstructural shape column

Bearing plates shall be no less than 1/2-inch thick and shall beattached to the bottom by continuous full-fillet welds.

4. Fabrication

4.1 General

A. Miscellaneous Substances to be Avoided

Materials that may cause corrosive attack when the tank part is heated shallnot be used, including the following:

• Marking inks (containing halogens)



• Lubricants

• Crayons

• Adhesives, except as required in Appendix C

• Tapes (e.g., duct tape)

• Coatings to prevent adhesion of weld spatter

• Paints containing sulfur

• Chlorine and other halogen compounds (e.g., chlorine compounds thatmight decompose to hydrogen chloride)

• Materials causing carbon pick-up

• Harmful metal or metal salts such as zinc, lead, mercury, cadmium, orcopper

C. Component Shipping Requirements

All flange faces and other machined surfaces shall be protected againstcorrosion and from physical damage during shipment and before placementon the tank.

4.2 Shop Inspection

The Manufacturer shall visually inspect all plate edges before installing the plates inthe tank to determine if laminations are present. If laminations are detected, theManufacturer shall ultrasonically test such plates to determine the extent of thelamination. The Manufacturer shall reject the plate or submit a repair procedure tothe Purchaser.

5. Erection

5.1 General

A. The Purchaser may reject the use of any materials, equipment, or tools thatdo not conform to the specification requirements, jeopardize the safety ofpersonnel, or impose a hazard at the site.

B. All temporary internal clips, lugs, brackets, etc., shall be removed fromcolumns and internal surfaces of shell and bottom, and shall be groundsmooth. This work must be completed before the application of internalcoatings, the air raising of a fixed roof, the initial floating of a floating roof,and other any other circumstance whereby temporary projections maydamage the tank.

C. The tank bottom shall be protected from standing water during erection as amatter of agreement between the Manufacturer and the Purchaser.



5.2 Details of Welding

All welds shall be free from coarse ripples, excessive undercuts, grooves, overlaps,abrupt ridges, and valleys to avoid stress concentration points and interference withinterpretation of NDE results.

5.3 Inspection, Testing, and Repairs

5.3.2 Inspection of Welds

All vertical welds in shells fabricated of quenched and tempered materialshall be fully radiographed.

5.3.4 Inspection of Tank Bottom Welds

Water shall not be pumped under the tank as a leak detection method.Inspection of the tank bottom welds by any method other than vacuum boxtesting requires Purchaser’s approval of the procedure and the acceptancecriteria. Before any coating is applied to the bottom, all weld joints must bevacuum box tested.

5.3.6 Testing of the Shell

A. Tank shells shall be hydrostatically tested per API 650. TheManufacturer shall be responsible for:

1. Preparing the tank for testing. This shall include removal ofall trash, debris, grease, oil, weld scale, weld spatter, andany other foreign matter from the interior and the roof(s) ofthe tank.

2. Furnishing, laying, and removing all lines from the watersource and to the water disposal point as prescribed on theData Sheet, Line 14 (see Section 1.2.C)

3. Filling and emptying the tank

4. Cleaning, rinsing, drying, or other prescribed activityindicated on Data Sheet, Line 14, following the hydrotest tomake the tank ready for operation

5. Taking settlement measurements (unless explicitly waivedby the Purchaser on the Data Sheet, Line 14)

6. Furnishing all other test materials and facilities, includingblinds, bolting, and gaskets (see Section 2.9)

7. Checking the wind girders for proper drainage during orfollowing the hydrotest (see Section 3.9.C)

B. For carbon and low-alloy steel tanks, the tank metal temperatureduring hydrostatic testing shall not be colder than the minimumdesign metal temperature plus 30°F, unless specified otherwise onthe Data Sheet, Line 14.

C. See the Data Sheet, Line 14, for test water treatmentresponsibilities. Clean water of drinking quality is the preferred



water for hydrotesting. This does not preclude the use of condensate,reverse osmosis water, well water, or sea water. In any case, waterthat does not contain mud and/or other material that will settle out isrequired. Some issues to be considered include:

• Low temperature brittle fracture

• Freeze damage

• Scalding of observers

• Amount of suspended solids

• Sanitation issues

• Animal/Plant incubation and/or growth

• Acidity

• General corrosion

• Pitting

• Protecting against cathodic cells

• Microbiologically induced corrosion

• Material dependent sensitivity to trace chemical attack

• Disposal

• Rinsing

• Residuals left in vessel after emptying

In addition, consider the following specific conditions:

1. Carbon Steel - For carbon steel equipment where watercontact exceeds 14 days, including filling and draining (e.g.,adding oxygen scavenger and a biocide, and raise the pH ofthe water to 12.5, minimum, by addition of caustic)

