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Research Papers: Pipeline Systems

Develop Acceptance Criteria of Pressure Test of Buried Pipeline Using Uncertainty Analysis

[+] Author and Article Information
Husain Al-Muslim

 Saudi Aramco, P.O. Box 10217, Dhahran 31311, Saudi Arabiahusain.muslim.2@aramco.com

Amro M. Al-Qutub

Department of Mechanical Engineering, King Fahd University of Petroleum & Minerals, Dhahran 31261, Saudi Arabiaaqutub@kfupm.edu.sa

J. Pressure Vessel Technol 133(1), 011704 (Jan 21, 2011) (8 pages) doi:10.1115/1.4002263 History: Received February 27, 2010; Revised July 03, 2010; Published January 21, 2011; Online January 21, 2011

Hydrotest is one of the most important inspection activities to assess the integrity of pipelines prior to starting transportation of hazardous liquids. If the pipeline is buried, and welds cannot be inspected visually for leak, it is required that the hydrotest pressure is held for 24 h to ensure that the pipeline is leak free. Ideally the pressure should remain constant, but this is practically impossible due to changes in temperature. Pressure and temperature of the pipelines are recorded continuously and evaluated at the end of the test. The pressure drop should be in line with the temperature drop based on compressibility relationship. However, nonconformance is expected due to accuracy of the individual instruments used to measure the pressure and temperature. It is then ambiguous to the evaluator whether the nonconformance is attributed to small leak or to instrument accuracy. In this paper, general uncertainty analysis with parametric study is used in the planning and designing phase of pressure test. The objective is to develop an appropriate acceptance criterion for the pressure test of buried pipelines. Actual field hydrotests are used to illustrate and validate the outcome of the analysis. The results show that high uncertainty values reduce the validity of the actual hydrotest. This is because the test would most probably pass regardless of the actual pressure drop measured.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic illustration of typical set-up for pressure test of buried pipeline (10)

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Figure 2

Installation of temperature measurement device on the pipeline (10)

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Figure 3

Temperature chart for field hydrotest 1 (unit=°F)

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Figure 4

Pressure chart for field hydrotest 1 (unit=psi (gauge))

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Figure 5

(top) Change of pressure drop as a function of pipe diameter; (bottom) change of pressure drop uncertainty (%) as a function of pipe diameter

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Figure 6

(top) Change of pressure drop as a function of pipe thickness; (bottom) change of pressure drop uncertainty (%) as a function of pipe thickness

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Figure 7

Change of pressure drop uncertainty (%) as a function of temperature drop

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Figure 8

Change of pressure drop uncertainty (%) in terms of diameter uncertainty (%)

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Figure 9

Change of pressure drop uncertainty (%) in terms of thickness uncertainty (%)

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Figure 10

Change of pressure drop uncertainty (%) as a function of temperature uncertainty

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Figure 11

Temperature chart for field hydrotest 2 near the facility end (unit=°C)

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Figure 12

Temperature chart for field hydrotest 2 near the manifold end (unit=°C)

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