P91/P92 Updated Information

[pjdobson]

I have read quite a few threads concerning P91 material, and a few on P92 material, but the information is a little dated (circa 2004/2005). There have been some updates to the ASME codes (allowable stresses, PWHT temperatures, etc.). Can anyone tell me if there has been any other developments with these two materials, or any other problems that have been experienced with these two materials in the past 12+ months?

 

[metengr]

pjdobson;
Yes. The ASME Boiler and Pressure Vessel code committees are finally taking a much closer look at these creep strength enhanced ferritic materials by implementing specific rules for separate PWHT tables, separate base metal qualification and numbers, and formability; bending and cold working strain limitations with and without post forming heat treatments.

Related to in-service failures, there are a number of users inspecting existing Grade 91 pipe spools and fittings pertaining to HRSG installation for the last several years. The main concern is improper heat treatment of bends and pipe spools during fabrication.

Grade 92 does not seem to have the reputation related to improper heat treatment because of use.

 

[pjdobson]

metengr: Thanks for the response and information. I would be interested in finding out the results of the HRSG inspections. Do you know how I can get access to that?

Pertaining to you comment on P92, I respectfully disagree that Grade 92 does not seem to have the reputation related to improper heat treatment because the chemistry of Grade 92 is very similar to Grade 91, and could consequently run into the same PWHT issues that Grade 91 encounters, especially if the Ni+Mn content is not fully taken into account.

 

[metengr]

Pertaining to you comment on P92, I respectfully disagree that Grade 92 does not seem to have the reputation related to improper heat treatment because the chemistry of Grade 92 is very similar to Grade 91, and could consequently run into the same PWHT issues that Grade 91 encounters, especially if the Ni+Mn content is not fully taken into account.

My comment regarding reputation in the above was from a use standpoint, where the use of Grade 92 is much less in comparison to Grade 91 pipe/fitting material in service. Creep strength enhanced ferritic steels like Grade 91 and Grade 92, do indeed share the same risks despite the fact the Mo in Grade 91 is substituted by increased tungsten in Grade 92 material.