Hydro Test

This forum is dedicated to the Live Steam Hobbyist Community.

Moderators: Harold_V, WJH, cbrew

doublereefed
Posts: 199
Joined: Wed Jan 30, 2008 7:24 am
Location: Manhattan Beach, CA

Hydro Test

Post by doublereefed » Fri Dec 14, 2018 11:29 am

I need to hydro test my Allen Mogul boiler.

Having observed and participated as several clubs test my boilers over the years... wondering what the basic parameters are for best practice?

- 150% of working pressure?
- Test the sight glass to this pressure, or isolate using the top and bottom valves?
- Test the pressure gauge, presuming it is has the range to handle the testing pressure?
- How long should the pressure hold, and what is an acceptable pressures drop over time? i.e. No more than 5 psi over 15 minutes, etc.
- After the hydro, then test the safeties under air (or steam?) pressure to make sure at what psi each releases?

What constitutes failure? Rapid loss of water/pressure, etc. but also:

- Weeping at the front or rear tube sheet?
- Sight glass leaks?
- ???

I understand why hydro is the safe way to go, i.e. water is not compressible. Given that, how reasonable would it be for me to do an air-over-water hydro test? Fill the boiler and with water, and then use air compressor to run the pressure up to 150%. My air compressor will put out 150 psi, which would work for me if the test pressure of 150 psi on 100 psi operating pressure constitutes a fair test. (Although I can't remember what the safeties are actually set to right now... 80? 100? 120?)

Thanks,

-Richard

User avatar
pat1027
Posts: 235
Joined: Sat Oct 09, 2004 3:45 pm
Location: Michigan

Re: Hydro Test

Post by pat1027 » Fri Dec 14, 2018 11:58 am

150% is most common. Depending on the service factor some people like to go higher with a new boiler. Mostly you are looking for leaks. A 150% hydro won't reveal firebox sheets and stay bolts that are nearing failure. I have seen two locomotives fire box sheets down to 1/32" in places that passed a hydro up to the day the sheets cracked.

In the tests I did as a club boiler inspector and what the state does since they took over is to hold pressure long enough to do the visual inspection. There will be enough leakage through cold valves that unless your looking at just the raw boiler you can't really saw hold pressure for x minutes.

After hydro I liked to test the safeties cold to know they opened. It wasn't uncommon when a locomotive had two safeties for the higher valve to stick if it rarely opened. The state inspectors want to see them open with steam. It's o.k. for me as I've always done my own inspection before I call the state.

Failure when I did club inspections was typically leaking tubes. Either rolled tubes leaking on the fire box end or mild steel tubes that had corroded through. I never had to tell anyone they couldn't run. If there were leaking tubes to a man as soon as the owner saw it he said he wasn't running. Leaking as in running down the tube sheets I'd fix. A little water beading at the end of the tube we let go. Aside from leaking tube all the articles and club procedures I've read talk about listening for popping stay bolts. I never heard any. I had a leaking stay bolt weld last year that the state missed but I saw.

I hydro the sight glass and the gauge. I like to have everything that will be under steam included in the test. If the gauge doesn't have enough range take it off and plug the connection.

doublereefed
Posts: 199
Joined: Wed Jan 30, 2008 7:24 am
Location: Manhattan Beach, CA

Re: Hydro Test

Post by doublereefed » Fri Dec 14, 2018 12:30 pm

Thanks for that Pat, much appreciated.

Another question: I have a good hand pump in the tender in this locomotive. Wondering... can that hand pump generate the 150% for the test, is that a practical avenue to explore in reality?

User avatar
Builder01
Posts: 633
Joined: Mon May 18, 2015 5:26 am
Location: Erie, PA

Re: Hydro Test

Post by Builder01 » Fri Dec 14, 2018 12:59 pm

A good hand pump will easily make enough pressure for a hydro test. I do this for all my hydro tests. In fact, a proper feed water hand pump will pump to very high pressures, be careful!

David

User avatar
Fred_V
Posts: 4361
Joined: Sun Jan 12, 2003 3:26 pm

Re: Hydro Test

Post by Fred_V » Sat Dec 15, 2018 7:39 am

A boiler inspector for an insurance company told me that they only hydro to working pressure. The thinking is to not stress the boiler, just look for leaks.
any thoughts??
Fred V
Pensacola, Fl.

User avatar
Builder01
Posts: 633
Joined: Mon May 18, 2015 5:26 am
Location: Erie, PA

Re: Hydro Test

Post by Builder01 » Sat Dec 15, 2018 9:23 am

I have no idea what inspectors do for full size boilers and I'm sure the rules are quite different as compared to miniature boilers.

For miniature boilers, newly constructed boilers are hydro tested to two times the working pressure. New boilers that are taken to the 2 times working pressure, usually have all fittings removed and all bushings plugged except the one going to the hydro test pump. (A hand pump works fine for this) Subsequent tests are done at 1-1/2 time the working pressure, this is typical for the annual test. Most live steam clubs use these pressures for newly built boilers and annual tests for existing boilers.

