Utilizing On-stream Inspection Techniques in the Petroleum/Petrochemical Industry in Lieu of Internal and Turnaround Inspections

This is part two of a three part article describing some of the advanced on-stream inspection (OSI) methods available for use in inspection of pressure equipment in the petroleum and petro-chemical industry. These methods can be used, under the right circumstances, to supplement or in lieu of invasive and turnaround inspections, usually at much lower cost. Cost savings associated with using OSI techniques in lieu of internal inspections may include lower total inspection costs, lower turnaround costs, avoiding lost production opportunities, and avoiding vessel cleaning and decontamination costs. On-stream inspection also avoids the safety hazards associated with confined space entry of vessels. However, to achieve these savings and benefits, and still maintain high levels of pressure equipment integrity, the owner-user must understand the technologies in order to intelligently select, apply and interpret the results of these non-destructive evaluation (NDE) methods.
In part one of the article, we covered some pit-falls and precautions when using OSI techniques in lieu of internal inspections. Parts 2 and 3 of this article, provide some information on the main types of OSI techniques available, along with their advantages, disadvantages and relative cost.

Ultrasonic Guided Waves for Piping Inspection

One recent and important development in OSI NDE is the application of ultrasonic guided waves to piping inspection over long distances. This technique is capable of detecting internal and external corrosion as much as 100 feet away from where the sensors are mounted on the pipe. This distance may be considerably reduced by certain types of insulation, wrapping, and backfill. Applications include finding corrosion under insulation (without insulation removal, except for the small areas where you mount the sensors), finding corrosion on buried piping without digging up the full length of piping, finding corrosion under pipe supports without lifting the piping, and finding welds in insulated systems on which you may need to use positive material identification (PMI). The technique works best on straight pipes in the range of 4” to 12” diameter, and is a corrosion detection/screening technique, and not very useful for sizing. Welds, fittings, flanges, etc. can give false indications. This technique can also be used at temperatures above 200°F, but the launch and receiving attachments are limited to 200°F.