Background

Although various efforts are undertaken during the design, engineering, fabrication and operation stages of offshore structures to avoid fatigue cracks, the operators are obliged to periodically inspect the structures for the presence of cracks. Cracks that are too long for safe operation must be repaired. Cracks of an acceptable length must be followed up during successive inspections. However, the uncertainty of crack growth rates means it is not known when the cracks will reach their critical lengths. Therefore, operators either increase inspection frequency or reduce the allowable crack length, which leads to higher operational cost.

Interviews with offshore operators revealed that they seek an affordable, simple and robust system to monitor the length of detected cracks. Such system should only warn the operator when a crack has reached its predefined unacceptable length. The overall costs of the system should be competitive with the cost of additional visual inspection by a surveyor.