F-201 Atmsoferic Storage Tanks PDVSA

 ENGINEERING DESIGN MANUAL VOLUME 19 ENGINEERING SPECIFICATION SPECIFICATION

PDVSA N°

TITLE

ATMOSPHERIC STORAGE TANKS

F–201

3

DEC 00

GENERAL REVISION

16

Y. K.

A. A.

E. C.

2

ABR.94

GENERAL REVISION

37

L. T.

E. J.

A. N.

0

DIC.86

FOR APPROVAL

32 REV.

APPD.

APPD.

DATE

DEC.00

REV.

DATE

APPD.BY Alexis Arévalo

 PDVSA,

1983

DESCRIPTION DATE

DEC.00

PAG. APPD.BY Enrique Carmona

ESPECIALISTAS

ENGINEERING SPECIFICATION

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PDVSA F–201

REVISION

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Página 1 .Menú Principal

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Index SECTION 1 – SCOPE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1.3 1.4 1.5

2

Referenced Publications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (Addition) Drawings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (Addition) Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2 2 3

SECTION 2 – MATERIALS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4

SECTION 3 – DESIGN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4

3.4 3.5 3.6 3.10 3.12 3.13 3.14 3.15

Bottom Plates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Shell Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Shell Openings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Roofs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (Addition) Floating Roof Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (Addition) Floating Roof Seals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (Additions) Floating Roof Supports and Drains . . . . . . . . . . . . . . . . . . . . . (Addition) Design Additional Requirements . . . . . . . . . . . . . . . . . . . . . . . . .

4 5 5 7 7 9 9 10

SECTION 5 – ERECTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

12

5.2 5.3

Detail of Welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Inspection, Testing and Repairs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

12 12

SECTION 6 – METHODS OF INSPECTING JOINTS . . . . . . . . . . . . . . . . . .

13

SECTION 7 – WELDING PROCEDURE AND WELDER QUALIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

13

7.4

Qualification of Welders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

13


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PDVSA F –201 REVISION

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FOREWORD This specification covers minimum requirements for materials, design, fabrication, erection and testing of welded steel storage tanks for above ground atmospheric liquid hydrocarbons and chemical storage. This specification does not cover tanks for water storage. This specification is intended to supplement API Standard 650, Tenth Edition, November 1998. Paragraph numbers, figures and tables of this specification correspond to those in API 650. Paragraph numbers not found in API 650 are new paragraphs. Paragraphs shall be highlighted as shown below to indicate the type of change from the API Standard: (Addition) New paragraph or supplemental requirements/clarifications to an existing paragraph. (Deleted) Paragraph deleted. (Decision) A decision has been made as required. (Substitution)

Paragraph supersedes API in its entirety.

SECTION 1 – SCOPE 1.1.3

(Substitution) The SI measuring system shall be used in drawings. Dimensions of piping, flanges, nozzles and bolts shall be in English units.

1.1.9

(Substitution) The seismic design of tanks shall meet the requirements of PDVSA FJ – 251, “Seismic Design of Metallic Tanks ”.

1.3

Referenced Publications

1.3.1

(Addition) In addition to API 650 tanks designed according to this specification must comply with applicable Venezuelan codes, laws and standards.

1.3.2

(Addition) Tanks designed according to this specification must comply the requirements of PDVSA – FJ – 251 “Seismic Design of Metallic Tanks ”, and of PDVSA – FJ – 221, “Diseño Antisísmico de Instalaciones Industriales ”.

1.3.3

(Addition) PDVSA IR – M – 03 “Sistema de Agua Contra Incendio ”

1.3.4

(Addition) PDVSA IR – M – 04 “Sistema de Espuma Contra Incendio ”

1.4

(Addition) Drawings The PDVSA representative shall supply data sheets and schematic drawings of the basic design indicating tank capacity, properties of products to be stored,


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nozzles orientation, nozzles elevation, site location and environmental conditions. Contractor shall design the tank and provide a complete set of detailed mechanical drawings for shop and/or field fabrication, and installation procedures that will guarantee correct construction, within the tolerances indicated in code API 650.

1.5 1.5.1

(Addition) Definitions Low strength tank steels Steels having a specified minimum yield strength equal or lower than 43,000 psi and a specified maximum tensile strength equal to or lower than 85,000 psi.

1.5.2

High strength tank steels Steels having a specified minimum yield strength greater than 43,000 psi and a specified maximum tensile strength equal to or lower than 100,000 psi.