2. Stainless Steel - See API 650, Appendix S.

3. Seawater - Adjust fill height for specific gravity.



D. Foundation settlement tolerances are provided in API 650,Sections 5.5.5 and 5.5.6, but may be waived on the Data Sheet,Line 15. Further guidance may be found in API Standard 653,Section 10.5 and Appendix B. When settlement measurements arerequired (see Section 5.3.6.A.5), the maximum filling rates shall be:

Water Filling Rate

Bottom Course Thickness Tank Portion Filling Rate

Less than 7/8 inch - Top course- Below top course

12 inch/hr18 inch/hr

7/8 inch and thicker - Top third of tank- Middle third of tank- Bottom third of tank

9 inch/hr12 inch/hr18 inch/hr

Filling may continue while elevation measurements are being madefor tanks with diameters exceeding 50 feet. For tanks with diametersof 50 feet or less, filling shall be stopped while measurements arebeing taken. Unless waived as stated in Section 5.3.6.A.5, theManufacturer shall make shell elevation measurements inaccordance with the following:

1. Shell elevation measurements shall be made at equallyspaced intervals around the tank circumference notexceeding 32 feet. The minimum number of shellmeasurement points shall be eight.

2. Observed elevations shall be referred to a permanentbenchmark. The level instrument shall be set up at least1-1/2 times tank diameter away from the tank when tankelevation readings are taken. Six sets of settlement readingsare required:

a. Before start of the hydrostatic test

b. With tank filled to 1/4 test height (+/- 2 feet)

c. With tank filled to 1/2 test height (+/- 2 feet)

d. With tank filled to 3/4 test height (+/- 2 feet)

e. At least 24 hours after the tank has been filled tothe maximum test height. This 24-hour period maybe increased to as much as 3 days if the Purchaserso requires for conditions such as:

i. The tank is the first one in the area.

ii. The tank has a larger capacity than anyother existing tank in the area.



iii. The tank has a higher unit bearing loadthan any other existing tank in the area.

iv. There is a question regarding the amountof rate of settlement that will take place.

Note: If the Purchaser exercises the option ofkeeping a high water level in the tank and if themaximum test height is higher than the maximumproduct fill height, the draining of the test watermay commence after the initial 24 hours atmaximum test height when authorized by the fieldinspector (see Data Sheet, Line 15), but the testwater height may not be lowered below themaximum product fill height until the Purchaseragrees to draining the tank.

f. After tank has been emptied of test water

E. Any differential settlement greater than 1/2 inch per 32 feet ofcircumference or a uniform settlement over 2 inches shall bereported to the Purchaser for evaluation. Filling of the tank shall bestopped until cleared by the Purchaser.

F. For floating-roof tanks, the maximum and minimum annular spacebetween the shell and the roof rim plate at the maximum test fillheight shall be measured and recorded.

G. Internal bottom elevation measurements shall be made afterhydrostatic testing. Measurements shall be made at maximumintervals of 10 feet measured on diametrical lines across the tank.The diametrical lines shall be spaced at equal angles, with amaximum separation measured at the tank circumference of 32 feet.A minimum of four-diametrical lines shall be used.

H. All elevation measurements shall be included in the Manufacturer’sdata book.

5.5 Dimensional Tolerances

5.5.1 General

Unless waived by the Purchaser on Data Sheet, Line 15, the tolerances ofAPI 650, Section 5.5, shall be invoked.

5.5.2 Plumbness

The maximum out-of-plumbness of roof columns, guide poles, or othervertical internal components shall not exceed 1/200 of the total height.

5.5.7 Nozzles

Nozzles (excluding manholes) shall be installed within the followingtolerances:



A. Specified projection from outside of tank shell to extreme face offlange +/- 3/16 inch

B. Elevation or radial location +/- 1/4 inch

C. Flange tilt in any plane, measured on a diameter across the gasketsurface +/- 1/2 degree but not to exceed 3/16 inch

D. Flange bolt hole orientation +/- 1/16 inch

5.5.8 Manholes

Manholes shall be installed within the following tolerances:

A. Specified projection from outside of shell to extreme face of flange+/- 1/2 inch

B. Elevation or radial location +/- 1/2 inch

C. Flange tilt in any plane, measured across the flange diameter+/- 1/2 inch

6. Methods of Inspecting Joints

6.1.2 Number and Location of Radiographs

Radiography shall be in accordance with API 650 and the following:

A. Film for radiographs taken at junctions of vertical and horizontal weldjoints shall be positioned with the greater length oriented along thevertical seam.

B. The number of spot radiographs referred to in API 650 shall beapplicable on a per tank basis, irrespective of the number of tanks beingerected concurrently or continuously at any location.

