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Research Papers: Operations, Applications and Components

Local Hydrostatic Pressure Test for Cylindrical Vessels

[+] Author and Article Information
H. Al-Gahtani

Civil & Environmental Engineering Department,
King Fahd University of Petroleum & Minerals,
Dhahran 31261, Saudi Arabia
e-mail: hqahtani@kfupm.edu.sa

A. Khathlan

Civil & Environmental Engineering Department,
King Fahd University of Petroleum & Minerals,
Dhahran 31261, Saudi Arabia
e-mail: khathlan@kfupm.edu.sa

M. Sunar

Mechanical Engineering Department,
King Fahd University of Petroleum & Minerals,
Dhahran 31261, Saudi Arabia
e-mail: mehmets@kfupm.edu.sa

M. Naffa'a

Saudi Aramco,
Dhahran 31311, Saudi Arabia
e-mail: mahmoud.naffaa@aramco.com

1Corresponding author.

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received October 24, 2015; final manuscript received April 24, 2016; published online August 5, 2016. Assoc. Editor: Allen C. Smith.

J. Pressure Vessel Technol 139(1), 011601 (Aug 05, 2016) (6 pages) Paper No: PVT-15-1230; doi: 10.1115/1.4033533 History: Received October 24, 2015; Revised April 24, 2016

The juncture of a small cylindrical nozzle to a large cylindrical vessel is very common in the pressure vessel industry. Upon fabrication, it is required that the whole structure is subjected to pressure testing. The test can be expensive as it necessitates pressurizing the whole structure typically having a large volume. Hence, it is proposed to make a “local test,” which is considerably simpler as it involves capping the small nozzle and testing only a relatively small portion of the structure. This paper investigates the accuracy and reliability of such an alternative test, using the finite-element method. Two different finite-element types are used in the study, specifically a shell-based element and a solid-based element. The verification of the finite-element results for two different cases shows that the models used in the study are valid. It also proves that the two element types yield very similar stress results. In addition, the study includes a numerical investigation of more than 40 different nozzle-to-vessel junctures with a wide range of parameters for the nozzle and vessel. The results indicate that the use of cylindrical caps that are slightly larger than the nozzle is not recommended as it produces stresses that are significantly different from those for the original required pressure test. As such, the study provides an estimate of the smallest size of the cap that may be used in the local test to generate stresses that agree with the full test. For most practical geometries, it is shown that the size of the cap needs to be at least 2–30 times larger than that of the nozzle, depending on the geometrical parameters of the juncture.

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Figures

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Fig. 1

Geometry of the local test assembly

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Fig. 2

One quarter of a typical cylindrical vessel with cap

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Fig. 3

Finite-element mesh for the local test model (zoomed)

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Fig. 4

Comparison between shell-based and solid-based finite-element results for the axial stress (case I)

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Fig. 5

Comparison between shell-based and solid-based finite-element results for the hoop stress (case I)

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Fig. 6

Comparison between shell-based and solid-based finite-element results for the axial stress (case II)

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Fig. 7

Comparison between shell-based and solid-based finite-element results for the hoop stress (case II)

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Fig. 8

Normalized maximum stress versus cap radius for caseI

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Fig. 9

Minimum cap size (Rc)min for different values of Tv/Tn

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