OVERCOMING MATERIAL AND TEST VARIABILITY CHALLENGES IN IN-SITU MATERIAL VERIFICATION

In-situ material property verification for oil and gas pipelines presents challenges and opportunities. One challenge is to limit undue increase in testing and maintenance costs which inherently occur if a generic conservative approach is used in the implementation of the new regulation requirements. This paper provides statistical data as well as case studies showing that measurements below the expected grade are not uncommon. Engineering analyses should allow for identifying outliers that present an actual risk while not overly increasing the industry-wide maintenance efforts. Here, the data from in-situ material verification at more than one thousand field excavations are fit to a normal distribution curve. Further analysis is provided for data points where an expected grade was provided as part of the field project. From 491 pipes with provided expected grade, there are several data points below the expected grade, but only three samples show a deviation of more than 8% below the minimum requirement. For samples with an expected grade of X52, the distribution from nondestructive testing is very similar to published distributions of laboratory test results, which also showed measurements slightly below the expected grade. Further analysis on pipe populations provides insight into how comparative analysis may help build confidence in verifying grade.