Flex pipe

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fredrosse
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Re: Flex pipe

Post by fredrosse » Wed Sep 13, 2017 1:53 pm

The stainless braided fittings are generally good for over 1000 PSI @ 400F, in the half inch size. That is ratings with constant pressure, for pulsating pressure, use half the pressure, and for shock hydraulic loading, 1/6 the rating. Still good enough for most steamboat service.

The bronze flex connections are stated to be good for 450 PSI, but that rating is at 72F, and I could find no information on the de-ratings for high temperature, but the bronze (or any other copper alloys) would suffer more rapid rating reduction with elevated temperature compared to stainless. Also consider the de-ratings for pulsating service, which is generally what a main steam pipe to a reciprocating engine will see.

If using the bronze flex braided bronze stuff, be sure to use hard solder (over 1100F melting alloy) for making up connections. The trade industry only allows 120 PSI saturated steam as the maximum for copper piping joined with hard solder (or silver solder). That is in opposition to the live steam railroad boilers, often carrying more than 120PSI with hard soldering.
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Re: Flex pipe

Post by DetroiTug » Wed Sep 13, 2017 2:03 pm

Quote: "The trade industry only allows 120 PSI saturated steam as the maximum for copper piping joined with hard solder (or silver solder). That is in opposition to the live steam railroad boilers, often carrying more than 120PSI with hard soldering."

Or my buddies car with it's K copper coils brazed into it's steel drum Ofledt boiler, which runs routinely at 400 psi. I don't ride with him much. The car arena is a whole different world.

-Ron
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Re: Flex pipe

Post by barts » Wed Sep 13, 2017 10:30 pm

The coils in Otter's boiler are 1/2" OD copper, silver (57%) brazed into bored steel nipples welded into the drum. Max WP is 180 PSI limited by ASME max service temp for copper.

I've lost one once due to a low-water incident (bad reading sight glass). If I were doing this again, I'd use steel coils just for increased reliability.

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Re: Flex pipe

Post by Lopez Mike » Thu Sep 14, 2017 3:31 am

What thickness and diameter of pipe/tubing would you use? I have a friend who gave up on a boiler like yours and went to a scotch because he had so much trouble bending coils using schedule 40 pipe.
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Re: Flex pipe

Post by barts » Thu Sep 14, 2017 6:22 pm

Lopez Mike wrote:What thickness and diameter of pipe/tubing would you use? I have a friend who gave up on a boiler like yours and went to a scotch because he had so much trouble bending coils using schedule 40 pipe.
I used copper tubing filled w/ sand, and wound them over a maple mandrel w/ a half groove to match the tubing. If I were doing it in steel, I'd try and find some A106 seamless pipe which is made for bending; A53 pipe has been use w/ good success as well. A home made bender
(or giant 16" lathe w/ a really low back gear!) would likely bend 1/4" pipe w/o problems.

Here's an example of someone bending pipe (from this forum!) using a lathe:

http://www.thesteamboatingforum.net/for ... 4&start=15

Video of someone building a pressure washer coil:

https://www.youtube.com/watch?v=DCNrkC8IhmQ

You can also have them made:

https://www.youtube.com/watch?v=ieDrCR8xErI

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Re: Flex pipe

Post by Lopez Mike » Thu Sep 14, 2017 7:10 pm

After watching all of that stuff I know one thing. I will probably never build a water tube boiler. Horrors!

Not only are they frighteningly complicated, if you have one single bad weld you might as well throw the whole thing away. Unless you have a well trained squirrel to get in there in that mess and do some Mig work. And he would never find his way out.

Give me a VFT or a scotch any time. Roll in the tubes and maybe give them a sealing weld on the fire side of the tube plates. If a tube gets old, grind off the sealing weld, ream out the old tube to the tube plate size and slide in a new one.

I am received of good deal of sniveling about the quantity and weight of the water in a water tube boiler. I took the time to measure the amount recently. From dry to within two inches of the top of the glass (and that is within four inches of the steam exit) took six and a half gallons on my VFT30. That's about fifty pounds. The center of gravity of the complete and full boiler is 15 inches above the cabin sole. Yes, it weighs much more than a well constructed water tube unit. But the difference between 350 lbs and 500 lbs at fifteen inches height doesn't seem like a major threat to stability. You should see some of my passengers!

Strong opinions, I know, but wouldn't the forum be boring without them?
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Re: Flex pipe

Post by DetroiTug » Fri Sep 15, 2017 12:37 am

I consider myself a proficient welder, and I'd never attempt to use a Mig welder for boiler construction, they are notorious for areas of irregular heat (lighter and heavier mass)promoting poor penetration. Regular old stick welder with a good quality 7018 rod, root passes, clean out and finish off with fan passes.

