Welded Tanks for Oil Storage

8/12/2019 Welded Tanks for Oil Storage

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API 650

WELDED TANKS FOR OILSTORAGE

A Tank GuidanceDwi Hermawan


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Content

Introduction

Scope

Appendices

Responsibilities

Design Materials

Loads

Capacity

Special Considerations

Shell Design Construction of tanks

Fabrication

Inspection & Testing


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Introduction

Storage Tanks Types

Fixed Roof Tanks

Floating Roof Tanks

Classification based on internal pressure Atmospheric tanks

They are usually operated at internal pressure slightly aboveatmospheric pressure. The fire codes define atmospheric tank asoperating from atmospheric up to 3.5 kN/m2 above atmosphericpressure or having pressure up to 2.5 psig

Low pressure tanks

Within the context of tanks, low pressure means that tanks aredesigned for a pressure higher than atmospheric tanks, This alsomeans that tanks are relatively high-pressure tanks. Tanks of thistype are designed to operate from atmospheric pressure up to about100 kN/m2

Pressure vessels (high pressure tanks)


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Fixed Roof Tanks


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Scope

This standard establishes minimum

requirements for material, design, fabrication,

erection, and testing for vertical, cylindrical,

aboveground, closed and open top, weldedcarbon or stainless steel storage tanks in

various sizes and capacities for internal

pressures approximating atmospheric

pressure

The internal pressure not exceeding the

weight of the roof plates


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Appendices

Appendix A

It provides altenative simplified design

requirements for tanks where the stressed

components such as shell plates and reinforcingplates, are limited to a maximum nominal

thickness of 12.55 mm(1/2 in), including any

corrosion allowance and whose design metal

temperatur exceeds the minimums stated in theappendix


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Appendices

Appendix B

It provides recommendations for the design andconstruction of foundations for flat-bottom oilstorage tanks

Appendix C

It provides minimum requirements for pontoontype (single and double deck type) externalfloating roofs

Appendix D

It provides requirements for submission oftechnical inquiries regarding this standard


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Appendices

Appendix E It provides minimum requirements for tanks subject to

seismic. An alternative or supplemental design maybe mutually agreed upon by the Manufacturer and thePurchaser

Appendix F It provides requirements for the design of tanks

subject to a small internal pressure. This appendixapplies to the storage of non-refrigerated liquids (see

also API Std 620, Appendices C and R). Formaximum design temperature above 93oC (200oF)see Appendix M

Appendix G It provides requirements for aluminium dome roofs


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Appendices

Appendix H It provides minimum requirements that apply to an internal

floating roof in a tank with fixed roof at the top on the tank shell

Appendix I It provides acceptable construction details that may be specified

by the Purchaser for design and construction of tank andfoundation systems that provide under-tank leak detection andsubgrade protection in the event of tank bottom leakage andprovide tank supported by grillage

Appendix J It provides requirements covering the complete shop assembly of

tanks that do not exceed 6 m (20 ft) in diameter

Appendix K It provides a sample application of the variable design point

method to dettermine shell plate thicknesses


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Appendices

Appendix L It provides the Data Sheet and the Data Sheet instructions

for listing required information to be used by the Purchaserand the Manufacturer. The use of the Data Sheet ismandatory unless waived by the Purchaser

Appendix M It provides requirements for tanks with a maximum design

temperature exceeding 93oC (200oF) but not exceeding260oC (500oF)

Appendix N It provides requirements for the use of new or unused plate

and pipe materials that are not completely identified ascomplying with any listed spesification for use inaccordance with this Standard


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Appendices

Appendix O

It provides recommendations for the design and

construction of under-bottom connections for

storage tanksAppendix P

It provides requirements for design of shell

openings that conform to table 5-6 that are

subject to external piping loads. An alternative or

supplemental design may be agreed upon by the

Purchaser or Manufacturer.


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Appendices

Appendix R It provides a description of the load combinations used for

the design equations appearing in this Standard

Appendix S

It provides requirements for stainless steel tanks Appendix T

It summarizes the requirements for inspection by methodof examination and the reference sections within theStandard. The acceptance standards, inspector

qualifications, and procedure requirements are alsoprovided. This appendix is not intended to be used alone todetermine the inspection requirements within thisStandard. The specific requirements listed within eachapplicable section shall be followed in all cases


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Appendices

Appendix U It provides requirements covering the substitution of

ultrasonic examination in lieu of radiogaphicexamination

Appendix V It provides additional requirements for tanks that are

designed to operate under external pressure(vacuum) conditions.

