CJP 316SS Plate 3

[novot]

Is is permisiable per AWSD1.6 to make a single sided CJP weld without a backing bar? Fabricator tells me that using an initial GTAW pass eliminates the need for backing and also for backgouging. Plate is typically 3/8" thick. Are there any additional testing or WPS requirements for this type of procedure?

 

[Koz]

Hi You,

Boy, this thread has been hanging around for a while. I guess the others were hoping you would buy D1.6 to answer these questions. It's really a good idea.

I'll pitch in a little.

Sure, you can weld without a backup bar, but you have to backgouge the root to get complete pen or qualify the WPS. GTAW into the air (open root) 1) is a one side only weld with no backing, just like a pipe weld and 2) is a bad idea without backing gas because your weld oxidizes. It may not matter if you are using this for strength only (like a wear plate) and not corrosion resistance. Yeah, there is plenty of testing required to qualify this procedure. Hundreds of dollars.

The welders have to be qualified to weld open root welds, too. You have to test them, too. Essential variables, doncha know

Maybe you should get your supplier to buy a copy of D1.6 so he quits blowing smoke at you.

Koz

 

[Koz]

Hi Novot,

My wife just smacked me for being such a wise guy. I'm sorry if I was offensive with my smart-ass answer. The data is good, the delivery stunk. That is the problem with the submit key. Sometimes it goes to quickly. I hope you take it in good spirit and I will try to be more considerate in the future.
Koz

 

[unclesyd]

Koz,
Have you seen any coupons with the NEW flux coated S/S TIG wire. I was shown two samples, 6" Sch 10 304L that looked pretty good. This was a 2 pass, walking the cup weld.
I didn't see them welded but they were supposed to have been welded with only the ends capped with no purge.

I'm try to get a 6" Sch 40 S/S coupon welded for a better check.

 

[Koz]

Hi Unclesyd,

You know, I have read about fluxed GTAW wire. I think it was in Welding Design & Fab. The welds look great. And I believe the flux protects the root side just fine. The flux doesn't care which side of the weld it covers. It just floats to the surface, inside or out. It works for E6010. I don't think you would even have to cap the ends, since the flux is integral to the weld puddle.

I think if I were drafting the WPS, I would list the "supplementary" flux as an essential variable. I wouldn't want someone to pick up unfluxed wire to weld the root. I'm sugar-free. Any thoughts?
Koz

 

[unclesyd]

A few notes on supplementary flux.

We have some WPSs that cover the use of a supplementary flux paste on the inside of large diameter S/S 304L pipe as a adjunct to purging. We have seen no detrimental effects of the use of flux even though our process, HNO3/Organics, is extremely corrosive. The reason for allowing the use of flux is we have found over the years that “sugar” on welds is very detrimental in this area as this process material is much more corrosive (2 to 3 times as much) in crevices, even very small ones. On very large systems we will use the flux paste with an N2 purge/Argon shielding gas. This has worked very well.

The caveats with brush-on flux are:
A pretty even coat of flux is required.
Dilution of the flux can cause problems.
Not all TIG welders can handle this procedure. We tend
to gravitate our more proficient welders to this area.
If a welder “keyholes” a weld it does present problems. Again choosing welders is critical.
We have had a few problems with welders not carrying/adding enough filler wire, especially on the hot pass.

Most of our welders use "Feather Edging" and“Walking the Cup” when TIG welding.


I’ve talk with the proper people to see if I can get a test spool made with the new flux covered wire and installed in a process test loop that I had made and have used for a quite a number of years testing both piping and welding. This loop will test the corrosion resistance of the spool very quickly as the apparent corrosion rate is 12 to 20 mpy on 304L S/S.

If one can achieve the apparent quality of the weld that I observed in the test coupons in the field, I would have no problems incorporating the wire in a weld procedure.

I have no idea know how long it will take to accomplish this test, but the savings and expected productivity and quality increase of the welding should get some action.

