This calculation indicated that the crack was not critical at the time of inspection. However, the team realized that the crack had grown over time due to fatigue.
The stress intensity factor is a measure of the stress field around a crack tip, and is defined as:
The team recommended that the pipeline be replaced with a new one, fabricated using a improved welding process and inspected regularly using non-destructive evaluation techniques. principles of fracture mechanics rj sanford pdf pdf work
The team used the following equation to calculate the stress intensity factor:
K = 85 MPa√m < KIC = 100 MPa√m
The team used the Paris-Erdogan law to model the fatigue crack growth:
da/dN = C * (ΔK)^m
The team concluded that the pipeline had failed due to a fatigue crack that had grown to a critical size. The crack had formed in the weld region, which had a lower toughness than the base metal.