welding of P91

Date 03-04-2005 00:51

You need to look at your WPS. The jobs I have been on that had P91 we did no do any intermediate PWHT. We kept the ceramics on at pre-heat temp until we were ready for PWHT, and then went right into PWHT. All the ASME codes give you some criteria. Sec. I B31.1. All that I have written is per our WPS.

By snbhakat29 Date 11-29-2006 06:11

Can you mail me WPS for ASTM 335 p91 to ASTM 335 p91 material,thickness 10 mm to 32 mm.
as per ASME sec IX latest edision.

s.n.bhakat

By chuck meadows (***)

Date 11-29-2006 14:28 Edited 11-29-2006 14:31

Please excuse me if I am speaking out of line or incorrectly, but according to Section IX, QW-201 "Manufacturer's or Contractor's Responsibility", mailing a qualified WPS is not ethical in my opinion. The WPS should be information taken directly from the data recorded during actual welding of a test coupon. In my opinion, you should do your own WPS with information taken from the PQR that you generated from the test coupon your company, or representative, actually welded. Please reference QW-200.1, "Each manufacturer and contractor SHALL prepare written Welding Procedure Specifications which are defined as follows:" It then lists the 5 different Code requirements. Also reference QW-200.2, "Each manufacturer or contractor SHALL be required to prepare a Procedure Qualification Record which is defined as follows:" It then lists the 6 requirements of the Code. In closing, I would not feel right by just e-mailing an approved and qualified WPS done by my company to someone that has not done the work to do his/hers own welding test coupon. Sorry, but this is just my own feelings. I could be very wrong, but this Forum is all about personal and documented issues. Thanks and no intentional hard feelings intended.

Chuck

By jon20013 (*****)

Date 11-29-2006 15:49

Chuck, I don't disagree with you, at least not completely. There is merit to what you say... all too often people will simply take what is provided them and work directly from that rather than qualiifying their own WPS... that is as wrong as it can get.

I have no problem providing copies of my company WPS/PQR to people I am well familiar with and who simply want to reference the variables I've used in order to perform their own testing, but providing this stuff upon request to people who have previously NEVER made a single posting in this Forum is treading dangerous territory. That said, I agree with you.

By chuck meadows (***)

Date 11-29-2006 16:42

I guess I was assuming that the WPS was requested to be used in production welding. To me, that could bring up a liability issue. Still, performing one's own WPS, derived from a qualified PQR, is the safest and most accurate way to proceed. Example, suppose a company shares a WPS with another intity and Company A's machines are correctly calibrated, and Company B's machines are not calibrated....Sharing a WPS is like saying that Company A knows this is a workable Specification, but Company does not get the same results. Personally, I would rather not get into that potential liability issue. Still, your points are well taken. Thanks..

Chuck

By 3.1 Inspector Date 06-26-2008 07:58

And you are not bothered with the untempered martensite?

Sorry, just looking through some P91 threads :)

By Jim Hughes (***)

Date 06-26-2008 12:48

I don't get the connection. Please clarify.
Jim

By 3.1 Inspector Date 06-26-2008 14:15

If you dont allow for full martensitic transformation(going into PWHT straight from preheat temp)
For P91 you need to let it cool to 80-100 degrees c before PWHT

By Jim Hughes (***)

Date 06-26-2008 16:31 Edited 06-28-2008 20:59

We go into a bake out cycle, bring it down to 200 Deg. F and then go into PWHT. I was incorect in my prevous post.
Jim

By 3.1 Inspector Date 06-30-2008 07:07

Jim,
I knew you either was confused because of my sometimes bad english, or you simply just misunderstood what I was trying to say.
In any case, I was sure you did not do as stated in your first post :)
But thanks for replying....

3.1

By chall

Date 03-04-2005 15:05

There is an opinion out there that if you use SMAW for the welding and will not immediately perform PWHT, it is a good idea to do an intermediate "bake out". Some say that this is to reduce the possibility of hydrogen migration.

We do an intermediate back out when we do heavy wall welds and wish to perform informational RT prior to conducting PWHT.

Charles

By snakejhj (*)

Date 03-09-2005 00:11

another question:i want to know the time of RT for P91 welding? before PWHT or after PWHT?

By ajoy

Date 03-09-2005 06:31

Chrome moly steels are prone to re-heat cracking. Thus most of the project specifications would call for RT before and after PWHT.

You may find the requirement in the applicable specifications. However, it is advisable to carry out RT after PWHT.

By andy

Date 03-09-2005 09:33

I agree with ajoy.

RT really ought to be carried out after all the processes (which usually involve heat) that have occured that could change the material have occurred - for example reheat cracking in some low alloy ferritics.

Commerically it is often good practice (espeically if it is a big weld) to inspect after welding but before PWHT to ensure that any defects that might need repair or rework are addressed before an expensive and time consuming PWHT is carried out.