Appendix W It provides recommendations covering commercial

and documentation issues. Alternative orsupplemental requirements may be mutually agreedupon by the Manufacturer and the Purchaser


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Limitations

The rules of this Standard are not applicablebeyond the following limits of piping connectedinternally or externally to the roof, shell, or bottomof tanks constructed according to this Standard :

a.The face of the first flange in bolted flangeconnections unless covers or blinds are provided aspermitted in this standard.

b.The first sealing surface for proprietary connectionsor fittings.

c.The first threaded joint on the pipe in a threadedconnection to the tank shell.

d.The first circumferential joint in weldingend pipeconnections if not welded to a flange.


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Responsibilities

The Manufacturer is responsible for complyingwith all provisions of this Standard

Inspection by the Purchasers inspector does notnegate the Manufacturers obligation to provide

qruality control and inspection necessary toensure such compliance

The Purchaser retains the right to providepersonnel to observe all shop and job site workwithin the scope of the contracted work (includingtesting and inspection). Such individuals shall beafforded full and free access for these purposes,subject to safety and schedule constraints


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Responsibilities

In this Standard, languange indicating that the

Purchaser accept, agrees, reviews, or

approves a Manufacturers design, work

process, manufacturing action, etc., shall notlimit or relieve the Manufacturers

responsibility to conform to specified design

codes, project specifications and drawings,

and professional workmanship.


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Importance Definitions

Design Thickness The thickness necessary to satisfy tension and

compression stregth requirements by this Standard or, inthe absence of such expressions, by good and acceptableengineering practice for specified design conditions,

without regard to construction limitations or corrosionallowance

Design Metal Temperature The lowest temperature considered in the design, which,

unless experience or special local conditions justify

another assumption, shall be assumed to be 8o

C (15o

F)above the lowest one-day mean ambient temperature ofthe locality where the tank is to be installed.

The temperatures are not related to refrigerated-tanktemperature


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Important Definitions

Maximum Design Temperature The highest temperature considered in the design, equal to

or greater than highest expected operating temperatureduring the service life of the tank.

Requirement The criteria must be used unless the Purchaser and the

Manufacturer agree upon a more stringent alternativedesign

Recommendation The criteria provide a good acceptable design and may be

used at the option of the Purchaser and the Manufacturer.

Tack Weld A weld made to hold the parts of a weldment in proper

alignment until the final welds are made.


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Service Conditions

The Purchaser shall specify any applicable specialmetalurgical requirements.

When the service conditions might include the presence ofhydrogen sulfide or other conditions care should be taken toensure that the materials of the tank and details of

construction are adequate to resist hydrogen-inducedcracking.

The purchaser should consider limits on the sulfur content ofthe base and weld metals as well as appropriate qualitycontrol procedures in plate and tank fabrication.

The hardness of the welds, including the HAZ in contact withthese conditions should be considered. As a reference,Rockwell C 22 and can be expected to be more susceptibleto cracking than un welded metal is.

Any hardness criteria should be a matter of agreementbetween the Purchaser and the Manufacturer


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Materials

Use of cast iron for any pressure part or any part attached tothe tank by welding is prohibited

Because of hydrogen embrittlement and toxicity concern,cadmium-plated components shall not be used without theexpressed consent of the Purchaser

The tensile test shall be performed on each-plate if heattreated

Subject to the Purchasers approval, controlled-rolled orthermo-mechanical-control-process (TMCP) plates (platesproduced by a mechanical-thermal rolling process designed

to enhance notch toughness) may be used where normalizedplates are required

Each plate-as-rolled shall receive Charpy V-notch impactenergy testing. The test specimens shall be Type Aspecimens (see ASTM A370)


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Materials


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Materials


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Toghness Requirements

The thickness and design metal temperature of ashell plates, shell reinforcing plates, shell insertplates, bottom plates welded to the shell, platesused for manhole and nozzle necks, plate-ring

shell-nozzle flanges, blind flanges, and manholecover plates shall be in accordance with Figure 4-1

In addition, plates more than 40 mm (1.5 in) thick

shall be of killed steel made to finegrain practiceand heat treated by normalizing, normalizing andtempering, or quenching and tempering, and eachplate as heat treated shall be impact tested


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Toughness Requirement

Plate less than or equal to 40 mm (1.5 in) thick

except controlled-rolled plates may be used at

or above the design metal temperatures

indicated in Figure 4-1 without being impacttested.