Initial testing of miniature boilers should be done with water, not air, until the boiler is proven for working pressure. Doing initial tests with compressed air is dangerous.

Leaks at fittings are usually acceptable. This would include the sight glass.

Leaks at tube sheets, stay bolts, and any joints on the boiler are not acceptable.

Safety valves are usually left on during the hydro test to see that they open with water at about the correct pressure. Once they open, they are removed, bushings plugged, and the test resumes taking the boiler to 1-1/2 time the working pressure.

A "hot" test is usually required as well. This is to prove that the safety valves will lift using steam, and, to prove that the safeties will dump steam faster than the boiler can generate it. The hot test also is to prove that you can put water into the boiler while under steam pressure.

David

User avatar
Marty_Knox
Posts: 1508
Joined: Thu Jan 09, 2003 6:50 pm
Location: Michigan, USA

Re: Hydro Test

Post by Marty_Knox » Sat Dec 15, 2018 9:28 am

Fred_V wrote:
Sat Dec 15, 2018 7:39 am
A boiler inspector for an insurance company told me that they only hydro to working pressure. The thinking is to not stress the boiler, just look for leaks.
any thoughts??
The hydrostatic test is NOT a leak test. The idea is to stress the boiler with warm water to find any weak spots.
FRA rules for testing boilers call for a test to 125% of working pressure, with the boiler between 70 and 120 degrees F.
They also call for an internal inspection after the hydro.
I remember the old FRA/ICC boiler Inspector I learned from saying he was worried about how things would go once the old heads were gone.

User avatar
Bill Shields
Posts: 5993
Joined: Fri Dec 21, 2007 4:57 am
Location: Somewhere in the World
Contact:

Re: Hydro Test

Post by Bill Shields » Sat Dec 15, 2018 9:39 am

I second Marty's comment about the FRA / ICC inspector.

fortunately there are enough stationary boiler inspectors around who can at least understand and describe principles of a boiler inspection.
Too many things going on to bother listing them.

Soot n' Cinders
Posts: 849
Joined: Wed Jun 27, 2012 5:24 pm
Location: Marietta, Georgia

Re: Hydro Test

Post by Soot n' Cinders » Sat Dec 15, 2018 12:17 pm

A friend of mine is a boiler inspector and he says common practice in the refinery boilers is hydro to the setting of the upper safety. Over pressuring while cold could actually damage the boiler
-Tristan

Projects
-2.5" scale Class A 20 Ton Shay

User avatar
Builder01
Posts: 633
Joined: Mon May 18, 2015 5:26 am
Location: Erie, PA

Re: Hydro Test

Post by Builder01 » Sat Dec 15, 2018 1:34 pm

I think some of the disagreement is full size boilers versus miniature boilers. While these are similar, they are not the same and rules that apply to one can not be used for the other. The 2 times working pressure for new boilers and 1-1/2 for annual testing is for miniature boilers, not full size. These two hydro testing pressures have been used for years on miniature boilers and works very well. I imagine most state boiler inspectors know very little about miniature boilers. Using full size boiler tests on miniature boilers and vice versa, is not the thing to do.

David

User avatar
gwrdriver
Posts: 3150
Joined: Mon Jan 06, 2003 10:31 am
Location: Nashville Tennessee

Re: Hydro Test

Post by gwrdriver » Sat Dec 15, 2018 5:22 pm

David's statement above is a clear and simple statement of the historically good and safe practice in model boilers, and good advice which can't be emphasized enough. Our boilers aren't designed or managed anything like industrial power boilers and introducing talk about how industrial power boilers are treated only serves to confuse the issue.

We all probably differ on a few details, IMHO on the initial test (2xWP) the fittings should not be included in the test - we want to test the boiler vessel for soundness, not the fittings. On subsequent tests (1.5xWP) it's your call whether to leave the fittings installed, including the water glass, due to the work involved in removing them, so almost everyone leaves them in place. Personally I isolate or remove the gauge glass when I do secondary tests.

Richard, your pressure gauge for normal running should not be included in a test. Use a separate gauge of 2X the expected TEST pressure.
Builder01 wrote:
Sat Dec 15, 2018 1:34 pm
I think some of the disagreement is full size boilers versus miniature boilers. While these are similar, they are not the same and rules that apply to one can not be used for the other. The 2 times working pressure for new boilers and 1-1/2 for annual testing is for miniature boilers, not full size. These two hydro testing pressures have been used for years on miniature boilers and works very well. I imagine most state boiler inspectors know very little about miniature boilers. Using full size boiler tests on miniature boilers and vice versa, is not the thing to do.
David
GWRdriver
Nashville TN

User avatar
Fred_V
Posts: 4361
Joined: Sun Jan 12, 2003 3:26 pm

Re: Hydro Test

Post by Fred_V » Sat Dec 15, 2018 5:57 pm

Tristan and I have been talking to the same Guy. i brought this up to see what the opinion was from you guys.
Fred V
Pensacola, Fl.

Post Reply