By dragon

Date 06-30-2008 12:40

to PWHT P91, induction type heating equipment or resistance type heating equipment be deployed?

By js55

Date 06-30-2008 13:36

Resistance stuff is OK. Its used all the time. But induction won't work. You'll hit the Curie point before you reach HT temp.

By 803056

Date 06-30-2008 18:31

Are you saying that once the Curie Point is exceeded, induction heating won't work, it won't increase the temperature above the Curie Point?

What am I missing?

Best regards - Al

By GRoberts (***)

Date 06-30-2008 19:22

Induction heating only works on magnetic material. If you pass the curie point, it isn't magnetic anymore.

By js55

Date 06-30-2008 19:55

Induction heating will work above the Curie, but it takes a whole lotta power. A whole lotta power. We did thousands (literally) of induction bends on grade 91 at hot form temps higher than HT, but the machine was a beast. You wouldn't use something like that on stress relief. My problem then was draggin the input voltage down plant wide on some of my older welding power sources.

By 803056

Date 06-30-2008 20:36 Edited 06-30-2008 21:50

That's what happens when you don't have a "Honda" stand-by generator.

I agree that it takes a lot more power to heat nonmagnetic metals, but it can be done. I had two clients using induction heating for brazing. One was brazing pure manganese and the other brazing carbon steel. The steel heated up easily whereas the manganese took considerably more power to heat. However, I do remember both materials could be easily melted if the power wasn't controlled. As a matter of fact one of my other clients had an induction furnace for maintaining molten cast iron (at temperature for pouring) in a foundry. So, it will melt steel and iron. How much power is consumed is a different story.

I was under the impression most stress relief operations were performed at temperatures somewhat less than the Curie Point. I guess I have to go back and review my books to see what the temperature differential is between the Curie Point and the low temperature of transformation.

Is the issue due to the T1 of the P91 in comparison to T1 of plain carbon steel? And are we limiting the PWHT to simply stress relief below the T1 temperature?

Best regards - Al

By js55

Date 06-30-2008 22:18

You know Al, I do not offhand remember where the Curie is for Grade 91(I'll have to look it up-PWHT is 1400deg). I do know we hit a wall with only 25kw.
The guy at the quickie market next door had borrowed our Honda.

By 803056

Date 07-01-2008 02:12

:)

Al

By DaveBoyer (*****)

Date 07-01-2008 04:13

I dont know much about induction heating, but I do know that having the proper frequency for the job has a lot to do with efficiency.

By dragon

Date 07-01-2008 09:59

in the book <guideline for welding creep strength-enhanced ferritic alloys> of EPRI, states" Although induction heating techniques offer many advantages for preheating( fast upramps, welder comfort, etc), the technology does experience limitations due to the curie point on heavy wall (thick than 2-inch wall) P91 weldments."

By js55

Date 07-01-2008 13:18

dragon,
Good point. And if I may add to that. Its 2" and 16" diameter in consideration of cross sectional area. You can increase the thickness but must reduce the diameter. You can increase the diameter but must reduce the thickness.

By dragon

Date 07-27-2008 04:03 Edited 07-27-2008 04:07

Thanks j55, I saw lots of your post in this forum.

Have you ever used MILLER PROHEAT 35 induction heating machine?

Our owner require use induction heating machine to PWHT OD953*35, OD431.8*82 P91 weld joints, we did this with resistance heating machine before.

By js55

Date 07-31-2008 18:40

I have used the Miller induction machines. But its been awhile and I haven't kept up on it. Don't remember the trade names. They are quite good if you use them for what they are capable of doing and not more. We used them frequently on critical interpass regime materials. They are much faster than infrared, much easier than electric resistance, and much safer.
The folks you need to talk to though is Miller. Its their baby. I'm sure they would provide you with all the info you need.

By jeff parker (**)

Date 07-05-2008 16:40

every time I work with p91 when done welding on the fit for the day or finished with the weld all together you bake the weld at 600 degrees for a couple of hours and then after the weld has been shot (Xrayed) then they do the pwht. but those temps and procedures are different with each company and clients.

By Razor20 Date 07-29-2008 14:56

Holding the preheat is essential during the welding cycle. Our preheat/interpass range is from 400-600`F and held until all welding is done. After the welding is completed, the weldment is cooled to below 400`F but not less than 300`F and held at that temperature until placed in the oven for PWHT. If it become necessary for the temperature to be dropped to room temperature; then the weldment must be heated to 480`F and held for (2) hours and allowed to slowly cool to room temperature. I assume this is the intermediate heat treatment someone referred to. Care should be taken while handling the material to not drop the part, (shock) or subject it to a freezing temperatures. Also as previously stated, all the temperatures and times have to be qualified by the particular company welding the material based on the intended service of the end product.