Abstract: As a major carrier of long distance oil and gas transportation, the performance of large-scale deformation submarine pipelines is crucial. Reel-lay progress of submarine pipelines with large deformation develops from traditional s-lay and j-lay, which is an onshore welding and laying technique. During the process of reeling and laying, pipelines subjects to large plastic deformation which is over yield strength. The deformation is beyond the common mechanical application range of metal. Therefore, it is necessary to give an engineering critical assessment (ECA) of the pipelines for security. The mechanical evaluation of metal with defect on the plastic stage is crucial for the application of large-scale plastic submarine pipelines. The common method of ECA includes EPRI approach, reference stress approach and reference strain approach. EPRI approach is introduced, including the J-integral solution of pipeline with circumferential cracks under bending condition, the limit load solution of high and low mismatch V grove weld, and equivalent method of metallurgical clad pipe with V grove weld by slip-line theory. Reference stress approach is introduced, including the optimization of pipeline limit load solution and its modification under biaxial stress condition. The modification of reference strain approach is introduced, and it can be used in the evaluation of severe cracks. At last, advantages, disadvantages and application range of different approaches are summarized. Issues of ECA are proposed.

Key words: engineering critical assessment(ECA), GE-EPRI, reference strain approach, reference stress approach, slip-line pattern