The Inspection of Circulating Water Lines

The Xcel Energy – Harrington Station recently had a water leak where the circulating water pipe goes through the concrete basement floor. The ruptured pipe flooded the basement in a matter of minutes causing substantial damage to the plant’s motor controls. This section of circulating water pipe is susceptible to O.D. corrosion due to condensation that forms. The concrete prevents the piping from being examined from the outside; therefore most of the piping has never been inspected or replaced. The circulating water piping ranges from 36” diameter up to 72” diameter. Wall thickness ranges from 0.375” to 0.500”.

The inside diameter of these pipes have a thick rough scale which prevents performing a visual inspection. Xcel Energy has made it a priority to inspect the circulating lines in their plants. TesTex utilizes a Low Frequency Electromagnetic Technique (LFET) inspection method that can be used to examine these pipes. A four inch wide LFET scanner is moved across the pipe axially. The LFET method is able to detect changes in the wall thickness of the pipe as it is moved across the surface. This technology excites a driver coil to inject an electromagnetic field into the metal and uses pickup sensors to measure the response. The return signal increases when the scanner is moved across a thinned section of pipe and decreases as the scanner is moved across a thicker section. Any thinned areas found during the LFET scan are identified for ultrasonic thickness prove-up. The LFET inspection requires the ID scale to be sandblasted off. The surface does not need to be polished but the scale does need to be removed.

Xcel Energy had TesTex inspect the Cherokee Station #3 Inlet Circulating Lines in Denver, CO and the Jones Station #2 Circulating Lines in Lubbock, TX. The Cherokee Station Circulating Lines were carbon steel with a 48” OD and a nominal wall thickness of 0.350”. TesTex inspected a length of approximately 40” axially on these lines. Several indications were noted on each pipe. The ID surface of the pipe was rough due to pitting. A grinder with a flapper wheel was used to smooth the surface in order to obtain ultrasonic thickness readings. The lowest thickness reading found was 0.109” with all indications under 0.300” being reported to the customer. Each pipe took a two-man team one shift to complete.

TesTex inspected six pipe sections that penetrated through the concrete with a two-man team in five days at the Jones Station. The #2 East and West Manway Lines and the #2 East and West Discharge Lines were vertical. The #2 East and West Main Lines were horizontal. The Manway Lines had a diameter of 36”, the Main Lines had a diameter of 52”, and the Discharge Lines had a diameter 60”. All of these lines had a nominal wall thickness of 0.375”. Once the scale was removed by sandblasting, holes were visually detected in both discharge lines and one of the manway lines. The concrete behind the pipes has kept them from leaking. In addition to the holes, there were several areas found with less than 0.150” wall remaining in the two manway and discharge lines. The horizontal main lines did not show any areas with less than 0.200” wall remaining. The plant welded patch plates over the holes and thinned areas.

Xcel Energy has provided TesTex with the pipe specifications for their plants. TesTex is currently manufacturing curved scanners for the specific pipe sizes. The Low Frequency Electromagnetic Technique Inspection method has proven to be a successful way to inspect these pipes.

During the test, 6 areas of cracking were identified. The areas were repaired and then reinspected. The Hawkeye 2000 Inspection was completed in one shift. This allowed the plant to focus on other pressing issues during the outage.

If you have any questions on Circulating Water Line Inspections, please contact us at 412.798.8990 or click here.