C. Tungsten inclusions in gas tungsten arc welds shall be evaluated asindividual rounded indications. Clustered or aligned tungsten inclusionsshall be removed and repaired.



Appendices

These requirements apply whenever the Data Sheet, Lines 6 and/or 8, has API 650Appendices selected. The following requirements supplement the requirements in some ofthe API 650 Appendices. These requirements are in addition to those in API 650, and may bemore restrictive. References may be made to PIP VEFTA100 that may not yet be published;in such cases, the Purchaser and the Manufacturer must develop mutually acceptable details.



APPENDIX C

External Floating Roofs

C.1, C.2 Scope and Materials

Pan Type Roofs

Pan type floating roofs shall not be used.

Other Roof Types

The type of roof and seal to be provided shall be as specified on the Data Sheet,Line 30. If the type is not specified, the Manufacturer shall provide the mosteconomical and suitable type for the intended service.

Bids

A. Bids for tanks having external floating roofs shall contain sufficientengineering data, including material specifications for both metallic and non-metallic components, nominal thicknesses, and sufficient information as perSections C.3.4.1 and C.3.4.2 to permit an independent evaluation of thematerial compatibility and adequacy of the proposed roof design to remainafloat and undistorted.

B. Manufacturer shall list in the quotation all roof accessories furnished andincluded in the base price of the roof. If any accessories are purchased fromother suppliers, the Manufacturer shall provide that supplier’s name and themodel or part number.

C. Manufacturer shall specify size, number, and type of primary drains with thequotation.

D. Manufacturer shall state the lowest operating level of roof in the quotation.

E. Manufacturer shall clearly describe the extent of electrical grounding andshunts included as a part of the floating roof design.

F. Manufacturer shall include a cross section of all seals showing materials andcomplete details of construction with the bid.

G. The bid shall state if a wind skirt, a top-shell extension, or overflows will berequired for proper functioning of the roof seal.

H. The Manufacturer shall submit with the bid the minimum and the maximumallowable annular space between the roof and shell, as well as the maximumand minimum annular space the proposed roof seal system canaccommodate.



C.3 Design

C.3.1 General

A. The application of corrosion allowances shall be a matter of agreementbetween the Purchaser and the Manufacturer. Corrosion allowance shall beadded to the minimum nominal thickness required by API 650 or, when nominimum nominal thickness is required, added to the minimum calculatedthickness required for functionality.

B. Sleeves and fittings, other than nozzles, that penetrate the single deck orlower decks of annular pontoons or lower decks of double deck roofs shallhave a minimum wall thickness of 1/4 inch unless otherwise specified on theData Sheet, Table 5. Such penetrations shall extend at least 6 inches into theliquid.

C. The annular space between the roof outer rim and the product side shell shallbe designed for proper clearance of the designated roof seal. Allappurtenances and internals shall have adequate clearance for the properoperation of the completed roof assembly.

D. Single deck pontoon floating roofs greater than 200 feet in diameter shall bedesigned to avoid flexural fatigue failure caused by design wind. Suchdesigns shall be a matter of agreement between the Purchaser and theManufacturer.

C.3.3 Decks

A. The deck of single-deck pontoon floating roofs shall be designed to be incontact with the liquid during normal operation, regardless of service. Thedesign shall accommodate some deflection of the deck that may lead topockets of trapped vapor on hot days.

B. Rim and bulkhead plates shall have a minimum nominal thickness of3/16 inch.

C. Lap joints that are not adjacent to girders, support legs, or relatively stiffmembers on the underside of an uncoated roof shall have full-filletintermittent welds of 2-inch lengths on 16-inch centers. If the underside ofthe roof is to be coated, all underside lap joints shall be welded withcontinuous full-fillet welds. The underside surface of deck plates exposed toproduct or vapors shall be seal-welded to each roof leg sleeve for removablelegs and to each fixed leg with a 3/16-inch minimum leg fillet weld.

D. Top decks of double-deck roofs and top decks of the pontoon portions ofsingle-deck roofs shall be designed, fabricated, and erected with a slope tominimize accumulation of standing water (e.g., pooling adjacent to a rollingladder’s track) when primary roof drains are open. (See API 650,Section C.3.3.4.) This requirement is not intended to completely eliminateisolated puddles. When out of service, water shall flow freely to the primaryroof drains.



E. All removable roof openings except roof drains shall have gaskets or othersealing surfaces and shall be provided with at least a liquid-tight cover.

