Stainless steel boiler/exchanger?

[Pontiacguy1]

Stainless steels also do not transfer heat very well through them, so making your tubes out of stainless would likely make your boiler not steam as well. this is also why you wouldn't make a heat exchanger or feedwater heater out of stainless.

I would echo what someone said above... There is a reason why 90% or more of large scale locomotives have welded mild steel boilers with copper tubes in them... It the most cost-effective way to build a reliable boiler for your locomotive that will perform well. With some care and regular clean-out it should last you 20+ years. I've seen some fail after only 7 or 8 years, and I've seen some that were still OK after 40 years. Depends on your water, how clean you keep it, how you lay it up, how often you run it, how often you blow down while running, boiler treatment used, etc... lots of different factors.

I've seen several boilers fail, and even had one fail on me. Like was mentioned before, the boiler always developed a leak which was not dangerous but that made the boiler not able to perform. In my case, a tube started leaking around the rear tube sheet and would put out the right hand half of the fire.

[Trainman4602]

I have stainless steel flues and my boiler makes plenty of steam. The difference in a small boiler is minimal and I rather have the luxury of knowing that I won't have a leaky flue.

I'm a firm believer that copper flues will leak after a while.

[DavidF]

I have stainless steel flues and my boiler makes plenty of steam. The difference in a small boiler is minimal and I rather have the luxury of knowing that I won't have a leaky flue.

I'm a firm believer that copper flues will leak after a while.

Do you know what grade stainless was used??

[Trainman4602]

316

[Comstock-Friend]

Stainless steels also do not transfer heat very well through them, so making your tubes out of stainless would likely make your boiler not steam as well. this is also why you wouldn't make a heat exchanger or feedwater heater out of stainless.

As I noted before, Doug (Alkire) in 'So you want to Built a Live Steam Locomotive' did have some misleading comments about the heat transfer aspects of a stainless boiler. He put copper tubes in his for the better conductivity. The gas to tube heat transfer coefficient is controlling and much less than either the copper or stainless conductivity and especially less than the boiling heat transfer on the tube to water side. You would not notice any difference in steaming qualities between stainless or copper (David S is correct). We could go through the heat transfer calculations but I see everyone's eyes glazing over already....

John
(Retired ASME Section I and Section 8 boiler and pressure vessel chief engineer/process designer)

[Pontiacguy1]

I knew of one boiler that was built with tubes made from Monel. A bit overkill, I think, but it steamed and ran well enough. It was an Allen boiler, and most of those seem to fail in the mud ring and firebox area when people let it get packed up with crud.

[Comstock-Friend]

As already been mentioned ss is no good for boilers because of the metallurgical problems that accompany it.
Having said that. It is used in in UNFIRED pressure vessels and process piping. Provided it doesnt reach the temp at which carbide precipitation occurs its all good.
Fireside of heating surfaces is where the problem could occur. Same with flues. Superheater units are out of the question.
The only way ss might be useful is on outer shell and plate surfaces not exposed to the direct heat of combustion.

Not accurate. I analyzed the failure of a hydrocarbon vaporizer for my former employer. Carbon steel vessel, T316 stainless coil inside containing the hydrocarbon (steam inside the vessel to vaporize). The design stresses were less than an eight of allowable, yet the stainless coil cracked at the attachment to the coil headers. Came out that the customer hydrotested the unit prior to startup with Rhine River water, which had a very high chlorine concentration. Classic chloride stress corrosion failure of a non fired pressure vessel.

Again, there are successful stainless boilers; Tom Miller's, Doug Alkire's and Dave Moore's stainless boilers are all T321H (Titanium stabilized). Water care to exclude chlorides is followed.

John

[Sftyvlv]

As already been mentioned ss is no good for boilers because of the metallurgical problems that accompany it.
Having said that. It is used in in UNFIRED pressure vessels and process piping. Provided it doesnt reach the temp at which carbide precipitation occurs its all good.
Fireside of heating surfaces is where the problem could occur. Same with flues. Superheater units are out of the question.
The only way ss might be useful is on outer shell and plate surfaces not exposed to the direct heat of combustion.

Not accurate. I analyzed the failure of a hydrocarbon vaporizer for my former employer. Carbon steel vessel, T316 stainless coil inside containing the hydrocarbon (steam inside the vessel to vaporize). The design stresses were less than an eight of allowable, yet the stainless coil cracked at the attachment to the coil headers. Came out that the customer hydrotested the unit prior to startup with Rhine River water, which had a very high chlorine concentration. Classic chloride stress corrosion failure of a non fired pressure vessel.

Again, there are successful stainless boilers; Tom Miller's, Doug Alkire's and Dave Moore's stainless boilers are all T321H (Titanium stabilized). Water care to exclude chlorides is followed.

John

I stand corrected. Thanks for the heads up.
Dave

[Sftyvlv]

Comstock. Could not carbide precip be a factor as well even with austenitic and/or low carbon content on fireside surfaces?

[Comstock-Friend]

Comstock. Could not carbide precip be a factor as well even with austenitic and/or low carbon content on fireside surfaces?

T321H titanium stabilized to prevent carbide precip...

John

[Sftyvlv]

Comstock. Could not carbide precip be a factor as well even with austenitic and/or low carbon content on fireside surfaces?

T321H titanium stabilized to prevent carbide precip...

John

[gwerhart0800]

There is a 4" scale porter on DLS that has been up for sale for a while. The owner proudly describes the boiler:

"New Boiler in 2010- 10-1/4" x 33" EXTRUDED STAINLESS STEEL with mild steel sheets front & back with 17 schedule K copper flues. "

When I saw that, I immediately factored a new, non-stainless steel boiler into the price. I would love to have an engine like that, but the boiler is an issue ... new or not.

https://www.discoverlivesteam.com/disco ... /index.htm