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.
K = 85 MPa√m < KIC = 100 MPa√m
where ac is the critical crack length.
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:
The team compared this value to the fracture toughness:
The team also discovered that the pipeline had been subjected to a series of pressure cycles, with pressures ranging from 500 to 900 psi. These cycles had caused fatigue cracks to form and grow in the weld region. The team concluded that the pipeline had failed
K = (σ√(πa)) * Y
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.
da/dN = C * (ΔK)^m
The investigation revealed that the pipeline had been fabricated using a welding process, and that the weld had not been properly heat-treated. As a result, the weld region had a higher yield strength and a lower toughness than the base metal.
The team decided to apply the principles of fracture mechanics to analyze the failure. They used the stress intensity factor (K) to characterize the stress field around the crack tip.