Types of Welding

Date 03-08-2007 15:53

These are base metal designations used to identify specific alloys for ASME codification, for example SA-335, or Section IX. In this case they are CrMo alloys generally intended for high temperature service. P9 is a 9Cr alloy, P11 is 2 1/4 Cr, alloy and P91 is a 9Cr alloy with creep resistant hardeners such Cb, and N, tossed in. P9 has been a traditional alloy in petrochem applications while P11 and P91 are more generally used in power piping applications.
They are welded with preheat and interpass temperature regimes, can be crack sensetive, and require PWHT.

By js55

Date 03-08-2007 16:02

And one needs to be careful in distiguishing the qualification P prefix's of ASME Section IX 9i.e. P1 thru P6X for example) and the alloy P prefix's of specs such as SA-182 or SA-335 (P1, P3, P5, and P91 for example). It is just a quirk of the industry that P prefix's are used for both. It has been a source of confusion.

By jon20013 (*****)

Date 03-08-2007 16:50

Walt Sperko, Vice Chair of ASME Section IX has an article on his website regarding welding of P91. Here's the link for info:

http://www.sperkoengineering.com/html/Grade%2091%20R%2010-05.pdf

By js55

Date 03-08-2007 16:57

There are also some excellent threads in the forum on Grade 91. M-Squared has frequently provided excellent info. Some good ones on P11 and 9Cr too. My suggestion is that these materials are not to be taken lightly. And a thorough knowledge is critical. Grade 91 especially (for power applications) is used in services of extreme pressure and temperature (main steams and hot reheats).

By jon20013 (*****)

Date 03-08-2007 16:59

Jeff, I could not agree more with your precautionaries!