I weld sch 80 cs with an 1/8 th gap at 65-70 amps. I weld stainless at the exact same amperage. Your point it's mute. Prove to me that stainless Carries more heat through the tube instead of carbon steel.

 

My point is not moot. Maybe I should have been more specific. The amps I listed are using a TIG with the pulser at the same interval, pedal to the floor, and moving at the same rate of speed. I can weld .020" stainless with 200amps if I'm easy on the pedal....
I'm trying to figure out why you seem so determined to prove using stainless is based purely on "nutswinging". The properties of each material listed are documented in any text book or on online and based on that information, anyone would come to the same conclusion as to which material is best for exhaust, given it ability to withstand heat, and corrosion. You're a pipe fitter and I've build exhaust components for 13yrs. My preference to build exhaust out of stainless is based entirely on experience. If mild steel worked as well, I'd use it. It's typically a 1/3 less cost for materials which would make what I do less cost prohibitive for numerous people and allow me to make more money. Automotive manufacturers use it exclusivesly in exhaust systems on production cars. Why would they invest in more expensive materials if science hasn't determined which material is better...to make less money??
If you can provide a link to information regarding mild steel as even equivilentl to stainless in its ability to handle exhaust heat I'd love to read it. I'd be far less inclined to believe you're just on here trying to start an arguement.

From Burns site: "Typical 1010 carbon (mild) steel conducts 219% more heat per foot than do the types of stainless steel we use in header fabrication. By contrast, quite a bit more heat stays inside the stainless header tubes and does not get passed into the surrounding air. By not allowing the contraction of the cooling gases as they flow down the tubes, more exhaust velocity is retained which promotes better scavenging at the collector. This retention of velocity increases the overall header efficiency."

 

From a quick search
ALUMINUM: The thermal conductivity of pure aluminum is approximately 235 watts per kelvin per meter. Aluminum alloys can have much lower conductivities but are rarely as low as steel.

CARBON STEEL: The thermal conductivity of carbon steel is much lower than aluminum at approximately 45 watts per kelvin per meter.

STAINLESS STEEL: The thermal conductivity of stainless steel is much lower than carbon steel at approximately 15 watts per kelvin per meter.

I did find a graph I thought was interesting regarding the above. Mild steel's thermal conductivity drops fairly quickly as heat goes up until 800*c where it levels off. Stainless's thermal conductivity rises linearly and more slowly in comparison. However, at 1000*c they are equal.
graph is here:http://www.mace.manchester.ac.uk/pro...Properties.htm

 

I would use steel weld els before stainless. then ceramic coat inside and out. done right ceramic coated steel/cast steel lasts a looong time. where ceramic coated stainless flakes off pretty quickly. my ceramic guy is best I have seen. coats inside of even turbine housings and it works very well.

I know from experience coated stainless flakes off very easy. dont know why. but I assumed it was because of how quickly it expands and contracts.

 

If it did break up inside a header you wouldn't expect any turbine damage to occur?

 

It would break off in hot small chunks not enough to damage severely.

Ok so how hot does a turbo header normally great up to?

No argument but I'm trying to have an intelligent conversation and hard proven facts.

I'm a pipe fitter and welder.

And you guessed it I've built a manifold too. Trying to understand the reasoning foot not switching to mild. I can weld mild way faster and no purge. I can also get it coated to guarantee a pretty finish for it's life duration.

 

Where are you getting those prices? I honestly haven't shopped around in a long time and McMaster is simply the easiest for me to pull prices from. I was also crossing properties up in my head and I didn't bother checking my info. You are correct, thermal expansion isn't much different between mild and stainless. Thermal conductivity (as pointed out by Drifto) on the other hand is greatly different and I was swapping the two around.

I do think you have to throw out the manufacturers argument though for stainless. Yeah, all of them use 409 stainless for exhaust systems, but most use cast manifolds. If you are using pipe, you are up there in thickness with sand cast manifolds. Even if the mild steel did corrode, we are still talking almost 0.15" of material to rust. It's going to take a while and ceramics will cut that down dramatically.

From a fabrication stand point, backpurging simply ensures a smooth internal finish that is good for flow. Having to pack purge isn't an issue to me at all. Stainless sure is hard on the cutting tools though and mild steel would have a big advantage there. I would bet labor for prep is also 2X higher on stainless.

It's a solid argument, I made it to myself a couple years ago as the turbo snowmobile guys were doing mild-steel manifolds and I thought they were crazy at first until I found out they were lasting for years on stuff that sees A TON of vibration and huge temperature swings (even while operating as snow hitting the manifold isn’t uncommon). I looked into it and just didn't see the point when I saw weld-els in mild steel were more expansive.

As for ceramic flaking off of stainless, the good ceramic (Swaintech and HPC Extreme2000) holds up well. The outer color coat on the HPC stuff will flake, but the base ceramic is TOUGH stuff. I had to make a repair on a buddies manifold that was HPC 2000 coated and getting the ceramic off to weld the piece was a total *****. It was also crazy how much less heat I had to put into the part to weld it. Those ceramics work pretty well, considering how thin they are. I still think they should be thought of as corrosion barriers though and not heat barriers. If you want to control heat, you are going to need a ceramic blanket material with some thickness. Something that HPC did tell me long ago is new stainless can be trouble as it will have oils in it that prevent good bonding. The solution to this is pickling the metal before coating it, I have no idea if that is part of their process though.

