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Up Topic Welding Industry / General Welding Discussion / Stainless back purge issues
- - By spgtti (**) Date 12-14-2008 05:56
    We have been working on jacketed 304 stainless lube-oil piping for a new construction coal fired power plant. The pipe consists of 26" sch10 jacket with a 10" sch40 carrier. The turbine manufacturer will not allow dissolvable purge dams to be used and there is no way to guarantee complete removal of cardboard or plastic dams. We have tried everything we know of to try and get a decent purge without using dams on this size pipe but now that the header has grown to 120' long it has gone out of our range of knowledge as to what to do.

  We have multiple liquid doer bottles hooked up along the length of the header w/ 3/4" air line hose clamped directly to the outlets on the tanks. The argon lines inside the header have rags taped over the ends of the hose to act as diffusers. We then use heavy plastic trash bags and duct tape to seal all the nozzles coming off the header as tightly as possible. Once everything is ready we hook an O2 meter at the far end high point and crack the valves on the tanks.

  It usually takes about 3 hours and 2 doers of pushing gas to get the meter below the required 1% reading. Even then when we start welding the roots are very dark and close to sugaring. We have tried all kinds of ways to deliver argon and pushed it in all different directions. We can't seem to get the volume of argon we need without creating turbulence and causing mixing with air.

  This is frustrating and unhealthy environment to work in and we aren't getting any information or ideas from supervision, management, engineering, or the manufacturerer. The pipe has now grown to the length where we probably won't be able to produce root welds that meet the acceptance criteria and we're tired of sucking tons of argon into our lungs anyway.

  I'm not on here to gripe or tear any one group down but everyone on our crew has always used soluble or manufactured dam plates for welding stainless which we aren't allowed to use or aren't manufactured for this application. I am just fishing for ideas at this point.
Parent - - By Superflux (****) Date 12-14-2008 06:37
Can you find an inner tube to fit the required O.D. and I.D.? A loose fit on the O.D. of the carrier dimension would be the most critical with a "permanent" hard pipe connection to the valve stem. Remove valve core first. Stabbing in the dark with you.
Parent - By spgtti (**) Date 12-14-2008 16:25
  Thats a great idea thanks Superflux, thats some awesome brainstorming. Unfortunately there are 1 1/2" round bar supports welded through the jacket pipe and weld to the carrier to keep the inner supported and centered. I'll have to try to bootleg some pictures off the site so everyone can get a better picture of what we're dealing with.
Parent - - By tim105 (**) Date 12-14-2008 08:15
I don't know if this is an option for you or not, our company would bring in a nitrogen tanker truck and we would purge with it. The root would still bediscolored but no sugaring.
Another option is to weld the root with 70s2 wire and it comes out nice and clean, but I believe that is one of those farm code procedures.
Parent - - By 803056 (*****) Date 12-14-2008 15:33 Edited 12-14-2008 15:39
I would be surprised if you can weld the root pass of 304 stainless with carbon steel filler metal without cracking. Never mind the metallurgical problems associated with the dissimilar filler metal in the root causing cracking problems, imagine the potential for corrosion problems when the line is put into service.

By the way, what is sugaring? You wouldn't be referring to root oxidation would you?

Now for something more constructive; is there an open end that would permit you to use an inflatable bladder to reduce the volume of argon needed to purge the area being welded? Some of the bladders  available can be removed through a fairly small opening after the weld is completed.

As for the complete removal of the paper dams; they seem to work in many of the systems I've seen them used on. It is usually a matter of flushing the system completely before placing it into service. Warm water will work better than cold water at removing the soluble dams. A demonstration for the upper management may be in order. Nothing like a good dog and pony show to get their attention.

Wee Haa!

