Mig welding power piping

[Brew]

Hi guys,
I'm looking for some input about welding some SS piping. Currently we are using Tig on all our power piping, but I'm hoping we can improve our efficiency/costs by utilizing the Mig process.
Does anyone have any thoughts, experience or suggestions they would be willing to share? We must have full penetration on all our welds, and meet ANSI B31.1 requirements at a minimum(no concavity, porosity, lack of fusion, etc.).
Thanks for sharing your knowledge.

[Mike Sherman]

Brew, I am not as familiar with B31.1 as I would like to be. But I believe you will have trouble convincing the engineers to go with short circuit mig. Welding Journal had a nice article on using short arc mig for the root pass without using a purge. It was very informative and potentially useful. Flux core stainless is another option, but again engineers are not very fond of this. SMAW is a bona fide alternative. It is faster than GTAW. Please follow up on this if you find you are allowed to use GMAW on power piping. I have to go now or I would comment more, I need to get my Harley to the shop for it's 1000 mile check up before they close.

[Brew]

Mike, congrats on the new sled!

Engineering doesn't care how it gets welded, unless the customer specs out GTAW only, which is rarely the case. I cant recall seeing anything in B31.1 about which process is preferred, but I'll double check before I start making product.

One of my Mig weldors is experimenting right now, but without the success we're looking for. There have been some promising results using hard wire w/tri-mix and Argon purge, but we're not sure if that's the way to go or not.

BTW, what is SMAW?

Thanks,
John

[Seldom]

Hi Brew,
Like Mike, I’m not up on the B31.1, the B31.3 is my arena but I’d be shocked if the Project Engineers allowed it unless somebody sold him/her a bill of goods. I’ve had many years of experience with CS & SS mig-SC along with some nickel and I’ve found that anybody can run it, but few can run quality welds consistently with it!
As an example-
Two welders successfully pass ASME Sec IX 2G/5G CS pipe tests with mig-SC. One welder, welding in a shop atmosphere welds 6-16” SO flgs and when installed in a city water line (50psi) all welds leaked. That means 12-16” fillet welds couldn’t hold city water pressure! The other qualified welder welds an entire 3”xhy hydraulic system consisting of over 300 welds, many in fixed position and several were mirror welds under the floor. The finished system was hydro’d with hydraulic fluid to 3000psi and surged to 4500psi twice with no leaks (dust rolled out the building windows from the lines slamming the walls though)!

Without stepping on any toes and only making a general comment, mig-SC is pretty much unverifiable by radiography. Sure you can see internal porosity, and incomplete penetration but not “cold lap” unless it’s extreme and that’s a tremendous limitation hands down when it involves critical work! That’s why when you test to ASME (you’re familiar with that) it’s a bend test, no radiograph for mig-SC. Industry as a whole understands there’s a reason for that and it’s called cold-lap. I’ve observed projects using UT (ultrasonic testing) to verify short-circuit welds met a specified quality criteria (B31.3 & D1.1) but even then, nobody was comfortable with the results regardless of how well the calibration.

I’ve heard from other plant site engineering locations over the year’s negative thoughts/comments about flux-core SS and CS and each time I’ve asked specific questions trying to pin the problem down. Each instance I found the folks seem to have confused mig-SC or Inter-Shield with dual-shield (gas-shielded) flux-core. I guess if you’re a non-welding or welding educated person (engineers & designers) some processes all look and sound the same, I don’t know. LOL

When Shield-Bright SS flux-core came out back in the mid-80’s we used it over tig root on many projects including 16”xhy running at 1500 psi. Today, the vast majority of ASME pressure vessel and pressure piping, as well as structural steel fabrication shops that supply my old chemical plant site have and still use gas-shielded flux-core since the 80’s.
Please excuse the long post.

[Brew]

Thanks for the reply, Seldom!

We have to meet 31.3 quite often too. 31.1 has pretty much the same requirements, except doesn't require testing, just visual inspection. There may be other differences, but they are very similar in operation.

So should I use a backing gas with SMAW? What should I use? Also, what sheilding gas? Wire recommendations?

One other thing...we also have the opportunity to do some CS pipe, so I could use information on that process too, if you dont mind!


Thanks again,
John

[Seldom]

Hi Brew,
I’m sorry but I can’t answer your questions because it’s far more involved then what you’re asking for here on this Forum. I’ll try to explain, if you’re project specs require you to satisfy the requirements of ASME B31.1 (CO is a “code state”); you’ll have to satisfy the requirements of Sec IX as well. This means you’ll have to develop and qualify welding procedures and write subsequent welding specifications (welding recipes) and the welders doing the work will have to be tested/qualified in accordance with the same. This requires a formal initiative on your company’s part to develop and have this documentation available for review and most importantly, acceptance by the Project Engineer or Owners Rep.