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Material Selection (Figure 4-1)


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Material Selection


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Design

Loads

a. Dead Load (DL)

The weight of the tank or tank component, including any corrosion

allowance unless otherwise noted

a. Design External Pressure (Pe)

Shall not be less than 0.25 kPa (1 in. of water). This Standard does

not contain provisions for external pressure greater than 0.25 kPa (1

in. of water). Design requirement for vacuum exceeding this value and

design requirements to resist flotation and external fluid pressure shall

be a matter of agreement between the Purchaser and the

Manufacturer (see Appendix V)a. Design Internal Pressure (Pi)

Shall not exceed 18 kPa (2.5 lbf/in2)

a. Hydrostatic Test (Ht)

The load due to filling the tank with water to the design liquid level


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a. Minimum Roof Live Load (lr)

1.0 kPa (20 lb/ft2) on the horizontal projected area of the roof

a. Seismic (E)

Seismic loads determined in accordance with E.1 through E.6 (see DataSheet Line 8)

a. Snow (S)not defined in Indonesiafollow ASCE 7

a. Wind (V)

Follow ASCE 7, and windward & leeward horizontal wind loads on theroof are concervatively equal and opposite (not included in the abovepressures

a. Stored Liquid (f)

The load due to filling the tank to the design liquid level (see 5.6.3.2) withliquid with the design spesific gravity specified by the Purchaser

a. Test Pressure (Pt)

As required by F.4.4 or F.7.6

Design


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Tank Capacity

The Purchaser shall specify the maximumcapacity

Maximum capacity is the volume of product in

a tank when the tank is filled to its designliquid level as defined (see Figure 5-4)

The net working capacity is the volume ofavailable product under normal operating

conditions. The net working capacity is equalto the maximum capacity less the minimumoperating volume remaining in the tank, lessthe overfill protection level (or volume)

requirement (see Figure 5-4)


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Scheme of Tank

S h f T k (Fi 5 4 API


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Scheme of Tank (Fig. 5-4 - API

650)

F d ti d C i


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Foundation and Corrosion

Allowance

Foundation The adequacy of the foundation is the responsibility of the

Purchaser

Sliding friction resistance shall be verified for tanks subjectto lateral wind loads or seismic loads

Corrosion Allowance Guidance to the Purchaser for considering corrosion

allowance

Corrosion allowance for anchor bolts shall be added to thenominal diameter

Corrosion allowance for anchor straps and bracket shall beadded to the required strap and bracket thickness

For internal structural members, the corrosion allowanceshall be applied to the total thickness unless otherwisespecified


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Shell Design

One foot method

Allowed for shells with diameter lesser than 60 m

(200 ft)

Sdand Stis selected from the table 5-2 of permissiblematerials and allowable stresses

The 1-foot method calculates the thickness required

at design point 0.3 m (1 ft) above the bottom of each

shell

Course. Appendix A permits only this design method

The required shell thickness, including any corrosion

allowance, or the hydrostatic test shell thickness but

the shell thickness shall not be less than the following

:


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Shell Design

Unless otherwise agreed to by the Purchaser, the

shell plate shall have a minimum nominal width of

1800 mm (72 in)

Plates that are to be butt-welded shall be properly

squared

Shell Design S and S Table


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Shell Design - Sdand StTable

5-2


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Shell Design

One Foot MethodEquation in SI unit


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Shell Design

Variable Design Pt Method

Shell with diameters greater than 60 m (200 ft)

See Appendix K

Only be used when the Purchaser has not specifiedthat the 1-foot method be used and when the

following is true


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Shell Design

Bottom course design The bottom course thickness t1dand t1tfor the design and

hydrostatic test conditions shall be calculated using the followingformulas

For the design condition t1dneed not be grater than tpd

For the hydrostatic test condition, t1tneed not be greater than tpt To calculate the bottom-course thickness, preliminary values tpd

and tptfor the design and hydrostatic test condition shall first becalculated from the formulas in one foot equations


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Shell Design

Second course design

To calculate the secondcourse thickness for

both the design condition and the hydrostatic test

condition, the value of the following ratio shall becalculated


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Shell Design

Elastic Analysis Method (FEA)

For tanks where L/H is greater than 1000/6 (2 in

US units), the selection of shell thickness shall be

based on an elastic analysis that shows thecalculated circumferential shell stresses to be

below the allowable stresses given in Table 5-2

The boundary conditions for the analysis shall

assume a fully plastic moment caused by yieldingof the plate beneath the shell and zero radial

growth


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Fabrication

Shop Inspection

Materials

Welders qualification

Factory acceptance during farication, shaping (can bedone)

Erection

Tanks and their structural attachments shall bewelded by the shielded metal-arc, gas metal-arc, gas

tungsten-arc, oxyfuel, flux-cored arc, submerged-arc,electroslag, or electrogas process using suitableequipment

Use of the oxyfuel process is not permitted whenimpact testing of the material is required


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Fabrication

No welding of any kind shall be performed when thesurfaces to be welded are wet from rain, snow, or ice;when rain or snow is falling on such surfaces; or duringperiods of high winds unless the welder and the work areproperly shielded

