[315] Current progress in the use of potential drop for condition monitoring of creep in high-temperature/pressure industrial plant
A Wojcik1, M Waitt2, A Santos2 and A Shibli2
1UCL, UK
2Matelect Ltd, UK
3European Technology Developments Ltd, UK
Electrical potential drop (EPD) is a well-established method for laboratory crack growth measurement and in-field NDT. We describe here the application of the two separate variants of EPD (alternating current potential drop (ACPD) and direct current potential drop (DCPD)) to monitor the progress of creep damage in pressure vessel materials and components, in an online continuous monitoring context. ACPD and DCPD have been employed by the authors in a long-term programme, over four years, carried out on a range of specimens and vessels. The results have been very encouraging and have consistently revealed an ability to detect creep damage many months before final failure occurs and to stop long-term tests ahead of final fracture/failure, when close to a component’s end-of-life. A variety of EPD responses have been seen in tests, making data interpretation challenging, but not impossible. EPD readings can be influenced by a variety of phenomena, many unrelated to creep damage, so it has been necessary to develop an approach based on a ‘signature’ of EPD data from multiple monitored locations on a particular test-piece. The combination of AC with DCPD has helped deconvolute the various unrelated phenomena from that due to creep damage (which is sometimes much more subtle). We report on the methods employed, plus the practicalities of physically connecting to plant in the field, ways of ensuring long-term connection efficacy and reliability and the benefits of the combined AC/DC instrumental approach. We speculate on the possible extension of our methods to other time-dependent degradation mechanisms in industrial plant, such as high-temperature hydrogen attack (HTHA) and hydrogen embrittlement (HE). The overall methodology holds great promise for condition monitoring of power plants, pipelines and their end-of-life prediction.