Exact Legal Patchwork in the US for Boilers on Boats

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Re: Exact Legal Patchwork in the US for Boilers on Boats

Post by barts » Fri Nov 03, 2017 6:42 am

fredrosse wrote:CB is thinking transient conditions, where the heat gets to the metal, but not to the bulk of the water, that condition is rare, but might happen with some special circumstances.

The steady state / isothermal case is where the material of the piping and pressure vessel has a large thermal coefficient of expansion. PVC and CPVC have thermal expansion coefficients several times that of steel.

However, even steel containers can have more thermal expansion than several liquids. A good example is water, heated from 33F to 39F!
Ok, that makes sense even if it's a bit of a special case:
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Re: Exact Legal Patchwork in the US for Boilers on Boats

Post by Lopez Mike » Fri Nov 03, 2017 11:24 pm

Aside from from being enough of a dolt to let your boat freeze, my original musing was whether after hydroing at 225 p.s.i. at an ambient temp of around 60F, and leaving the pressure on as I drive down the road in full sunshine at 80F, might the pressure increase?

I have lots of room for higher pressures but it is something to provoke thought.
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Re: Exact Legal Patchwork in the US for Boilers on Boats

Post by barts » Sat Nov 04, 2017 2:42 am

Lopez Mike wrote:Aside from from being enough of a dolt to let your boat freeze, my original musing was whether after hydroing at 225 p.s.i. at an ambient temp of around 60F, and leaving the pressure on as I drive down the road in full sunshine at 80F, might the pressure increase?
Probably a bit... but this is all a wonderful academic exercise, since even a small bit of air will make this all come to naught. Air is far more compressible than water.

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Re: Exact Legal Patchwork in the US for Boilers on Boats

Post by fredrosse » Sat Nov 04, 2017 7:31 pm

"Aside from from being enough of a dolt to let your boat freeze, my original musing was whether after hydroing at 225 p.s.i. at an ambient temp of around 60F, and leaving the pressure on as I drive down the road in full sunshine at 80F, might the pressure increase?"

Back to the software, water contained in a leakproof pressure vessel (16 inch OD x 3/8 wall steel) at 225 PSIG/60F, temp rise to 80F, results in climbing to 650 PSIG if there is no relief.

Same conditions but with 16 inch OD x 0.15 wall steel, pressure rise to 500 PSIG, due to the extra stress/strain available on the thin wall vessel.

"this is all a wonderful academic exercise, since even a small bit of air will make this all come to naught. Air is far more compressible than water."

Yes, if there is a small amount of gaseous air in the vessel, pressure rise would be very small, however, with 60F at 225 PSIG, the trapped air would most likely already be dissolved into the water, so there would be no gaseous air trapped when the heating to 80F began.

I have observed this phenomenon when changing filter cartridges in my home water system, which has a clear plastic filter casing. After changing filter, and re-flooding the casing, there is always about a 1 cubic inch bubble trapped and visible. When I open the filter to full house water pressure (70 PSIG), the bubble compresses to zero volume, which was totally unexpected the first time I saw this. I was expecting it to compress to about 20% of its initial volume, but it disapeared entirely. It was not swept downstream, it was just totally absorbed by the water.
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Re: Exact Legal Patchwork in the US for Boilers on Boats

Post by barts » Sat Nov 04, 2017 8:03 pm

fredrosse wrote: I have observed this phenomenon when changing filter cartridges in my home water system, which has a clear plastic filter casing. After changing filter, and re-flooding the casing, there is always about a 1 cubic inch bubble trapped and visible. When I open the filter to full house water pressure (70 PSIG), the bubble compresses to zero volume, which was totally unexpected the first time I saw this. I was expecting it to compress to about 20% of its initial volume, but it disapeared entirely. It was not swept downstream, it was just totally absorbed by the water.
This is exactly what happens when it takes several 'pump ups' to reach and hold hydro pressure... there's air somewhere, and it's dissolving into the water. Neat that you can see this w/ a clear pressure vessel. Given that soda containers can handle full city water pressure, this would make a nice junior high science lab for a warm spring afternoon.

