Welding of A193 B7 material 3

[Italo01]

Hello,

In this thread (

https://www.eng-tips.com/viewthread.cfm?qid=157518),

metengr asserts that "it is not permitted to be welded under ASME B&PV Code" relative to ASTM A193 GR B7 material. I tried to find the clause but wasn't able to.

Does anyone know what specific clause of ASME B&PV prohibit the welding of this steel?

Thanks.

 

[gwalkerb]

There's not an explicit clause that says 'Though shalt not weld A/SA-193 Gr B7'. However, take a look at QW-421.1 in Section IX. SA-193 Gr B7 is not listed in table QW/QB-422. To treat it as an unlisted material, you would need to have an equivalent UNS designation. SA-193 does not list a UNS designation for B7, so how could you even try to apply an equivalent P-Number based on UNS?

And then there's also just good engineering judgment. Understanding how the strength of B7 is based on it's specific heat treatment processes, it is obvious that uncontrolled heat input from welding would have deleterious effects on this strength. This article, while not specifically referencing the BPVC, provides more explanation.

https://www.portlandbolt.com/technical/faqs/welding-high-strength-anchor-bolts/

 

[r6155]

DO NOT DUPLICATE POST !

Regards

 

[MJCronin]

I believe that 99% of the time that this question is asked, it is because the original poster wants to provide "locking" for existing nuts on existing flanges.

He has either forgotten to provide a locking mechanism, or his psychotic client has imposed this locking criteria late in the project cycle ... Either way, the nuts, bolts and studs are already installed, and the piping fabricator offers to " weld sting" each and every nut as a "quickie fix".

There are other reliable options for providing locking mechanisms for studs, nuts and bolts ...

Well, here is the problem ...

----- While this is a quickie fix and it has been done before, it is not permitted by SOME STANDARD INDUSTRY PRACTICES (Shell EXXON and NORSK, for example) it can compromise the fastener and ruin both the stud AND the nut

----- If indeed that this is to be a "fix" to an existing system, there will be flange locations that are physically inaccesable to the welder/fitter and he will ask if it's OK to skip the fasteners that he cannot reach

----- A situation where there are some flanges with locked fasteners and others where there is not can be very dangerous

----- If this situation is the result of a Project Management/MBA proclaimation that "ALL NUTS MUST HAVE LOCKING BY WELD STINGS" .... well, inept and inexperience project management has cost billions of dollars in the past. Not all flanged systems require positive fastener locking

MJCronin
Sr. Process Engineer

 

[Italo01]

Hello,

Sorry for the late response and sorry for the duplicate post. I posted first in this forum but then thought that the forum about bolier and pressure vessel could be more adequate due to the quoted code be directioned to Boilers and pressure vessels.

I asked this question only because of curiosity and not because i have a need to weld A193 Gr. B7 steel. I ended up reading the thread and saw the response but couldn't find the specific clause and asked here.

Thanks gwalkerb and thanks MJCronin. Although the question was asked just for curiosity, you gave valuable information.

 

[geesaman.d]

Not to derail, but this happened last week at a site installation. The hardware in question was not A193B7 but it was stainless 316 and the site maintenance manager went on a big loud lecture about how he's not signing off on anything unless the fasteners are welded because it costs them a boatload of money to enter the vessel and broken / loose hardware that goes down the vessel drain damages expensive equipment.

Long story short, they had spec'd double nuts and we compromised to allow a small tack weld across the second nut to the protruding bolt end. We would have invalidated their warranty if it was a single nut or if they wanted to weld the bolt heads to the base metal. Clearly there was no communication between the corporate who wrote the spec and the site who insist on welding hardware together.

Their concern is valid - some competitors design and manufacture these parts in such a way that hardware failure and component failure in the vessel is common. Our components in the vessel only fail if installed or operated out of specification.

This seems to be a persistent issue for my industry - the site has welding capabilities and if they can 'fix' a problem using a welder, their site practices seem to evolve around welding being the solution to everything.

 

[DekDee]

Not in ASME but stumbled on this in API 560 today

12.5.6 If the minimum service temperature is –18 °C (0 °F) or higher, bolting material shall be in accordance with
ASTM A307, ASTM A325, ASTM A193-B7, or equivalent. Below –18 °C (0 °F), A193-B7 bolts with ASTM A194-2H
nuts, ASTM A320-L7 bolting, or equivalent shall be used. No welding is permitted on A320-L7 or A193-B7 materials.

 

[DKTim]

gwalkerb is correct. Nowhere in the code does it say you can't, but nowhere in the code does it say HOW you can.

First, understand that SA193 B7 is a pressure vessel/piping specification. We need to dig deeper to find the answer.

How does SA 193 B7 come to existence? it starts are AISI 4140, then a qualified/certified manufacturer does some machining and fills out some paperwork and it turns into SA193 B7.

Under ASME rules you'll have a very tough time getting a WPS/PQR for welding of 4140 material. However, ASME isn't the gatekeeper of welding.

But we do have to respect the code and what it can teach us:

4140 has high carbon content, above the ASME weldability limit of 0.2% (it has 0.4%, that's what the 40 in 4140 represents).

4140 also has really high YTS and UTS. So you can't use your typical ER70-S6 wire (again, the 70 in ER70 is the min YTS of the wire).

4140 is typically hardened & heat treated. It's not a good idea to weld heat treated material, but it is possible, and it is done a lot and in many industries.

Do a quick google search and you'll find real professional resources for welding of high carbon steels. I can assure you, it is done all the time.

Now the final part; ASME compliance.

1. Does your proposed weld affect/alter the SA193 B7 bolt in such a way that it would affect it's proof strength.

Yes example:
You want to turn a Stud into a Swing Bolt and use it on a pressure vessel closure.
You want to weld two studs together and use them on a flange connection.

Any other examples even remotely close to this will not be ASME compliant.

No example:
You want to weld the nut to the back of a stud.
You want to tack weld a washer to a nut.
This outside the scope of ASME, use good judgement.

You want to tack weld nuts to the back of a ANSI flange.
This is within ASME jurisdiction, you'll need a QPS/PQR to address that.