Manual narrow-groove GTAW

[Mr168]

We have procedures developed for our orbital narrow groove welds in material 3"-5", but are contemplating making an attempt implement some manual procedures as well, primarily for tacks and possible repair work due to high/lows on the J-prep that can't be remachined in the field.

Does anyone have any experience with or even seen manual narrow groove on material this thick? We've got approximately .560" of space, and Weldcraft does make a torch small enough with a long enough neck to fit the space. We will likely attempt to pulse the root in as there is no room to walk the cup, but with only a 5/16 cup orifice, gas shielding is a major concern. If anyone has any insight or horror stories, please chime in.

 

[unclesyd]

We made two attempts, first and last, at narrow groove manual welding on a 3.5" thick CS shell. It turned out to be total disaster. When the weld was checked at half thickness appearance wise it was OK. Radiography showed a totally different animal. We ended up having to reprep the joint and call in a company that specializes in NG welding, machine. The company that we used did state that they were capable of doing manual NG welding on small dia. vessels.

The first problem we encounter was getting a little preheat into the weld area without cooking the welder.

Another was we couldn't carry the proper wire size for the job.

Visibility was a big problem.

 

[Mr168]

What sort of problems were showing up with the RT?

Our current preheat requirements call for 400 deg. I believe that if absolutely necessary, we may be able to go lower than that and still be within code requirements.

Visibility was a concern for us, which is why we are also looking into a 45 degree cup. We have not ruled out using a gamma plug and getting a camera in to watch the backside of the root.

Was the company you called in able to do the job without a significant failure rate?

Thanks for the response

 

[unclesyd]

There was lot porosity along with many areas with lack of fusion. The lack of fusion problem was probably compounded by the lack os sufficient preheat and the lack of good visibility of melt pool.

We could get to the backside of our weld. There were no problems with the root. We statred to have problems with the hot pass/passes.

The company was able to complete the job with no problems.

It was an orbital weld, tracked, with a hot wire TIG rig.

With your preheat one is going to hard pressed to get close to the action.

By the way what is the material spec that you are attempting to weld?

 

[metengr]

Stick with automatic narrow groove welding using hot wire GTAW even for tacks. This is a proven technology and manual is not recommended for this base metal thickness. We have used hot wire narrow groove automatic GTAW on high energy piping welds, HP steam turbine inlet leads and had no problems.

 

[Mr168]

unclesyd - This is going to be primarily P5A and P5B material.

metengr - This setup will pretty much be for the odd man out scenario. I should have emphasized it would be more for repairs than anything. On our last orbital project, we had 2 repairs out of 1400 joints, no narrow groove. On the current project with union welders, 7 out of 7 joints have needed repairs, which is absurd. They've seen a max offset of .020 out in the field, we ran the same program in our test facility with .080 offset, and still produced a root that would pass any NDE you threw at it, so I think you can piece the puzzle together here and grasp what the problem is.

We're currently developing our orbital narrow groove procedures with hot wire AMI units. We'd like to have this as the "just in case" backup plan, because if its physically possible to do, we've got some golden arms who can be brought in to do it.

 

[stanweld]

I have seen it effetively done for small tacks and small repairs only - not for root weld out. Specially sized (1 1/2" to >3" diameter) gas cups with gas lenses are required to permit flooding the area with inert gas (flow rate between 80 & 140 CFH depending on depth) without causing turbulence; the tungsten electrode is extended to reach the root or repair depth. Welders were highly skilled and trained in its use.

 

[Mr168]

I appreciate the response. I didn't assume it would possible to achieve that sort of stickout without creating turbulence or complete lack of shielding as you had mentioned.

We received a demo torch from Weldcraft with a 5" neck on yesterday, and its being flown out to one of our sites for mock up and testing. If it doesn't work, we will start looking into the gas lens possibility.

 

[Mr168]

Just as a followup, we had the torch sent to one of our sites, they mocked it up, and a few guys gave it a go. They were able to do it successfully, with the preference being the use of the 45 degree cup for visibility and manipulation purposes. We have the unit being sent over to our welding facility to develop legitimate procedures to implement, and to determine its limitations.