1.5.3

Peaking Deviation of shell contour from a true circle at vertical joints. It shall be determined over a horizontal span of 900 mm, centered on the weld.

1.5.4

Banding Deviation of the shell at horizontal joints from a vertical line. It shall be determined over a vertical span of 900 mm centered on the weld.

1.5.5

Annular plates Butt – welded bottom plates forming an annular ring upon which the shell is installed.

1.5.6

Fully stiffened pontoons Floating roof pontoons with top and bottom reinforced plates in order that the entire pontoon cross section is effective in carrying loads transmitted from the center deck.

1.5.7

Partially stiffened pontoons Floating roof pontoons having top and bottom plates reinforced in such a way that only part of the pontoon cross section is effective in carrying loads transmitted from the center deck.

1.5.7

Production impact test plates (As defined by ASME Code Section VIII, Par. UG84). Whenever the base material requires impact testing, production weld test coupons shall be made, tested and the results shall be delivered to PDVSA prior to starting the tank erection.


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The production test coupons shall be taken from the bottom, middle and top course longitudinal and circumferential weld seams. A test coupon shall be taken from each heat number used in the tank construction. The test coupon shall be welded as an extension to the end of the production weld. If it is not practical to do it, the test plate will be made under the same production conditions as the actual tank welds, using the same welding procedure, joint details, number of passes, position, and consumables required for the actual tank joint. Inspector refers to the PDVSA representative.

SECTION 2 – MATERIALS 2.1.4

(Addition) Material specifications for annular plates shall be the same of the corresponding first course.

2.1.5

(Addition) Cast fittings shall not be permitted.

2.1.6

(Addition) No welded piping (API 5L or equivalent) is permitted for nozzle an nozzle necks for tanks constructed with steels having a specified minimum Yield strength greater than 43,000 psi and a specified maximum tensile strength equal to or lower than 100,000 psi.

SECTION 3 – DESIGN 3.3.2

Corrosion Allowances (Addition) Corrosion allowance shall be considered as specified in the PDVSA data sheet, but never be less than 1.5 mm.

3.4

Bottom Plates

3.4.4

(Addition) PDVSA’s sketch shall specify the following requirements for bottom slope: ”None”, “Apex up” or “Apex Down”.

3.5

Annular Bottom Plates

3.5.6

(Addition) The annular bottom plate width shall be in accordance with Table 1 or as calculated per 3.5.2 of API 650, whichever is greater. TABLE 3.4A CATEGORY OF BOTTOM REQUIRED

Category of Bottom Specified

1

Predicted Settlement (2) Maximum at shell ≤

50 mm

ANNULAR PLATE WIDTH Tank Diameter (1)

Tank Diameter

Over 15 m to 45 m

Over 45 m Annular plates with a minimum radial width of 600 mm between the inside of the shell and any lap – welded joint on the bottom.

Per API Standard 650


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2

≤

3

≤

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150 mm

300 mm (3)

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Annular plates with a minimum radial width of 600 mm between the inside of the shell and any lap – welded joint on the bottom. Annular plates with a minimum radial width of 900 mm between the inside of the shell and any lap – welded joint on the bottom.

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Annular plates with a minimum radial width of 900 mm between the inside of the shell and any lap – welded joint on the bottom.

Annular plates with a minimum radial width of 1800 mm between the inside of the shell and any lap – welded joint on the bottom.

NOTES: a.

No special requirements for tanks 15 meters or under in diameter.

b.

Predicted settlements are based on the following conditions: –

Settlements include the initial water loading of the tank.

–

Differential settlements of tank bottom are defined as the deviation with respect to uniform soil settlements.

–

The bidimensional tank inclination is not considered to be harmful for the tank bottom.

c.

If the predicted tank settlement is excessive, means of improving foundation characteristics must be considered before tank construction.

d.

Bottom plates shall have two pass welds.

e.

The annular plate width shall not be less than calculated according to API 650.

f.

Annular bottom plate thickness shall comply with requirements of PDVSA – FJ – 251.

3.6

Shell Design

3.6.1.3

(Addition) The specific gravity used for the design shall be 1,0. Use actual value when the specific gravity of the fluid is greater than 1,0.

3.6.1.9

(Addition) The tank shell course thickness shall be designed according to the “1 – foot method of API 650 ”. Calculation of the thickness by the “variable design point method” requires PDVSA approval.

