Detection of creep degradation during pressure vessel testing using electromagnetic sensor technology

Abstract

9%Cr steels have been in use in power generation for over 20 years. Over this time, there have been a number of incidents of failure by Type IV cracking at welds initiating sub-surface, making surface inspection procedures unsuitable for crack detection. Replication to identify creep cavitation damage can potentially give an early warning of imminent cracking, but has proved unsuccessful in high Cr martensitic steels. Electromagnetic (EM) inspection can provide fast inspection of welded components with minimal surface preparation and some increase in inspection depth. This paper shows the results of accelerated creep tests carried out on a P91 pressure vessel, with EM inspections during regular test interruptions. The results show that EM inspection gave indications of damage in the latter stages of creep cavitation. EM is considered to have the potential for quick assessment of component through thickness damage, flagging up locations of potential problems for more detailed investigation.

Keywords:

• Steel
• creep
• pressure vessel
• electromagnetic
• magnetic hysteresis
• magnetic Barkhausen noise
• P91
• weld inspection, Type IV cracking

Acknowledgements

Thanks are due to the ‘P91-P92 Inspection and Life Assessment’ project partners and sponsors, in particular Dr David Robertson (ETD) who led the project, Drs Andreas Klenk and Alexander Hobt (MPA Stuttgart) who carried out the pressure vessel test, and Michiel Lot (Laborelec) who undertook replication, micrographs and hardness testing. The authors would also like to acknowledge the UK Engineering and Physical Sciences Research Council for supporting the electromagnetic measurements under grant reference EP/K027700/1 (Advanced electromagnetic Sensors for Assessing Property scatter in high value steels).