C.3.4 Pontoon Design

C.3.4.1 The rainfall rate identified in API 650, Section C.3.4.1.a (i.e., 10 inches in a24-hour period), shall be used as a minimum requirement for flotationevaluation when primary drains are inoperative. The rainfall rate for sizingthe roof drains in Section C.3.8 of this Practice may result in a largeraccumulated rainfall. The Manufacturer shall provide the Purchaser withcalculations confirming the buoyancy requirements of API 650, SectionC.3.4.1.a, for both single-deck and double-deck roofs using the smaller ofthe specific gravity in API 650,Section C.3.4.1 (0.7), or the minimum specific gravity of the productspecified on the Data Sheet, Line 5.

C.3.4.2 The Manufacturer shall provide evidence to the Purchaser that single-deckroofs shall have no permanent distortion and shall show no elastic orinelastic instability when subjected to the requirements of API 650, SectionC.3.4.2, either by calculation or a proof test outlined in API 650, SectionC.3.4.2.

C.3.5 Pontoon Openings

Access manholes to pontoon interiors shall have a minimum nominal diameter of20 inches.

C.3.6 Compartments

All internal bulkhead plates or sheets shall be single-fillet welded along their top,bottom, and side edges, as a minimum, thus providing a liquid- and vapor-tightcompartment.

C.3.7 Ladders

Each external floating roof shall have a rolling ladder that meets the followingrequirements:

A. Step assemblies shall be of open type and have non-slip walking surfaces.

B. Self-leveling treads shall have a minimum width of 28 inches and a 34-inchhigh handrail at the nose of the tread. When the roof is in its extreme lowposition, the slope of the rolling ladder shall not be less than 35 degrees tovertical.

C. Wheels shall be provided at the lower end of the ladder, sized to preventbinding of the ladder, and provided with maintenance-free bearings.

D. Ladders shall be grounded to both the roof and the gauger’s platform with atleast an AWG (American Wire Gage) 2/0 (0.104 square inches), non-tanglingcable. Cable shall be configured so that it will not freeze to adjacent surfacesin cold weather.



E. Ladder and track design shall minimize ponding by using trussed runways orother details.

C.3.8 Roof Drains

A. Primary Roof Drains

1. Primary roof drains shall be sized and positioned to accommodate therainfall rates specified on the Data Sheet, Line 40, without allowingthe roof to tilt excessively or interfere with its operation. Roof drainsshall be furnished attached to double-flanged, low-type nozzles on thetank shell with valves to be supplied by the Purchaser. A swing typecheck valve shall be provided at the inlet of drains unless otherwisespecified on the Data Sheet, Line 31.

2. Primary roof drains shall be a flexible stainless steel pipe coated with aflexible resin resistant to the tank’s contents and shall be able toprevent the flexible pipe from floating, kinking, or catching on anyinternal appurtenance or obstruction during operation, and from beingcrushed by landing legs on the floor.

3. As an alternative to Item 2 above, steel swivel (swing or pivot-jointed)pipe drains, designed and packed for external pressure and fabricated ofmaterials resistant to the tank contents, may be furnished if selected bythe Purchaser on the Data Sheet, Line 31. Rigid segments of drainpiping attached to the floor or the roof shall be guided, not rigidlyattached, to allow for differential thermal expansion and plate flexing.

4. Siphon type and conventional hose type drains are not acceptable asprimary roof drains.

5. Double-deck floating roofs up to 200 feet in diameter shall have eithera single center sump or a reversed-slope, top-center deck with threesumps connected to a single drain line, depending on the design rainfallquantity and the roof configuration. Double-deck floating roofs largerthan 200 feet in diameter shall have a reversed-slope, top-center deckwith three roof sumps having individual drain lines.

6. Inlets to single-deck primary roof drains shall have guarded trash stopsor screens to stop debris from entering and obstructing the drainsystem. The Manufacturer shall provide isolation valves to stop productflow onto the roof when the check valve fails, if specified the DataSheet, Line 31. Cut-off valves for this purpose shall have extensionhandles to permit actuation when puddles obstruct access to the valve.

7. Drains, sumps, check valves, and cut-off valves shall be protected fromfreeze damage when specified on the Data Sheet, Line 31. Anymechanically actuated cut-off valve shall permit actuation when thedrain pipe is partially obstructed by chunk ice or slush (e.g., a ramvalve or a metal-seated ball valve).



B. Emergency Roof Drains

Double-deck roofs shall have a minimum of three open-ended emergencyroof drains designed to provide drainage to prevent sinking the roof duringsevere rainfall events. Emergency drains are prohibited on single deckfloating roofs. Elevation of the emergency overflow drains shall be such thatthe outer pontoon rim cannot be completely submerged. These drains shalldischarge at least 1 foot below the bottom of the roof and shall consist ofopen-ended pipes, braced as necessary to the roof structure. The drains shallbe sized to handle the rainfall specified by the Purchaser, with a minimumdiameter of 4 inches. The drains shall be sealed with a vapor seal device(e.g., a slit or sliced fabric membrane) that will reduce the product-exposedsurfaces while permitting rainwater passage. The drains shall be fabricatedfrom Schedule 80 pipe, or heavier, and fittings with 1/4-inch thick roof deckreinforcing plates.