[Ed Heimbach]

Mike , if you only have a 1000 miles on the bike, it's time to close the shop sooner.

[Stu Bass]

Re: Mig welding power piping

Originally posted by Brew
Hi guys,
I'm looking for some input about welding some SS piping. Currently we are using Tig on all our power piping, but I'm hoping we can improve our efficiency/costs by utilizing the Mig process.
Does anyone have any thoughts, experience or suggestions they would be willing to share? We must have full penetration on all our welds, and meet ANSI B31.1 requirements at a minimum(no concavity, porosity, lack of fusion, etc.).
Thanks for sharing your knowledge.

Brew: You might want to check-out MagnaTech orbitol welding systems at www.magnatech-lp.com and ask for Rich Collins or Ken LaDuc. What they use in essence is a adjustable track with a tig tortch with a squirt gun attatchment ( wire feed tig tortch?) Machines are expensive but they do rent. Something you might want to look at. Stu-169 p.s. e-mail no. is [email protected]

[Brew]

Seldom,
I know I'd have to write new WPSs and PQRs, but I need to find the process that works well first. As soon as I get comfortable with the process, we'll do some 6G tests, and write up the documentation. I just need some help with the process, as I've never done much in the way of SMAW in my career, especially SS.

Stu, thanks for the link. I'll check it out.

[Seldom]

Hi Brew,
I’m glad you are familiar with the code requirements. I have to be careful initially because many times I shoot over somebody’s head and that causes confusion.

I think you’re somewhat confused when it comes to the process designations so this’ll help-
SMAW- stick
GTAW- tig
GMAW- mig (hard wire)
FCAW- flux core

Flux core SS-
The flux core process requires a backing whether it’s a weld such as a root bead with tig, mig, or stick or an inserted backing.
So after you put a root in keep the purge on.
Use a SFA# 5.22 F#6 & A#8 filler for austenitic SS (you pick manufacturer)
Use Argon 75% & 25% CO2 with a 30 cfh (same as mig CS)
Reverse polarity
Volts- 25-27 (27 works pretty well on heaver wall)
Amps- 180-200
Use a stick type technique to apply uphill only.
Since you didn’t mention pipe size, wall thickness and diameter can be a limiting factor for you.

Mig-SC SS-
Open root-same as with tig including the Argon back purge
Drag the root downhill, balance of weld uphill
Use a SFA3 5.9 F#6 & A#8 for filler
Shielding gas- 95HE-4AR-1CO2
Reverse polarity
Volts- 19-23
Amps- 150-190
Tip- Grind between passes to blend pass edges before applying the next pass

I’m sure you already have tig & stick PQR’s.

[Brew]

Thanks alot for the input!

The only luck we're having with Flux core is BAD! Cant get punch to save our lives, until we blow huge garage door-size holes. We're practicing on sch10 3" pipe, beveled and gapped .062".

Seldom,
Do you always 2 pass w/ Mig-SC? You mentioned earlier that it could NOT be verified by radiography?

And thanks for clarifying the SMAW thing!

[Seldom]

Yikes! Hold up Brew no wonder you’re spinning your wheels, flux-core is the wrong process to use on 3” sch10 for code work especially! Tig or mig would be far and away better and an orbital weld would be better still depending on conditions and your spec requirements. Put the flux-core away and save it for something 3” sch40 and larger.

To answer your 2-pass mig-SC question- it all depends on your PQR and yes, radiography is not applicable to mig-SC.

[Brew]

Thanks Seldom! But I already figured that out!

The reasons I'm asking these Qs is because some of our outside vendors are definately not using Tig on the piping, and most of it is smaller than 3". It looks like FC wire to me, but since we couldn't get that to work, I thought maybe someone here would know a better/faster process. Maybe they're using stick, I dont know. I'll push our QC dept to get me their WPSs. I'll be back if it's FC or SC.

Thanks for all your help!

[Seldom]

Brew,
I think it's a hybrid mig sort of a pulse machine. It's called SSC or SST. Dang it my memory is going and my files are boxed. They (indusrty) say this mode of transfer allows for radiographic examination because of HOW it pulses in and out of spray transfer.

Just as I was retiring a local shop qualified it and they called me out to see it. I watched a shop welder do several 11/2" sch40 open root in the 5G position and they looked like wedding bands both inside and out. I also reviewed the film or those welds and they were flawless. 2 passes, one down, one up. I also saw it being used on a job for my company down in Hanging Rock OH on CS and it was great.