Structural integrity assessment of dissimilar girth welds in lined and clad offshore pipelines installed by the reeling method

Abstract

The increasing demand for energy has motivated the oil and natural gas exploration in very hostile environments, including very deep water operation and the transport of corrosive fluids. Technological advances favor the use of high strength steel pipelines either clad or mechanically lined with a corrosion resistant alloy (CRA), such as Alloy 625, for the transport of corrosive hydrocarbons. Moreover, these pipelines are subjected to severe installation conditions and a case of interest is the pipe reeling process which allows pipe welding and inspection to be conducted at onshore facilities. While cost effective, fracture assessments and specification of critical flaw sizes for the girth welds of lined/clad pipes become more complex due to the dissimilar nature of these materials and the high levels of plastic strain imposed during installation. In particular, effective analyses of crack driving forces in undermatched or partially mismatched pipe girth welds remain essential to determine more accurate acceptable flaw sizes for the piping system based upon conventional ECA procedures. This work focuses on development of a procedure to determine the elastic-plastic crack driving forces for pipe girth welds with circumferential surface cracks subjected to bending load for a wide range of geometries and weld mismatch levels based upon the EPRI methodology and its applicability to ECA analysis of undermatched clad pipe girth welds.