Hi all.
My first time tig welding and I seemed to have messed up big time. I was trying to weld a 304 threaded shaft onto a 304 stainless boiler but my lack of experience and practice led me to make cracks/holes on the surface of the boiler. The boiler is about 3/32" to 1/8" thick. The threaded shaft is 5/16" (basically took a bolt and sawed the head off).
It looks pretty bad... the holes were close enough together that they sorta formed into one big half-inch crack. The area around the hole/crack is very dark grey... not quite black but it has a dark smokey color.
After doing some reading online, I think I had too slow of a travel speed and the heat blew through the metal. I looked on the inside wall of the boiler and I can see the holes/crack have gone through to the other side.
Now my question is.... is this fixable? Can I fuse the metal back to repair the holes/crack? I made an attempt to fix it by slowing moving the arc left and right over crack as I moved the torch along. After doing that, the weld surface did appear to "bridge" the crack but when I looked inside at the boiler wall the crack is still visible.
Is there any advice anyone can give me about this? Have I made an irreversible error and ruined the boiler? If it is possible to fuse the metal back together, will it still be strong or is that area now going to be weak?
=====prompt38 wrote:Hi all.
My first time tig welding and I seemed to have messed up big time. I was trying to weld a 304 threaded shaft onto a 304 stainless boiler but my lack of experience and practice led me to make cracks/holes on the surface of the boiler. The boiler is about 3/32" to 1/8" thick. The threaded shaft is 5/16" (basically took a bolt and sawed the head off).
It looks pretty bad... the holes were close enough together that they sorta formed into one big half-inch crack. The area around the hole/crack is very dark grey... not quite black but it has a dark smokey color.
After doing some reading online, I think I had too slow of a travel speed and the heat blew through the metal. I looked on the inside wall of the boiler and I can see the holes/crack have gone through to the other side.
Now my question is.... is this fixable? Can I fuse the metal back to repair the holes/crack? I made an attempt to fix it by slowing moving the arc left and right over crack as I moved the torch along. After doing that, the weld surface did appear to "bridge" the crack but when I looked inside at the boiler wall the crack is still visible.
Is there any advice anyone can give me about this? Have I made an irreversible error and ruined the boiler? If it is possible to fuse the metal back together, will it still be strong or is that area now going to be weak?
Prompt38.
'Bridging' does not repair the crack but would cover it up.
If you want to repair it, then I would suggest slightly grinding the crack with a thin cutting disk leaving a gap that you can weld a root pass from the outside of the boiler. It sounds like you already know where the two ends of the crack lies ... that is in the two holes that you accidentally made. Those two holes will also need to be filed to get rid of the black oxides on both the internal and external surfaces. The inside surface of the boiler will need to be sanded in order to get rid of that black oxide. You will need to prepare a small dam or cup on the inside of the boiler to trap your backing gas so it protects the inside surface of the boiler. The gas will protect the back surface of the weld from getting contaminated again.
During your welding of the shafts, and the following weaving during the 'bridging', you may of overheated the 304 stainless. Weaving and prolonged heating of 304 stainless considerably weakens it metallurgically and that would probably be the first area to corrode away. In that case, you may need to cut out a circle or oval of the 304 metal, making sure all the overheated area has been removed, and replace it by welding another piece of 304 to plug the opening. The welding would be similar to the crack repair welding above.
What rod did you use while welding the shafts?
Not knowing the size of the boiler ... what is the cost of replacing the boiler?
Do you know how you caused the holes in the boiler ... in order to avoid repeating it?
Others with more experience may have some better alternatives.
Alexa
Thank you for the response Alexa!
What you said about making a gap and welding a "root pass" does sound like it would make a good fix. Tell me if I'm wrong here but you are suggesting that I make a sort of channel between the crack and then weld the channel with filler?
As for protecting the inside with shielding gas, what is a dam and a cup? I'm not familiar with preparing a damn or cup.
I believe that I did overheat the stainless. That's how I think the crack occurred. I am trying to avoid cutting a piece of the boiler out because I'm not sure I am experienced enough to weld a plug on. Is there a way to tell if I have ruined the metal? It is dark grey on the welding surface and the other side (inner wall of boiler) is quite black where the weld cracked through. I will grind down the surface to get rid of the oxidization. If the metal underneath is bright and shiny, would that be an indication that I have not corroded/ruined it?
