304 .vs. 321 Stainless

[npez]

Guys,

I wanted to open this up for discussion as I've read various threads and many people are advocating the use of 321 for exhaust manifold fabrication but no definitive conclusions have been drawn on this. So I've done research, talked with steel suppliers, and looked at aftermarket turbo manifolds available for a variety of cars.

The reason I'm asking is I'm trying to select the material for my turbo manifolds and I'm having some self-doubts. So here it goes....

First, from the metal properties research I've done, 304 is heat resistant to approx 1600* F - from experience how hot does the plumbing actually get in a street /occasional track application (what I believe 80% or more people on the forum use their cars for - ok Superhatch/Steve is part of the 20% )? Most of the heat should be a function of the restriction the turbo places on the exhaust gases - with a larger turbo the restriction should be less. The higher the restriction the higher the heat generated. So is this as much of an issue with a properly sized turbo?

Second, from what I've seen in aftermarket manifolds of the tubular variety, most of them are 304. Treadstone is one exception that I saw that actually uses a 347 cast piece on the hot side while the rest is 304. Wouldn't these producers of manifolds be re-engineering their products if durability/reliability became an issue?

Third, according to Corky Bell (Maximum Boost): "The thermal load in an engine not originally designed for a turbocharger will cause an increase in component and cooling-system temperature when operating under boost. The components and system can handle the temperature increase for a limited period. ... Experience has led me to believe that the time limit at full boost is on the order of 20-25 seconds". So back to the heat resistance as it relates to thermal load on the motor. The arguement is that higher heat resistance and resistance to cracking are the major benefits of 321. At what point does the benefit of using 321 intersect the thermal load on the motor, or in other words, will 321's benefit be realized prior to the thermal load overtaking other components in the "system"?

So to re-state the question, under what situation does 321 become a necessity? In the scenario that 80% or more of us will be using our cars, is 321 required or does it become overkill?

I would like to hear your thoughts on this, maybe it'll re-affirm my thoughts of sticking with 304 or change my mind to go with 321. I believe drawing some sort of conclusion on this will also help other members who may be pondering this same question when doing their manifolds....

Thanks,Nick.

[gs14racer]

What are you using for the runners, thin wall tubing, sch 10 pipe or sch40 pipe. I believe this will come in to play as well.

[npez]

What are you using for the runners, thin wall tubing, sch 10 pipe or sch40 pipe. I believe this will come in to play as well.

I'm planning on using 0.064 wall tubing (I'm going with a relatively thinner wall to retain more heat inside the tube for improved spoolup. In addition I'm coating the tubing with HiperCoat Extreme as a thermal barrier to keep underhood temps low, but this will provide the additional benefit of further heat retention in the tubing.

Be aware though that the manifolds will not be holding the weight of the turbos as they will be hung with brackets/heim joints in the nose of the car. Imagine each manifold down-pipe going to a flex-tube connector then mating with solid mounted (ok maybe with an insulator) oval plumbing going underneath the car to the nose to mate with each turbo. Same thing on the return for each turbo/external wastegate.

I'm questioning the school of thought on the heat resistance of 304 for one thing, but also what other stressors other than thermal expansion and subsequent contraction on cool down (which should be handled by the heat resistance of the tube) would cause cracking. Are there mitigating things that can be done to prevent the other stressors, etc.

Thanks,Nick.

[ultrapulse]

I can't answer your tech questions, but definitely recommend going thicker wall. With that sort of temperature and small amount of vibration which every engine has I would go thickwall tubing. I wouldnt be concerned about thick wall sucking exhaust temperature out, I would be worried about longevity, as I have seen too many cracked turbo manifolds. I know the mounting is prob part of it, but dont forget everything flexes a little when this much load is being put somewhere.

[Chrispy300]

EVERYONE I know who has ever used a 304 thin walled turbo manfold has had it crack. Weld els FTW.

[Bart]

I have been told by an aircraft engineer 321 is more crack resistant due to repetative heat up and cool down. Apparently 321 is used in air craft and is very expensive. Burns stainless suggests 321 also.

