Deepwater and marginal oil and gas fields are often found to be at high pressure/ high temperature combined with high CO2 concentration in the production fluid. In order to develop the oil and gas fields with harsh environment, C-Mn line pipes is considered to uneconomical / nonviable and CRA Clad line pipes are increasingly selected for such situations. The CRA clad line pipe generally consists of C-Mn backing steel material with 3.0 mm (nominal wall thickness) metallurgically clad layer at the inner diameter made from nickel base alloys 825 or 625 or 316L stainless steel. Often small diameter line pipes (< 10" diameter) is made by joining two (2) 6m pipes using 309 Mo consumables.

These line pipes are typically welded on board the lay barge using 622 or 625 nickel base or 2509 super duplex consumables. The recent research has shown that the tensile and fracture toughness properties which is most important to ensure the integrity of the girth welds is very sensitive to the test temperature, specimen geometry, specimen sampling direction. Moreover due to planned and unplanned lateral buckling design the girth welds may be subjected to high peak strain/stress, sometimes in the range of 0.5 to 1.5% total strain. Engineering critical assessment (ECA) performed according to DNV OS-F101 appendix A is used to derive the weld flaw acceptance criteria for inspection of girth welds by automatic ultrasonic testing (AUT).

There are several challenges associated with HP/HT CRA pipeline such as i) under-matching girth weld as compared to the base metal yield strength, especially at elevated temperatures, ii) small tolerable flaws which are difficult to achieve with practical girth welding procedures iii) high noise level vs. signal during inspection of the girth welds using automated ultrasonic testing due to anisotropic nature of austenitic or austenic/ferritic weldments and CRA layer. Often welding specification requires that no detectable imperfections are present in the root pass and possibly also in the hot pass. The paper l discusses the above mentioned challenges in relation to HP/HT CRA pipelines and provides some solutions and guidelines for ECA of CRA clad lines.

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