C. Out-of-Service Supplementary Drains

Threaded pipe couplings and plugs with a 24-inch extension “T” bar handleshall be provided as supplementary drains when the roof is resting on its legsand when the primary drains are inoperative. Fittings shall be at least NPS 4.Plugs shall be brass or have threads coated with a non-stick coating or anti-seize paste such as tetrafluoroethylene. One supplementary drain shall belocated adjacent to the ladder track.

C.3.9 Vents

A. Automatic bleeder vents (vacuum breakers) shall be furnished for venting airto or from the underside of the deck bottom when filling or emptying thetank. The Manufacturer shall determine and recommend the number andsizes of bleeder vents to be provided based on maximum filling andemptying rates specified. Automatic bleeder vents shall have gaskets andshall be designed to be closed at all times when the roof is floating, exceptwhen the roof is being floated off or is being landed on the roof support legs.

B. When flexible metallic primary seals are employed, rim space vents shall befurnished unless specifically declined on the Data Sheet, Line 13. The ventsshall be capable of releasing any excess air or non-condensable vapors thatmay enter the tank through the filling line.

C. Unless specified otherwise by the Purchaser, the following minimum numberand sizes of rim vents shall be provided when using mechanical shoe seals:

Nominal Tank Diameter D(ft)

Minimum Number Size (NPS)

D < 140 1 4

140 < D < 275 2 6

275 < D 3 6



C.3.10 Supporting Legs

A. Floating roofs shall have removable support legs inserted through eitherfixed low legs or leg sleeves. The materials of construction shall be tabulatedon the Data Sheet, Table 5.

Removable legs shall have settings for at least two levels:

• a minimum setting specified by the Manufacturer to support the roofin the lowest position possible while clearing mixers, nozzles, shellmanholes, seals, and other appurtenances inside the tank by at least3 inches, and

• a maximum setting of 78 inches at the tank shell

When specified on the Data Sheet, Line 39, the two settings shall be fieldadaptable to allow for uneven tank bottom settlement (i.e., constructed topermit small variations from the required positions for each leg). Theremovable legs shall be provided with storage rack(s) on the top of thepontoon or deck appropriate for leg storage during normal operation orduring maintenance. Rack quantity and location shall be determined by theManufacturer to balance the roof live load and shall take into account theweight of the rolling ladder. Adjustable legs shall be capped on top.Removable covers shall be provided for leg sleeves or fixed low legs whenthe adjustable legs are removed.

B. Legs and sleeves shall be Schedule 40 or greater if specified on the DataSheet, Table 5. Removable legs shall be no smaller than NPS 2. Both lowand high legs shall have 1/2-inch by 1/2-inch square notches at the bottom topermit drainage of trapped product. High legs shall have a stop to preventtheir dropping through the low legs during installation. All removablesupport legs shall be identical. The top of the fixed legs shall extend no morethan 3 feet above the roof deck.

C. Roof legs shall have matching steel landing pads continuous full-filletwelded to the tank bottom with minimum dimensions of 3/8-inch thicknessby 14-inch diameter. The centerline of the legs shall coincide with thecenterline of the landing pads.

D. Roof support legs shall be plumb. Fixed legs or leg sleeves through singlemembrane sections of roof shall be reinforced with gussets.

E. All fixed leg or leg sleeve penetrations through the deck plate (top andbottom for pontoon and double-deck roofs) shall be attached to the deckplate(s) with continuous fillet welds made from the top side, as a minimum.

F. Covers and seals shall be provided at the top of the high support legs, at theannular opening between the high support legs and the low fixed legs orsleeves, and at any other openings (e.g., position-pin holes, if utilized) thatfunction to set the high, low, or adaptable positions of the legs.

G. When side entry mixers are specified and there is inadequate clearancebetween the roof and mixer components, the pontoon (or double deck) shall



be notched with a generously contoured, recessed pocket for mixercomponent clearance at the minimum operating position.

C.3.11 Roof Manholes

Manholes shall be located around roof to provide the most effective pattern foraccess, lighting, and ventilation of the tank flotation compartments and the productstorage interior.

The minimum number of manholes shall be as follows:

Nominal Tank Diameter D (ft) Minimum Number

D < 200 2

200 < D < 300 3

300 < D 4

C.3.12 Centering and Anti-Rotation Devices

A. A guide pole shall be provided as an anti-rotation device for the floatingroof. Locate the guide pole near the gauger’s platform.

