TWI Industrial Member Report Summary 1006/2011
By S J Maddox and C Johnston
Girth welds represent fatigue-critical features of steel catenary risers and sub-sea pipelines in locations where fatigue failure would be catastrophic. Validation or qualification fatigue testing of candidate girth welds is therefore required to ensure that safety is maintained. TWI has performed several thousand full-scale resonance fatigue tests on girth welds over the last 10 years and has therefore amassed a large database of fatigue test results obtained at ambient temperature in air.
Girth welds produced from one side are most relevant to the offshore pipeline industry and this review was confined to test results obtained from such joint. They currently conform to BS 7608 Class F2, representing a relatively low fatigue strength. However, this classification is not based on experimental data for girth welds and so there is a need to evaluate actual test data to determine whether a higher classification can be justified.
- Evaluate TWI's resonance fatigue test database for girth welds made from one side in full-scale steel pipes to identify trends that influence the fatigue performance of such welds.
- Determine the most appropriate fatigue design class(es) for single sided girth welds failing from the weld root.
- Evaluate data from weld cap failures to check whether the current classification of BS 7608 Class D is appropriate.