Not logged inAmerican Welding Society Forum
Forum AWS Website Help Search Login
Up Topic Welding Industry / Technical Discussions / Root Protection of ASTM A335
- - By ogola_alfred Date 06-23-2008 13:48
I want to weld ASTM A335 and was wondering when to consider root protection by having a backing gas. I mean, from what %age of chrome should root protection be considered? I'm thinking of grades: P5 (UNS: K41545), P11(UNS: K11597) and P22(UNS: K21590).
Thanks.
Parent - - By 3.1 Inspector Date 06-23-2008 15:32 Edited 06-23-2008 15:42
Above 3% Cr. Purgegas is a must.....
So you need purge when welding P5
Parent - - By 803056 (*****) Date 06-23-2008 19:40
By what standard?

Is this your personal opinion or can you direct us to a welding standard that requires purge gas on the root side of any base metal having more than 3% chrome? I'm not interested in an "in-house" requirement.

Best regards - Al
Parent - - By 3.1 Inspector Date 06-23-2008 20:01
ROFL...
Its not written in a welding standard
Good luck welding >3% Cr without purge

I asume TIG welding was to be used - my bad
Parent - - By pipewelder_1999 (****) Date 06-23-2008 22:53 Edited 06-24-2008 11:14
The acceptance criteria for ASME SEC IX, VIII, IX, B31.1 etc for the root side surface never addresses oxidation. Provided all of the other criteria is met, it may be possible. Will it look good ? NO.

I have made RT acceptable welds in alloys normally required to be purged by customer specifications that meet RT acceptance criteria for ASME SEC I and B31.1 (Edited, Was B31.1). These include 300 series SS and C-276. These were in situations in which the corrosion resistance of the material was needed for exterior surfaces.

I do think that it is easier to get a root in with backing gas. Flow is much nicer.

I hope your not ROFL at me. Im very sensitive :)
Parent - By 3.1 Inspector Date 06-24-2008 06:08
The "ROFL" was not at you.
And your post is correct
Parent - By pipewelder_1999 (****) Date 06-23-2008 22:46
There is an epri document that recommends this http://www.epriweb.com/public/000000000001012748.pdf .

But no code requirement.
Parent - - By Jim Hughes (***) Date 06-23-2008 20:29
ogla,
You need to refer to your WPS's for that information. It depends on how your welding procedures were qualified. If your P11 or P22 were qualified using purge gas then you have to weld using purge Gas.

Thanks
Jim
Parent - - By 3.1 Inspector Date 06-23-2008 20:40
Jim,
I interpret his question as he would like to start welding P5, P11 and P22 - which IMO means that he dont have a qualified WPS.

Unless he has to weld to some "exotic" criteria, there is no need to purge P11 or P22
Parent - - By Jim Hughes (***) Date 06-23-2008 20:56
3.1,
We have qualified P11 and P22 WPS's with purge in the Petro Chem industry to keep the root side clean. It depends on the application. On the other hand I have welded above 3% chrome content with no purge with no problem.

Jim
Parent - By 3.1 Inspector Date 06-23-2008 21:03
As for me saying "exotic" criteria, I meant like you said - it depends on the application, even in the oil and gas industri its not that common to purge P11 and P22
I really has a hard time thinking you have (GTAW) welded P5 without purge.....no offense.

Let me put it this way - I has NEVER made a PQR on P5 without purge - and I have done procedures for a third party company for more than 10 years.
Parent - - By pipewelder_1999 (****) Date 06-23-2008 23:02
With all respect, for ASME Sec IX, the variable for purge gas is non-essential.

With ASME Sec IX I can take two pieces of plate, lay them on the table flat, weld em, flip em, back gouge em, weld the backside and I have all the pqr I need for a WPS for pipe welded from one side with or without backing gas. This does not apply to ALL p numbers but in the context of this thread, I believe it does.

Codes of construction may modify this in some cases.

Have a good day

Gerald
Parent - - By Shane Feder (****) Date 06-23-2008 23:45
Hello guys,
This excerpt below was posted in 2005 in response to a question I posted.
Hope it helps,
Regards,
Shane

If you read "ANSI/AWS D10.8-96, Recommended practices for welding of Chromium-Molybdenum steel piping and tubing" in section 4.2 "root pass consideration" is mentioned that:

"...... the following common practices, which are based upon chemical composition of the filler metal, are often selected:
(1) under 4% Cr no back purging
(2) 4 - 6% Cr sometimes back purge (based on service requirements)
(3) over 6% Cr always back purge"

I can mail you the page from ANSI/AWS D10.8-96, if you need it.
Parent - - By pipewelder_1999 (****) Date 06-24-2008 00:09
Thanks for the info. Thre had recently been a lengthy discussion on the subject related to P91.
Parent - - By 803056 (*****) Date 06-24-2008 01:00
I am not a proponent of not using a purge where "high quality" welds are required. However, there are manufacturers welding stainless steel (304 and 316) everyday without purging the root side of the weld. Granted, there is oxidation on the root side of the joint, but it doesn't appear to affect the service life of the weld or joint in the operating environment they are expected to be used for.

