ASME B31.8S states that the objective of direct assessment is to determine the integrity of a pipeline. A pipeline requires repair when corrosion features exceed 80% wall thickness or when the length and depth of a feature are such that the line is at risk of rupture. A series of case studies are presented to investigate whether direct assessment can identify such features. Direct assessment for external corrosion is carried out in four stages: pre-assessment, indirect inspection, direct examination and post assessment. This paper considers the accuracy of the first two of these stages because they define where an excavation and direct examination of the pipeline will take place. The pre-assessment phase requires the collection and collation of all relevant data from which a preliminary assessment of the line is carried out. In effect this will be a corrosion risk assessment of some form that serves to allocate relative risk scores to each segment of the line. The pre-assessment phase is critical and plays a key role in the definition of the excavation sites for direct examination. Indirect examination in most instances equates to a close interval potential survey (CIPS) and a coating defect location survey, usually some form of direct current voltage gradient survey (DCVG). The indirect examination phase of Direct Assessment lacks the required precision to identify critical defects. In practice this indirect examination is the step in the direct assessment procedure from which target locations are identified for excavation and direct examination. The data presented raises serious questions regarding the value of indirect examination surveys in the direct assessment procedure because the survey data does not show an acceptable correlation with the occurrence of corrosion features. This underlines the importance of the pre-assessment stage because a preliminary risk assessment based on the working knowledge of the pipeline and pipeline history should allow a pipeline to be divided into segments with different levels of corrosion risk.


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    Title :

    Is external corrosion direct assessment a valid approach for pipeline integrity management?


    Contributors:
    Argent, C.J. (author) / Frolish, C. (author) / Healy, J. (author)


    Publication date :

    2008


    Size :

    15 Seiten, 13 Bilder, 3 Tabellen, 8 Quellen



    Type of media :

    Conference paper


    Type of material :

    Print


    Language :

    English




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