Each layer of weld metal or multiplayer welding shall becleaned of slag and other deposits before the next layer isapplied

The edges of all welds shall merge smoothly with thesurface of the plate without a sharp angle

All welding shall be free from coarse ripples, grooves,overlaps, abrupt ridges, and valley that interfere withinterpretation of NDE results

During the welding operation, plates shall be held in closecontact at all lap joints


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Fabrication

Erection - welding If protective coatings are to be used on surfaces to be

welded, the coatings shall be included in weldingprocedure qualification tests for the brand formulationand maximum thickness of coating to be applied

Low-hydrogen electrodes shall be used for all manualmetal arc welds in annular rings and shell courses,including the attachment of the first shell course tobottom or annular plates as follows : Where the plates are thicker than 12.5 mm (1/2 in) and

made of material from Groups I-III For all thickness when the plates are made of material from

Group IV, IVA, and VI


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Fabrication - Preheat

Requirement


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Fabrication - Sheet Joint

Vertical shell joint Shall be butt joints withcomplete penetrationand fusion attained bydouble welding

Vertical joint in adjacentshell course shall notbe aligned, but shall beoffset from each othera minimum distance of

5t (t : plate thickness ofthe thicker course atthe point of offset


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Horizontal shell joint Complete penetrationand fusion

Top angles may be

attached to the shell bya double-welded lap

joint.

Unless otherwise

specified, abutting shellplates at horizontal

joints shall have a

common vertical

centerline

Fabrication - Sheet Joint

Fabrication Roof & Bottom


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Fabrication - Roof & Bottom

Joint

Roof & Bottom joint

Fabrication Shell to Bottom


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Fabrication - Shell to Bottom

Joint

Shell to Bottom


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Fabrication

ErectionShell Plates to be joined by butt welding shall be matched accurately

and retained in position during the welding operation.

Misalignment in completed vertical joints for plates greater than16 mm (5/8 in) thick shall not exceed 10% of the plate thicknessor 3 mm (1/8 in), whichever is less; misalignment for plates lessthan or equal to 16 mm (5/8 in) thick shall not exceed 1.5mm(1/16 in)

In completed horizontal butt joints, the upper plate shall notproject beyond the face of the lower plate at any point by morethan 20% of the thickness of the upper plate, with a maximumprojection of 3 mm (1/8 in); however for upper plate less than 8mm (5/16 in) thick, the maximum projection shall be limited to 1.5mm(1/16 in)


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Fabrication

ErectionShell The reverse side of doublewelded butt joints shall

be thoroughly cleaned in a manner that will leave theexposed surface satisfactory for fusion of the weldmetal to be added, prior to the application of the first

bead to the second side. This cleaning may be doneby chiping; grinding; melting out; or where the back ofthe initial bead is smooth and free from crevices thatmight entrap slag, another method that, upon fieldinspection, is acceptable to the Purchaser.

For circumferential and vertical joints in tank shellcourses constructed of material more than 38 mm (1.5in) thick , multipass weld procedures are required,with no pass over 19 mm (1/4 in) thick permitted


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Inspection

Butt Welds Complete Penetration and Fusion

RT, UT

Fillet Welds VI

DPT (if required)

RT (one joint per 30m/100ft, if required)

Tank Bottom VI

Vacuum box test

Tracer gas test

Water test (A head of 150 mm (6 in) of liquid shall be maintainedusing a temporary dam to hold that depth around the edge of thebottom.


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Reinforcement platesAfter fabrication is completed but before the tank

is filled with test water, the reinforcing plates shallbe tested by the Manufacturer by applying up to

100 kPa (15 lbf/in2) gauge pneumatic pressurebetween the tank shel and the reinforcementplate on each opening using the telltale hole

Hydro-testing of tank

This hydrostatic test of the tank shall beconducted before permanent external piping isconnected to the tank


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Inspection

Hydro-testing of tank

Any welded joints above the test-water level shall

be examined for leakage by one of the following

methods: 1. coating all of the joints on the inside with a highly

penetrating oil, such as automobile spring oil, and

carefully examining the outside of the joints for

leakage

2. applying vacuum to either side of the joints or

applying internal air pressure as specified for the roof

test in 7.3.7 and carefully examining the joints for

leakage or

3. using any combination of the methods stipulated in


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Resume API 650

Used for the design, vertical storage tank

(aboveground cylindrical)

With pressure up to 2.5 psig and a maximum

temperature of 500 degree G Tanks have flat-bottomed

Roof can be open-topped, self-supported

conical or doomed roofs, or structurallysupported cones


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Thank you

Documents

Welded Tanks for Oil Storage