Hey all! Looking for some input on a little bit of my work. I work at a Praxair up in Maine, we do surface coatings here and work with a lot of furnace stuff/retorts. I mostly weld inconel here, and got the job with no prior knowledge about the metal and no one to really teach me about it or give any real tips.
I guess what I'm looking for is some feed back from what you guys can tell through some pictures.
Welder: Miller Syncrowave 250 water cooled, #20 ck flex head torch
size 7 cup with gas lens
I weld these retorts between 150-165 amps
3/32 2% lanthinated tungsten
These welds were to close up a crack below the seal of the retort and were about 25" long, followed the crack so thats why it isnt straight.
I'd say that we have a few things in common. I work for GE Aviation in Madisonville and I believe you do some coatings for us. I see a lot of Praxair boxes sitting around our plant. I was also a welder there for 9 1/2 years and I ran the coating furnaces for 9 years, so I'm familiar with what you are doing. I've seen the cracks in the Inconel cans that we used years ago and in the bells and bases that we use now. I can't say that I have any experience with welding the retort bells because we send ours back to Rose Metals to have them repaired. I have welded some of the Inconel racks that went into the furnaces and I can say that they are very hard to weld after they have been through a few furnace cycles. Sorry that I can't be much help with your welds. I know that it's difficult to weld on that stuff after it's been hot several times. We ran ours up over 1900 degrees and held them there for a few hours and then just pulled them out and let them cool in the air. It's pretty stressful for the metal.
D.,
I have a few general suggestions on Inconel and it would be helpful to anybody trying to help to know what the parent metal is, whether it be 600, 800 or what, and your filler rod.
As shiny as your weld looks in the pictures I would guess you were using Inconel 82 filler. If it's made of 800 series that would be the logical choice. If you're not sure what the parent metal is or if it is going to be joined to a dissimilar metal then 625 is usually preferred.
Cleaner is always better and I wouldn't grind all the way through the crack if you can't get to the back side to clean it. It's sluggish nature prevents impurities from making there way to the surface so you will end up with inclusions if it's not clean to start. Use a higher than normal flow rate for your cover gas and use the largest gas lens you have available. If you have to make more than one pass, keep interpass temps in the 300-350* range and clean the dirty looking oxide layer off between passes. Clean with abrasives made for stainless and if you use a wire wheel on your grinder, use stainless wire only.
More specifically to the weld you have pictured, since it's so close to what looks like a submerge arc weld and the cracks appears to be in the HAZ from it, I would consider trying to tie the two welds together with stringers to pick up that welds strength in the repair. This might keep it from just kicking the can further down the road, so to speak. It's not usual to try to get the stack of dimes look and it usually is done with a tight smallish weave, this lessens the chance for inclusions. A back purge is not required but definitely has never hurt and if the back side can't be cleaned, it's a big help.
I don't have a lot of experience with welding it personally but I do have quite a bit of experience working with the people who do. I also have some experience with the problems caused by it not done right. I work mostly with piping at very high temps and failures cost big money and cause a significant safety risk so done right the first time is required.
I work with inco 600 and yes I am using inco 82 filler rod. I grind down the surface the best I can l, but can not get to the inside to clean, these retorts are constantly being heated up in furnaces to 1900° and put back in a cooling chamber, so they crack often. From what I've seen since I have worked here is that my welds haven't been cracking, it's always somewhere else on the retort. So that's good I guess! But they go through a lot of stress.
D.,
The Inconel 82 is fine for welding 600 series as long as it's used for welding 600 to 600, or in your case, crack repairs. You get the same dilution of the parent metal into the weld. The sub-arc weld was more than likely done with 82 also.
Inconel is different than other base metals but it's not Alchemy, it just has it's own little quirks. Like I said, my only suggestion for you is to advance in smaller steps while welding to keep the gas coverage on the puddle behind and to keep it fluid a little longer. A small, tight weave accomplishes this fairly well. Hopefully others with more experience in a broader range of uses will chime in.
I will definitely try a weaving pattern next time, usually these inconel welds don't get that stack of dimes look unless i stay in one spot for a few second. (which is what happened here since I was moving so slow)