For the filler rod I used a 1/16" 308
I don't know the cost to replace the boiler but I will probably have to find out soon since I'm not confident I can fix it
The holes happened because when I tried to bond the shaft to the boiler, I noticed the arc would turn the shaft red hot and distort the corner that I was focusing on. It gets hot real fast but the boiler would not puddle as quickly. In an effort to get the boiler surface to bond with the shaft I focused the arc too much on the boiler and did not move it much... I didn't realize I was making holes/crack along the boiler until everything cooled down.
What you said about making a gap and welding a "root pass" does sound like it would make a good fix. Tell me if I'm wrong here but you are suggesting that I make a sort of channel between the crack and then weld the channel with filler?
As for protecting the inside with shielding gas, what is a dam and a cup? I'm not familiar with preparing a damn or cup.
I believe that I did overheat the stainless. That's how I think the crack occurred. I am trying to avoid cutting a piece of the boiler out because I'm not sure I am experienced enough to weld a plug on. Is there a way to tell if I have ruined the metal? It is dark grey on the welding surface and the other side (inner wall of boiler) is quite black where the weld cracked through. I will grind down the surface to get rid of the oxidization. If the metal underneath is bright and shiny, would that be an indication that I have not corroded/ruined it?
For the filler rod I used a 1/16" 308
I don't know the cost to replace the boiler but I will probably have to find out soon since I'm not confident I can fix it
The holes happened because when I tried to bond the shaft to the boiler, I noticed the arc would turn the shaft red hot and distort the corner that I was focusing on. It gets hot real fast but the boiler would not puddle as quickly. In an effort to get the boiler surface to bond with the shaft I focused the arc too much on the boiler and did not move it much... I didn't realize I was making holes/crack along the boiler until everything cooled down.
I grinded down the surface to get rid of some of the oxidization on the outside of the boiler. Here's what it looks like now.
I did a close up to show the holes. The heat from the welds caused a channel/pathway/gap to form along the holes.
To avoid any confusion, the big opening you see there is normal. The part I'm welding is a flange that bolts down a manifold onto the boiler.
Any advice? Is this salvageable?
I did a close up to show the holes. The heat from the welds caused a channel/pathway/gap to form along the holes.
To avoid any confusion, the big opening you see there is normal. The part I'm welding is a flange that bolts down a manifold onto the boiler.
Any advice? Is this salvageable?
- Attachments
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- Here's an inside shot of the back end of the weld. You can see the bleed through. My other problem now is that the surface where I welded buckled a little and caused the surface to sag down.
- IMG_4068.JPG (144.21 KiB) Viewed 894 times
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- Holding up the threaded shaft to show what I tried to do...
- IMG_4059.JPG (151.98 KiB) Viewed 894 times
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- I ground away the failed welds and filler.
- IMG_4065.JPG (144.12 KiB) Viewed 894 times
I did some research about a "purge dam" to protect the back side of the weld.
I think my best bet would be to install a Tee to my argon line with a open/close valve. Then run a copper/alum tube inside the boiler to direct the shielding gas from the outlet side of the valve to the back side of the weld area.
*sigh* I wish I had just did a couple tack welds instead of trying to run a bead around the shaft. Instead of fixing a small problem, I've created a larger one
I think my best bet would be to install a Tee to my argon line with a open/close valve. Then run a copper/alum tube inside the boiler to direct the shielding gas from the outlet side of the valve to the back side of the weld area.
*sigh* I wish I had just did a couple tack welds instead of trying to run a bead around the shaft. Instead of fixing a small problem, I've created a larger one
Prompt38.
The whole idea is to not let air reach your puddle while welding.
If you have room to weld onto the inside surface of the boiler, you may need to repeat the process from the inside. Slightly filing or grinding down along the crack to remove oxides and to reach clean metal, and then fill it with weld metal.
You have probably overheated that area of the boiler. Repairing the crack will again heat the metal at the same location. The repair you should be able to perform from a welding point of view. The boiler will have a shorter life in that location. When you do your repair welding, try not to make weaves and try to weld a bead, then let it cool, before welding more in the same location. To speed it up you can sponge water on it (because it is 3xx stainless), but make sure it is dry before continuing to weld.
In reference to welding the bolt (a thick piece) to the boiler (a thin piece), it is important to orient (aim) your arc upon the thicker piece.
Break a leg.
Alexa
The whole idea is to not let air reach your puddle while welding.
