Assessment Criteria and Burst Pressure Prediction for Pipelines With Long Blunt Defects

Corrosion assessment analysis and burst pressure prediction for an aged pipeline with blunt corrosion defects are essential to its integrity. It has been known that the flow stress based corrosion criteria including ASME B31G and PRCI RSTRENG are often conservative to use, but can be non-conservative in practical applications. The ultimate tensile stress based corrosion criteria such as PCORRC and LPC models largely improved the burst pressure prediction for corrosion defects, but the practice still showed certain non-conservatism of these newer models. This paper reviews and evaluates the commonly-used corrosion criteria. In order to improve the existing criteria for predicting burst pressure for long corrosion defects, three new theoretical models with consideration of strain hardening response for the corroded pipe are developed in terms of Tresca yield criterion, von Mises yield criterion, and a new multi-axial yield criterion, i.e., average shear stress yield criterion proposed recently by the present authors. The existing corrosion criteria and the proposed theoretical models are evaluated using experimental burst data for long machined defects and for long real corrosion defects removed from service. It is found that ASME B31G is over-conservative for long defects, but can be non-conservative for deep defects with intermediate lengths. RSTRENG is conservative for short defects. In contrast, PCORRC (or LPC) and the proposed ZL model predict reasonably conservative results for long corrosion defects.