3.6.1.10

(Addition) All vertical and horizontal shell joints shall be designed and specified using complete penetration and fusion welding procedures.

3.6.1.11

(Addition) Single butt welds are not permitted.


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3.7

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Shell Openings

3.7.1

General

3.7.1.9

(Addition) The minimum number of shell and roof manholes shall be as follows: Nominal Tank Diameter ( meters) Up to 6 m From 6 to 20 m From 20 to 30 m Greater than 30 m

Shell 1 2 2 3

Fixed 1 2 2 2

Roof Floating 1 1 2 2

3.7.5

Shell Manholes

3.7.5.1

(Substitution) Shell manholes shall conform to Figures3 – 4A and 3 – 4B and Tables 3 – 3 through 3 – 5, except that the minimum size shall be equal or greater than 24 in. Other shapes are permitted by 3.7.1.8. Manhole reinforcing plates or each segment of the plates if they are not made in once piece shall be provided with a 6 – mm (1/4 – in.) diameter telltale hole (for detection of leakage through the interior welds). Each hole shall be located on the horizontal position centerline and shall be open to the atmosphere. All tanks shall have at least one manhole of 30 in.

3.7.8

Flush –Type Shell Connections

3.7.8.12

(Addition) Flush type shell connections shall be provided with a flow guide box.

3.8.4

Roof Manholes

3.8.4.

(Addition) Manual Gauging and Sampling for Fixed Roof Tanks. A gauging hatch shall be installed on a roof manhole cover, with a minimum diameter of 200 mm. The gauging hatch shall have a heavy stay – back cover and a seal with a corrosion resistant seat, suitable for a pressure of 2 oz/sq. in, or the design pressure of the tank, whichever is greater.

3.8.7

Water Draw –off Sumps (Substitution) Water draw – off sumps shall be as specified in Figure 3 – 16 and Table 3 – 18, with the exceptions indicated herein and according to PDVSA sketches. Tanks for hydrocarbon service shall be provided with a minimum of one water draw – off connection:  

For tanks of 6 m in diameter or less a water sump is not required. For apex down cone bottom tanks, a sump is not required. The draw – off line shall be piped to the center of the tank, turned down and terminated 100 mm above bottom.


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

3.9.4

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For tanks over 6 m in diameter a water sump is required. The end of the draw – off pipe shall be 100 mm from the bottom of the sump.

Stiffening Rings As Walkways (Substitution) A stiffening ring or any portion of it that is specified as a walkway shall have a width not less than 760 mm clear of the projecting curb angle on the top of the tank shell. It shall be located 1050 mm below the top of the curb angle and shall be provided with a standard railing on the unprotected side and at the ends of the sections used as a walkway.

3.9.6

Top wind girder

3.9.6.4

When a curb angle is required at the top of the shell of floating roof tanks, the horizontal leg shall extend outward (Figure 3 – 20, detail b, API 650).

3.10

Roofs

3.10.1

Definitions

3.10.1.b

(Decision) Self – Supporting roofs are permitted only with PDVSA approval.

3.10.2.3

(Substitution) Roof plates of supported cone roof shall not be attached to the supporting members. For tanks to be operated at high temperatures, the rafter to shell connection shall be designed to allow differential thermal expansion between the shell and the roof rafters.

3.10.2.5.3 (Addition) A frangible joint at the roof to shell junction shall be provided for supported cone and self – supporting cone roof designs. 3.10.2.9

3.12

(Addition) The horizontal leg of the roof – supporting angle shall be turned inward. If the shell top angle is butt – welded to the shell (API 650, Fig. F – 2 (d) or (i), a double side weld is required.

(Addition) Floating Roof Design

3.12.1

The design of floating roof tanks with specified flush type nozzles shall permit the outer pontoon to reach a point within 380 mm of the tank bottom, unless limited by obstructions such as mixers, roof drains, etc.

3.12.2

Tank roof design for tanks larger than 18 m in diameter shall be as follows a.

Roofs shall be of the low deck (minimum vapor space) type.

b.

Center decks greater than 45 m in diameter shall have channel stiffeners on the under side of the deck. Stiffeners shall be 6in, 8.2 lbs/ft, or 160 mm, 13.3 kg/m minimum and shall be installed as concentric rings with a maximum radial spacing of 6m. In addition, the underside deck plates shall have


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continuously welded lap joints at a radial distance of 12 m from the center of the roof. 3.12.3

Roofs for tanks greater than 46 m in diameter shall be designed for elastic stability against “gross out of plane ” buckling and “local” buckling of the outer pontoon, due to the radial load imposed by deflection of the center deck. This radial load shall be determined from the 250 mm of rainfall loading condition as defined in API 650, Appendix C.3.4. or punctured center deck loading condition, whichever governs. For prevention of gross out of plane buckling, the following relations shall be satisfied: a.

