Reliability of Inspection for Root Flaws in Riser Girth Welds

The fatigue loading on deep water risers leads to a requirement for the detection of small root flaws during manufacturing inspection. Mechanised welds for offshore pipelines are also subject to extreme loads during laying, leading to a similar requirement. Automated Ultrasonic Testing using zonal methods have been adopted as the inspection method of choice for these inspections, but there is little information in the public domain regarding the expected reliability of the various systems available. Extensive individual inspection qualifications are carried out for each installation. The extent of these could be reduced by the availability of such background information. This paper reviews data from joint industry projects in the area carried out by TWI, and compares results from these with such data as is available in the public domain. An analysis of future requirements and capability of currently available theoretical models for extending the range of qualifications is also given.