Al
Parent - - By OBrien (***) Date 12-14-2008 15:58
Sugaring is the oxidation in the root and how it looks like burnt sugar.
Parent - By scrappywelds (***) Date 12-14-2008 16:34
call your gas supplyer and ask for a nitrogen tanker truck. if it is feasable to run the hoses in the building. we had on on a natural gas line system years ago, if i remember right we had a flowmeter that would put outup to a 1000 psi though a 1" hose. purged over a 1000' of 12" sch. 80  1 1/4 chrome pipe, with no problems.
Parent - By spgtti (**) Date 01-03-2009 18:23
Management has determined that a flush is not necessary and they'll just fill it with oil and circulate it through the filters, definitely not the brightest bunch we're working for .
Parent - - By cmays (***) Date 12-14-2008 16:41 Edited 12-14-2008 16:46
I usually use purge bladders that can either inflate on either side of the weld area or I use a purge damns(a rubber winged stopper on each end of a short, rigid or flexible rod with a gas diffuser in the middle)  on the smaller stuff. There are alot of companies that make and sell these parts over the web. Kind of pricey but thats what it takes to get quality welds in some situations. Arc-zone.com has alot of these parts thats who I usually use for this type of stuff. If your local supply store is anything like mine you will get nothing but "deer in the headlights" looks asking for this stuff. Thats why I had to turn to web based supplier. As for the nitrogen truck deal be very careful with that stuff. Nitrogen works fine for purging in some situations but you cannot be 100% sure that you have 100% nitrogen in those trucks. As long as you have an open end somewhere you can get the bladders out. Most of them have a cable ring on the end so you can pull them out with cable. They can even blow them out.
Parent - - By welder5354 (**) Date 12-21-2008 22:18
Spgtti, Lincoln has  a very impressive welding power source that can weld stainless steel without purging.
It is called the Power Wave 455m/STT.  Of course this is welded using solid wire (preferably 0.45.)
Ask your Lincoln rep about it or go online and look for info.  It may be a little difficulty to weld the sch 10,
but will not be a problem welding the SS sch. 40.
We have been welding root passes on duplex 4", sch 120 (no purge).  Very nice bead on the inside.
Parent - - By Lawrence (*****) Date 12-21-2008 23:29
Powerwave is nice. STT is nice

It will NOT remove a purge requirement...

The STT (surface tension transfer) technology allows for great open root pipe production in all positions... It is a Pulse style short circuiting transfer mode that can adjust automatically for slight discrepencies in edge prep and operator angles... It will not put a gas shield on the back of a weld that requires one.

Miller has a similar thing called RMD (regulated metal deposition)

Feronis has CMT Cold Metal Transfer.

All are speical inverter based short circuiting programs that can do amazing things.
Parent - By Shane Feder (****) Date 12-22-2008 03:51
Hi guys,
Got this off the Lincoln website regarding STT of stainless.

" An often-asked question is whether, using this low heat input process, welds could be made without backing gas. Although in practice welds are made without backing gas, it is not recommended for those applications where strict corrosion requirements are set."

You would think Sch 120 duplex has got some serious chemicals going through it so I am unsure how the use of STT unpurged complies with the specific corrosion requirements.
Regards,
Shane
Parent - - By Kix (****) Date 12-22-2008 13:57
It's a good idea to check the root opening with the o2 meter just as a precautionary method sometime.  We had this problem once and it was due to ice in the pipe.  Somehow one of the spools got water in it and frooze.  I don't see why they won't let you use a dam because they flush those lube oil lines to the turbine for a long time and keep checking it for debry below a certain micro level.  I guess you can never be to careful when it comes to the money spent on one of those jobs. ;-)
Parent - - By js55 (*****) Date 12-22-2008 15:25 Edited 12-22-2008 16:12
The idea of welding SS without a purge with STT has been abused from the very beginning.
The original paper on the subject was written by Pat Patrick at Fluor. It was subsequently published by the Welding Journal with ciritcal proviso's left out, to Pat's consternation.
The conclusion. It can be done. Is being done, but with limited application and non critical service. Certainly NOT Duplex.