For “Fully stiffened ” pontoons: N< 7.5 EIx /R3

b.

For “Partially Stiffened ” pontoons: N < 5.0 EIx /R3 Where: N = Design radial inward load, lb./in. E = Modulus of elasticity, psi. R = Mean radius of pontoon ring, in. Ix = Moment of inertia of full pontoon cross section with respect to horizontal axis through its centroid, in 4.

Or: a.

For “Fully Stiffened ” pontoons: N < 7.5 x 10 – 3 EIx / R3

b.

For “Partially Stiffened ” pontoons: N < 5.0 x 10 – 3 EIx / R3 Where: N = Design radial inward load, Newtons per millimeter. E = Modulus of elasticity, Kpa. R = Mean radius of pontoon ring, mm. Ix = Moment of inertia of full pontoon cross section with respect to horizontal axis through its centroid, mm 4.

c.

3.12.4

The radial unsupported width of “Partially Stiffened ” plates shall not exceed 3m.

The inner rim of “Partially” and “Fully Stiffened ” pontoons shall have the following minimum thickness:


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TANK DIAMETER 60 to 75 m 75 to 90 m

3.12.5

3.12.6

3.13

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RIM THICKNESS 16 mm 19 mm

For tanks over 60 m in diameter the following calculations and tests are required to substantiate the elastic stability of the roof pontoon design: a.

Where the roof design has not been previously approved by PDVSA, the vendor shall submit test data of a roof of similar diameter, to validate the design.

b.

Where validation has not been made, the vendor shall conduct a proof test on the largest tank to be supplied. The proof test shall be based on the most critical design load condition. Calculations shall be submitted to PDVSA for approval.

Tanks greater than 90 m in diameter shall have the following roof construction: a.

The roof shall be double deck type.

b.

The top edge of the inner rim plates in the first two central compartments shall be welded with continuous single fillet welds.

c.

All circumferential compartments other than the outer compartments shall be provided with a minimum of four radial partition plates.

(Addition) Floating Roof Seals

3.13.1

Roof seals shall contact the liquid level at the shell for at least 90% of the circumference of the tank. The maximum permissible gap between the primary seal and the tank shell is 6 mm.

3.13.2

Toroidal type seals shall be equipped with a weather shield unless secondary seals are specified. Liquid mounted toroidal seals are preferred.

3.13.3

Floating roofs with a flexible steel shoe type primary seal shall be equipped with an abrasion resistant, weather and product proof, flexible seal in order to close the space between the seating ring and the rim of the floating roof and shall be designed to avoid any jam between the shell and the shoe when the roof is moving.

3.13.4

Secondary seals shall be installed if required by PDVSA in the inquiry documents and the design shall be approved by PDVSA.

3.13.5

The design of primary seals, secondary seals and weather shields shall permit installation and removal from the top of the roof.

3.14 3.14.1

(Additions) Floating Roof Supports and Drains Supports shall be made of carbon steel pipe, schedule 80 minimum thickness. They shall be provided with a  in hole at the bottom for drainage.


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3.14.2

The clearance between the support and the roof support sleeve shall be 3 mm nominally at all points.

3.14.3

Supports shall be adjustable to two positions: a.

The lower position shall permit the roof to reach 75 mm below the specified lowest operating position, without interference with any internal accessory or roof seal mechanism.

b.

The upper position shall provide a clearance of 2 meters between the roof and the tank bottom, for cleaning purposes.

3.14.4

Bearing plates shall be centered under each support, welded to the shell bottom by a 5 – mm continuous fillet weld. Plate dimension shall be 24 in square by 3/8 in thick.

3.14.5

The length of the leg support sleeves shall be such that any opening will be above the liquid level when the deck is deflected by the 250 – mm rainfall or by a punctured center deck loading condition. The height of the support sleeves for a single deck pontoon roof shall never be less than the tank diameter divided by 60.

3.14.6

Emergency drains shall not be provided when the pontoon area is less than 50% of the roof area. Only for double deck type roofs may credit is taken in the roof design when emergency drains are furnished.

