Lessons Learned on Identification of Weld Overlay Locations During Pressure Vessel Survey

摘要

Weld overlay was applied on the exterior of an approximately 7 m diameter cylindrical steel pressure vessel in order to regain thickness lost to corrosion damage. Weld overlay is an attractive maintenance option as it is faster and easier than replacing original plate, but weld overlay may be detrimental to structural integrity due to modification of residual strains and the introduction of additional distortion. Therefore, it is vital that the locations and extent of weld overlay on the pressure vessel be identified to help determine any operation limitations. A survey of the pressure vessel was conducted in October 2009 during which geometric measurements, residual strain measurements, and measurements to locate weld overlay were taken. This paper covers the lessons related to weld overlay identification learned from the survey. Several technologies were used in an attempt to differentiate between weld material and base material: visual inspection, hardness measurements, chemical composition analysis, and electromagnetic interrogation. A map of the weld overlay locations was created from the various technologies. The survey resulted in a better understanding of the strengths and weaknesses of each technology and how to utilize them for future surveys, as well as strategies to improve calibration and data interpretation in the field. These lessons learned will help to improve the accuracy and fidelity of future pressure vessel surveys.