[nat0Z]

321 is originally engineered for 'mild' furnus applications, where temp cycles from hot to cold regularly, ie excess of 800*C.304 is prone to cracking due to the lack of carbon and other alloying elements which stabilise the material (titanium or tantalium i think, without refering to my handbook but) state when hot. it also cracks mainly due to vibration (ie fatigue cracking) mixed along with the thermal stresses of repetitve heat & cool cycles too.

321 is quite expensive,compared to 304 and the 'lack' of availability of tube & pipe bends deems it prohibitive, hence the reason all aftermarket gear is 304, cheap and easy to obtain, take nothing away from 304 but, as it is a very good & stable grade of stainless and widely used in nearly all applications where i work except where higher corrosive resistance is warranted.

904l is another better grade of stainless suited to higher temps and continuous cooling cycles. although again quite expensive and also poor availability, it also has a pretty good corrosion resitance.

when welding 304 you use 308 wire, when using 321 s/s you use 347? wire (will have to check but from what i recall it was this or 327 or something) but use 316 on 316???? go figure, nah, there is a reason for this, but i dare not begin.....

disregard the comments in relation to the cooling system, as it pertains to all other components of the cooling system not the turbo manifold, or asscociated turbo gear, just to steer you straight.

To summarise, 321 is not worth it go for the thicker wall 304 and be done with it, and or 'fully anneal' the welded assy before a final machine accross the header flange to true up before installation. heavy bracing of the suspended turbo weight and also restraining the turbo weight from flexing the manifold due to torque of motor twisting the header pipes @ the header flange (most common spot of cracking).

i hope the above helps you all out a bit, i can if you must, dig up the metalurgy data behind it all, but the above is the general gist. feel free to fire any q's at me to, as you may have guessed it, i have a bit to do with stainless steel and other exotic metal fabrication.

cheers nat0

[npez]

Thank you everyone for the feedback. Nathan, you are the man You can't find this kind of knowledge on the Internet! I guess until now when this post will appear in Google at some point You are spot on with the filler wires you mentioned and yes it is Titanium that's added to 321.

On the wall thickness what would you recommend 0.081, 0.102, or even thicker than that?

Please advise.

Thanks,Nick.

[nat0Z]

um yea ok, i wondered why my pipe chart had odd sizes, lol, like 2.77mm wall and 3.05mm wall. (shown as sch 10 pipe & bends etc.)

either of those would be fine.need to ensure you weld the header pipes around the inside of the flange and only positioning tacks around theouter fillet edge of the pipes. ie slip the pipe through the flange and weld a nice fillet around rdge exposed to the ex port on the head, clean them up only a lilbit, it round them off but no more, as you will lose strength, in terms of fatigue resistance not overall join strength. only tack the outside when seting up the weldment much like what you see on a stock vh45 exhaust manifild!!! also BRACING BRACING BRACING, helps the world spin around....and helps 'prevent' fatigue cracking as its the vibration of the engine making the turbo hanging of the header flange vibrate like a tuning fork and only takes a small smount of time due to the cyclic fashion of an IC motor for it to crack & fail.

no probsnat0

some of what i have regurgitatid is from my boss and some from my materials training when i did my eng studies a lil while back, but i get to be exposed to this sort of gear and other during my day at work.ie welding copper titanium, coper nikel alloys etc etc, as since the late 40's and early 50's our company has specialised in fabrication of exotic allows, now we specialise more in stainles and general fabrication, along with alot of defence and water industry work.

[dsagers]

Instead of putting the hi temp coating on the outside, what about putting the coating on the inside of the tubes?

