Hi Zakaria,
Dissimilar welds between Grade-91 to other lower alloyed steels e.g grade 11 and grade 22 are quite common. However a straight change from Grade-91 to Carbon steel is a Bad Design, unless the margins provided by the OEM takes care of the service induced damages.
A straight service induced damages could be a few as mentioned:-
- Grade-91 steel operates at very high operating temperature regime (550-560 Deg C), which is is not safe for P1 material. P1 materials in the vicinity of the weld is likely to get exposed to spheroidization (on exposure to this temperature range) and may result in failures by creep
- Thus welding of a intermediate or transition spool piece such as Grade-22 steel would be a better design.
Grade-91 to Grade-22 could be welded in a few ways, see the following tables for welding materials selection and subsequent PWHT.
You may qualify a WPS /PQR , however that does not always mean that the good engineering design basis is maintained.
Also please see below the comments on your queries.
Thanks
Pradip Goswami,P.Eng.IWE
Welding & Metallurgical Specialist
Dissimilar Welding Filler Metal Selection-
Recommended PWHT Temperatures (
0F) for Dissimilar Welds
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of Zakaria ghrab
Sent: Saturday, October 20, 2012 6:29 AM
To: materials-welding@googlegroups.com
Subject: [MW:15720] PQR - WPS - PWHT P91 to CS
Dear experts,
Need your support.
We performed one PQR P91 grade ( P number 15E) to Carbon steel (P number 1) welded GTAW/SMAW ER90S-B9 / E9015-B9, 11mm thickness, PWHT @ 740°C - 40 minutes.
PQR and related WPS already approved by our client. but the Owner consulting agency sent to us some comments :
1- No possible to weld P91 directly to CS shall add transition material P11 grade : We answer that it's design issue and i requested some explain / calculation from design. -- This is a good and conservative design. If accepted one may have to weld the transition pieces, i.e involving welds between P91-P4 & P4-P1 base metal.The PWHT may be controlled to the better extent such that the P1 base metal would not get over tempered.
2- Should use filler metal compatible with lower grade material : i answer that can make choice of filler metal between to material grades (included) so we can weld with lower, heigher or iontermediate filler metal when mechanical properties is ok and don't have ebjection from project spec. --If you're welding in the above sequence recommendation would be :
Need your support.
We performed one PQR P91 grade ( P number 15E) to Carbon steel (P number 1) welded GTAW/SMAW ER90S-B9 / E9015-B9, 11mm thickness, PWHT @ 740°C - 40 minutes.
PQR and related WPS already approved by our client. but the Owner consulting agency sent to us some comments :
1- No possible to weld P91 directly to CS shall add transition material P11 grade : We answer that it's design issue and i requested some explain / calculation from design. -- This is a good and conservative design. If accepted one may have to weld the transition pieces, i.e involving welds between P91-P4 & P4-P1 base metal.The PWHT may be controlled to the better extent such that the P1 base metal would not get over tempered.
2- Should use filler metal compatible with lower grade material : i answer that can make choice of filler metal between to material grades (included) so we can weld with lower, heigher or iontermediate filler metal when mechanical properties is ok and don't have ebjection from project spec. --If you're welding in the above sequence recommendation would be :
- P91-P4 -welds use -E/ER 8016/18 electrde/ filler metal
- P4--P1 -welds use -E/ER 8016/18 electrode/ filler metal
3- this is the main issue : PWHT @ 740 °c is heigher than lower critical temperature for CS so we must perform PWHT in intermediate Temperature : in this case if will do like this WPS will not supported by Prepared PQR; --740Deg Cis quite high a temeprature for P1 steel , which could cause over tempeating of this steel
PQR approved by Client and weld already done, i propose to perform hardness test, PMI and metallographic replic in production ( just one weld) to confirm.
Need your support .
Regards.
--
زكرياء غراب
GHRAB Zakaria
GHRAB Zakaria
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