P91 User's Group
The P91 User's Group is a Knowledge Management program set up by ETD Consulting to collect the latest experience with the steel P91 from around the world, then pass this information on to members through a series of regular reports that provide state-of-the-art knowledge and procedures.
Join P91 User's Group
If you are interested in joining the P91 User's Group and benefiting from international knowledge and experience please contact us.
The ASTM P/T91 martensitic steel is highly regarded in high temperature industry and its use as thick section components (such as headers, steam pipes etc.) and compact plants (CCGT, HRSG) has been very beneficial to the power plant industry in raising plant temperature and efficiency. However, plant experience indicates that this steel may be prone to mechanical problems such as Type IV cracking and steam-oxidation as well as problems caused by a lack of understanding of the material and inadequate quality assurance/inspection programs.
There are issues regarding the integrity and life assessment of the P/T91 components. This steel does not appear to show creep voids or easily observable and quantifiable microstructural damage until very late in life and therefore new methodologies need to be developed to account for this. One way of successfully managing performance and life of components made from this steel can be the development / use of appropriate monitoring and inspection methods and techniques for components made from this steel and therefore we need to learn from the existing experience of other plant operators and researchers.
There are concerns about tempering temperature limits for this steel. Similarly, there are also concerns about the criticality of the heat treatment of this steel after welding and forming operations. Other concerns have been raised about the time taken to do the post weld heat treatment after welding. Indeed, a number of manufacturers and service providers are still unsure of this aspect and some of the existing practices have indeed been questioned. In short, unlike the low alloy steels that the industry has had a good deal of experience with and where the industrial heat treatment could be relaxed within the achievable limits, the precise control of heat treatment of high alloy martensitic steels can be critical to its satisfactory performance and much needs to be learnt about this. Indeed, there are differences between the North American, European and Japanese standards and codes on the allowable limits and ASME standards, as a result, has formed appropriate sub-committees which are re-considering the recommendations by this standard.
What is the P91 User's Group?
All these aspects can result in failures relatively early in life, as experienced by some of the plants in the UK and elsewhere. Information from R&D work on cross-weld specimens and the testing of feature specimens of 9Cr martensitic steels appears to support this view. However, in the last decade extensive work has been conducted in both industry and academia to find solutions to the problems; resulting in improved heat treatments, advanced coatings and specific quality assurance and inspection procedures.
The need for this 'International P91 Users Group' was first discussed in December 2005 at a meeting held in London by P91 experts, plant manufacturers and operators. The Group aims to discuss many issues that today concern P/T91 producers, power plant/HRSG manufacturers and plant owners/operators using P/T91 - not just the power plant but also the petrochemical industry where use of this steel is now becoming better known.
The P91 users group has now been active for 7 years, providing a forum for the discussion of issues and producing 15 reports so far on P91 usage. ETD send's experts in the 9%Cr steels to conferences, events and plants around the world to discuss the latest issues and experience. The collected academic and industry knowledge is evaluated by our experts and useful information and solutions are provided to members through reports issued 3 times a year.