Historically, the primary focus of direct examination (commonly referred to as "bell hole inspection") was to assess coating condition and describe the attributes of mechanical damage or corrosion in addition to verifying wall thickness, diameter and perhaps seam type. With recent regulatory emphasis on verifying the accuracy of pipeline data, the role of in-situ, nondestructive determination of metallurgical attributes becomes increasingly important.
This paper describes nondestructive analyses that can be performed on operating pipelines to evaluate steel composition, yield strength and tensile strength, hardness, microstructure, and crack morphology. The relevant technologies include visual examination, portable spectroscopy, laboratory analysis of steel filings, portable hardness testing, automated ball indentation testing, and metallography using replication techniques. The data can be used to support selection of optimized welding procedures, determine the lower bound yield strength of a pipeline segment at a selected confidence level, determine the acceptability of "hard spots" and weld heat affected zones, estimate toughness, determine the origin of planar flaws (manufacturing flaw, fatigue crack, high-pH stress corrosion cracking (high –pH SCC), or near neutral pH-SCC), and differentiate between electric resistance weld (ERW) seams having high temperature versus low temperature post weld heat treatments.
