Boiler Build Issue

[jlakes85]

Hi All,

I've run into a pretty big issue which began with some porosity showing on the left hand side of the final pass on the 3/8" half coupling shown in the picture. The resulting void is where I'm at as I'm trying to chase/grind out all bad material.

I already did the other 6 or so couplings with the same torch setup no issue, so base material isn't a concern. As with those joints, both sides of the mating barrel were prepped to shiny metal (not shiny slag..lol). The second photo shows my attempts at backing up the void with more of the same 5/16 SA-516 plate that was used for the side sheets (also prepped shiny all over).

I'm guessing somehow the porosity traveled through that material as well, which now has to be replaced, judging by the photos.

Process is all TIG..3/32 2% thoriated tungesten, #7 cup and gas lens argon set at 20 cfh using a 20 water cooled torch. The gas supply currently is not a concern as multiple times i ran a test immediately after running into yet more porous material, but running a bead on some 1/2 scrap steel which wasn't the cleanest. That test bead came out fine, no issues on travel or adding filler material.

Any suggestions as to how to proceed to save the barrel are greatly appreciated.

[jlakes85]

Here is the first of two pics showing outside and inside of joint area

[jlakes85]

and second

[BClemens]

Any suggestions as to how to proceed to save the barrel are greatly appreciated.

Can you pull back and give an over all photo of the entire area. Sort-of unclear what and where you are welding. It doesn't make sense that you were successful on all but this particular area where you suspect 'porosity'. Porosity doesn't just pop up in a piece of material unless it was previously welded and somehow a polluting element was alloyed into the molten area as an active inclusion. Aluminum will do this... silver solder will, bronze/brass will - when alloyed into a molten puddle of steel. Actually oil will do this... Makes an unweldable mess and what you're doing - grinding it out - is all you can do. Get everything back to clean and pure - even your tungsten.

I operate an electron beam welder usually welding niobium (2468°C), anything other than Nb will explode! Aluminum will alloy and explode, blowing a sizable hole in the Nb... Everything must be super clean - along with no touching. The oil from skin will also explode.

BClem

[jlakes85]

Hi Bill,

I have some larger photos however I run into the issue of attachment size limitations. The only previous welding work around the site was the 3/8 half coupling which is partially visible on the right hand side of the picture. The porosity issues started on the left hand side when the final pass was welded in

[BClemens]

Looks like it could be simply an overheat issue? That would also blister and cause a drop through. I would suggest that you continue with the grind out and a slow build-up with 70S rod from both sides. Fill a little, then fill from the opposite side working all around the hole - but slowly. Allow some cooling and peen the welds as they cool to stress relieve them - use a slag hammer for the peening. Work slowly but deliberately with a plan of attack. There is no reason why you cannot recover using this method. Just don't let it get too hot.

BClem

Try: http://www.faststone.org/FSResizerDetail.htm for your photo resizing....

[jlakes85]

Hi Bill,

Sounds good. I think I still have additional material to grind out on the outside as I'm still running into porosity. Would overheating alone cause porosity in otherwise good and properly prepped material?

-jlakes85

[BClemens]

Very well could but usually due to some pollutant in the puddle. Overheated steel will basically blister and boil - and drop.

One of the problems with welding - and electron beam welding especially - is that the molten metal is out-gassing and actually evaporating from the puddle. In the EBW instance where we weld in a vacuum, the metal will condense on the insides of the vacuum chamber walls. This is proof that welding is very unsafe to breathe fumes from - especially copper. Molten steel and its contained alloys do out-gas.

[BClemens]

jlakes85,

Something else to be aware of - when you super-heat steel while welding (if that was the case), it can become very hard - like crystallized. It will cool too fast. You can detect that by watching the wear during the grinding. It can be so bad that carbide burs will dull - chipping the cutting edges off. If you see this - you need to grind beyond that and patch the whole area....

[jlakes85]

Hi Bill,

I'm glad you brought that up because that was happening too, but I'd didnt think much of it..I just wanted to get past all of that porosity

[BClemens]

That sounds like a serious defect. That is repairable but you are going into an area that even pro welders will cringe. There is a 90° elbow prominent in the first photo - it may pay to remove that and work the area without anything to complicate the issue since the elbow looks pretty close to your defect. Patch that area and then replace the plumbing. ...take your time....

[jlakes85]

Hi Bill,

It sounds like if I had to patch the whole area, including the void created by moving the coupling/plumbing, I should use plate underneath to build up the weld on? I have plenty of 5/16 PVQ material on hand. Would using 7018 be a faster way to build up the patch?