A Modified Criterion for Evaluating the Remaining Strength of Corroded Pipe

Research Agency:		Kiefner & Associates, Inc.
Author(s):		Vieth, Patrick H.; Kiefner, John F.
Publication Date:		December 1989
Pages:		133
Catalog Number:		L51688B
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Abstract:

The purpose of this project was to develop modified criteria for evaluating the remaining strength of corroded pipe that assures adequate pipeline integrity, while minimizing the excess conservatism embodied in the ASME B31G criterion. This project expanded the burst test database used to validate the B31G criterion by obtaining data from companies who have performed their own burst tests. The proposed criterion was made less conservative by modifying the method in which flow stress of the material is considered and by changing the format of the stress-intensifying effect of metal loss. The criterion presented can be used with detailed measurements of the metal loss and successive trial calculations to predict a minimum failure pressure for an area of metal loss based on its "effective" area. It is less conservative than the existing B31G method when used to assess the allowable length of a corroded area and when used to calculate a reduced operating stress level for all stress levels exceeding 55 percent of SMYS. It is more conservative than the existing B31G criterion when used to calculate a reduced operating stress level for stress levels below 55 percent of SMYS. In addition, the proposed new area representation permits more accurate (less conservative) assessments of long defects.