The use of the potential drop technique for creep damage monitoring and end of life warning for high temperature components

Abstract

Electrical potential drop (EPD) is a well-established technique for the measurement of crack initiation/growth in metals. Two variants exist, one using AC excitation, the other using DC. EPD provides crack dimensions (principally depth) in contexts such as fracture/fatigue testing, and in-field NDE. Whilst it has been employed for on and off-line assessment of creep damage, use within a non-lab (i.e. industrial) context is limited by connection issues and, significantly, data interpretation – especially with regard to detecting subtle changes in EPD over general background ‘noise’. We describe, here, a methodology where high sensitivity detection of creep damage can be achieved by looking for a characteristic ‘signature’ within data. This is based on the combination of AC-EPD with its DC equivalent so as to generate a synergistic approach to damage detection. The methodology has been successfully applied to a semi-industrial context to provide prior warning of failure in excess of several weeks.

Keywords:

• Electrical potential drop
• EPD
• ACPD
• DCPD
• creep
• on-line monitoring

Acknowledgements

The authors would like to thank Dr. A Shibli and Dr. D Robertson of ETD Consulting of Leatherhead UK for their help and support in undertaking the work described here and MPA Stuttgart for access to their facilities and universally helpful staff (especially Dr. A Klenk and Dr. A Hobt).