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During the construction of a 56km long 16 in. carbon steel sour gas pipeline, repetitive surfacepreparation failures were detected during visual inspection of pipeline girth weld internal surface prior tocoating application. Such failures represented 67% of the total pipeline girth welds and were manifestedby excessive sharp-edges at the root pass. To identify the failure causes, an investigation wasperformed through reviewing the pipeline, fabrication and coating application specifications andprocedures, quality control records and performing an extensive visual inspection through an advancedvideo robotic crawler on all pipeline girth welds made. Upon investigation analysis, the failures werecaused by sharp-edges in the root pass which were attributed to improper practices duringmanufacturing, field fabrication and pre-coating quality control. The failure analysis indicated that themechanized Gas Metal Arc Welding process, with the parameters used, was not suitable for internalgirth weld coating application. In addition, a more stringent requirement should be applied to theacceptable pipe-end diameter tolerance and pre-coating quality control to ensure absence of similarpremature surface preparation failures. The pre-coating quality control can be improved throughutilization of robotic laser contour mapping crawler for precise detection and sizing of unsatisfactorysurface weldment defects, including sharp edges.
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The integrity of new pipeline projects is critical to Saudi Aramco to avoid any short or long-term impact on the supply of energy. During construction activities, pipeline internal welding inspection is carried out in compliance with international and Saudi Aramco requirements. The visual inspection of internally cladded girth welded pipes requires extra care to avoid any improper field fabrication errors during welding, especially at the root pass area. Such errors can limit the inspection capability and compromise the integrity of pipeline network with possible degradation of corrosion resistance at/near the weld rot, resulting in premature failures. Currently, projects utilize conventional tools such as borescope which is time consuming with limited inspection capabilities (up to 150 meters inside the pipe) and system maneuverability at inspection locations.The Saudi Aramco Inspection Department enhanced their active inspection technology program and collaborated with a local technology developer. They trialed a wireless crawler robot, which is a high resolution remotely operated robot capable of inspecting internal girth welds with 5000 meters travel capability inside the pipes. The robot can inspect internal girth welds in the field, and inside pipelines with internal diameters of 6 inches and above, and wirelessly transmits the visual inspection results to the outside control room for a timely assessment and critical decision making. The internal visual inspection with wireless crawler robot will help in improving the project progress, reducing repair costs, by identifying defective welds before coating application.
Conducting a materials failure analysis requires a carefully planned series of steps intended toarrive at the cause of the problem. Consistent with the current trend towards better accountabilityand responsibility, failure analysis purpose has been extended in deciding which party may beliable for losses, be they loss of production, property damage, injury, or fatality [1]. Hence itincreases the importance of proper implementation of characterization tools in failure analysis torightly identify the failure mode.Present work discusses a few case studies to shed light upon the importance of the metallurgicalcharacterization tools and techniques in identification of correct failure mode. Some typical casestudies where metallography plays a very important role have been discussed, such as improperwelding joints which led to premature failure, sensitization and stress corrosion cracking in S.S.,improper heat treatment and forging indicated the microstructures which led to the prematurefailure. These cases are examples of only a few laboratory based investigations which justify thatwithout metallography it is not possible to diagnose the causes of premature failures.Generally, examination of failed components commence with the low-power stereomicroscopewhereas hand-held magnifying lenses are still in wide use by experts to study fractures mostlylimited now for field purpose [2]. Metallographic examination typically is performed after nondestructiveand macroscopic examination procedures while using the light optical microscopywhich helps to assess the failure mode with respect to material defects, shortcomings inprocessing, metallurgical changes etc. Since light optical microscopy has limited value for directobservation of fracture surfaces (more limited for metals than non-metals), with still more factualinformation can be gathered by scanning electron microscopy at higher magnification.