Eddy Current Testing (ECT) of condenser tubes is essential to maintaining good plant reliability and availability. Early identification of defects can allow for adequate remedial action and prevent forced outages caused by condenser tube leaks. The well-known catastrophic failure in the nuclear industry in Japan has not only raised concern in Japan over aging nuclear power plants, but has also raised concern over safe operations in the United States and around the world. Ongoing reliability and instability issues due to reported leaks in condensers have also been the topic for nuclear watchdogs. This focus on the nuclear plant condenser has brought to light the various levels of sophistication and capability in ECT.
In ECT, the type of defect present in a condenser tube is determined by the characteristics it presents under test. The tubes must be adequately cleaned prior to testing and some awareness or evidence of the type of defect to be uncovered should be available to the testing team. In cases where defects are discovered that are inconsistent with prior awareness further exploratory testing is common. Exploratory testing can proceed to test areas of suspected defects in the tubing, and it may result in a complete redefinition of the test procedure, inclusive of instruments, probe types and other key ECT criteria. A comprehensive knowledge of testing options and their practical application is necessary to redefine a test that will yield meaningful results and achieve the intended objective; to identify the type and extent of defect and take remedial action therefore preventing failure.
This paper addresses such a case at the South Texas Project (STP) Nuclear Power Plant where peculiar defects were undeterminable under standard ECT procedures. The defects continued to negatively impact reliability and stability at the plant until a new ECT process and test procedure were developed, demonstrated and deployed. The result achieved was accurate defect detectability and improved nuclear plant reliability.