[nat0Z]

Instead of putting the hi temp coating on the outside, what about putting the coating on the inside of the tubes?

lol, no offence.

but not on both, as i would retain the heat in the material, acts like mirrors on the material surface, but some of the coating would not with stand the actual gas temperature, would have to look into it to confirm however.

nat0

[ktzed]

lol, no offence.

but not on both, as i would retain the heat in the material, acts like mirrors on the material surface, but some of the coating would not with stand the actual gas temperature, would have to look into it to confirm however.

nat0

There are coatings made for piston tops and combustion chambers so I wouldnt worry about the temp issue too much.As for the SS question, I have seen many failed attempts at making manifolds out of SS due to all the reasons listed above. 304 and 321 both can be made to work well if proper fabrication techniques are used. I know this is a 304 vs. 321 argument but all things considered, mild steel is a great material for exhaust manifolds. The fatigue strength, price, and easy of fabrication are all in its favour and if your worried about the bling factor, there are some good looking ceramic coatings that should be quite durable.Another note on bracing. Be sure that your bracing supports the weight of the turbo/exhaust system but does not restrict the thermal expansion of the (somtimes quite long) exhaust runners. I have seen some poor bracing designs that quickly cause a manifold to fail do to the TE forces ripping the manifold apart.

[npez]

There are coatings made for piston tops and combustion chambers so I wouldnt worry about the temp issue too much.As for the SS question, I have seen many failed attempts at making manifolds out of SS due to all the reasons listed above. 304 and 321 both can be made to work well if proper fabrication techniques are used. I know this is a 304 vs. 321 argument but all things considered, mild steel is a great material for exhaust manifolds. The fatigue strength, price, and easy of fabrication are all in its favour and if your worried about the bling factor, there are some good looking ceramic coatings that should be quite durable.Another note on bracing. Be sure that your bracing supports the weight of the turbo/exhaust system but does not restrict the thermal expansion of the (somtimes quite long) exhaust runners. I have seen some poor bracing designs that quickly cause a manifold to fail do to the TE forces ripping the manifold apart.

Thanks for the feedback. Your points are very well taken - design/execution is a very big part of reliability. As far as the coating I'm planning on using it is HiperCoat Extreme not very bling (grey) but 2000*F stable (used in Nascar/IRL/Aerospace). Not sure if it's intended to coat inside of the pipe.

Let me clarify my situation though as I don't believe it has come across very well as many responders are talking about manifold bracing for the turbos.

- My turbos will be hung in the nose of the car with turbo hangers/heim joints. - There should be no weight bearing stress on the plumbing at all from the turbos.- The manifolds will look similar to the factory ones with the exception of the addition of a flex-joint at the bottom (what one would consider the "downpipe" of the NA manifold) of each one mating to a tube that will eventually "Y" and go to the turbo flange and wastegate flange.- The return from the turbo as well as the dump from the wastegate will go into a return tube that will go from the front of the car to a flex-joint and then will couple to the triangular flange on my random technology cats.

So to sumarize the manifold will bear the manifold's weight, the tubing feeding the turbos as well as the returns from the turbos will be semi-solid mounted at the cross-member with an insulator of some sort (to allow for expansion) and the turbos themselves will be semi-solid mounted - the heims will allow for some movement that will be limited to the movement of the semi-solid mounted feed/return tubes. Torque movement from the engine will be handled by the flex joints.

I hope this clarifies my specific application - I am waiting on pricing on both thick wall (.120) 304 as well as 16 gauge 321 to see what the price difference will be. In the meantime as I don't have my stock manifolds here at the moment, can someone tell me the size of the primaries/log? I believe they're 1-5/8" with a 2" log, but I'm not 100% sure if I'm recalling these correctly.

Thanks,Nick.

[npez]

I picked up my manifolds from the exhaust shop so I can have them here and noticed something peculiar. There is some surface rust on the "stainless".

Does that make the material 409? I've read 409 can have develop some oxidation that in turn prevents further oxidation - does anyone know for sure the material composition of the factory tubular manifolds?

Please advise.

Thanks,Nick.

[Chrispy300]

I know that 304 and 316 and even 329 will corrode pretty quick if the welds aren't pickled, I would think that's whats happened.

