Repair welding influence on offshore pipelines residual stress fields: An experimental study

• Repair welds change distribution of residual stresses in the weldments.
• This paper reports result of residual stress measurement in five different cases.
• Hole drilling and sectioning methods were employed to measure the residual stresses.
• Full repair increased the residual stress magnitude compared with partial repair.
• Repair repetition influenced on rates of residual stresses close to welding line.

Repair welds, are frequently used in steel structures either to remedy initial fabrication defects, or to rectify in-service degradations of the components. Some previous investigations indicated that repair welding is likely to pose adverse effects on the long-term integrity of the structure exposed to high pressure and temperature actions. It is believed that high residual stresses, associated with the repair process, most probably play an important role in many of subsequent failures. Repair welds might aggravate the size, magnitude and distribution of the tensile residual stresses in the weldments. These adversely affect the component structural integrity and remaining life. So far, no generally accepted guideline is available to provide reliable evaluations on the possible side effects from the repair welding in offshore oil/gas pipelines. This paper reports the result of residual stress measurement on single/double and partial/full repair welds in offshore pipelines. The semi destructive blind hole drilling and destructive sectioning methods have been employed to measure the residual stress fields in each case. In general, the results of the two measurement methods are in reasonable agreement. Residual stresses which are caused by full and partial repairs in the studied samples slightly increased the residual stress distribution when compared to the as-welded condition. Repetition of repair welding in same area influenced the residual stresses' magnitude and distribution especially in areas close to the weld centre line.