A Few Common Issues with Non-Destructive Testing (NDT)

August 2, 2010

(Predictive Maintenance and Condition Monitoring Management)

Many facilities shy away from Non-Destructive Testing because they don’t understand the technologies or the services their NDT contractors provides. Some struggle with how to implement NDT with their equipment. Below are a few tips to help you get started:

Insure that you understand the failure mode of the equipment. Take the time to complete a Failure Modes Effect Analysis (FMEA) on your critical assets. When you request NDT work to be completed, insure that you tell your technician exactly what you are looking for from a failure mode standpoint and where you expect the failure should occur on the machine. This will insure that they use the right technology and technique to best identify the specific failure defect.

Know your contractor. What are their capabilities? What training have they had? Have they had experience with similar equipments or failure modes that match your facilities failure expectations?

Specify what you expect in the NDT report. Make sure that your NDT technicians provide clear defect location identification so that you can find the defect later for repair and replacement.

NDT is not just a reactive technology. It can be used for more than known defect measurement. Use your critical equipment list and list of prioritized failure modes to design a NDT schedule that lowers risk of failure and allows for trending of the data. Once you trend your measurements you can see if defects are progressing and plan replacement or repair. Some defects just don’t progress and therefore can just be monitored.

Stainless steel offers unique challenges. If you have thin walled stainless and you are using contact ultrasound be aware that metallurgical structure changes at the site of a weld can mask defects. Also identifying pitting corrosion (the most common corrosion in stainless) by thickness test is not recommended.

Don’t limit yourself to one technology. None of the technologies, even when applied by a well trained individual in perfect conditions are one hundred percent accurate. By applying multiple technologies and complementary techniques you increase your accuracy. You might consider using Magnetic Particle Testing or Inspection (MPI) with contact ultrasound. These two technologies will complement each other increasing accuracy. You may see contact ultrasound used with a range of angle probes to vary the techniques again providing improved detection.

Lastly you will improve your results if you can make the analysis as easy as possible. Clear the area, clean the equipment, add platforms or scaffolding, and orient the area to be easily tested if possible.

All these can increase the overall value you receive from NDT and your NDT provider.

Shon Isenhour, CMRP and Neil Henry
ABB Global Consulting