Building a turbo manifold - 304 or mild?
 

I can get both easily in sch40, but gut feeling says mild steel might be more durable in the face of repeated heat cycles.

321 might be better but being outside the industry is difficult for me to find.

It seems flanges are more plentiful in 304, would it be a bad idea to use 304 flanges with mild steel runners?

All insight welcome as my metallurgy knowledge amounts to about three pissteenths of eff-all

Ahh, speaking my language! How are you welding them? The 304 to mild is no problem if you use 309 filler for those welds.

304/321 is really good if you're welding them in a good fashion, with a small heat affected zone and big chamfers, and back purging. 321 will definitely heat cycle better long term better than 304, but most people will still never need 321. If you go 321, I can link you to where to buy them. Make sure to use 347 rod.

I'm biased to stainless, but both will work well. :)

I've thought about mild steel also. I saw mild steel flanges on mazdatrix. I was considering using mild steel and getting it jet hot coated. Overall it would cost more than a stainless steel manifold, but it would be coated.

Thanks GleaseMan, Awesome info, I wish I had have seen this earlier.
I ended up picking up a couple of flanges and some sch40 in mild steel, along with a torch, rods and bottle for my little 170a inverter.
Ive never done TIG before so will be playing with scraps and offcuts untill the new turbo turns up, hopefully wont make too much of a mess of it. I think the mild steel might be a more beginner friendly medium anyway.
Planning to back-purge, and got a slab of 12mm to bolt the flange down to.

The mild steel doesnt really work out that much cheaper (than 304 at least). Considering the amount of work involved the cost difference shouldn't really enter the equation.
The last one i did was mild steel, (well i did everything but lay the welds) and i used that VHT Flameproof paint just to prevent rust. Really good stuff, unmarked after about 5000km of fiery rotary goodness.
Was looking into getting the inside ceramic coated, but couldn't be assured it would not chip off and kill my turbine. Especially with mild steel - something to do with shedding carbon through heat cycles and flaking the coating. Didn't want to coat the outside and cause even more heat build up in the steel. At least that was my thinking anyway. So $20 can of paint. Surprisingly good result and saved several hundred in coating. Hopefully all the 2t oil will stop the inside from rusting, will have a look when the turbo comes off.

Glad to help, if you'd like a few tig tips just shoot me a PM.

One benefit to using mild steel flanges, is they are less susceptible to warpage when welding.

Probably find 316 is more readily available locally anyway. One of the fabricators here who does a lot of manifolds, pretty much finds the mild steam pipe survive better long term...you still end up fly-cutting or facing flanges from time to time no matter what.

Thanks man, might hold you to that. Been watching Youtube tutorials, had a little play today, need to keep working on my technique and playing around with amp levels, seems like decent results are not too far away, its a scratch start set up though, so getting the arc started without munting my tip and then stopping it while keeping gas on the weld are going to be a bit hit and miss.
EDIT, actually, its not looking that great. Will probably end up tacking everything with the MIG and getting someone else to do it.

Hmm, yeah that's going to be a problem then. All you would need is a button start setup at the minimum, wouldn't be much. But a pedal would be a great investment, you'll get a ton of use from it. Try www.arc-zone.com, we get everything from them, they can hook you up.

^ cheers, i'll keep persevering with my stick welder scratch tig set up for a bit, i think with better technique might be ok on heavy steel, but in the meantime keeping an eye out for a good deal on a tig machine.

This actually thinking about back purging mig welds. I'm sure if you bevel the edges and purge with a mig, it would hold up but not look nice

^ That's what exhaust wrap is for :suspect:

Im eyeing off this machine on ebay. Any good?
Lotos TIG200D 200A DC TIG Stick Welder Square Wave Inverter | eBay

find an old miller syncrowave or at the very minimum an econotig.

got my econotig for $600 and paid a shop $65 to rewire it for 220V from 440v, 440v is VERY uncommon and why it was cheap. the cheaper you go with a machine, the less ideal the result and the more you will be fighting the machine for an uphill battle. i've yet to see a sub $500 machine produce any sort of desirable results, you could probably weld better with a mig than a cheap tig, even with aluminum(however it is impossible to weld aluminum with a mig without having porous welds, i don't care what anyone sais).

serious welding requires serious equipment, if you're only planning on a few projects then paying a professional shop may just be a better alternative. a mig works just fine on steels anyways, it just doesn't produce as clean of an end product, tig is more for soft metals where low heat control is very important and for presentation where money talks(after a few thousand miles and discoloration the presentation effect doesn't seem to matter anyways). most often i go for the mig because setting up and keeping an area dedicated to the tig is just a bit of a pain, it takes a workbench and both hands unlike the mig which can be used just about anywhere and with 1 hand and the job will be done before i am done even just setting up to begin tig welding. i haven't had one of my mig welds crack, i just certainly wouldn't put a mig'd manifold on a display stand.

for mig i use an Astro 130 powermig that i've had for 20 years, and i've never managed to need to turn it on full hot setting even when welding on car frames and cast iron. it may be small but it has never not accomplished what i needed it to do, or ever quit on me.

^^^Probably a lot more Kemppi and Fronius out here if you're talking professional machines - and they're nicer to use. Syncrowaves still bring good dollar, but Miller is a minor brand here now....and assumes he has 3 phase.

I'd probably buy off Token or similar than some random off ebay going by the final price, you might expect at least them to be around when it goes tits-up.

Fwiw, never heard of the brand and no idea where that machine is made, we bought in a couple of chinese throwaway dc tigs years ago in one container, about $50 landed each. Other than the cheap switchgear and wrestling a snake, inflexible hoses, they welded ok, last I heard, one at least is still going with infrequent use.

^ Thanks for the good advice guys. Unfortunately i ended up winning that auction. Ill see how it goes, but yeah might have to fork out in future for a brand-name ac/dc unit.

Just tooling around with the stick welder scratch tig, I'm seeing potential for really nice welds on the pipe steel, just wishing i had more control over power and lighting out. I had a play with my 130a mig on the same material - its definitely easier, but not really enough penetration. Did a half-arsed job bevelling the joins though. How are you getting max penetration on your mig?