B. Guide pole sections shall be welded with full penetration butt welds.Backing strips are not permitted. Provision must be made for draining andventing of unslotted pipe.

C. The guide pole shall have all required emission control devices around thewell opening where it penetrates the roof, such as those described inSection C.3.14.A.1 and specified on the Data Sheet, Line 37.

C.3.13 Seals

A. Primary rim seals shall be either mechanical shoe seals or envelope seals, asspecified on the Data Sheet, Line 33. Seal design shall be subject toPurchaser’s approval.

B. Mechanical shoe seals shall consist of the following:

1. The metal shoes employed in the sealing device between the roof andthe tank shell shall be steel per API 650, Section C.3.13:

Mechanical Shoe Material Minimum Shoe Thickness

Galvanized steel Manufacturer’s Standard Gauge 16(0.0598 inch)

Uncoated steel As specified on Data Sheet, Line 35

ASTM A240 austenitic SST Old U.S. Standard 18

For tanks storing aviation gasoline or jet fuels, austenitic stainless steelshall be used for all metal parts of seals.

2. Primary seal fabric shall span between the top of outer rim and sheetmetal shoe. Fabric shall allow full range of rim space movement forwhich roof and seal are designed. Fabric shall be compatible withproduct liquid and vapor.



3. If necessary, lower portions of metallic seal assemblies shall bemodified to eliminate interference between assemblies and bottom shellcourse accessories (e.g., side mixers).

4. The seal shoe and compression mechanism shall be installed beforehydrostatic testing. Excessive settlement during the hydrotest maycause binding. Section 5.3.6.E requires a cessation of tank filling andnotification of the Purchaser whenever such excessive settlement ismeasured. It may be necessary to remove the seal shoe after thehydrotest to accommodate cleaning, application of interior coatings, orany situation where the installed shoe might interfere with the process.The fabric seal may be installed after the hydrostatic testing.

5. All fasteners and washers for installation of seal joints, including fabricseal joints, shall be austenitic stainless steel. (See restrictions oncontact between galvanizing and stainless steel in Section 1.5.G.18.a.)

C. If used, toroidal or envelope seals (e.g., foam logs) shall be liquid-mounted,foam-filled seals consisting of an open cell polyurethane foam core enclosedin the liquid tight envelope. Seals shall be attached to and supported by theouter rim of the floating roof. Rough spots on the shell that could damage theseal assembly shall be ground smooth. The envelope material shall becompatible with the liquid and vapor phases of the stored product.

D. Unless otherwise specified on the Data Sheet, Line 36, secondary seals(wiper type) shall be supplied and installed by the Manufacturer. Specificrequirements are:

1. The seals shall be designed for a temperature range extending fromdesign metal temperature less 15°F to the maximum operatingtemperature.

2. The seal shall be designed or tested for at least 2000 cycles of tankfilling.

3. The secondary seal shall permit inspection of the primary seal withoutremoval.

4. Blowing sand and product scale shall be deflected back onto the roof bydesign.

5. Unless otherwise specified on the Data Sheet, Line 7, theManufacturer shall maximize the design liquid level and accommodatethe minimum and maximum possible rim spaces based on thetolerances and dimensions of the shell and the roof. The top of the sealshall remain below the top edge of the shell or wind skirt when the roofis at the maximum operating level.

6. Lengths of seal sections shall be as long as practical. No holes oropenings shall be permitted in the completed seal.

7. Provisions shall be made to prevent damage to the seal due to anyoverflow openings in the shell.

8. Installation and removal shall not require draining the tank.



9. The seal shall attach to the outer rim of the roof.

10. Seal materials shall be compatible with the stored product and shall bebased on the design temperature, permeability, abrasion resistance,flammability, chemical resistance to aromatics and other products. Theselection of such materials is a matter of agreement between thePurchaser and the Manufacturer and shall be tabulated in the DataSheet, Table 5. The following non-mandatory table provides guidanceon frequently used materials for selected products.

Fluid Stored Seal Material

Crude oil Fluoropolymers

Refined products Fluoropolymers, urethane, urethanelaminate, or Buna-N-Vinyl

Gasoline/MTBE blend PTFE laminate

E. Bonding shunts shall be provided on the floating roof and shall be locatedabove all seals. Shunts shall be 2-inch wide by 28-gage (1/64-inch thick)austenitic stainless steel as a minimum, or shall provide equivalent corrosionresistance and current carrying capacity as stated in NFPA 780. Shunts shallbe spaced as follows:

Tank Diameter D (ft) Maximum Shunt Spacing (ft)

D < 140 10

140 < D < 275 7

275 < D 5

C.3.14 Gauging Device

A. Each roof shall be provided with gauging ports with tight caps as indicatedon the Data Sheet, Line 37, with one port located adjacent to the gauger’splatform and remote from regions of turbulent flow. These ports may be:

1. Slotted guide pole gauge wells: These are vertical anti-rotation pipesthat can be used for gauging. The pipe shall have two rows of 1 inch by12 inch vertical slots on staggered 11-inch centers, located 180 degreesapart. Slots shall range from the maximum fill height to near the tankfloor. Well and pole shall be equipped with all required emissioncontrol devices, such as gasketed sliding well cover, pole wiper, polesleeve, float, float wiper, and pole cap (see API MPMS 19.2 forillustrations of some of these devices).

