PWHT essential or non-essential?

By jon20013 (*****)

Date 08-31-2007 09:27

Mr. Ver, your client is correct in this instance.

The Code paragraph reads a little difficult but essentially means any change in time, temperature, addition OR deletion of PWHT is an essential variable. Anything which would effect the mechanical structure of the weld (even if deemed beneficial) is an essential variable.

By js55

Date 08-31-2007 13:44

jon,
If I may, time and temp essential variables?

By jon20013 (*****)

Date 08-31-2007 13:56

Good catch, js55! Sorry for the confusion, only essentials when codes require notch toughness, hence those elements are Supplementary Essential Variables. Thanks Buddy! ;-)

By js55

Date 08-31-2007 14:06

jon,
Had to make sure. I haven't exactly kept up with Section IX most recently, and even though I know most of them fellas are quite conservative, it threw me because usually when it comes to IX if you say its so, its so. But I won't tell anybody.

By jon20013 (*****)

Date 08-31-2007 14:43

LMAO!!!! Thanks again Buddy, but to tell you the truth, I'm only smart enough to know how little I know when compared to the big picture! Speaking of which, I just got an e-mail from Damian Kotecki yesterday and he is officially retiring from Lincoln today... man, soon the folks here in the Forum will be the only ones left who hold any knowledge, lol!!!

By js55

Date 08-31-2007 15:02

Whoa!!! Damian retiring??
From just Lincoln, not the industry I hope. He just doesn't seem like the 'basking on a beach with a Pina Colada (spelling) in Boca Raton' type guy to me.
I suspect and hope he'll still be hangin around.
Though I wonder what the future holds for that vast article library he has in his office. Of course, its not like I haven't got enough to read already. Hold on a second I've misplaced my keyboard.

By jon20013 (*****)

Date 08-31-2007 16:07

LMAO!!! No, he isn't retiring professionally, just forming Damian Kotecki Consultants...

By Mr. Ver Date 08-31-2007 15:07

Thanks jon! It's one part of the code that's really confusing. I've just joined this forum today and this is my first posting. I came here by accident while searching for site hosting ASME code interpretations. I'm glad I found this. Browsing through some of the postings, I knew at once that there's a lot to learn from this site.

If it won't be too much of an asking, has anyone got some links where I can find ASME Interpretations? Particularly ASME-IX and ANSI B31.3?

Thanks again!

By jon20013 (*****)

Date 08-31-2007 16:06

Here is a good place to begin:

http://cstools.asme.org/csconnect/CommitteePages

Good hunting!

By Mr. Ver Date 09-01-2007 11:48

Hi again!

Thanks! The server however is not open for public. I get the following message when I follow the link
http://cstools.asme.org/csconnect/CommitteePages :

Web Server Security Alert

This website uses a special security software that monitors suspicious network traffic and behavior. If you feel that you have caused this security error unintentionally, please contact the website administrator at the address below and be sure to include the reference ID in your message.

Email contact: administrator@asme.org
Reference ID: 20070901373431

By Kraj Date 09-03-2007 08:04

Hi John,
Gone thru the topic and you gave the right direction. I have a case with me. As per B31.3 all the piping welds above 19.05 mm has to undergo PWHT. NDT of the weld has to be done after the PWHT. We got some repair and the repair welding is completed. Now, we have to re-do the PWHT to release the stresses induced during the welding.

Sceneria # 1. My Project team is recommending to have a separate PQR with 2 times PWHT as the actual weld and demonstrate that no changes to the mechanical properties and structure of the weld.

Sceneria # 2. My contractor says that after the first time PWHT, all the stresses are got released and the weld material is back to simailar condition of parent metal. when we do the weld repair, similar to first time welding the same amount Heat Input and other changes are occuring and after performing the second time PWHT all the stresses are released and the weld will be back to similar of initial weld.

I have to justify and agree with any one of the above sceneria and need to convince the other party. If you have technical suggestions, please guide me.

Regards,

By jon20013 (*****)

Date 09-03-2007 12:47

There may be an exemption for materials of these thickness, provided an elevated preheat is applied. If not, one might look into doing a temperbead PQR to avoid a second PWHT on PQR. My eyes are open for input from others.

By Kraj Date 09-04-2007 06:53

Hi John,
Thanks for your comments.
I have summarised the outcome of this issue and expecting the comments from our members.

The primary reason for PWHT is to relieve the residual stresses in a welded joint or fabrication. Stresses occur during welding due to the localised heating and severe temperature changes that occur.
This PWHT or Stress relief been carried out at 600 - 630oC, which well below the lower transformation temperature of 723oC.

Stress Relief
To release the stresses caused by welding. Hence this has been called as Stress relief by Mechanical Engineers.

Heat Treatment
To restore the ductility in the weld metal and lower the Hardness in HAZ. Thus why the metallurgist calls this as Heat Treatment.

As a result of first time PWHT [Stress relief] on welds, all the stresses induced on the weld joint to the extent of 80 - 90 % will be relieved and toughness will increase [Charpy impact] and Hardness will reduce. This will cause a slight reduction of Tensile strength up to 1- 2% and some cases there won't be any change also.

Now, we have done the repair on the weld and PWHT has been done second time on the same weld to relieve the stresses caused due to weld metal excavation by gouging/grinding and re-welding. This will relieve the stresses to the extent of 80 - 90 % and effect of toughness and hardness can be seen as explained in first time PWHT. Similarly, there may be slight variation [reduction] of Tensile strength. If our selected filler weld metal is just meeting the minimum requirement of material strength [> 5-10%] then there may be a chance for failure.

Please Comment
1. A separate PQR is required to demonstrate meeting of mechanical properties after second time PWHT
2. Separate PQR is not required and existing one time PWHT PQR is OK.

Regards,

By jon20013 (*****)

Date 09-04-2007 09:06

As long as the time qualified on the original PQR have not been exceeded your WPS should be valid for another PWHT after repairs, thats my opinion.

By js55

Date 09-04-2007 14:11

RT after PWHT is common with alloys subject to reheat cracking (CrMo's etc.), which I am assuming you are involved with. The solution that seems to work best is just to shoot before you cook. There is added expense to be sure, but if you price it up front (explaining in to your customer-whjich not only helps relieve your costs but demonstrates to your customer your knowledge of the alloy) you're good to go. In any case, the cost of shooting first could be much cheaper than repairs and cooking again, depending of course on your reject rate. As for time at temp, it is an engineering decision as to whether or not this is problematic. There is nothing inherently different with multiple PWHT as opposed to continuous PWHT for most alloys. Another heat treat just continues the process begun in the initial heat treat, (carbide precipitation, etc.). The good news is for most alloys the time at temp is a diminishing returns reaction. In other words the first hr will see a greater response than the 4th hour for most alloys.