Selection of line pipe material and specification of welding procedures are extremely important for successful arctic pipeline projects.  For arctic service based on limit state design, the behavior of the line pipe under bending must be fully understood.  An Engineering Critical Assessment (ECA) is usually required to establish an allowable strain level, and to specify allowable flaw size that can be accepted during welding of the line pipe.  Allowable flaw sizes are increased by specifying a combination of pipe with a low SMYS (X-52, for example), which typically provides good ductility, a special pipe chemistry, and a slight grade over-match of the weld electrode material.

Experimental testing may be necessary to validate the limit state design capacity of the pipeline.  For the BP Northstar design, a dedicated bend test program was performed to check collapse and fracture limit states.  The test program validated the high quality line pipe and welding process to be used for an arctic offshore pipeline subjected to limit state design conditions.  Pipeline non-destructive testing (NDT) capabilities and procedures are an integral component of this design process.