2. Non-guide pole gauge wells: These shall be NPS 8 pipes projecting atleast 6 inches above the roof’s outer rim. For sample hatches withoutgauging apparatus, see Section C.3.15.3.

B. Each gauge well shall have a B16.5 Class 150 bolt pattern, flat-face pipeflange with a full-face gasket at its top, and shall be attached to a non-sparking cap that complies with all environmental requirements.

C. Each gauge well shall have a permanent gauge mark or tab just inside thecap on the pipe wall called a “reference point” or “knife edge.”



D. When specified on the Data Sheet, Line 37, a datum plate shall be attachedto the bottom of the slotted guide pole at the distance designated by thePurchaser.

E. If striking plates are specified on the Data Sheet, Line 37, they shall beprovided on the tank floor beneath the guide pole or under the gauge well ifno guide pole is specified.

F. A gauger’s platform shall be located at an elevation that remains above andclear of the roof, its sealing system, and foam dam even during an overflowevent. Unless specified otherwise on the Data Sheet Tank Plan, the platformshall be located upwind of the prevailing wind.

C.3.15 Other Roof Accessories

C.3.15.1 Wax Scrapers

If wax scrapers are specified on the Data Sheet, Line 33, they shall belocated such that the scraping action occurs below the liquid surface.Design of wax scrapers shall not interfere with bottom shell courseaccessories.

C.3.15.2 Foam Dams

A foam dam, if specified on the Data Sheet, Line 31, shall be installed ontop plates of pontoon or roof deck within 1 foot but no more than 2 feetfrom the edge of the roof to contain foam fire-fighting solution. The damshall be fabricated from 3/16-inch thick by 24-inch high steel plate (ortaller for foam injection impingement plates) and 2 inch by 2 inch by 3/16inch mitered knee brace angles installed on the side of the foam damclosest to the center of the tank at a circumferential spacing ofapproximately 5 feet on center. Bottom of plate shall have 3/8-inch slottedweep holes. The dam shall be attached to the top deck plate by acontinuous fillet weld on each side and seal-welded at any other edge toprevent crevice corrosion. Compliance with NFPA 11 is required.

C.3.15.3 Sample Hatches

If specified on the Data Sheet, Line 37, the Manufacturer shall install anNPS 8 sample hatch with funnel on the roof deck with remote access fromthe gauging platform. Manufacturer shall install a recoil reel on thegauging platform. The hatch shall be equipped with a self-closing liquidtight cover that can be opened and closed from the gauger’s platform.

C.3.15.4 Automatic Level Gauge

a. Tanks shall have a ground-level reading, automatic float-level gauge,unless otherwise specified on the Data Sheet, Table 4.

b. Access for maintenance and repair shall be considered.

c. Level gauge shall be located such that the float well is away from anyappurtenances that produce turbulence.



d. The bottom of the float well shall be approximately 6 inches above thetank bottom when the floating roof is at its lowest position.

e. A gasket shall be installed beneath the cover of float wells.

C.3.15.5 Side Entry Mixers

a. Mixers shall conform to the Data Sheet, Line 26.

b. Each mixer shall be installed in cover plates in dedicated shell nozzlesor manholes.



APPENDIX E

Seismic Design of Storage Tanks

E.3 Seismic design factors shall be specified by the Purchaser in an Alternate SeismicCriteria document if so selected on the Data Sheet, Line 8 (e.g., when jurisdictionrequirements differ from those given in API 650, Appendix E, or for geographiclocations not listed therein).

E.8 Additional Considerations

A. Unless otherwise indicated on the Data Sheet, Line 8, tie rods (3/4 inchdiameter or larger) shall be placed between rafters in the outer ring whenever“H” or “I” sections are not used (see API 650, Section 3.10.4.4).

B. Refer to the Data Sheet, Line 8, for any additional freeboard, called “sloshheight” as per API 650, Section E.8.1. The design liquid level may beimpacted by the slosh height. If slosh height is specified, the columns shallmeet the lateral resistance requirement of API 650, Section E.8.2, and loadsshall be indicated on Data Sheet, Line 11.



