Sciencemadness Discussion Board

What temp is considered super heated steam and what materials will withstand these conditions?

RogueRose - 8-10-2019 at 19:48

I'm trying to figure out is a 10 bar vessel (180C/357F) would be considered super heated steam, and if steam of that temp would rapidly degrade iron/steel. I need to find a material that can handle this temp in both a containment vessel (~1-1.5L) as well as tubing that can carry the steam from the vessel into a turbine system. I'm also looking at something that will allow for the 180C to be further heated as a couple coils (maybe 3-5ft long) are passed through a hot fire (1500-2000F) to further increase the temp after it leaves the vessel. In this case it would most likely be used to pass over hot carbon, not run into a turbine - though I'd like to test that was well and see if there is significant increase in power output.

I'm leaning towards 304/316 SS for the vessel (appropriate thickness) with a blow-off valve (brass OK?), and then the same material for the tubing (probably 3/16" - 3/8" ID) or if possible some thick walled copper if it is strong enough to handle the pressure and IDK if hot steam degrades copper the same as it does iron/steel.

Twospoons - 8-10-2019 at 20:22

I would try to use the same material throughout, no matter what you choose, otherwise galvanic corrosion may be a big problem , unless you select materials carefully.
Espresso machines operate in the vicinity of your stated conditions : https://www.wholelattelove.com/blogs/articles/espresso-machi...

SS is probably your best bet, so long as there's no chlorine/choride in the water.

[Edited on 9-10-2019 by Twospoons]

Vomaturge - 8-10-2019 at 21:45

In the case of steam, superheated means the temperature is greater than the boiling point of water at a given pressure. 180C and 10 atm is close to saturation, so probably not superheated. Also, I don't think e.g. 180C steam at 5 atmospheres would be more corrosive than 300C steam at 90 atm, simply because the former was "superheated" and the latter was not.

I'd say you could use normal carbon/mild steel pipe, or even copper at 180C, (although soldered joints may start having problems at temperature). For the 800C superheater, stainless steel and realize its strength will be a half to a quarter of what it is at room temperature

For either setup, assume there will be a few catastrophic failures, due to engineering flaws temperature/pressure excursions, etc. before you get it running smoothly. Be safe and have fun.

PS why is espresso brewed at high pressure? Is it to enable liquid water at ~200C, or is it just part of forcing the water to flow through the grinds? The espresso websites talk about final (in the cup) temp, pressure while brewing, but not brewing temperature.

Yttrium2 - 9-10-2019 at 07:57

I think it's to move the water through the grinds

Good question!

I wonder how pressure cooker coffee would taste, it might be the next best thing!

Ubya - 9-10-2019 at 09:00

Quote: Originally posted by Twospoons  
I would try to use the same material throughout, no matter what you choose, otherwise galvanic corrosion may be a big problem , unless you select materials carefully.
Espresso machines operate in the vicinity of your stated conditions : https://www.wholelattelove.com/blogs/articles/espresso-machi...

SS is probably your best bet, so long as there's no chlorine/choride in the water.

[Edited on 9-10-2019 by Twospoons]


maybe you misread, espresso machines have never used steam at 180°C.
coffee grounds would char at that temperature.
maybe you read 200° F as 200°C

Twospoons - 9-10-2019 at 13:02

I was referring to the pressure. Coffee is ideally brewed at 95C. But there are also single tank espresso machines that heat the tank to ~120 to 130C for steaming milk. So not exactly the same conditions, but a similar sort of engineering problem.

rockyit98 - 10-10-2019 at 03:27

aluminium would do fine up to 350 Celsius it can handle the pressure.
do careful research about stainless steel type. this old tony
https://www.youtube.com/user/featony

Metacelsus - 10-10-2019 at 04:03

Quote: Originally posted by rockyit98  
aluminium would do fine up to 350 Celsius it can handle the pressure.


Wouldn't chemical reactivity with 350 °C steam be an issue? I don't think the surface oxide layer would be stable under those conditions.

[Edited on 2019-10-10 by Metacelsus]

andy1988 - 10-10-2019 at 10:01

You may enjoy this read on boiler corrosion, and perhaps similar material.

A great discussion here on creating a magnetite layer.

Also a good read on magnetite.

[Edited on 10-10-2019 by andy1988]