Welding Tips and Tricks

OK, I see that stainless steel oxidation looks horrible. I also see that the surface is not smooth. I also assume that a tiny part of the weld will be weak because it has become oxidized. For food applications, I guess that a porous surface could lead to buildup of different substances or bacteria. Am I missing something more?

I am planning to make my custom exhaust and I am thinking whether to purge or not. The inside won't be visible, it won't restrict exhaust flow either and obviously no bacteria? What can happen with an oxidized weld? Can it spread further inside? Will it be much weaker than a purged one?. I am aware that backpurged welds look great but are they much better?

The problem is that the tiny part of the weld you are refering to is the root, which is the most critical part of the weld-everything on top of the root is just reinforcement. thats also why so much attention is givin to the root-on some weld tests, if you fail the root inspection you cant even finish the test, you bust out right there. Even a visually pleasing root pass improperly done will split like a pop top on a tuna can if its done incorrectly.

So that brings us to what your actually using the procedure for-Exhaust. If your using it for a custom set of headers on a mild build i.e. no supercharger/nitrous shit like that, you'll be probably be fine without the back purging, considering most exhuast on vehicles is held together with little more than hose clamps. If your running a system with high cylinder pressure/back pressure, you may want to consider purging to give you a more sound weld.

How much weaker the joint would be I cant say, its beyond my expertise. My thoughts on the matter is that if its worth doing its worth doing right, and if your going to spend the money on the stainless exhuast I would make it as perfect as I could possibly make it.

kermdawg wrote:

How much weaker the joint would be I cant say, its beyond my expertise. My thoughts on the matter is that if its worth doing its worth doing right, and if your going to spend the money on the stainless exhuast I would make it as perfect as I could possibly make it.

Because of the application, (a continual heating and cooling, expansion and contraction of the metal), the service life of the header will most likely be reduced considerably because of cracking. I would recommend the same as Kermdawg.

I remember what I was going to write now Solar flux! Slap some of that puppy on the back of the joint before you fit it up, should prevent that sugaring on the back side of your weld.

I'm also doing a SS header but really want to purge backside. When taking course at Lincoln I saw just how nice a SS weld can be. However at home I don't have endless equipment.
I'm thinking of using my 75/25 ArCo2 cylinder from my Mig machine and setting the flow rate real low as I can purge the length of tube in just a few seconds at 2 CFH.
I was taught to tape one end shut and punch a few small holes in tape to let air out. Other end gets a wad of steel wool with the hose fed into the steel wool
Tilting pipe will help as Ar is heavier than air.

This will avoid the need to buy a new regulator. I figure 75/25 should be just about as good as 100% and for street hot rod it should be strong enough as high heat from high RPM is not expected with my application.

Comments?

Hi there,

Not sure about the mixed argon co2. I have (accidentally) used it for shielding a tig and well, lets just say it wasn't such a great outcome. But for purging?? Dunno. The co2 will probably screw it all up.(Try it and see but don't hope to spin gold from straw) Just buy a y piece and use the one argon cylinder/reg for both. The pressure should be alright for a non critical weld.

Mick

Mick
Thanks for quick reply. Am off to supplier this AM and maybe will get fittings to be able to try the Ar/Co2 and also to try a split Ar setup where I have a 2nd valve to reduce the flow. Alternately if I can keep the but joint fit tight enough maybe I will not leak a lot of gas.

I will capture some pictures and post to show what the inside of tube looks like.