High-Resolution Sizing Capabilities Required for Automated Ultrasonic Inspection of Offshore Pipeline and Catenary Riser Welds

摘要

The Canadian land-based pipeline industry pioneered the conversion of inspection from radiography to automated ultrasonics in the early 1990's as a result of adopting mechanized welding. The experience gained during that time provided the catalyst for conversion to AUT in the Gulf of Mexico in the mid-1990's. The first hurtle to overcome in the GOM was a conversion from the zonal approach of defect evaluation to a more quantitative defect sizing approach necessary for application to the Appendix of API 1104. This required a change in inspection philosophy that also introduced a sustained program of technology qualification not experienced previously in the Canadian industry. Inspection in the GOM involved a far more diverse set of inspection requirements as a result of heavier pipe walls, smaller diameters and a broader cross-section of bevel profiles. This combined with higher production and around the clock pipelay requirements changed the methodology and operation of the automated ultrasonic equipment working in the region. Exhaustive work by companies like Shell Oil to assist in qualification of the technology and development of additional inspection guidelines have set a new benchmark for technology requirements. These requirements have and continue to evolve the AUT technology for fracture-based applications and have become necessary for fatigue-based applications. The ever increasing capabilities of the higher resolving ultrasonic inspection technology has not only improved the process control for welding but continues to assist in reinforcing the safety level designed into pipelines as pipelay depths continue to expand.