 

[Koz]

Hi Unclesyd,

Nice primer on flux paste! So many questions. I haven't seen it used, yet. How fun for you to see the weldments in use. I was in fabrication. Everything was bright and pickled when it left the shops.

I can really see the value of using flux paste on large diameter piping. Why do you use the purging gas at all? Insurance?

This is subtle and I never passed a GTAW pipe test, but I see the welders use the filler rod to almost span the root gap, walking the arc across it. There is sufficient arc energy to completely melt the filler metal into a true root bead, but there is no key-hole visually verifying melting away the feather edged root. So I assume the key-hole you mention is a spot where welders get stuck and let the puddle get away from them, creating a gap around the filler rod. The welder of course, fixes this on the fly by adding more rod to sink the heat out of the area, filling in the locally widened root gap, and then moves on according to preferred technique. We would see more penetration and heavier root on the ID in that spot. Do you think you run into "problems" because you no longer have intimate contact of the root pass with a flux or with sufficient flux? Would this condition be alleviated with an externally coated GTAW rod providing flux to the weld at all times?

I've found that adding as much filler metal as you can carry makes for a better weld, metallurgically and mechanically. The deoxidizers in the rod, et. al.....

What do you dilute the flux with? Does the mfg offer guidance?

Your corrosion rate. What are the units? How frequently do you do thickness checks on, say, a problem zone? I assume straight-beam UT?

And this final one. This one I thought of late at night so watch out!!! Do you suppose you'll have hydrogen pick-up in the external flux coating? Are you going to build an oven to store the rod?

BTW: Have you read the recent manufacturer's recommendations for in-process storing of FCAW spools? See Lincoln Inner and Outershield catalogs back page in response to FEMA 353 that came out of Northridge. It's all good.


Koz

 

[unclesyd]

I started the out the same with all S/S being pickled on site. TIG wire cleaned prior to use, one stick at a time. All TIG welds had a wash pass. All SMAW welds were stringers, no weave what so ever.

We used a N2 purge just for insurance and a little added protection. We still used an Aragon Gas shield on the torch.
The keyhole is a slip up on the welders part. The problem stems from the loss of the flux coating at this point. There apparently was not enough flux available to cover the area again. The flux apparently lost fluidity once it melted.
Yes I think that the flux coated TIG wire would completely eliminate this problem as you state by covering the weld metal at all times.

Totally agree on carrying all the metal you can handle. It is imperative that this be accomplished on some materials. I have solved a lot of welding problems by changing a welder from one that carries the minimum to one that carries all he can.
Most of the flux paste used alcohol or water. It was always stated on the tech sheet.

The corrosion rates in this area at the time were anywhere from 3 to 8 mils/year. As I stated the process material love crevices. If the material was trapped the rate would go to approximately 25 mils/years. This was determined by measurements in vessels at attachments and where we deliberately created a crevice. Gaskets surfaces were a major problem as the corrosion was extremely high on the gasket surface. Not possible to weld repair.

All groove welds were 100 % RT with zero tolerance on nearly every parameter. Even using the feather edge and walking the cup our reject rate was below 0.5% essentially no cutouts. I wasn’t overly fond of this technique at the beginning, but the results changed my mind as the weld spoke for themselves, both by testing and in service.

We used straight beam UT a minimum of twice a year in the hot areas > 110°C. Some of the worst areas have gone to Ti Gr 2. 0 corrosion rate.

I can see no problem with H2 in welds in this area as the material is all 304L S/S with 0.020 C or less. The sulphur and phosphorous are also controlled. We do ask for low Silicon if available.

We actually welded some test pieces with damp SMAW rods and saw no problem on bent coupons before and after an in service test.
This process had major problems with end grain attack, Accelerated IGC. To eliminate this problem we required all nozzle in vessels to fusion welded.

AS stated the process was HNO3/Organics up to 120°C. Very bad stuff in more ways than one.