Corrosion metal loss in one of the major damage mechanisms to transmission pipelines worldwide. The remaining strength of corroded pipe subjected to internal pressure loading has been extensively researched and guidelines for assessing corrosion are well defined. Methods including ASME B31G, RSTRENG and LPC have been developed, validated and matured to the extent that they are now incorporated in standards and regulatory requirements. However, these methods are based on the assumption that the pipe fails via a ductile mechanism, i.e., the line pipe material has sufficient toughness to prevent a toughness dependent failure. This limits the application of the existing methods to materials that have sufficient toughness. It is possible that some older pipelines operate with the material in the ductile / brittle transition region of the Charpy transition curve, or even on the lower shelf. It is also possible that under fault conditions, a pipeline normally operating on the upper shelf could be temporarily in the transition region. In these circumstances, existing assessment criteria may be non-conservative. At present there are no rigorous criteria available for assessing corrosion defects in low toughness pipe. This paper presents an approach for removing the uncertainty in the use of existing methods for assessing corrosion defects in older, low toughness pipelines based on the Beremin approach to brittle cleavage fracture. Comparison of the Beremin results with existing assessment methods allows an ‘effective transition temperature’ to be defined as the temperature at which the existing method is no longer conservative. The results suggest that, for the corrosion defects investigated, the effective transition temperature is sufficiently low that existing assessment methods will remain conservative.

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