[nat0Z]

im pretty certain the vh ex manis are m/steel. or similar as mine were/are quite rusty.

all stainless forms a chromium oxide after it has be scratched linished or ground whatever. it replenishes itself just being exposed to atmo.if no oxy is allowed to get in contact with the exposed un oxidised area it WILL rust even 316, stailess steels rely on this layer to protect themselves.and passivating the stainless activates this layer explicitly, ie drop it in acid, it attacks the top layer so when exposed it will re-form, i occasionally drop some of my parts in the acid @ work to bring them up before doing any polishing etc.

any pics??

pickling the welds does the same thing as passivating, (well is the same really) acid strips the outer layer (on welds is quite full of carbon, from weld burn) and lets the weld and surrounding area re-oxidse completely.

check the rusty look you are seing is not any form of flux from MS wire or anything similar, or even other inclusions/comtaminants.

nat0

[npez]

im pretty certain the vh ex manis are m/steel. or similar as mine were/are quite rusty.

all stainless forms a chromium oxide after it has be scratched linished or ground whatever. it replenishes itself just being exposed to atmo.if no oxy is allowed to get in contact with the exposed un oxidised area it WILL rust even 316, stailess steels rely on this layer to protect themselves.and passivating the stainless activates this layer explicitly, ie drop it in acid, it attacks the top layer so when exposed it will re-form, i occasionally drop some of my parts in the acid @ work to bring them up before doing any polishing etc.

any pics??

pickling the welds does the same thing as passivating, (well is the same really) acid strips the outer layer (on welds is quite full of carbon, from weld burn) and lets the weld and surrounding area re-oxidse completely.

check the rusty look you are seing is not any form of flux from MS wire or anything similar, or even other inclusions/comtaminants.

nat0

Nathan/Chris,

I'll take some pictures this evening and post them up here as I'm going off to work in a few minutes. Nothing on the manifolds has been welded yet - I had dropped the manis off a couple of months back to get them done, but with all the delays decided to do them myself. The oxidation is not "scaly"; it's very light brown color and powdery in appearance and is in several spots on the tubes not necessarily the factory welds.

I'll post the pics this evening.

Thanks,Nick.

[Mettler]

Does that make the material 409? I've read 409 can have develop some oxidation that in turn prevents further oxidation

In my stainless steel book, it classes Ferritic 409 Stainless Steel's application as being for automotive exhaust components, and describes its properties as follows:

"Ferritic heat resistant chromium steel. Good workability, formability and moderate resistance to corrosion."

Refer to http://www.matweb.com/index.aspx Matweb, for in depth information.

[npez]

In my stainless steel book, it classes Ferritic 409 Stainless Steel's application as being for automotive exhaust components, and describes its properties as follows:

"Ferritic heat resistant chromium steel. Good workability, formability and moderate resistance to corrosion."

Refer to http://www.matweb.com/index.aspx Matweb, for in depth information.

Mettler,

This is what I found in my references that led me to believe it may be 409:

"Corrosion ResistanceGrade 409 resists atmospheric and exhaust gas corrosion. A light surface rust will form in most atmospheres; this rust retards further corrosion but makes the surface undesirable for decorative applications. The corrosion resistance is about the same as that of 3CR12 and the 12% chromium martensitic grades such as 410, and inferior to the 17% chromium grade 430.

Heat ResistanceGenerally 409 is classified as resistant to scaling in intermittent service up to 815°C and up to 675°C in continuous service, but these temperatures are dependent upon the exact service environment."

I'll post the pics of my manis shortly. Maybe we can figure out what the material actually is. The flange looks like regular steel as there are no reliefs for expansion like what I've seen in SS flanges.

Thanks for your feedback.

Nick.

[npez]

Here are the pics. I noticed that there is a relief on the flange that has a welded piece of metal over it - pretty interesting.

Anyway, let me know what you guys think - is it 409 or something else?

Thanks,Nick.

Oxidation Pictures

Oxidation on Flange + Welded Plate over Relief

Another Picture of the Relief from the side
Modified by npez at 6:35 AM 9/5/2008