How Inferior UT Procedures and Practices on Pressure Vessels Cost $1 Million in Turnaround Repairs – Part 2

Introduction

This is Part 2 of a two-part case study discussing the costly repairs that were needed on newly fabricated pressure vessels. During the fabrication process, all of the Category “D” nozzle welds required ultrasonic examination per the requirements of Appendix 12 of the Section VIII, Div. 1 ASME code. Upon delivery to the job site, the receipt inspection revealed seven of the eight vessels contained poor workmanship and rejectable defects in the Category “D” nozzle welds. A total of 57 nozzle repairs were needed prior to placing the vessels into service. The discrepant areas identified in this case study are as follows:

• Inadequately written UT procedures
• Improper and poor implementation of the UT procedures
• Inadequate UT reporting
• Poorly trained UT examiners

Once again, it should be noted that the ultrasonic examination method is an excellent volumetric diagnostic tool for evaluating ASME pressure vessel welds. As with any NDE method, the application must be performed properly in order to provide reliable and accurate results. This case study is intended to provide a more user-friendly explanation of a presentation that was given during the 7th Biennial API Inspection Summit entitled “Unreliable UT Examination of Category “D” Nozzle Welds.” The purpose of this case study is to shine a light on some very common industry problems that can be fixed with a better understanding of what is actually required.

As was the case with Part 1 of this case study, this discussion is an attempt to explain, in very simple terms, key ultrasonic principles that govern the examination. The following is a further discussion of the discrepant areas identified in this case study. Please note Items #1-5 were discussed in Part 1, published in the November/December 2019 issue of Inspectioneering Journal.