Aberrant P91 and its inspection, monitoring and life assessment^*

* Paper for HIDA-7 Conference, University of Portsmouth, UK, May 2017.

Abstract

There have been many cases of power utilities around the world finding aberrant’ or ‘abnormal’ P91 base and/or weld metal components in their power plants. Although it is now well known that correct heat treatment is critical in achieving full strength of high Cr martensitic steels, it is clear that, for various reasons, many materials suppliers, manufacturers or welding companies have failed to realise this criticality. As a result, there is a worldwide problem with P91 base metals and/or whole welded joints that have not been heat treated to the Standards specifications and/or best practices, resulting in hardness levels below the acceptable limit and/or the microstructure not in the fully martensitic condition resulting in premature Type IV failures. To ensure the safe operation of such components, it is therefore important to generate long-term creep strength data on the typical aberrant microstructures often found in high temperature plant. The first part of the paper discusses this issue. To make matters worse, traditional NDE techniques are failing to find damage in high Cr martensitic steel components, including the more vulnerable components containing aberrant microstructures, at an early stage in life and as a result plant operators are finding it difficult to assure the safe performance of such components. In view of this, an international industrial community, led by ETD, started a three-year duration project on the development and demonstration on ‘normal’ P91 and P92 welded pipes, tested in controlled laboratory conditions, of new and more sensitive NDE techniques to detect such damage early in life and relate it to the component remaining life. Some of these findings will be discussed in this paper. A new project, open to new partners, on the testing of pipes containing ‘aberrant’ microstructure and further validation of some of the NDE techniques found to be more promising has now been launched.

Keywords:

• P91
• P92
• aberrant microstructure
• life assessment
• new NDE techniques
• heat treatment

Notes

* Paper for HIDA-7 Conference, University of Portsmouth, UK, May 2017.