The Use of an Eddy Current Inspection of Brass Tubes in a Surface Condenser to Provide a Condition Assessment

A Borelex, Inc. Power Plant in Ashland, Maine had a need to evaluate their Surface Condenser. The unit had 27 tubes that were previously plugged. The unit had steam impingement troubles in the past and the plant wanted to focus the inspection in this area. The condenser contains 6,084 tubes that are 7/8^″ OD, 0.049^″ wall, 303^″ long, admiralty brass. The plant decided to use the Eddy Current Technique (ECT) to inspect 600 tubes. The condenser uses local river water. TesTex told the plant the unit could be inspected and a color-coded tube sheet map showing the results could be completed in one shift. The contractor arrived at the plant at 7 am. The crew went through the usual plant indoctrination and safety training. Testing on the condenser using an Air-Assist System, the contractor was able to inspect the 600 tubes, perform analysis, and present a color-coded tube sheet map by 5 pm. A total of nine tubes showed wall thinning greater than 60%, which were recommended for plugging. The preliminary report provided listed the flaw locations and whether the defects were located on the I.D. or O.D. of the tube. In addition to this inspection, the plant also performed a hydro-pressure test to find any additional tube leaks. A few more tube leaks were found in areas that were not inspected with eddy current. These leaks along with the 9 tubes recommended for plugging were plugged. Prior to this inspection the plant felt the issues with the condenser were leaks in the joint between the tube and the tubesheet, where the tube has been rolled. The inspection showed the most severe wall losses found were on the O.D. of the tubes at various locations along the length of the tube. The tubes with wall losses less than 60% showed I.D. thinning at various places along the length of the tube. The effects of the tube plugging were that the water chemistry is better than ever and the vacuum pressure is higher than before.