PS:
Before doing it, I would read Pat's paper.
Parent - By welder5354 (**) Date 12-23-2008 05:50
Do you have that link to Pat's paper?
TKS
Parent - By ZCat (***) Date 12-22-2008 23:06 Edited 12-22-2008 23:09
You might try doing all your purging from the furthest point from the weld. Purging from multiple locations is probably just causing turbulence between the argon and the air in the pipe. I wouldn't bother with diffusers on that large a pipe.
Are you using high volume flowmeters? You need oxygen gauges modified with argon fittings.
+1 on water contamination inside the pipe, if you have water in there somewhere you will never get a good purge.

You might also be trapping air in the nozzles on top, try putting a small vent hole in the nozzle dams to let the oxygen escape.
Parent - - By tighand430 (***) Date 12-23-2008 05:39
If my memory serves me right, a couple of hands I worked with told me about some stainless rod that had a flux or somethin on it that kept them from havin to purge out the line. They said the contractor was usin it cause it was cheaper than havin to purge with argon. Only problem he said they had was that you had to be careful when tying in cause if you stayed too long it'd sugar. Other than that, everything else was good. I aint never welded with anything like that but figured I'd throw it out there.
Parent - - By Shane Feder (****) Date 12-23-2008 06:14
Hello guys,
This is all I could find on google relating to "Pat" Patricks paper.
It certainly looks like he is advocating the use of no purge.
Would be interesting to read what was in his original statement.

3:00 p.m.
Welding Stainless Steel Piping with No Backing Gas
For the first time in welding history, Fluor and partners are welding austenitic stainless steel with no backing gas (NBG) in shop and field. The achievement combines an inverter power source, high content silicon filler wire, and a tri-mix shielding gas to successfully produce quality Code welds that directly contribute to the reduction of overall welding and setup costs. A commitment to innovative thinking, quality improvement and reduction of construction costs moved "welding of stainless steel piping with no backing gas" from concept to reality!
Charles W. Patrick, Fluor Corp., Sugarland, Texas

Regards,
Shane
Parent - - By Flash Date 12-23-2008 10:25
Hi All
as TIGhand states there are flux cored tig wires available for SS
they require practice to use, but if client is worried about paper dams they will most probably get a bit upset about slag left on the root,
Further to comments re low Heat input on Duplex, mmmmmm be careful low heat input can be as bad as high heat input
low heat input does not allow time for the adequate dispersion of ferrite and you can end up with chromium nitrides and therefore cracking
It might be a bit out there but could you arrange a tube with a U shape at the end and put it thru the joint and point it to the back of the joint and get better coverage in addition to your purge and have someone foolow you around
let me know what you come up with
R
Flash
Parent - - By Shane Feder (****) Date 12-23-2008 21:15
Hi all,
This has turned into an interesting subject (hopefully I am not hijacking the post) but I was initially in agreement with Lawrence and Jeff that the welds couldn't be performed successfully without backing purge but after a bit of research I am unsure.
If you read some of the literature below it appears STT is being used "successfully" without purging on s/s pipes.

Miller RMD
Potential to eliminate backing gas. The shielding gas coming out of the gun remains relatively undisturbed by the controlled metal transfer of the RMD Pro process. As a result, enough shielding gas gets pushed through the root opening to prevent sugaring (oxidation) on the backside of the weld. Some fabricators have qualified procedures to weld some of the 300 series stainless steels without a backing gas, improving productivity by up to 400 percent.

Fluor Corporation
http://files.aws.org/conferences/abstracts/2003/11e.pdf

http://www.fiatech.org/pdfs/Roadmap2004/E4_FA4_P4.pdf

The original article written by Charles "Pat" Patrick would be very interesting reading especially if it has been re-released in the Welding Journal with some differences from the original.

