Corrosion Detected in Pipelines using LFET
A former refinery site in Illinois is currently in the process of reclaiming the polluted land on which it sits. A major component to the reclamation of this brownfield site is the pumping of groundwater underneath the former refinery. The water is then treated to remove the contaminants. This also lowers the water table underneath the refinery, forcing surrounding groundwater to flow into the low spot. With this system in place, the contamination will not spread throughout the surrounding water table, which is primarily under residential areas.
The carbon steel piping that carries the contaminated groundwater to the treatment facility is critical to the process. Any unplanned down time caused by a piping failure could potentially cause the water table to rise and spread the contaminants to residential groundwater. With these conditions in place, inspection is vital to ensure that the piping is in good working condition, as well as to have contingencies in place for scheduled repairs.
Pipe specifications are as follows: 3″ OD x 0.216″ NWT Carbon Steel, 6” OD x 0.280” NWT Carbon Steel, 8” x 0.322” NWT Carbon Steel, 10″ OD x 0.365″ NWT Carbon Steel, and 12” x 0.406” NWT Carbon Steel.
Due to the heavily rusted surface of the piping as well as the existence of isolated pits, spot ultrasonic inspection would not be comprehensive enough; therefore the most practical method with which to conduct the inspection was to use the TesTex, Inc. developed 32-channel Linecat System. This system, designed for 360 degree pipe scanning, is based on the principles of the Low Frequency Electromagnetic Technique (LFET). The adjustable scanning system has the ability to quickly and accurately inspect multiple sizes of piping. The use of this system requires very little surface preparation; many times the removal of the insulation is all that is needed. When it is set up for a specific size, the system has the ability to scan the entire surface of the pipe between supports or obstructions. Pipes less than 10” in diameter can be inspected in just one scan.
Almost the entire inspection utilized the TesTex, Inc. developed Viper Magnetic Crawler to move the scanning array down the pipe. This ensured a constant pull speed and allowed the technicians to be located away from the pipe. This system also works well for piping which is difficult to scan manually, due to accessibility issues.
Fig 1: Linecat system with Viper Crawler
TesTex, Inc. was able to complete the inspection scope over the course of 4 days. The versatility of the Linecat System allows scanning pods to be easily added or removed, enabling it to scan many different diameter pipes using one system. Over 230 flaw indications were discovered and marked during the inspection. A-Scan Ultrasonics was used in verifying the indications; however some of the indications were confirmed by a third party using Automated Ultrasonic Technique (AUT). The AUT was only able to be performed on the sections of the piping that had the insulation removed. The un-insulated sections of piping had surface corrosion and pitting that was too severe to successfully perform the AUT.
Fig 2-4: Waveforms from the inspection, all depicting localized wall loss
0.062” wall remaining
0.067” wall remaining
0.025” wall remaining
After the inspection was completed, the site management team was able to plan the necessary repairs to the pipelines in areas below acceptable wall thickness criteria. TesTex, Inc. provided the customer with a fast and cost effective method to inspect their piping for pitting, wall thinning, and corrosion allowing the company to prevent forced shutdowns, while protecting the surrounding residential areas and water table from contamination.
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