The effectiveness of the British Gas elastic wave in-line inspection tool for finding and characterizing cracks along DSAW seams was clearly demonstrated by its use in 42 miles (67.59 km) of Colonial Pipeline Company’s 32-inch (812.8-mm) OD Line 4. Fourteen crack-like anomalies were located and characterized. Subsequent cut outs of the anomalies revealed these to be cracks along and at the toe of the longitudinal seam. All initiated at the OD surface. Some apparently were transit fatigue cracks with no indication of growth in service. Others showed evidence of having been extended by fatigue from service-pressure cycles.
The sizes of the defects were such that they were too small to have failed if the pipeline had been subjected to a hydrostatic test to 100% of SMYS. This was demonstrated not only by calculations for the cutout anomalies, but by the hard evidence of burst test results in which the failures occurred at levels of 126% of SMYS and higher. The results show unequivocally that the elastic wave tool provides a significantly greater validation of pipeline integrity (assuming the located anomalies are removed or repaired) than a hydrostatic test to 100% of SMYS. The results suggest that the reinspection interval for the elastic wave tool could be significantly longer than the hydrostatic retest interval on an equivalent-risk basis.
