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Research Papers: Materials and Fabrication

Determination of Failure Pressure Modes of the API Specification 12F Shop-Welded, Flat-Bottom Tanks

[+] Author and Article Information
Andres Rondon

Civil and Environmental Engineering,
University of Washington,
201 More Hall,
Seattle, WA 98195
e-mail: rondon@uw.edu

Sukru Guzey

Lyles School of Civil Engineering,
Purdue University,
550 Stadium Mall Drive,
West Lafayette, IN 47907
e-mail: guzey@purdue.edu

1Corresponding author.

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received January 5, 2017; final manuscript received March 17, 2017; published online April 26, 2017. Assoc. Editor: Xian-Kui Zhu.

J. Pressure Vessel Technol 139(4), 041409 (Apr 26, 2017) (14 pages) Paper No: PVT-17-1004; doi: 10.1115/1.4036430 History: Received January 05, 2017; Revised March 17, 2017

Shop–welded, flat-bottom tanks for storage of production liquids are designed and fabricated in specific dimensions and capacities for internal pressures close to atmospheric pressure in accordance with the API 12F specification. This study addresses the failure pressure on the eleven (11) current API 12F shop-welded steel tanks as well as two proposed sizes through finite element and stress analysis of more than 350 different tank models. An elastic analysis was carried out to determine the yielding pressure of the shell-to-bottom and roof-to-shell joints. An elastic buckling analysis and a post-buckling analysis including imperfections was performed to determine the buckling modes of the equipment. The redistribution of stresses due to inelastic deformations and plastic collapse were evaluated through a plastic stress analysis considering the stress–strain hardening of the ASTM A36 mild steel material. Moreover, the design pressure increase to failure pressure or 24 oz/in2 (10.3 kPa) was investigated regarding the stress levels and bottom uplift of the 13 flat-bottom tanks. The presented research provides meaningful insights and engineering calculations to evaluate the current design of the API 12F shop-welded, flat-bottom tanks as well as to establish new design internal pressures guaranteeing a safe performance of the equipment.

Copyright © 2017 by ASME
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References

Figures

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Fig. 1

Typical shop-welded, flat-bottom, storage tank with proposed semicircular top clean-out

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Fig. 2

API 12F finite element tank model: (a) view of the bottom plate and shell mesh and (b) view of roof deck and shell mesh

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Fig. 3

Typical roof-to-shell joint. tb is the thickness of the roof plate, wc is the maximum width of participating shell, wh is the maximum width of participating roof, Rc is the inside radius of tank shell, and tc is the thickness of the shell plate (3/8 in = 9.5 mm).

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Fig. 4

(a) Typical rafter's configuration and (b) central column and rafters detail

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Fig. 5

Typical welded joint

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Fig. 6

Stress–strain curve of mild steel material

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Fig. 7

Wind pressure distribution around the circumference of the cylindrical shells

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Fig. 8

Springs arrangement on the tank bottom

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Fig. 9

Effect of the tank height in the top joint yielding failure pressure. Shell thickness 4.8 mm (3/16 in).

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Fig. 10

Effect of the tank height in the top joint yielding failure pressure. Shell thickness 6.4 mm (1/4 in).

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Fig. 11

Relative strength ratio (shell-to-bottom strength/roof-to-shell strength) for tanks with 3/16 in (4.8 mm) shell thickness

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Fig. 12

Relative strength ratio (shell-to-bottom strength/roof-to-shell strength) for tanks with 1/4 in (6.4 mm) shell thickness

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Fig. 13

Yielding pressure and uplift pressure for tanks with 3/16 in (4.8 mm) shell thickness

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Fig. 14

Yielding pressure and uplift pressure for tanks with 1/4 in (6.4 mm) shell thickness

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Fig. 15

Buckling pressure versus roof-to-shell yielding pressure

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Fig. 16

(a) Typical roof-to-shell joint buckling mode and (b) typical shell-to-bottom joint buckling mode

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Fig. 17

Load proportionality factors for tanks subjected to internal pressure and vacuum. Tank diameters: 9.5 ft (2.9 m), 12 ft (3.7 m), 21.5 ft (6.6 m).

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Fig. 18

Typical buckling mode for a tank built with imperfections and subjected to: (a) internal pressure and (b) vacuum

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Fig. 19

Typical tank model subjected to internal pressure until rupture or plastic collapse

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Fig. 20

Typical internal pressure–strain curve

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Fig. 21

Average rupture-to-yielding ratios for tanks with 3/16 in (4.8 mm) shell thickness

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Fig. 22

Average rupture-to-yielding ratios for tanks with 1/4 in (6.4 mm) shell thickness

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Fig. 23

Stress levels of a tank near the clean out

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Fig. 24

Uplift distribution for a typical tank base. Units in inches. (1 in = 25.4 mm).

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Fig. 25

Scaled deformation and stress levels due to wind pressure (stresses in psi) (1 psi = 6.89 kPa)

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