The use of Engineering Criticality Assessment (ECA) in offshore pipeline projects is now a common practice, in combination with Automatic Ultrasonic Testing (AUT). The ECA allows defining either allowable defect size for anticipated extreme load conditions or allowable stress and strains for pre-defined defect allowance as per good WorkManShip (WMS) standard. Sometimes ECA is linked to the specification of non-standard testing, e.g. to get allowance for defects significantly greater than the ones prescribed by good WMS standard or in the need for strain based design, in frontier projects where girth welds cannot avoid to tackle severe seismic environment and/or ice gouging effects (arctic and sub arctic offshore pipelines). The objective of the paper is the following: - to describe how to account for internal pressure in ECA of offshore pipelines subject to high (in the order of 0.5-1.0%) strains in service as an example due to bottom roughness or in service buckling; - to propose a procedure to account for the internal pressure load in a standard ECA as per BS 7910; - to discuss how to overcome the contradiction of strain based ECA using stress-based fracture mechanics models and relevant parameter testing; - to give recommendations on how to qualify the strength capacity of girth weld when strain-based design (greater than 1%) is a must.
The criticality of ECA on girth welds of offshore pipelines
Die Gefährlichkeit von ECA (technische Gefährdungseinschätzung) an Rundnahtschweißungen von Offshore-Fernrohrleitungen
2007
12 Seiten, 8 Bilder, 25 Quellen
Conference paper
English
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