[cj737]

If you're working with heat-sensitive tube-to-tube joints, this can be your best friend:



That is what I use, if needed. 1/2" wide, tinned copper braid. I use it to wrap both sides of the weld joint, at least 1/2" high, about 3/4" away from each other (~3/8" from each side of the weld joint).

Testing it out on titanium:




It serves two important and beneficial purposes:

• It creates an argon dam to help the argon linger around longer to protect the hot weld bead from oxidizing
• It quickly wicks out heat due to copper being the 2nd best thermal conductor, which in turn helps out the above bullet point about argon needing to protect the weld bead while it's still to hot to be allowed to encounter oxygen

If it works on titanium, which is notoriously worse for oxidizing than SS, it can work for pretty much anything.


Perfectly silver welds? Perhaps not, but it sure creates a huge buffer to counter unfavorable welding conditions. Thicker tubes/larger diameter tubes would probably benefit from wider braid and or higher number of wraps. The best thing is, as long as there is enough space to do so, you can't over do it---the more heat sinking ability you have, and the better the argon coverage, the better the welds can end up.

...and what about internally? A larger cup offering more coverage can easily accommodate better coverage. Not saying this braided tape isn’t useful, just seems superfluous when a #12 or > cup suffices.

[Oscar]

Internally you still have to purge. This is solely for external aesthetics, but unlike just using a larger blanket of argon coverage where you still still have to allow the part to cool, this can cool it down faster for you, saving just a little bit of time and purge gas.

[Arno]

For inside exhaust pipes and mufflers where it's sometimes impractical (or too costly) to fully purge I'll sometimes use Solar-Flux 'B' to protect the back of welds.

You make a paste of it (it's a powder) with some solvent (they advise some methanoil) and apply it to the back of a weld for TIG (both sides for oxy). Let the solvent evaporate away and start welding..

It basically turns into a glass like layer on the back which binds to any free xoygen and seals the weld from the back.

Not a perfect product, but works well enough for me to be an extra tool in the arsenal. The glass-like residue left is not an issue on exhausts and the like. Would be a problem on food grade stuff, so not suitable for that.

BTW.. Using 316 for exhausts is no problem, it's usually just more expensive than 304. Can be argued that it's actually most useful in the final section/silencers as that's where most of the condensation occurs (and stays...) so the most corrosive environment. A car exhaust system geared for maximum life would be 321 (or inconel) for a manifold/header and perhaps a first cat, 304 for the mid sections/resonator and 316 for a rear silencer and pipes/tips.

Bye, Arno.

[noddybrian]

If you do much exhaust work I feel a tube expander is your best friend - whenever possible I will expand the end of one side of a joint so I can make a slip joint rather than a butt - this allows easier assembly / alignment - greater mechanical strength & mostly as the weld is now a lap joint if careful you can weld without purge & achieve sufficient weld strength without full penetration hence no need to purge - it also saves on prep time as the ends do not need to be accurately cut.

[Vicoor]

309 filler will join 316, but it will not be as strong. But this is not the cause of your weld appearance.