The existing welding practices and procedures used in conjunction with maintenance and tie-in welding on the Trans-Alaska Pipeline System (TAPS) have not been significantly revised since they were prepared shortly after original construction in the mid-1970s. The originally qualified procedures have served the operator, Alyeska Pipeline Service Co., well to date, and there is no evidence that the procedures are unsound. However, operating conditions on the pipeline have changed over time, while some new developments have occurred in in-service welding technology that may be appropriate for Alyeska to consider adopting. The purpose of this project was to examine alternative procedure options for avoiding hydrogen cracking during in-service welding on TAPS, and to recommend and assist in the requalification of new procedures, if required. The procedure requalification exercise that was carried out allowed the suitability of procedures to be demonstrated for the current and projected future operating conditions for TAPS using current industry-based guidance. The initial procedure that was qualified involves no preheating and a minimum required heat input of 40 kJ/in. The acceptability of these parameters under these conditions for material with a CE(ind.IIW) up to 0.42 is based on GSP results. Because of anticipated difficulty to reliably achieve a heat input of 40 kJ/in. in the field, a second procedure was qualified that involves a reduced level of preheating (from the level in the existing procedure) and a reduced level of heat input. The acceptability of these parameters under these conditions for material with a CE(ind.IIW) up to 0.39 is based on the results of the procedure qualification testing that was performed. The data from the procedure qualification exercise were incorporated into a single WPS by Alyeska. Analysis of confirmation welds taken in conjunction with an RGV replacement operation indicates that both procedure variations are suitable under actual in-service conditions for material with a CE(ind.IIW) up to 0.43.


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    Title :

    Maintenance welding on the Trans-Alaska pipeline


    Contributors:

    Published in:

    Publication date :

    2004


    Size :

    5 Seiten, 11 Bilder, 3 Tabellen, 4 Quellen



    Type of media :

    Article (Journal)


    Type of material :

    Print


    Language :

    English