TesTex Graphitization Status Update Report
IntroductionTexTex is working on developing examination procedures for the detection and possibly classification of graphitization in carbon-moly tubing and piping. TesTex has performed examinations on five different sections of piping and tubing that was believed to contain graphitization using the Balanced Field Electromagnetic Technique (BFET). Listed below is a brief summary of each study.
- Sections of superheater tubes from two different plants that were near tube failures that occurred from graphitization examined at TesTex’s headquarters in Pittsburgh, PA. The superheater tube study proved successful in detecting graphitization.
- Sections of piping from the Homer City Station were examined with BFET. The pipe sections were from a high energy lines that failed due to graphitization. The study successfully detected graphitization along with detecting an area that showed a lower level of graphitization.
- TesTex examined some roof tubes and also a section of the superheater for graphitization in a boiler in New York. The indications noted by BFET were inclusions.
- A superheater tube inspection was performed in California for graphitization. Several indications were identified with BFET. Four of the indications were removed and a metallurgy examination was performed. Graphitization was found in two of the samples and the other two samples showed clusters of non-metallic linear inclusions/rounded oxides.
- Sections of the Kendal Station High Energy Piping were sent to EPRI. This line had been replaced due to it containing areas with graphitization. TesTex examined these pipes and identified several areas. Graphitization was detected on the EPRI study on the Kendall Station pipes, but no notable difference was detected in the severity of the indications called out by BFET.
- A study was performed in an effort to determine if Ultrasonic Flaw Testing could successfully detect inclusions in piping as an inclusion can also distort the BFET signal. Sections of the Homer City Pipe, Kendall Pipe, and some reheater pipe were examined. Suspect BFET signals were noted and the ultrasonic flaw testing showed possible inclusions at some of the locations. A core sample was removed in an area in the Homer City pipe that showed a BFET signal and no evidence of an inclusion through the ultrasonic flaw testing. A core sample was also removed on this same pipe where there was no BFET response for comparison. Both areas showed graphitization. EPRI’s Metallurgist labeled these indications as “Low Risk” and did not see any inclusions in the samples.
TesTex does have a few samples of High Energy Piping that is suspected to contain graphitization to conduct some further studies. To date, the only way to prove up the indications that are detected with our BFET system is to remove core samples which destroy our test pieces.
TesTex feels we need to collect additional samples suspected to contain graphitization. These samples would be labeled with unit details and would be tested with several BFET probes. Any indications found will be marked and their locations recorded. TesTex is hoping to continue to learn what the BFET thresholds are for detecting and sizing graphitization and also gain knowledge on how to distinguish between the severities of graphitization.
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