Best Practice for the Assessment of Defects in Pipelines – Gouges and Dents

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  • Topic: Fracture mechanics, Charpy impact test, Pipeline transport
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Engineering Failure Analysis 12 (2005) 720–745
www.elsevier.com/locate/engfailanal

Best practice for the assessment of defects in
pipelines – gouges and dents
K.A. Macdonald
b

a,*

, A. Cosham

b

a
University of Stavanger, 4036 Stavanger, Norway
Penspen Integrity, Newcastle Business Park, Newcastle upon Tyne NE4 7YL, UK

Received 12 July 2004; accepted 13 December 2004
Available online 13 April 2005

Abstract
Oil and gas transmission pipelines have a good safety record and are a demonstrably safe means of transporting hydrocarbons. This is due to a combination of good design, materials and operating practices. However, like any engineering structure, pipelines do occasionally fail. The major causes of pipeline failures around the world are external interference and corrosion; therefore, assessment methods are needed to determine the severity of such defects when they are detected in pipelines.

Defects occurring during the fabrication of a pipeline are usually assessed against recognised and proven quality control (workmanship) limits. These workmanship limits are somewhat arbitrary, but they have been proven over time. However, a pipeline will invariably contain larger defects at some stage during its life, and these will require a Ôfitness-for-purposeÕ assessment to determine whether or not to repair the pipeline. Consequently, the past 40 years have seen a large number of full scale tests of defects in pipelines, and the development of a number of methods for assessing the significance of defects. Some of these methods have been incorporated into industry guidance, others are to be found in the published literature. However, there is no definitive guidance that draws together all of the assessment techniques, or assesses each method against the published test data, or recommends best practice in their application. To address this industry need, a Joint Industry Project has developed a pipeline defect assessment manual (PDAM). PDAM documents the best available techniques currently available for the assessment of pipeline defects (such as corrosion, dents, gouges, welding defects, etc.) in a simple and easy-to-use manual, and gives guidance in their use. PDAM is based on an extensive critical review of pipeline fitness-for-purpose methods and published test data. It is intended to be another tool to help pipeline engineers maintain the high level of pipeline safety. In addition to identifying the best methods, PDAM has served to identify a number of limitations in the current understanding of the behaviour of defects in pipelines, and the empirical limits in the application of existing methods. This paper discusses the PDAM project, in the context of both the current best practice available for defect assessment and the limitations of current knowledge.

Ó 2005 Elsevier Ltd. All rights reserved.
*

Corresponding author.
E-mail addresses: kenneth.macdonald@uis.no (K.A. Macdonald), andrew.cosham@penspen.com (A. Cosham).

1350-6307/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.engfailanal.2004.12.011

K.A. Macdonald, A. Cosham / Engineering Failure Analysis 12 (2005) 720–745

721

Keywords: Pipeline; Defects; Defect assessment; Integrity; Dent

Nomenclature
2c
d
t
A
CV
D
E
H
H0
Hr
K1
K2
R

r
rh
rY
rU

length of part-wall metal loss defect (mm)
depth of part-wall metal loss defect (mm)
pipe wall thickness (mm)
fracture area of a 2/3 Charpy specimen (53.55 mm2 for a 2/3 Charpy specimen) (mm2) 2/3 thickness specimen upper shelf Charpy V-notch impact energy (J) outside diameter of pipe (mm)
YoungÕs modulus (207,000 N mmÀ2)
dent depth (mm)
dent depth measured at zero pressure (mm)
dent depth measured at pressure (mm)
non-linear regression parameter
non-linear regression parameter
outside radius of pipe (mm)
flow stress (N mmÀ2)
hoop stress at failure (N mmÀ2)
yield strength (N mmÀ2)
ultimate tensile strength (N mmÀ2)

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