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

Introduction

The ultrasonic testing method is an excellent volumetric diagnostic tool for examining ASME pressure vessel welds. As with any non-destructive examination (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 light on some very common industry problems that can be fixed with a better understanding of what is actually required.

This discussion is an attempt to explain, in very simple terms, key ultrasonic principles that govern the examination. The following discussion will address the discrepant areas which have been identified in this case study.

30 days prior to a major turn-around, delivery was taken on eight ASME Section VIII, Div. 1, pressure vessels. During the fabrication process, all the Category “D” nozzle welds required ultrasonic examination per the requirements of Appendix 12 of Section VIII, Div. 1 ASME Code. Upon delivery to the job site, receipt inspection revealed seven of the eight vessels contained poor workmanship with 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