Preventing catastrophic failure of engineering components is critical during the exploration and production of oil and gas resources from the offshore deep-water fields. These critical components include the subsea pipeline system used to flow production from the seabed to the production unit platform at the sea surface. A viable alternative for transporting oil from the bottom of the sea (wellhead) to platforms is to use steel catenary risers (SCRs) because they have lower cost and higher structural capacity when compared to flexible pipes. However, the use of API 5L class structural carbon steel pipes can have a serious obstacle to the development of these new producing fields due to their susceptibility to corrosion. Pre-salt reserves are associated with high concentration of aggregated elements to hydrocarbons, particularly carbon dioxide (CO2) and hydrogen sulfide (H2S). In the presence of water (which is also invariably associated with oil and gas production), they can produce highly corrosive elements that can damage the entire pipeline system.  
One solution to this problem is to apply a metal liner made of corrosion-resistant alloy (CRA) internally to the carbon steel pipe. Such a bi-metallic configuration, commonly referred to as a lined pipe or clad pipe, consists essentially of a relatively thin CRA material pipe physically or metallurgically joined to the main carbon steel outer pipe. Although effective against the harmful effects of corrosion, the use of these bi-metallic pipes in subsea pipelines introduces several additional challenges. These include the fabrication of welded joints with dissimilar materials with obvious mechanical and metallurgical inhomogeneity, which give rise to specific working conditions that are not fully covered by traditional design standards. Another point of attention is the proper characterization of the fracture toughness of the circumferentially welded joint of these pipes using Single Edge Notched Tension (SET) specimens under these conditions. The main goal of this experimental study is the development of a methodology for calculating the fracture toughness at the root pass weld of the girth weld of a clad pipeline. Two methodologies are tested: the single specimen using the unloading compliance and the multi-specimen technique. The experimental campaign reveals the uncertainties in determining the fracture toughness (R curve) of the clad material. Defining uncertainty in toughness values is a key ingredient in the process of evaluating defect criticality. Generating this information for typically clad joints is another very important benefit for the industry, which will allow significant progress in assessing the structural integrity of this type of pipelines.


Comparison of J-R Curves Obtained by Single and Multi-Specimen Methodologies for a Pipe Having an Undermatched Girth Weld

Division / Sponsors: 
Pressure Vessels & Piping (PVP)


Paper Proceedings: https://asmedigitalcollection.asme.org/PVP/PVP2020/volume/83815

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