3.15 3.15.1

(Addition) Design Additional Requirements Level Gauge for Tanks . Gauge type and installation shall be specified or approved by PDVSA ’s representative. At least one level gauge per tank, readable from grade, shall be provided.

3.15.2

Vertical tanks shall be gauged in accordance to API 2550.

3.15.3

Roof Vents For fixed roof tanks, design and installation of normal and emergency vents (including vacuum vents), shall be as specified in API STD 2000. Floating roof tanks shall be equipped with a bleeder vent, designed to open automatically when the roof lowers to a level of 75 mm. When flexible, steel shoe – type seals are employed and the shoes extend into the liquid more than 100 mm, the roof shall be equipped with a vent or vents between the roof rim and the seal shoe. These vents shall release excess air or non – condensable vapors entering the tank through the filling line.


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3.15.4

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Connections for Temperature For fixed roof tanks a NPS 25 mm threaded connection shall be installed for a thermowell, at a minimum level of 5 ft from the bottom of the first course. A flanged thermowell with a minimum size of 38 mm is also acceptable with PDVSA approval. For floating roof tanks and fixed roof tanks with internal floating covers, the type and method of installation of the temperature measuring device shall be specified by Vendor.

3.15.5

Fill Nozzles Fill nozzles shall be sized to meet fluid velocity requirements according to API RP 2003.

3.15.6

Foam and Firewater Systems Foam system shall be in accordance with PDVSA Guide IR – M – 04, “Sistema de Espuma Contra Incendio ”. Firewater system shall be in accordance with PDVSA Guide IR – M – 03, “Sistema de Agua Contra Incendio ”.

3.15.7

Tank Heating Coils Coils and associated piping shall only have welded pressure joints. The design shall consider differential thermal expansion and other loads affecting the tank.

3.15.8 a.

Pressure test holes in reinforcing plates at nozzles and manholes shall be plugged with a plastic sealant after testing.

b.

Fill and discharge nozzles shall be API Low Type unless otherwise specified.

c.

Shell nozzle 50 mm and larger for internal pipe tank connections shall extend into the tank as per API 650.

d.

Unless otherwise specified, all instrument connections, except thermowells, shall be NPS 2 flanged, and thermowells shall be NPS 1 threaded.

3.15.9

Platforms, Walkways and Stairways

3.15.9.1

Atmospheric and low – pressure tanks up to a maximum height of 6 m shall be provided with a vertical protected marine ladder. Tanks of more than 6 m in height require a peripheral stairway in accordance to API 650, tables 3 – 18 and 3 – 19. Platforms, if any, shall be in accordance to API 650, table 3 – 17.

3.15.9.2

For fixed roof tanks handrails shall be installed along the edge of the roof, extending at least 4500 mm beyond the platform in each direction.

3.15.9.3

Standard design handrails shall protect stairways and platforms. A typical handrail consists of top and intermediate railings with the required posts. On


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walkways and platforms posts will be installed on the base plates on all sides except at the access. 3.15.9.4

Dome roof tanks shall require walkways from the edge to the center of the roof for maintenance of accessories. These walkways will have handrails on both sides and around working platforms. A swinging door shall be installed at access.

SECTION 5 5.2 5.2.5

–ERECTION

Detail of Welding Roofs (Addition) Cone and dome roofs shall not have depressions that will allow accumulation of water.

5.3

Inspection, Testing and Repairs

5.3.1

General

5.3.1.5

(Addition) Hardness of hot – formed sections, weld metal and the heat – affected zone (HAZ) of all welds shall not exceed 200 Brinnell. The tank erector shall check the weld hardness of the initial production weld for each welding process, filler metal, and technique used. If the clearances are such that it is not possible to check the production weld, a mockup under identical conditions shall be used.

5.3.4

(Substitution) Inspection of Tank Bottom Welds a.

All bottom plate joints shall be vacuum tested using soapsuds solution at 10 psig.

b.

Annular plate butt joints shall be 100% radiographed or shall be magnetic particle inspected from the topside after completion of the root pass and again after completion of the full weld.

c.

Bottom to the shell joint shall be inspected as follows:

–

•

The inner fillet weld shall be leak tested after depositing at least one layer and prior to starting the outside fillet weld. This leak testing shall be performed with penetrating oil after slag removal. All oil shall be removed before welding the outside fillet and before completing any partially filled inner fillet weld.

•

Examination for inner fillet toe cracks shall be performed, using either the liquid penetrant or magnetic particle method.