Regards,
Shane
Parent - - By ZCat (***) Date 12-23-2008 21:39
I've seen that STT wire in action. It makes a decent root without purge, the problem comes in when the hot pass gets too hot and sugars the root.
Parent - - By welder5354 (**) Date 12-24-2008 03:51
Our facility as one of those Powerwave 400STT dual wire feeders and it is a fantastic work of art.
We can use one of the guns to weld the root pass and then pick up the other gun and complete
the fill and cap with flux cored wire without having to go back to the machine and program
the WFS and Trim or Voltage. Both wire feeder can be programed independed of each other.
    There are around 190 programs with the powerwave 400 welder.  Each program can be programed
to six different memory schedules.  Very easy to program for anybody, if you understand welding.
So far, i haven't seen and sugaring of the root passes.  I found that the .045 wire was much better
than the .035 wire for welding of first pass.  For those of you who have condemed the STT process,
then that means you haven't tried it.  I have read Pat's paper and it was very impressive.
The welder did the welds with the STT process and the procedure passed, so there lies the proof.
Parent - - By David Liptrot Date 12-24-2008 05:26
Anyone used Solar Flux in place of back purging?

What is SOLAR FLUX?

SOLAR FLUX is a complex chemical compound in the form of a very fine powder - finer even than a lady's face powder. SOLAR FLUX, is mixed with alcohol (methanol/methyl acohol preferred) and brushed on the back of the weld joint. It is formulated to shield the BACK of the weld joint from oxygen, dissipate heat and unwanted oxides, and to clean the surface of the metal. It will aid in the flow of filler metal over base metal and form a protective barrier to prevent re-oxidation and heat scale.
Type B for welding Stainless Steel and Alloy Steels
Type I for welding High Nickel Super Alloys

A USER'S COMMENTS

The following is the content of a letter mailed to us.

"The project is a new High Explosive Synthesis Facility. The process and the stainless steel piping is complicated. Quality control is essential. We set up to test a 3-inch 316 open butt weld at the 6g position using SOLAR FLUX in lieu of argon purge gas. I was amazed as I watched the stringer bead being welded. The joint was excellent. We had to have x-ray quality. The radiographer's first shot was an elliptical view and it was perfect. Then I asked for a contact shot and it, too, was perfect. I highly recommend SOLAR FLUX without hesitation."

J. R. Talley, CWI
Quality Control Superintendent
Kimmel Mechanical, Inc.

SOLAR FLUX type B conforms to the requirements of United States Military Specification MIL-F-7516B, classes 2 and 4.

SOLAR FLUX type I conforms to the requirements of United States Military Specification MIL-F-7516B, classes 1, 2, 3 and 4.

The shelf life of SOLAR FLUX that has never been mixed with a mixing fluid and remains in the closed can, is infinite.
All batches of SOLAR FLUX are compounded, manufactured, inspected, tested and packaged in accordance with our original formulas and patents, in conformance with accepted procedures and quality control requirements.

SOLAR FLUX is inert, non-flammable, and non-explosive. It can be shipped safely in any quantity by any means of transportation.

Certificates of conformance are available upon request on your purchase order.
Types of SOLAR FLUX
Certificate of Conformance for SOLAR FLUXSome of the Common Applications for SOLAR FLUX
Pipe and tube welding (except in those few cases where removal of the thin, glass-like residue is required)

Maintenance welding

In-field welding

One-of-a-kind welds

Unusual shapes and configurations

Large diameter pipes and ducts

Certain specified aircraft airframe and jet engine repairs

...... and many, many more
Parent - By Joseph P. Kane (****) Date 12-24-2008 18:40
I have used Solar Flux on two jobs where it was specified.  It worked as advertised. (At least I never heard any complaints.) On another job, an associate used it on a special flue gas scrubber assembly, and the product self destructed in a few months. He was sued out of business!

