High pressure boiler design

ChrisJ

This really isn't the right forum for this, but I figured I'd run it up the flag pole.

If I were to design and build a small steam boiler intended to run around 200 PSI how would I go about getting it tested to make sure it's safe? What pressure would I want to actually design it around, 400 PSI?

Jamie Hall

400 psi would be good, @ChrisJ . The high pressure boilers I've played with -- railroad steam engines -- are tested hydrostatically; that is with water pressure. A lot safer and better than air, since although water does compress -- a little -- and the boiler does expand -- a little -- if something breaks the pressure is off immediately, with no expansion to throw the bits around the shop (which can ruin your whole day). Further, a leak is obvious -- the water pressure drops dramatically.

ChrisJ

Jamie Hall said:

400 psi would be good, @ChrisJ . The high pressure boilers I've played with -- railroad steam engines -- are tested hydrostatically; that is with water pressure. A lot safer and better than air, since although water does compress -- a little -- and the boiler does expand -- a little -- if something breaks the pressure is off immediately, with no expansion to throw the bits around the shop (which can ruin your whole day). Further, a leak is obvious -- the water pressure drops dramatically.

Would you think this is a test I can perform and trust, or would it need to go to a shop specialized in such a task?

STEVEusaPA

Wouldn't you want (need) an engineering stamp (of approval)?
Don't they usually test things to failure? If you're doing that, make a video (remotely of course).

Keep in mind with the old steam locomotives, they had to be completely ripped apart and rebuilt quite frequently, but that was due them rotting out via constant fresh water.

Maybe if the Wall has someone who worked on an aircraft carrier, they could weigh in on high pressure steam/testing/maintenance.

Sounds like a job for MythBusters (are they still on the air).

ChrisJ

STEVEusaPA said:

Wouldn't you want (need) an engineering stamp (of approval)?
Don't they usually test things to failure? If you're doing that, make a video (remotely of course).

Keep in mind with the old steam locomotives, they had to be completely ripped apart and rebuilt quite frequently, but that was due them rotting out via constant fresh water.

Maybe if the Wall has someone who worked on an aircraft carrier, they could weigh in on high pressure steam/testing/maintenance.

Sounds like a job for MythBusters (are they still on the air).

I'm looking into building a small model steam engine for my own use.

I don't think it needs any stamps.
I just want to know without a doubt that it's safe.

KC_Jones

@ChrisJ to certify this you need an approved shop to test and sign off, even with that the approved shop is required to have an Authorized Inspector sign off (in most cases). We don't do boilers here, but we are a Section VIII U2 stamped pressure shop with certified welders etc. We self certify for production, but are required to have periodic inspections and every design gets tested to failure (burst test) prior to approval of anything.

The test pressure is a function of the design or operating pressure and a multiplier for the temperature the unit will operate at. Since the test is at ambient the safety factor gets adjusted for different temperatures. For us that typically means testing to 7-8 times the design pressure and we test to failure (burst). I am not an expert, but have been witness to several of these tests and inquired about many aspects. I'm sure I've missed some details here.

EBEBRATT-Ed

I doubt that ASME applies to something that small and I don't think you need any stamps or approval.

Build it and test it at double your operating pressure. Put some type of safety valve on it

Have to look in ASME, I am sure their is an exception for small stuff.

I would look on other model builders site for more info. This has been done before

Solid_Fuel_Man

It certainly is easier to build something small and strong than it is something big and strong. Funny how surface area works.

How big are you talking Chris? Most steam engines operate at the 100-150 psi range. Are you thinking of a water tube design?

STEVEusaPA

Solid_Fuel_Man said:

...Most steam engines operate at the 100-150 psi range...

That's what I was getting at. Is he trying to flick 45000 lb jet fighters off of a ship?
I'd have redundant safeties and relief valves...

Keep us posted, I'm curious.

jumper

Authorities made me do a hydrostatic cold water test at 150% of stamped rating. Popped some stays. At the time I was irate because boiler operated at 0 psig . But the law was that if stamp says 50 then one must test for 75 psi. Always tried to avoid pressure vessels ever since.

For home made 200 psi I'd use containment vessel.

ChrisJ

> @Solid_Fuel_Man said:
> It certainly is easier to build something small and strong than it is something big and strong. Funny how surface area works.
>
> How big are you talking Chris? Most steam engines operate at the 100-150 psi range. Are you thinking of a water tube design?

Small.... Maybe a gallon or two.

Not sure on what design yet either.

Right now I'm trying to see what my options are.

AMservices

I see where your going with this.
Modified pressure cooker with 1/4" copper lines going to PRV at radiator inlet. Steam traps, boiler feed pump, bada bing! Low mass steam boiler.

Am I getting warm?

Danny Scully

I’m thinking it’s something sneaky too @AMservices

ttekushan_3

Tom Waits will help those of us with perhaps overly vivid imaginations. 😏

https://www.youtube.com/watch?v=Y0gCCJsjemU

ChrisJ

> @ttekushan_3 said:
> Tom Waits will help those of us with perhaps overly vivid imaginations. 😏
>
> https://www.youtube.com/watch?v=Y0gCCJsjemU
>

What's he building in there?
There's a tire swing in a pepper tree. He has no children of his own you see.

ttekushan_3

And back to your original point, I remember a live steam guy telling me they typically did a 2X hydrostatic test on small scale tube type high pressure boilers.

If your use allows for a water tube type to function reliably, it’s a lot less frightening in the event of a mishap.

I’ve always asked myself “what’s the worst that could happen?” And as I get (much😀) older, that “worst” gets more informed as time goes on! Perhaps watching too many YouTube videos.

Sounds fascinating and I hope you come up with something that does what you want. Working steam on any scale is a joy.

ratio

A while back I was thinking about something similar. Turns out you can get a manually operated hydrostatic test pump starting at less than 35 bucks for the Chinesium ones.

I must have lost interest in the project though, as I don't seem to have one.

HVACNUT

In the past I serviced Fulton high pressure 100 psi, oil down fired boilers for laundry cleaners. I really only did the burner and operating controls side of things but yearly state inspections needed to be done. To this day I hate hand holes and gaskets. When I got certified at Fulton in Pulaski NY, they showed a video of a boiler blasting off like a rocket and landing in a parking lot a block away. Be careful @ChrisJ .
I joined this forum Feb of '17 and reading some of your topics, I've come to think you're some kind a mad scientist. 🔬🧪⚗🤯

Jean-David Beyer

If I were to design and build a small steam boiler intended to run around 200 PSI how would I go about getting it tested to make sure it's safe? What pressure would I want to actually design it around, 400 PSI?

When I used to hang out with live steam 12 inches to the foot scale model railroad locomotive enthusiasts, they had to be inspected annually by a representative of Hartford Steam Boiler Insurance Company (or some such name) to maintain their liability insurance. I know the pressure gauge on the locomotives went a little over twice the release pressure of the safety valves on the locomotives. I am pretty sure they operated their locomotives at 125 psi or a bit more. These were fire-tube boilers, but I do not think any had super-heaters. From time-to-time they had to replace the fire tubes and boiler stays. You do not want one of those things to explode. A 125 psi steam boiler exploding is way worse than the same volume compressed air tank operating at the same pressure; WAY WORSE. 125 psi steam is usually at about 350F.