•

The gap between the bottom shell ring and the lap welded bottom plates at the radial weld locations shall be a maximum of 3 mm.


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5.3.6

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Testing of the Shell c.

d. e. f.

g.

(Addition) If method a) is selected, the hydrostatic test shall filling and emptying. If salt water is used for this purpose and will remain in the tank for more than 30 days, an oxygen scavenger and a corrosion inhibitor shall be added. These additives shall be approved by PDVSA. (Addition) For floating roofs, contractor shall install the covers of deck manholes before filling. (Addition) Contractor shall furnish, install and remove all piping required for testing. (Addition) Contractor shall clean out any standing water, silt or dirt, left in the tank after hydrostatic testing so that the tank interior is totally clean and ready for operation. (Addition) The water – filling rate shall not exceed the following: BOTTOM COURS THICKNESS (mm) Less than 22 Equal or Greater 22

h.

TANK PORTION Top course Below Top Course Top Third Middle Third Bottom Third

FILLING RATE mm/hr 300 450 225 300 450

(Addition) The PDVSA inspector shall take note of water levels in the tanks. The hydrotest shall be maintained for at least 24 hours.

SECTION 6 – METHODS OF INSPECTING JOINTS 6.1.6

Determination of Limits of Defective Welding

6.1.6.1

(Addition) The following imperfections, in addition to those specified in API 650, are unacceptable: a.

Individual slag inclusions longer than either 6 mm or 1/3 of the plate thickness, whichever is greater.

b.

Porosity with comet tails.

c.

If radiographs show unacceptable defects, the defective parts shall be cut out and re – welded as directed by the PDVSA Inspector.

SECTION 7 – WELDING PROCEDURE AND WELDER QUALIFICATIONS 7.4 7.4.4

Qualification of Welders (Addition) For the fillet welded bottom plates, a minimum of two welding passes are required. The geometry and qualification procedures are as follows:


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a.

Fillet weld geometry:

b.

Using the same type of electrode (same manufacturer ’s designation), plate (same material and thickness), and welding procedure, as will be used for the tank bottom, 600 linear mm of lap weld shall be made.

c.

75 x 400mm tensile test strips shall be cut of this weld. The minimum breaking strength of the strips shall be at least 70% or 80% of the specified or guaranteed minimum tensile strength of the non – welded plate for a 70% or 80 % joint efficiency, respectively. Weld failure shall be at least 95% of the shear fracture.

d.

From a separate test plate consisting of 300 mm of the first pass of the bottom plate fillet weld, three cross sections of the weld shall be taken to show the penetration into the base material. The minimum penetration at the heel to be  mm, as shown in the above sketch, and complete fusion shall exist throughout each cross section.


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APPENDIX B – RECOMMENDATIONS FOR DESIGN AND CONSTRUCTION OF FOUNDATIONS FOR ABOVEGROUND OIL STORAGE TANKS . B.2 Subsurface Investigation and Construction B.2.6 (Addition) Settlement Measurements for tanks larger than 15 meters in diameter: a.

Shell settlement measurements shall be made after tank erection, prior to hydrostatic testing and during water filling at the ,  and full levels, corresponding to the maximum filling height of the tank. Water shall be held at the  and  levels for 24 hours and settlement data assessed for unexpected soil behavior. Shell settlement shall be taken at the beginning and end of each hold period. Settlement measurements shall be taken at equally spaced intervals of approximately 10m around the tank shell on well – marked locations on the annular plate or on clips welded to the shell.

b.

Ten (10) bottom internal measurements shall be made after hydrostatic testing at 3m intervals (see Fig. 1) and the following: Tank Diameter Meters

From 69 to 99

Number of Diameter Axes 4 6 8

Greater than

10

Less or equal to 46 From 46 to 69

Additional measurements shall be made in the annular plate region at approximately 10 meters intervals around the tank shell. At least 3 measurements shall be made at each location commencing inward from the inside surface of the tank shell and equally spaced on a radial line. A 100 % visual examination shall be made of the tank bottom to detect any localized depression.


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Línea diametral Punto de medición en placa anular

≤

3m Placa del fondo

≤

3m

Placa anular

Punto de medición en placa anular

Punto de medición en la pared

Fig 1. MEDICION DEL FONDO

APPENDIX E – (DELETE) SESMIC DESIGN OF STORAGE TANKS

F-201 Atmsoferic Storage Tanks PDVSA

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