Metal for diesel exhaust

[DanStro]

I am working on a project where a housing needs to withstand the diesel exhaust environment. The main hurdle is the temperature (~500 degrees C) because the housing is somewhat isolated from the gaseous part of the environment. I've looked around and found that the most common materials are SS409, Aluminized SS409, and SS304.

Can anyone suggest reasons why one is better (or worse) than the others? Or are there any other materials that I need to consider?

This is an optical application so I need to keep the lens secured at the high temperature so I am also looking for a different material that has a relatively high CTE (>18e-6). How high depends on the CTE of the housing material but that 18e-6 is in the ballpark. Can anyone suggestion options for this?

Thanks,
Dan

Han primo incensus

 

[arunmrao]

I have seen both the grades 409 and 304 being used for exhaust systems.

Have you considered Invar alloy for high temperature stability.

I'm just one step away from being rich, all I need now is money.
( read somewhere on the internet)

 

[CoryPad]

Type 304 stainless steel is better for temperature resistance and general corrosion resistance. Type 409 is barely stainless steel, it was developed as the lowest cost option to meet 10-year corrosion requirements for automotive exhaust systems. Aluminized 409 is an improvement on standard 409 for both oxidation and chloride ion corrosion resistance.

There are a multitude of alloys to consider, which requires more information about your design and the operating environment.

 

[tbuelna]

DanStro-

How will the exhaust system be fabricated? I would assume there is some welding of tubes involved, but will some of the components be cast, or require extensive multi-axis CNC machining, or maybe even be rapid prototyped using DMLS?

You also mentioned a requirement for a material that has a CTE >18ppm/degC. The only readily available corrosion resistant high-temp alloy I can think of that comes close is 304 cres (~17.3ppm/degC). There are some exotic nickel alloys like Carpenter 22-3 or 19-2 that are designed to provide the high CTE you desire (19.8ppm/degC for 22-3 and 20.3ppm/degC for 19-2). While you might be able to use these materials for something like a seal or a bushing, I don't think they would be suitable for constructing the bulk of your diesel exhaust system. Without having more details I would have to agree with CoryPad's inital suggestion of using 304 cres.

Hope that helps.
Terry

 

[EdStainless]

At higher temps the aluminized 409 will be every bit as good as 304.
If there are areas that get colder, say under 200C then you will need to worry about acid attack.

If you want to go easy, and cost isn't a driver then build it all out of 316L.
Better strength and corrosion resistance than 304, and easy enough to find in many product forms.

You want a high CTE? Doesn't you glass have a much lower CTE? There are special alloys that are designed to match different glasses (902, 903) so you should be able to select one that matches.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[mighoser]

Haynes 230 is a good option and has much better long term stability over 316L at 500C. I would recommend 347 or 321 if you were going to go stainless. It sounds like this is a small housing inside a diesel exhaust system so perhaps material cost is less of a driver. Ed is right your comment on CTE are backward. Metals and plastics have higher CTE's than glass and ceramics. Why aren't you trying to match your lens CTE?

 

[DanStro]

Sorry it's been a while. I haven't had a chance to address any of this until now. Unfortunately I can't attach a sketch because of NDA issues but I'll try to explain it. The operating temperature is 500 degrees C and from what we've been told the system is isolated from the exhaust gasses by an 'air knife', but it will see the temperature listed. The lens is fused silica which unfortunately has a very low CTE (~0.5E-6/degC). So there is no chance that I'll be able to hold the lens around its OD. I am instead looking at athermalizing it by using a retainer that is designed to lengthen in the direction of the lens, this will provide the holding force and the radius of the lens will help keep it centered. The OD of the lens and the ID of the bore can then be large and the system should still work.

That being said I was originally thinking of using 409 (CTE~13e-6) for the housing and probably 304 (CTE~19e-6) for the spacer. But after reading some of the posts and doing more research I am thinking that aluminized 409 is the better option.

Han primo incensus

 

[tbuelna]

DanStro- For a diesel exhaust system that will be exposed to 500degC gas temps, 304, 316 or 321 cres should all work fine. I would recommend 304/316/321 cres for the simple reason that tubing and mandrel bends are readily available in these alloys. This would make it much easier to fabricate your exhaust system.

Just out of curiosity, what is the purpose of the optical lens in the exhaust system? Is it for measuring the soot in the exhaust gas flow?

 

[DanStro]

Thanks tbuelna. I am strongly leading towards 304 for some parts. But if I do that then I'll need to find a material that has a significantly larger CTE than 304, otherwise the athermalization won't work. I can't get into too much detail about what they are looking for but they are analyzing the makeup of the exhaust gases.

Han primo incensus