L52294 Corrosion Assessment Guidance for High Strength Steels

For the burst tests on high strength line pipe investigated in this report, standard assessment methods used by the pipeline industry generally give conservative failure predictions. For a small number of test points the ASME B31G, Modified ASME B31G and the LPC-1 methods gave non-conservative failure predictions when used to assess defect depths greater than 50% of the pipe wall. However, for machined defects, particularly those that are rectangular flat bottomed patches the use of ASME B31G and Modified ASME B31G to predict failure pressures may be inappropriate because the area of metal loss can be underestimated. Therefore the results need to be treatedwith caution. The RSTRENG method is the most reliable and conservative method forpredicting the failure pressure of corroded pipelines. RSTRENG predicts conservative failure pressures for defect depths up to 80% of the pipe wall in line pipe of strength grades up to X100. Modifying the flow stress to equal the arithmetic mean of the specified minimum yield strength and the ultimate tensile strength adds conservatism tothe calculated failure predictions. The non-linear FE method gives failure predictions within a scatter band of ~±10%, although in a number of cases the failure predictions are nonconservative. This level of scatter is typical. More accurate modeling of the geometry and material properties, to take into account of any through wall variation, should reduce the observed scatter.