The way turbo headers should be made.
 

Here are some pics, of the quality work AMS does.

They will be make some headers for me in the near future.

check this out: http://forums.evolutionm.net/showthread.php?t=312655.

I know AMS produces some top quality parts but I'm not sure why they are stating back purging is one of "their" processes in welding their stainless headers. ALL performance stainless headers need back purging during the welding process to prevent the molten stainless on the back side of the weld joint from crystalizing in the open atmosphere which makes the joint extremely brittle after it has cooled and prone to cracking with thermal cycles.

All headers I build are backpurged. Been doing that for the past 15+ years. Nothing special really :(


Either way, be nice to see the final product for your car.

Boxxer, all metals are composed of crystalline arrays.
During fusion welding all metals require some sort of shielding from the atmosphere to eliminate the possibility of hydrogen or oxygen embrittlement (depending on the alloy it will be more susceptible to one or the other).
Even if the weld is not a full penetration weld, without shielding there is still the risk of embrittlement.

Not if you are welding carbon steel, you do not need a purge

Correct.
Like I said, depends on the alloy.

I would like to see a photo of the inside of the welds,to see if they are just butted up and fused or did they take the time to put a gap in the welds to get a flush penetration of the filler metal. Also to purge with argon is kind of expensive when you can accomplish the same results with a nitrogen purge.

Due to actual, real-ilfe experiences with header fitment and issues which reside outside of manufacturing techniques, I'd use a known setup.

A well-known Turbo man really likes.............the OBX headers. Yep.

Not to start a fuss here but did you read my post? I know what you're saying is correct as I'm an AWS certified welder ;)

In my post I was simply saying there was no reason for AMS to post about back purging being "one of their" welding processes like it was something they do special in their shop, as anyone who makes stainless headers properly MUST be back purging.......or welding the components in a complete sealed chamber like I do when welding most titanium parts of reasonable size(braces,bracket, etc). It's just a rule of thumb. At the absolute LEAST, on stainless you should use a solar flux B or BL compound if you cannot get a back purge setup.

964 T #304, also pending the alloy you should be adjusting the shielding gas for the purge yes. Titanium for example requires a good helium complex, or xenon, to get effective weld results but the latter is ruthlessly expensive and reserved for things like nuclear reactor components. Even helium is expensive these days and makes argon look like free air in comparison :)

WE are talking about welding pipe not plate and hangers. I welded on a lot of nuclear power plants in the 60s and 70s on reactor main steam lines and don't rember any Titanium there, but have welded a lot in climate controled rooms in pipe fab shops, along with hastoloy,inconel ,monel, titanium ,all types of ss, and various other metals , but we are talking about a set of simple ss headers for a car. My statement about the price of nitrogen vs. argon wasen't an invitation for a schooling about welding.

I agree with previous posters. Back-purging (which we call "root-gas") has been done since beggining of time. When I had headers made it was done by just taping the rubber hose into the pipe and turning up the Argon so it purged air from tubes. There is nothing special about it.

AMS sure makes some pretty welds but I personally don't care about the looks as long as geometry inside the tubing is right. Some of welds look very pretty...almost as he just fused the pipes together.

But yeah...AMS are probably good. It's just that I don't understand the marketing of back-purge as something inventive and theirs. Do it without and inside of weld will be full of swampy molten droplets.

Looks nice maybe a bit to little of filler metal as it does look a little to concaved but they do have nice purge blocks but again they are probably do this in some sort of production runs or make it work for a bunch of different models..

We purge everything as well as most everybody in the industry.. Nobody wants to see sugar on the inside of the header.

I see nothing wrong with them saying that they back purge. There are still a lot of fabricators that don't back purge. Why do you think there is all that FOD on turbos.

This is funny

In the AMS pictures I can't help but think that's a mig bead half way along the curved runners. seems odd.

964T #304 You mention you've been around inconel and hastaloy. I have a small repair to do in the next few days where there is a discrepancy surrounding the parent metal being inconel or hastaloyX. (these may be the same for all I know, and care) Regardless, I obtained a repair procedure manual but there is no mention of back purging, likely due to difficulty within the repair environment. I'm curious, do you know if inconel and hastaloyX develop the same rough crystal structure on the backside as non-purged 304/321?

I would suggest the back purge for your repair as well. I have seen sugar on hastaloy and inconel non backed.