Manufacturing defects of pipeline
Wall thickness variations are commonly found in seamless pipe, especially in the older designs. Specifications such as API 5 L for seamless pipe allow a maximum of 12.5% reduction on wall thickness. With wall thickness variation, the operator must consider whether these variations are acceptable (see attached picture).
Inclusions are a discontinuity (e.g. an area of manganese sulphide) in the microstructure of a steel. They can cause cracking if atomic hydrogen diffuses into these areas when operating in sour operating conditions, e.g. hydrogen-induced cracking. When operating in these conditions, a pipeline should be monitored through repeat inspections