APPENDIX H

Internal Floating Roofs

H.2 Types

If the Purchaser does not indicate “Other” on the Data Sheet, Line 30, the internalfloating roof design shall be one of the following types defined in API 650,Appendix H:

• Welded carbon steel or stainless steel pontoon or double-deck roofs

• Bolted aluminum or stainless steel roof on floats (tubular pontoons).The deck skin shall be deformed at its seams by the clampingmembers to effect a tight seal.

• Bolted aluminum sandwich panels with polyurethane or isocyanuraterigid foam cores, or bolted aluminum sandwich panels with analuminum honeycomb core bonded to aluminum top and bottomsheets so that each panel is self-buoyant

• Composite glass reinforced resin panels with self-buoyant cores

H.4 Design Requirements for All Types

H.4.2 Internal Floating Roof

H.4.2.6 The Manufacturer shall design the floating roof using the smaller ofthe specific gravity of API 650, Section H.4.2.6 (0.7), or theminimum specific gravity of the liquid stored in the tank as shownon the Data Sheet, Line 5.

H.4.2.7 Anti-Static Bonding

• A minimum of four anti-static cables shall be provided fromthe internal floating roof through the fixed roof. These shallbe stranded stainless steel, 1/8 inch diameter. The length ofthe bonding cables shall be at least twice the normal travelof the roof.

• All movable cover accessories (hatches, manholes, pressurerelief devices, and other openings) on the internal floatingroof shall be bonded to the internal floating roof to preventstatic electricity sparking when they are opened.

H.4.3 Joint Design

H.4.3.5 Joints that must be liquid-tight include, but are not limited to, deckpanels in contact with the liquid, bottom deck to rim plates, bottomdeck to bulkheads, rim plates to bulkheads, intersections betweenbulkheads, and all joints of floats. Joints that must be vapor-tightinclude, but are not limited to, all deck joints and for tubularpontoon supported roof, the deck to periphery rim joint. All metalliccomponents in direct contact with aluminum shall be aluminum or



austenitic stainless steel, unless specified otherwise. All hardwareused for a stainless steel shoe seal shall be austenitic stainless steel,unless specified otherwise. The use of plated fasteners shall bepermitted only when connecting steel components, or if specified bythe Purchaser.

H.4.4 Minimum Thickness

The minimum thickness of inner rims and bulkheads is 7-gauge, inclusive ofcorrosion allowance.

H.4.5 Peripheral Seals

H.4.5.4 In addition to the floating roof primary perimeter seal, secondaryperimeter seals shall be provided as specified on the Data Sheet,Line 36.

H.4.5.5 The inside of the shell shall be free of obstructions that woulddamage the seal. The floating roof installer shall perform a survey ofthe tank before roof installation to ensure proper operationalperformance.

H.4.7 Roof Supports

H.4.7.3 Unless otherwise specified by the Purchaser, two-position landinglegs shall be provided. The low roof position shall be the lowestpermitted by the tank internals. The high roof position shall providea 78-inch clearance between the lowest position of the roof and thetank floor. Whenever landing legs are used, provide landing padsthat are continuously full-fillet welded to the bottom.

H.4.7.6 Miscellaneous Roof Support Issues

• Where propeller-type mixers are used, the support legs shallprovide an adequate clearance (e.g., 12 inches from theunderside of the internal floating roof to the tip of the mixerpropeller).

• For tanks with internal coatings, the support legs shall bedesigned to prevent damage to internal tank coatings and toevenly distribute the weight of the internal floating roof onthe bottom plates.

• When specified by the Purchaser on the Data Sheet,Line 39, a cable-supported floating roof shall be providedwith externally adjustable supports.

H.6 Openings and Appurtenances

H.6.2 Vents

H.6.2.1 Pressure-Vacuum (Bleeder) Vents

Bleeder vents shall be designed to open automatically when the rooflowers to 3 inches above its lowest operating position and to close



automatically when the roof raises more than 3 inches above itslowest position.

H.7 Fabrication, Erection, Welding, Inspection, and Testing

H.7.2 Any flotation component that is completely shop-fabricated or assembledin such a manner as to permit leak testing at the fabricating shop shall beleak tested at the shop as well as retested in the field for all accessibleseams.

H.7.3 Manufacturer shall supply all closures required for testing. All temporaryclosures (including gaskets, fasteners, test blanks, etc.) shall be removedafter completion of the test.

H.7.5 Internal floating roof components that are fabricated or attached bywelding (e.g., clips, gusset plates, etc.) shall be completely seal-welded.

H.7.6 Internal floating roofs shall be installed in accordance with the instructionsprovided by the internal floating roof supplier.

atmospheric storage tank specification (api 650) vesta002-0600

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