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

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.