Before anyone does any welding on Austenitic Stainless, duplex stainless and other more exotic stainless base metals, or ANY other base metal where back purging is required, I urge you run the proposed alternate backing method (Including Nitrogen) past the NACE Corrosion Engineer.  The NACE Forum site is rife with weld problems associated with both normal and "deviant" welding practices.  In fact the NACE Forum Site has much more technical welding information on welding than the AWS Forum does!  There are horror stories about multi-million dollar vessels self destructing.  Some of these stories are real scary!
Parent - - By medicinehawk01 (**) Date 12-24-2008 22:46
I am not a big fan of solar flux.................. but it works. You might have to qualify a procedure and certify the welders who are going to be doing the welding, but in the long run you'd save a ton of money on argon and not to mention the health of the crew. While argon is inert, it displaces oxygen so you all might be at risk of starving you body of much needed oxygen. I get light headed thinking about what you guys are doing. Be careful and good luck.
Parent - - By spgtti (**) Date 12-30-2008 01:51
Solar flux, along with a qualifying weld test is what has finally been decided on. Although not the best answer it will end the predicament we're in now as the header is almost done and the smaller branch connections to the header are all that is left. The line is now almost 200' long and we are done trying to make acceptable welds with barely enough gas coverage.
Parent - - By 803056 (*****) Date 12-30-2008 03:53
Expensive lessons are to ones we remember the best.

Al
Parent - By cudaxtreme (*) Date 01-02-2009 04:57
Have you tried Hi-Selon?

Its 100% dissolvable if not burned.
Parent - - By 3.2 Inspector (***) Date 01-02-2009 19:39
May I ask why you constructed a 200 foot header, and waited to weld all the branch connections?
I am just curious as it seem a little backwards in my opinion.

3.2
Parent - - By spgtti (**) Date 01-03-2009 01:50
Because Kiewits freshly graduated engineers and professional resume writer superintendents don't know anything about basic pipefitting and won't listen to any of the craft on the job. Did I mention that this line is now hung 80' off the ground in rigging (no easy feat) with NO hangers installed. Welcome to the circus.
Parent - - By 3.2 Inspector (***) Date 01-03-2009 09:28
I almost feel your pain all the way to europe!

3.2
Parent - By spgtti (**) Date 01-03-2009 18:19
Oh its not just the trades either. QC guys are also battling management daily over ignored hold points and out of spec welds. No respect for anyones skills or knowledge just daily ego battles. I'll be easing on soon.
Parent - - By 522029 (***) Date 01-02-2009 15:08
Tighand,

This may be the link/product you are thinking about.

http://www.qwpinc.net/NEW/tigwire.htm

Griff
Parent - - By chris2698 (****) Date 01-02-2009 20:24
Griff that is pretty cool, I never knew you could tig the roots with no purge on stainless just useing this wire.

Does it weld alot different then if you were to purge a pipe??? I wouldn't mind getting some of this wire

Thanks
Chris
Parent - - By js55 (*****) Date 01-02-2009 20:51
What about the HAZ?
Parent - - By Shane Feder (****) Date 01-03-2009 00:45
Griff,
The only problem with flux coated or flux cored tig wire is the slag (and it is not easy to remove).
If the client will not allow water soluble dams I can hardly imagine them being keen on having root runs coated in slag with no way to get in and remove it,
Regards,
Shane
Parent - By 522029 (***) Date 01-03-2009 01:04
Shane,

Cannot argue with your points as they are valid and I have personally not used this product, just that I was aware of this filler.

Griff
Parent - By tighand430 (***) Date 01-03-2009 00:58
I'm sure that it's pretty much like using solar-flux. U just aint gotta mess with mixin the crap up an aint worryin about bakin it off before you finish welding.
Parent - By tighand430 (***) Date 01-03-2009 00:44
Yep, that's what it is. Not sure if that's what they was using but the same kind of wire.
Parent - By spgtti (**) Date 01-03-2009 01:56
It does leave a thick slag that is hard to chip off and welds crapier than solar flux.
Up Topic Welding Industry / General Welding Discussion / Stainless back purge issues

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