Just a thought, but have you ever tried the ceramic tiles with the foil tape? We use them alot but our application is not the same as yours.

They have a good assortment of sizes and shapes.

If you are interested send me an e-mail and I can give you more info.

Hi Boilermaker,
There are a couple of different approaches that have worked with a joint and diameter similar to yours. You didn’t mention if you were using GTAW for the entire weld or not but it shouldn’t matter with these two.

First off let me say I’ve never liked putting an alloy (SS in your case) GTAW root in a large diameter weld such as yours from the outside unless forced to by lack of access, which was very seldom.

If you have access to the inside, tape the outside of the joint and purge it while running the root bead from the inside. When the root is finished, switch. Tape over the root on the inside and purge while you finish welding the outside. By following this or a similar procedure, back-gouging/grinding is minimized in the V-groove. Also, you maintain gas coverage while filling out the joint until you’ve reached a weld thickness that doesn’t promote oxidation to the inside root surface.
I’ve seen SS GTAW roots put in from the inside without backing tape outside, back-ground (not much) and finished off with FCAW (SS). Though initial lack of filler metal wetting on the outside was evident prior to dressing (grinding), no problems were encountered meeting ASME Div I, Sec.VIII radiographic quality requirements.

There is always the ceramic tile/tape on the inside/weld from the outside which I’ve only been infrequently involved with but has been around for a long time and certainly has a following. Because of they’re reputation, are certainly worth investigating.

This one has a little more grinding involved but is still very workable and is not uncommon to see in vessel shops. Can you use GMAW on your weld? If you can, use that process on the inside to put your root in with/without a backing gas depending on your WPS. Hopefully without, but still not a big deal. You’ll undoubtedly have to do more back grinding from the bevel side but you should wind up with a solid GMAW bead left for backing yet still maintain a full depth GTAW weld available for radiography. The principle of this procedure actually uses the GMAW-CS weakness of low penetration to provide a backing. This is an important consideration whenever using the GMAW-CS process for welds that have to meet a radiographic quality requirement.
Good luck,

I once saw some SMAW electrodes marketed for welding roots of S/Steel without purge gas. If I am not mistaken, it was an AVESTA product.

While we never used it, it may be an option for your aplication.

Regards
Niekie

I've never found a GOOD substitute for argon! If you have access to the interior of the vessel you can make a very simple back purge chamber. This is nothing more than a piece of 1" channel rolled toes out to match the ID of the vessel, cap the ends and attach some method of securing the purge gas hose. Hold the channel in place by propping it from the opposite side. Tape the outside and you're ready to go.

If you use several pieces and cover the entire circumference you will not need to cap the ends and you will not have to crawl into the vessel as often. WARNING!! The latter is very important as you are now entering a confined space where an asphyxiant has been introduced. Follow confined space entry procedures!

I too have used the ceramic backing in many applications with no problems passing UT PT and MT inspection has long as the welder is proficient in the process being used.We have an ESAB Digi-Pulse GMAW machine that has proven very satisfactory results in welding stainless
(309,410 and 17-4PH).We have also experimented with Inconel 625 with very good results using certain gas mixtures,(Argon,Helium and CO2 mixtures).I have been very impressed with this mode of GMAW but the welder should be familiar with GMAW.Our welders were all sent to a training course in this process and most have good results whereas a couple have problems at times.
Overall,with the high deposition rate and the quality of the weld that can be achieved, I feel this ia a viable option in the sometimes difficult welding of different alloys.

Good luck

It appears you have not considered use of Inverted T inserts.We can supply to you inserts in coil shape.You can fit it to suit a given size of pipe/shell.We regularly supply T shape inserts in grade SS308L and others to nuclear power corporation who need 100% assurance of good root fusion.Of course back purging with Argon gas is a must.
In you want to avoid gas purging and want to use standard hand held TIG filler wire try flux cored TIG wire brand TGX 308L sold by KOBELCO -Japan.This one will avoid necessity of back purging and yet give good root fusion. C C GIROTRA /WELDWELL SPECIALITY-BOMBAY-INDIA