I am about to start my manifold for a BW s372R turbo. Is making manifold with SS material or Carbon Steel more reliable?

Thanks.

 

Carbon Steel.

 

Arguable both ways, stainless is technically "stronger" in the general sense, but think of it this way: which one is stronger when it is glowing blood red? Which one would be cheaper to repair?

Listen to RC

...and ceramic coating is your friend :D

 

stainless would be better

 

Ceramic coated carbon steel, we coat our headers inside and out. My manifolds have survived pikes peak and the baja1000, that's likely reliable enough for any street application.

The problem with stainless is it expands and contracts a lot more during heat cycles when compared to carbon steel.

 

is carbon steel the same as mild steel like sch 40??

 

Yep, you can get different grades of it though.

 

ok good im building mine out of sch40 mild good to know its stronge

 

Maybe for rust protection but not for reliability and strength, carbon steel is the way to go.

 

rc can u get like sch 30 or 20 corbon steel cuz all we get aound here is sch40

 

Pretty much just sch10 or sch40.

 

Let me see what I can get, it might be a little more because of the demand is low.

 

both have their own problems.

Mild steel is susceptible to corrosion and wont look that great after a while compared to a stainless one. However heat distortion is far lesser with mild steel than with stainless, so for example manifold studs wont break off at the head/flange joint. Also cost wise its far cheaper to make a mild steel manifold...

 

Can any of you provide us with information as to why steel is better?, a grade reference would be good. When some of you state CS holds better when glowing red, then why do high end teams use manifolds with high rates of Cr? as in 17%+ of the total element break down?

quick comparison...
I've given comparison to AISI 1018 steel, non quenched or hardened... its not likely you'll find it in a steel weld el. We still don't exactly know what steel grade is being used in a non-stainless schedule "xx" hand built manifold.

AISI Type 304L Stainless Steel properties.

Density = 0.289 lb/in³
Hardness, Rockwell B = 82
Elastic modulus = 28000 - 29000 ksi (tension)
Tensile Strength, Ultimate = 81800 psi
Heat capacity = 0.12 BTU/lb-°F
melting point = 2550 - 2640 °F

316L will take some of those values further.

AISI Type 1018 steel :

Density = 0.284 lb/in³
Hardness, Rockwell B = 78
Elastic modulus = 28000 - 29000 ksi (tension)
Tensile Strength, Ultimate = 70300 psi
Heat capacity = 0.116 BTU/lb-°F
melting point = 2000 - 2800 °F dependant on carbon content.


Some terms can be simplified in http://www.wikipedia.org for quick refernce...

To add.. i had researched the method of finding out what the element break down is, or grade/properties of a steel weld 90*, a few years ago. You have to find the manufacturer (most likely overseas) and give them a stamping # or production # etched/inked onto the metal. Good luck, I thought to myself. If anyone has a further or better documented method, I'm all ears.

 

[QUOTE Also cost wise its far cheaper to make a mild steel manifold...[/QUOTE]
how so? all the carbon steel i have found is about 2 dollars more per 90 el.

 

how so? all the carbon steel i have found is about 2 dollars more per 90 el.[/QUOTE]

I'm in the uk and find they are similar priced, but the flanges are MUCH cheaper in mild than stainless.

 

sch40 1.5" 90* weld el should cost about $1.80 , if you are paying more than two or three times that you are getting totally hosed.

If you are paying less than $8 per weld el for SS ones I can just about guarantee its offshore.

The main advantage to using steel is the lower thermal expansion, the more steel expands and contracts the more stress the welds and joints see, which can lead to failure. Any manifold that is glowing red hot with a CR content is going to lose a lot of its CR by being exposed to air. It will rise to the surface and oxidize. No manifold regardless of being made of steel or stainless should glow red, its bad for either material. Ceramic coating is extremely valuable.

 

If you are refering to Cr as Chromium... Chromium is used to aid in corrosion resistance/oxidizing and a further strengthening element in stainless to make it stronger in high heat situations... hence its melting point at ~3400F, and why they use it in ceramic coatings etc etc... And also why you will see a Wolher curve charting an austenitic steel (stainless) as a better metal over plain steel.



These sorts of charts are sited through a couple editions of CISC Steel Constuction handbooks.

As far as thermal expansion goes its very minimal... working out your thermal expansion rate with the proper equation will only yield a change of ~1.5mm on 13 inches of .5" plate at 500deg on most honda head flange designs. Some peoples designs may yeild a different # but still minimal. Obviously that amount will change on a tube but that is why we have a matching filler rod for each type of stainless. IMO, If you don't know what the element break down is of the steel weld EL then how can you pick a proper filler rod for it. I can pick up the phone to my local supplier and get an element break down of my last order of 304L in 5min.

 

You are right, but if your non coated SS manifold is glowing red, especially in a non inert atmosphere, you are going to lose some of the valuable Cr content. For industrial applications, like steam lines and the like we typically use steel, if it goes into a production area where there cannot be any corrosion we use hastelloy, or AL6XN or something of the like, 304 and 316 simply expand too much.

Don't get me wrong, I love working with SS, the majority of the work I do these days is SS, but I don't think it should be used in pressurized application, with internal gas temps up to 1800*F.

I also do not think mild steel is the best choice, unless it is coated.

Having an internal and external ceramic coating really changes the game, suddenly we are no longer talking about the heat capacity of the material because it is NOT a major factor anymore, mild steel expands less, is cheaper to buy, and doesn't eat tooling like SS. If it comes down to practicality and reliability, ceramic coated mild steel takes the cake.

If you don't want to use coatings well, I think the real question is, why not?

 

be a baller and do it out of inconel.

 

I'm not a coatings expert by any means, but from what i've seen and been told, for the most part you can only ceramic coat as far inside something as you can see. Since it's a spray, there is really no way to get all the way inside a runner.

How are you doing so Dave?

 

Everyplace I call, they want 8 dollar each for a CS weld elbow, guide me HT!

 

We made some spray nozzles on flex head shafts kind of like you see on bore scopes, we put misting nozzles on the head and spray the coating through the shaft, the misting nozzles spray on a 90* angle, around the entire circumference of the nozzle.


Some guys I hear dip them, I'm not interested in doing that for obvious reasons.

 

I only buy from local suppliers, so that means Canada, here are a few places you can get them from:

Andrew Sheret LTD. 604.850.1987

Southern Drip. 604.792.0041

Pipco Industrial Supplies. 604.795.6064

These are just the local guys within 20 minutes of our shop. I bet there are 10 or more within 45 minutes. I don't believe no one in the states sells 1.5" sch40 90* weld el's for less than $2.50/piece.

 

those guys wont ship just those to me here in the USA