RT indications on dissimilar-Inconel welds (IN625 & 718Plus)

By Fabricadabra Date 04-09-2019 11:30

I am not a CWI and I have never welded Inconel.

With that being said, I have experienced enigma linear indications twice. We cut and bent the samples (they were test pieces so this was possible) and they both passed. It is to my understanding this can occur when welding dissimilar metals. I was also told that since Inconel welds have a tendency to crack, it is important to make sure it most definitely isn't a crack instead of an "enigma" or "ghost" line. A crack would most likely be jagged rather then a smooth blurry line.

As far as how to eliminate it, you would have to figure out what it is that is causing it. Is there any pre/post heat or a specific cleaning method? The fact that this is only happening "periodically" tells me there is something going on there and I'm sure it can be remedied.

I'm sorry I don't know very much on this specific topic but since I've seen this before I figured I'd throw my 2 cents in. :smile:

By wkyeo82 Date 04-12-2019 08:43

Thanks.

Yes the linear indication is not jagged, and in addition the linear indications on the film are not dark density lines for cracks or incomplete fusion, or dark density band for incomplete joint penetration. Visually on the weld, the weld metal penetrated through the joint thickness.

Are these linear indications highly possibly due to the X-ray diffraction of the dendrites as a result of weld solidification?

For preweld cleaning, isopropyl alcohol and clean paper cloth are used. There is no preheat carried out.

For the welding process, it is manual and constant current is used.

Will robotic welding be able to solve the issue as the current welding speed is dependent on individual welders, or pulsed TIG welding can be used if manual welding were to be continued using?

Attachment: RTIndicationonFilm-DissimilarInconelWeld.pdf (166k)

By Fabricadabra Date 04-12-2019 11:01

"Are these linear indications highly possibly due to the X-ray diffraction of the dendrites as a result of weld solidification?"
- This makes sense. Maybe try a post heat to slow cooling.

"Will robotic welding be able to solve the issue as the current welding speed is dependent on individual welders, or pulsed TIG welding can be used if manual welding were to be continued using?"
- If you have the resources to use robotic welding then give it a shot. That would rule out human error (for the most part). Pulsed TIG may help as well.

This is if what we are talking about is, in fact, the problem. Now I am very curious to how this turns out.

Best of luck to ya!

By gmatsko Date 05-22-2019 22:54

These shadowy linear indications you are seeing in the root are what I call 'linear dimples' in the root pass. I have experienced this many years ago while testing welders at the DAEC (Nuclear Plant). Please bear with me as I am an 'old welding (fart). We were testing welders on Inconel. The 1st. Inconel pipe weld test was visually unacceptable and rejected because the root exhibited a shallow 'linear dimple'. It was not 'suck back'. The welder could not expain it and neither could I. I had inspected the root pass before allowing the welder to proceed further. It was very good and acceptable. Later, the 2nd.test, was rejected for the same thing. A linear 'dimple'. It looked like a tiny valley was occurring in the root pass. It looked like something was causing the root to 'cave' in. This was my 1st. time testing welders on Inconel and I did not have an answer. I called the office and presented my case to the 'Ivory Tower' welding / metallurgical guys. They proposed to me to have the welders run small weld stringer beads on the 2nd. pass TIG and the SMAW passes. They told me to limit heat input by running small stringer beads. Back in the day we did not have computers or Google to help us. They also mentioned to try Puled TIG. So, I had the welder run the root pass again. It was very good and acceptable. I had the welder run small split stringers on the 2nd. pass TIG. As the welder was depositing the SMAW passes I also had him run small
split weld beads all the way out including the cap. Always allowing the test coupon to cool between passes.
BINGO, no more linear dimples. The weld test was accepted visually and the RT was acceptable also.
You get the same type of 'linear dimple' in the root pass when welding dissimilar open butt TIG such as CS to SS. Because of this phenomenon
fabricators will weld in a short PUP piece and have the root pass back ground. Then proceeding to weld your field weld, CS to CS or SS to SS you do not get a 'linear dimple'. I hope this helps.

By gmatsko Date 05-22-2019 22:59

You can verify this phenomenon in the Test Shop if you mock it up. Just use a piece of clear plastic over the end of your coupon so you can view this phenomenon occurring while it is being welded.

By Atuuel

Date 05-29-2019 12:31

Were you able to resolve this problem? I have seen such problem in GTAW welding of ss 304 grade. In X ray radiography a line running through centre of deposited weld metal with no effect on mechanical strength.

By Tommyjoking (****)

Date 05-31-2019 02:23

I am very curious about your indications. Could you please post all the parameters, process etc. about the methodology of the process you are using. If your wish mention the code you are inspecting to as well.

By wkyeo82 Date 06-27-2019 00:58

For further understanding, the joint is of a stadium geometry, and the curved portions are welded using horizontal rolled position.

The positioner speed was increased to experiment and determine if these indications can be minimized or avoided, as of now there are no parts rejected for indications by RT.

The heat input was calculated to be approximately 10.71 kJ/min when the positioner speed was increased, but do take note that the calculation is an approximate due to manual welding process.

A weld cut-up was also managed to be carried out for areas of the weld joint with indications, and only dendrite structures were observed in the weld metals for the transverse sections of the cut-up. No defects were observed. Therefore we deduced that the indications are due to X-ray diffraction.