Lastly, I simply put up these charts.


I've seen turbo manifolds go cherry red...
http://www.smex.net.au/reference/steelcolours.htm
600-1000C, the mild steel is lower in REALTIVE strength then the stainless materials. 304L is in the 900MPa range to start, where 1020 cold rolled is 350MPa. Even when stainless at the 50% point, it's still ahead of room temperature 1020 mild steel on stength. This should also clarify the difference between 316 and 304 for those that are interested. 316 also has better corrosion resistance then 304 as an additional benefit.

 

Damage is damage to the wheel I would suppose reliability is the reason big companies don't typically coat the inside...
I'd like to get the white hot coating myself but they won't coat the inside.

 

my evo X hta green is going on three years. coated turbine housing. inspected perfect a few weeks ago. the coating is far too soft and too thin to possibly do any damage.

 

Those coating don't do anything for temperature control. They help external corrosion, but they are FAR too thin to do anything for heat management. The Swaintech and HPC Extreme2000 coatings are FLAME SPRAYED. It's a completely different process all together and requires EXPENSIVE tools.

Anyway, one more chart. Compared to Inconel 625...stainless is a waste of time.
Not enegineering quality data, but it gives you an idea of how materials compare at temperature.

 

the coatings I use manage heat very well. there is noticable torque increase from less heat lost to manifold. funny trying to weld to the ceramic. tryed mig welding once and it was fascinating to see weld bead just bubble up and roll right off. like water on hot frying pan. engine compartment temps drastically lowered. dont know where you get they dont insulate???

 

Inconel is however major expensive isn't it vs ss counterpart ?

http://swaintech.com/race-coatings/r...aust-coatings/

Is that temperature control?

 

Unless that stuff is considerably different then what I've seen in the past? I was so unimpressed with that shiney crap 10 years ago that I've paid it no real attention since then. I suppose it could be completely different now, despite looking the same.

Although, I just had to weld a mild steel exhaust piece for a turbo RZR and that shiney stuff wasn't at all comparable to the thick flame sprayed ceramics I am talking about. It burned and flaked off up to almost 1/2" away from the weld area. Also, I was talking grinding off the area first and welding next to the coating, not actually trying to weld with the coating on. That thick stuff, I only ground it back maybe a 1/8" on either side of the bead and even with it being that close, it didn't try to burn or flake at all. I was very suprised.

Just from what I have seen, that shiney stuff might as well be chrome engine paint. With it being shiney, I suppose it could have a signifigant impact on radiant heat though which is a large amount of the heat that makes it to the engine bay. Put your hand near that header after a pull though and it doesn't block any where near as much heat as the thicker coatings. It also goes dull in no time.

The Swaintech White Lightening and the HPC Extreme 2000 (now called TC1???) coatings APPEAR to be very similar. The HPC coating just has a thin top coat for color, but the base ceramic is white. They are both fairly thick and a total PITA to grind off. I know HPC started calling there normal stuff a 2000* ceramic and then their good stuff something like 2600* ceramic for a while, looks like they changed names again though.

Either way, I'm a fan of fiberglass wrap for thermal management. Ceramic coat to protect the metal from corrosion and then wrap the hell out of it. I did this before and I could litterally put my hand on the header for several seconds directly after a drag pass. The next manifold I make though, I'm probably going to try out the lava rock blankets and possibly an inconel heat shield over it to pretty it up and protect the blanket. Not sure if the metal will be a long-tube 321 thin wall header or 316 thickwall short runner/hybrid log manifold though.

 

The Thermotec "Copper" is the newer formula for the exhaust wrap and it works very well. I actually did some testing on it in an engine dyno test cell so the data is as accurate as it gets (CFR certified test lab).. Turbine outlet temperatires went up 45 degrees F from 790 on a 4 inch 304 pipe in identical conditions. We sometimes need to make subtle changes like this to replicate certain conditions and applications. We have some other extreme heat retention wraps that are very bulky and expensive that we use on our exhaust sampling system that would all but eliminate underhood heat from exhaust lol.
The newer OEM diesel stuff is very elaborate as well nowadays, with insulators sandwiched between more stainless layers to retain more heat for the DOC exotherm, especially now that oems are injecting hydrocarbons (for dpf regen) on the wasted stroke and going right past the turbine.

 

The guy I have used for a few manifolds uses them on his nitro pulling tractors and literally 5 minutes after a pulling pass he can take the turbos off the manifolds and obviously touch them, with gloves of course but still quite impressive.

Alright now that we have detoured our discussion! Whats the regular egts people see a manifold get on a dyno during a high pull? Or with a IR heat gun whats the hotest a manifold normally sees on a properly tuned car?

Im not a big fan of the fiberglass heat wrap, it traps way to much moisture and will make very quick work of a even a stainless manifold. It also creates points in which the manifolds are not allowed to swell and will cause a properly welded manifold to fail over time.

Inconel is not in a normal persons car budget. The only companies I could ever see using that stuff would be for a company that has nothing but money to waste for no reason. Inconel is some awesome stuff to weld and to heat treat. After we weld incoloy it is then heat treated to over 4k degrees, and you can smell the metal burning, when the heat treat is done the once shiny incoloy is then turned into a spot that looks like a person welded too long in one spot. We demo'd an 8" sch 80 section of incoloy that was 209 linear feet. And I believe it costs $11k for a 20' section, and this had several 90* bends too. On the job were on it was something like 250k just thrown away.