Sub arc setup for overlay on inside of barrel

Date 01-22-2008 14:35

The usual practice is to be up off of bottom center a little (yes, direction of travel), and using a slightly faster travel speed-this helps with dilution and bead thickness-but that shouldn't be causing you any discontnuities in and of itself. Something that big you probably have 12" range you can play with without difficulty depending upon your parameters. I've done miles of longitudinal ID overlays with the SAW right on the bottom.
You might help us a bit by saying what your discontinuities are.

By jrupert (*)

Date 01-22-2008 16:57

Here is some more info. The groove is about 3-4" wide and about 1" deep. It will be machined later for an o-ring. Travel speed in the areas where its just flat is about 18-20 ipm. When we approach the side we slow it down to 10 ipm, because thats the only way we've found to avoid centerline cracking. We've done a lot fo testing on mock up grooves on flat plate and have been very successful developing this procedure. As soon as we get into the barrel, we have a lot of problems. I have another guy welding up a similar groove on a flange and has no problems. That's why I'm thinking I have a positioning problem. We just got done doing a PT on the first pass of the second groove and it actually looks good on one side and the middle, but the opposite side has centerline cracking. I asked if he did anything different and he only recalls that for the passes where it was good he was directly on the centerline and the bad pass was in the direction of travel about two inches. Hope this explains a little better.

By js55

Date 01-22-2008 17:20

A couple things, shootin from the hip, as usual. Your slowing down on the sides makes sense. It makes your weld thicker (increasing the cross section dimension) which helps in accomodating your stresses to prevent centerline cracking, though too thick and you get it again. Also, when doing overlays in a groove as you have described, when your on the sides you have not only the greater stresses but greater base metal dilution which means more impurities from the substrate(what is your substrate by the way). Probably higher carbon, maybe even sulpher and phos, which are problematic for hot/centerline cracking in SS's.
An overall increase in travel speed will help to minimize hot cracking as a whole, and the last pass, if I have this pictured correctly will actually be similar to a groove weld with the two walls being the groove wall and the previous pass. You could actually increase your wire speed and travel speed at the same time to maintain a low heat input, and greater pass thickness and run up the ID a little higher.
Also, what is the angle of the groove wall. You might increase that to minimize stresses on the final pass.

By GRoberts (***)

Date 01-23-2008 00:17

Jon,
The main thing on displacement on roundabout welding is getting your weld to solidify while it is flat, as you mention. So the weld heads need to be in front of top or bottom dead center. A good rule of thumb is about 5 degrees, but it depends on your alloy, heat input, base metal thickness, etc. Your bead shape will tell you though. If your bead is concave, you need more displacement from bottom dead center if welding on the ID, and if you bead has a peak in the middle you need less displacement from bottom dead center when welding on the ID.

On your cracking issue, in addition to the already made comments, which are good, is that when you get to the side, one possibility is that tying in to the side can make your bead too concave, so you are having to slow down to eliminate excess concavity. Also, welding to the side changes the dilution level of the base metal into the weld, and that can affect the solidification mode. You could play around with the WRC diagram to see if that is a potential problem.