I`m having some problems welding on a stainless steel hot water tank at a car wash. I`ve welded stainless for a couple of years back in the 80`s when I worked in a fab shop,but not a lot since then. Now about 95% of my work is in the oilfields so I don`t do much stainless nowadays. Anyway I got called about a year ago to weld a leak on the top of the tank all the way around the outer edge where the concave top sets on the vertical portion. The original weld looked like it was done with a mig,and I it looked like a mediocre weld. The original weld flattened out nice but not a lot of metal was deposited,you could easily see the seam where the metal butted together.I welded the leaking area and mentioned to the owner that another looked like it would leak soon,a spot where you could easily see the seam. As I told him this I just rubbed my bare finger along the weld and instantly it sprayed out a fine stream of water.So again we drained down the water and along with it relieved the pressure.As I initially did I warmed up the area to be welded with my torch to dry out any moisture then welded it with 308L-16 stick welding.The owner wasn`t sure of the type of stainless the tank consisted of,so I assumed it was 304 which the tanks I welded consisted of. I eventually was called out a second time and welded the rest of the way around the tank where it was leaking. Later I got called out to weld 2 areas that I had welded that were leaking again. It`s leaking in the middle of the weld,kind of like a fine crack is developing. The welds actually are OK for about 3 months and then start leaking.The original welds showed no sign of porosity,so I ruled out any trapped pockets that I may have welded over. The owner still hasn`t found out the type of stainless the tank is and the tank has no visible sticker telling such. The tank is only about 3 years old. Any advice or suggestions appreciated. Thanks.
Grind it out start over and stack some good clean stringers on there until it is right. You can't make a good weld on top of an unknown weld you should have taken the whole thing out the first time. Just tell the guy you want to do it right and it is going to cost X per hour until your happy if he won't accept that role up and leave that's the down side of repairs we won't touch a cracked weld unless we take the entire weld out first. IMHO
Hello NMWELDING, I would offer up an additional few thoughts for your consideration. One item to consider is the amount of pressure that this particular tank is subjected to. Another might involve any sorts of pulsations that may be associated with it's use. A third could involve the Alkaline/Acidic nature of the content of the tank. To address the pressure and pulsation issue first, relatively high pressure and pulsations will cause a weld that doesn't have compete penetration to work and crack. So when you weld over a crack without completely removing it through the parent material it will just end up coming back to visit you again. you may need to do a very thorough excavation or grind-out of the cracked area and possibly even provide an internal purge to address this crack repair. In lieu of an internal purge you could possibly "paint" some Solar Flux through the opening along the edges to provide backside protection for the weld repair. As to the alkaline/acidic issue, if this particular tank is used for a portion of the wash function and has anything to do with the chemicals used for this purpose they could be affecting your attempt at the repair by possibly promoting/accelerating corrosion or something similar at the root area of the repair. This chemical residue could be affecting the weld deposit at the time of the repair and contaminating or degrading the integrity of it. Just a bit more for you to consider. Best regards, Allan
Good point about the pulsations. If a "water hammer" issue is the cause, IT needs to be addressed.
Thanks for all your input. If it cracks again I`ll grind it out and start over. I`ll also see if water hammer could be a problem. I`ll check into all your suggestions and advice. Thanks again guys.
On top of the pulsation issue the heat itself can be an issue. Heat alone will drop the pressure capacity of a vessel dramatically. Get that whole weld out. If it was me I would tig it out. Its cleaner and easier to get good penetration. Any porosity that you cannot see with the naked eye will get floated out of the weld as you go too.
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