If you have room to weld onto the inside surface of the boiler, you may need to repeat the process from the inside. Slightly filing or grinding down along the crack to remove oxides and to reach clean metal, and then fill it with weld metal.
You have probably overheated that area of the boiler. Repairing the crack will again heat the metal at the same location. The repair you should be able to perform from a welding point of view. The boiler will have a shorter life in that location. When you do your repair welding, try not to make weaves and try to weld a bead, then let it cool, before welding more in the same location. To speed it up you can sponge water on it (because it is 3xx stainless), but make sure it is dry before continuing to weld.
In reference to welding the bolt (a thick piece) to the boiler (a thin piece), it is important to orient (aim) your arc upon the thicker piece.
Break a leg.
Alexa
noddybrian
- noddybrian
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Weldmonger
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Posts:
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Joined:Thu Jan 24, 2013 12:13 pm
Hi - it's not entirely clear what the size or nature of this boiler is ( and I only repair regular steel boilers not stainless so maybe different rules apply ) but I'm very concerned that however good or bad the weldss are it appears you are trying to weld studs directly onto the outside of a boiler casing to secure a cover or outlet plate holding an unknown pressure - this being the case it is not a safe method - there will be unknown strength left in the studs after being heated & direct welding a thread onto the surface is not usually an accepted practice - alternatives would usually be to thread the stud in through the boiler & perform a sealing / method around the thread such as caulking if there is sufficient thickness - or weld a boss of sufficient thickness into a larger hole & do the same or thread the boiler case & secure the stud with a backnut internally - or bolts are screwed through from the inside out that have a tapered head that are wound tight into the hole ( bit like a wheel stud )
I hope I'm misjudging the situation - sorry if I am - but an innapropriately repaired / constructed boiler is pretty much an un-exploded bomb waiting to go off.
All the best with the project - whatever it is.
I hope I'm misjudging the situation - sorry if I am - but an innapropriately repaired / constructed boiler is pretty much an un-exploded bomb waiting to go off.
All the best with the project - whatever it is.
I am a bit apprehensive as well about this. The reason I thought it would be okay to weld on the stud is because that's what the manufacturer did. I looked at the inside of the boiler and they did not thread the studs. The operating pressure is about 150psi of water at just under boiling temps (200F). I guess the safe range would be for it to withstand 300psi of water pressure.
I understand that a bad boiler is very dangerous. I may just have to order a new boiler.
I understand that a bad boiler is very dangerous. I may just have to order a new boiler.
- Otto Nobedder
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Weldmonger
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Posts:
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Joined:Thu Jan 06, 2011 11:40 pm
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Location:Near New Orleans
On a pressure vessel, to attach something related to "work", as opposed to pressure, I typically weld a doubler, a patch of metal the same thickness, where the attachment will be. The doubler is usually not "live", i.e. does not see vessel pressure, and has a small hole drilled in it before it's installed, so a leak in the vessel behind the doubler is still apparrent. Then, you can weld threads or whatever to the doubler without fear of compromising the vessel, even if they're torn off.
I'm assuming this is someone's homebrew boiler, or maybe part of a steam-pressure washer? If it's a certified boiler under ASME codes, you have to be certified to touch the vessel with an arc, or the vessel's certification is void.
If this is the case, and certifications don't apply, I'd suggest a "live" doubler for the repair. Stop-drill the crack at each end, or drill the whole thing out, and lap-weld a patch over it (or under it, if possible, as to avoid interfering with replacing the threaded rod). Again, back-purge. That thin metal will "sugar" when it gets hot if it sees oxygen.
If there's any possibility the base metal is a casting (the first pic suggests sand-cast marks), preheat to 350 and use 309 rod.
This is fixable.
Steve S
I'm assuming this is someone's homebrew boiler, or maybe part of a steam-pressure washer? If it's a certified boiler under ASME codes, you have to be certified to touch the vessel with an arc, or the vessel's certification is void.
If this is the case, and certifications don't apply, I'd suggest a "live" doubler for the repair. Stop-drill the crack at each end, or drill the whole thing out, and lap-weld a patch over it (or under it, if possible, as to avoid interfering with replacing the threaded rod). Again, back-purge. That thin metal will "sugar" when it gets hot if it sees oxygen.
If there's any possibility the base metal is a casting (the first pic suggests sand-cast marks), preheat to 350 and use 309 rod.
This is fixable.
Steve S