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Re: Exact Legal Patchwork in the US for Boilers on Boats

Post by fredrosse » Sun Nov 05, 2017 10:32 am

"Back to the software, water contained in a leakproof pressure vessel (16 inch OD x 3/8 wall steel) at 225 PSIG/60F, temp rise to 80F, results in climbing to 650 PSIG if there is no relief."

Having a closer look, the above named software considers pressure stresses which stretch the pressure vessel in both diameter and length, with end connections considered rigid. That is as if the pressure vessel is free to have strain in the diameter and along the centerline axis. That analysis boundary condition results in lower pressure rise than would be found if the pressure vessel were experiencing less longitudinal stretching. That would tend to give a non-conservative answer, with higher pressure rise, if the pressure vessel had lots of strong/rigid longitudinal stay bolts prohibiting longitudinal strain, in other words, a VFT.

Conversely, the software does not address the flexibility of the end connections, which is highly variable depending on geometry. This flexibility of the end connections would tend to lower the resulting pressure rise somewhat.

The software also does not consider anything but liquid inside the vessel, no stay bolts, no tubes, etc. Material inside the vessel can result in computed answers which are higher or lower than truth.
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Re: Exact Legal Patchwork in the US for Boilers on Boats

Post by DetroiTug » Sun Nov 05, 2017 2:49 pm

I remember reading this page many years ago when I was still in the planning stages. It's a report of a hydro test left out in the sun.

http://www.mysidewheeler.com/boiler2.htm

Quote: ""I filled the boiler with water making sure to get all the air out as this will affect a proper hydro test. We all know that water will not compress so if there is a small leak it will show up instantly. The boiler showed no signs of leakage at city pressure So I brought it up to double the working pressure. It wound up just slightly above 250 lbs. Generally when doing a hydro you go 1-1/2 times the working pressure. Since this is all new and I'm not worried about bringing the pressure up a little higher. If this was a used vessel I would only have gone 1-1/2 the working pressure which would be about 190 lbs. per square inch.

After checking it for leaks I decided to leave the test on for 4 hours. I checked the gauge a couple of times in the next half hour and it looked good. I then started to work on the firebox door and got involved for about an hour cutting parts. I then remembered to check and see how the hydro was coming. I couldn't believe my eyes when the gauge was at 325 lbs. I opened a cock on the boiler and the pressure dropped back down to 250 losing only an ounce or so of water. It seems I filled it with fairly cold water at 10:00 AM and at noon the sun was beating down. It expanded the water to bring the pressure up over 300 lbs. I learned a valuable lesson to keep a careful eye on everything while doing a test. I'm just wondering how high this would have gone to if I hadn't noticed it and reduced the pressure. Well I guess it passed its hydro with flying colors."

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Re: Exact Legal Patchwork in the US for Boilers on Boats

Post by cyberbadger » Sun Nov 05, 2017 4:08 pm

DetroiTug wrote: learned a valuable lesson to keep a careful eye on everything while doing a test.
This is very good advice. Make sure you are looking at the right gauge as well! A few hydros back I thought I had destroyed my brand new boiler when I accidentally gave it a much higher hydro because I was confused why my pumping wasn't changing the pressure. The gauge I was looking at had been isolated from the pumping I was doing. :o

Luckily it been hydroed up to a higher pressure during construction and really didn't take it past what it had experienced before, but this was not intentional.

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Re: Exact Legal Patchwork in the US for Boilers on Boats

Post by DetroiTug » Sun Nov 05, 2017 4:43 pm

Yes, that is good advice, I was quoting Ken from his page. He seems to have dropped off the radar, stopped updating his website a long time ago. He's the one that pointed me towards Reliable steam and the Salty design. He built the Rebel sidewheeler in wood also from Reliable steam.

-Ron
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