Pinholes!!!!!

[Poindexter888]

Sorry to come cap in hand for my first post; I've been lurking for months, from Australia and have a small problem. A friend with a Fish n Chip shop had an element burn a hole through the rear of one of his frying tanks. He tried to fix it with his trusty handyman's arc welder and blew holes in it all over the place. Mobile welding tradesmen are all busy so he asked me what I thought. We got some 316 stainless wire, using Migshield M1 (Ar + 18%CO2). Can only access from inside the oil tub, cannot get to the rear of the tub. Filled his holes, but left pinholes, so ground it down and filled those, left different pinholes, ground it down and filled those etc!!! Cannot seem to seal the tank, always these damn pinholes, although the welds look great. Plan B is to grind it flat and weld a patch (cut from an old sink I have) over the entire area, Plan C is to admit defeat and wait for a professional to become available, but I'm too stubborn to give in unless my mate takes the decision away from me. Hey, so I'm flawed Any advice would be MOST appreciated.

 

[aametalmaster]

Try not grinding it down so much. You don't have any fans blowing from the rear do you and maybe blowing your gas away. Welding thin SS is tricky sometimes....Bob

 

[Hitch]

Something that springs to mind, the holes are contaminated with oil.... sounds like its pretty thin, so your probably not burning the remainder of the oil out when you weld it?

I trust your proficient normally? Your not streching beceause its awkward to get to and resulting in not enough gas coverage?

 

[Poindexter888]

I was pretty thorough about cleaning the oil off, worried about contamination. I'm working leant over the front of the tub which is just below waist height, but there is plenty of room for my handpiece (Lincoln SP170). The sheet is quite thin, made worse by my friend grinding some of the original sheet away trrying to tidy up and prep the job for me before I got there. I did also try to avoid grinding too much of my buildup away, but there is not a lot of room behind the element to build up with weld, otherwise the element will be the next thing to burn through. I was wondering if the weld pool might shrink and pucker as it cooled, and if I might be better off cooling it faster or slower.

 

[Poindexter888]

Oh, and yes I'm normally quite proficient, although the more I learn the more I realise I don't know. My first welding job was fitting out my kennel block with dividers and gates, fabricated from galvanised 30mm shs and 25x25x2.5mm mesh. There is over a kilometre off shs in that structure, I did most of it myself, and there was a definate evolution of welding ability. It's pretty obvvious which end I started at, and where I finished.

 

[crayefish]

Duct tape... always great for patching holes!

 

[Poindexter888]

I would have used Devcon Stainless Steel Putty if it was a little more heat resistant. Maybe some muffler putty....

 

[Drains]

A couple of things. Your gas is far too high in co2, which won't help.

And it's probably worth cleaning the area off with acetone and getting all the oil away from the weld zone. Pinholes are invariably a result of oil contamination (can also be from paint etc).

 

[runnach]

It may be an idea to switch on the element to heat the area up, then mop up any residual oil that weeps out?? I've done a few repairs similar in the past, normally very thin material, can be hit or miss to get a good result!

As for using devcon or other such substance, I doubt this will meet hygiene food standards?

 

[Poindexter888]

I was hoping to fudge it with the gas, as I didn't want to get another bottle for one small(!!!!!!!) job, and I've not heard of disposables over here. I never thought to use the element to dry heat the panel, or maybe with water? I was using water to test for pinholes, and then using a 150W floodlight to heat the metal and look for bubbles to locate the holes.
Oh, and the Devcon Stainless Steel Repair Putty is food safe http://www.devcon.com/products/products.cfm?brandid=1&familyid=105, but unfortunately only good for low temperatures (Wet: 120°F; Dry: 250°F). Thanks for the input guys, I'll be having another crack at it this weekend.

 

[Bruce]

Dont use putty. I had a similar problem...

http://www.mig-welding.co.uk/forum/showthread.php?t=6843

If you just cannot solve the welding issue you could resort to silver solder. It has worked very well with the kitchen sink and I can vouch for it's ease of use.