My personal recommendation would be that if the service justifies the use of stainless steel, then it should be worthwhile to purge the root, but who am I to argue with success?

Best regards - Al
Parent - By pipewelder_1999 (****) Date 06-24-2008 01:38
In some cases that I have seen on boilers, the material is used for fireside corrosion/erosion or for its strength at temp (T22). The inside is steam so corrosion is not an issue.
Parent - By Jim Hughes (***) Date 06-24-2008 12:20
Al,
I believe Mr. 3.1 is referring to weldability. It makes it harder to weld the joint without purge using the GTAW process. If infact that is what he is saying then I would agree. But it can be done. We as a company have done it.

Thanks
Jim
Parent - - By 3.1 Inspector Date 06-24-2008 06:06
Correct - except, you will not get good result on P5 without purge
Parent - - By Jim Hughes (***) Date 06-24-2008 12:13
What do you mean "you will not get good result on P5 without purge" ? We have qualified procedures for P5, P5B without purge. I don't know what else to tell you.

Jim
Parent - - By Jim Hughes (***) Date 06-24-2008 12:29
At this time I would like to think the academy (AWS) for my third diamond. :) Also I would like to thank 3.1 and everyone else that posted responses to the original question. I'm starting to tear up now so I better get off the stage (forum) I love you mom. :)

Jim LOL
Parent - - By 803056 (*****) Date 06-24-2008 13:47
And the crowd goes wild with bands playing, women fainting, men cheering, dogs barking, little boys whistling, and babies crying at all the commotion!

Best regards - Al :)
Parent - - By David Liptrot Date 06-30-2008 05:19
On my current project, a refinery revamp job, we're using Cr Mo 1.25%, 5% and 9%. We're purging for the CrMo 5% and 9% as in addition to ASME B31.3 and ASME IX, our Client requires us to follow, API 582, Welding Guidelines for the Chemical, Oil and Gas Industries. In API 582, Clause 7.3 states that back purging is required for welding materials having a nominal chromium content greater than 2.25%. For purging gas, we're planning to use nitrogen.
Parent - By jon20013 (*****) Date 06-30-2008 06:38
We're getting ready to run some A336, F22 PQR's here; GTAW root & hot, SMAW remainder.  This is for High Pressure ASME B31.3 stuff.  Our intent is to run the PQR WITHOUT purge but to use purge during production. 

This is some very costly, highly critical stuff and although not "technically required" to use a purge, as Welding Engineer for our project it makes good engineering sense to me. 

Okay, so we pay just a fraction more, but hold one more ace up our sleeves to help ensure our success.
Parent - - By 3.1 Inspector Date 06-30-2008 07:13
I knew it was written somewhere :)
Is nitrogen cheaper than argon?
Have you qualified your WPS with nitrogen - as most codes has gas composition as an essential.

3.1
Parent - By jon20013 (*****) Date 06-30-2008 07:45
QW-408.8 addresses the deletion of purge but not the addition so if one qualifies without a purge one can add purge without requalification.  In addition, in my case we're using a P5A so the variable doesn't even apply.  For project, our specifications do not allow nitrogen purge and yes, nitrogen is typically lest costly than argon but we'll use argon anyway because it's not worth tryinig to get specification concession.  ASME QW-256 doesn't address gas composition for purge, only for shielding.

Hence, in my own case, there are things one does because they simply make good sense and others we do because code mandates.
Parent - - By Jim Hughes (***) Date 07-05-2008 01:48
API 582 is a RP. A guideline not a mandated code requirement. Sorry 3.1. Note: As we celerbrate our nations founding lets remember the men and women that have given everything to make this a great country.

God Bless the USA

Jim
Parent - By 3.1 Inspector Date 07-05-2008 05:25
I know what API 582 is...
Hope you had a nice 4th of July
Up Topic Welding Industry / Technical Discussions / Root Protection of ASTM A335

Powered by mwForum 2.29.2 © 1999-2013 Markus Wichitill