In the case of the Ofeldt and welding in the coils, Mig won't work anyway, too bulky. Take the 7018 rod and slide a piece of heat shrink or some sort of insulating tube over it. Then the rod can be bent in any shape and those inaccessible areas are no trouble at all, keep peeling the insulator back as you go. I suppose a person could simply roll them in from inside the drum, Lune Valley esqe.

Comparing the Ofeldt to a Firetube boiler, the Fire tube doesn't fare too well, a water tube boiler is much higher output.

The old adage is: 10 square feet of heating surface per horsepower for the FireTube and 5 sq ft/hp on the water tube and I think that is just about right. The results being a much smaller boiler with higher output. A single 3 X 4 in a launch, a 20 square foot Ofeldt would run the hind end off of it. It takes a 30- 40 sq ft FT to do the same. A 20 sq ft Ofeldt could be built around 16" in diameter, 14" inches tall and weigh under a hundred pounds with a thousand PSI + working pressure if one so chose.

For winding coils, personally I'd never do that to my lathes, and too I have two steamfolks here in the area with self-built
coil winders, one will wind 3/4" sch 160 into a 4" circle. A real beast.

Mr Stephenson first used the firetube(s), they were invented by a man named Booth, work well in large scale, and satisfactory in small scale, but that was over 200 years ago, there are better ways. After hanging around with the car guys and building a WT myself and using both, the water tube is definitely the way to go. Stanley cars used and still use FT's and it takes them a half hour or better to start up. My car, once the main burner ignites, I have steam in a little over a minute. It takes longer to get the pilot vaporizers heated up and burning properly and heat the main vaporizer than it does to boil the six quarts of water in the boiler.

-Ron

Edited for accuracy. A man named Booth invented the firetube boiler design, Stephenson was the first person to use it.
Last edited by DetroiTug on Sat Sep 16, 2017 10:06 pm, edited 1 time in total.
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Re: Flex pipe

Post by barts » Fri Sep 15, 2017 1:41 am

I have a self-built water tube in Otter and a Scotch boiler in Rainbow. I really like both of them; they're different, but then so are the boats.

Otter has steam up from cold in 15 minutes or so; she holds a lot of water for a water tube (4 gallons or so) since I wanted to not panic when
feed pump issues arose. The oil fire can be easily shutdown if feed water fails. A float is essential for controlling the water level.

Rainbow takes about an hour from cold to steaming away. The wood fire has to be shoveled into a bucket and overboard if the feed fails. Rainbow will steam 20 minutes or so w/o attention; I'm adding a float to the hotwell for more flexibility in operation; she covers long distainces easily.

Both types of boilers work well in the right kind of boat. A VFT in a panatella-style hull is not a good idea; too narrow and too high a CG. A Scotch boiler works well in boats that can deal with the greater weight, and are not steamed up for a quick trip and left to cool.

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Re: Flex pipe

Post by Lopez Mike » Fri Sep 15, 2017 3:04 am

Well Ron, spoken like a good welder. But I'm not a welder and certified welders are a bit thin on the ground around here. The idea of trying to stick weld around a corner sounds like a trick to impress shop visitors but not for me.

The beauty of a fire tube boiler is that I can pre-assemble pretty much the whole thing with a few tack welds and then take it to someone who knows what they are doing. Walking up to them with a water tube unit would cause them to fall down in a grand mal seizure and then go to lunch.

I had my loco boiler done that way. He was a pipeline welder for several years with annual certifications and all that. His choice was to do the root welds with TIG and then fill in with 7018. Then he did a sealing bead around the protruding end of each tube after I had rolled them in. I traded for machine work.

I agree that MIG is not for critical stuff. My take is that is perfect for a dumb machinist like me where I just need to stick some mess together and can just cram the wire in there and move it along. Nothing under pressure and nothing over my head! And then beat the heck out of it afterwards (stress relieving?) just to see if it will hold.

I think the business about the center of gravity won't hold up to examination very well. Yes, a VFT is taller but, as I pointed out, it doesn't amount to that much. Making my stack out of thinner stuff would make more difference. It's a clunker now. Besides, traverse stability has as much to do with the shape of the hull as the height of the C.G. My weight is so low now that the boat has way too quick of a response to wakes. Jumpy and sharp. Ships ballasted that way tend to shed cargo in a seaway. Or, for that matter, passengers sitting on the side deck.

It would be interesting to know just where the center of gravity is on representative examples. What with the water leg on mine, I feel confident in saying that mine is at less than fifty percent of the height.

All that said, my main horror about water tube boilers is what appears to me to be frightening complications. And I would not want to be the person to have to try to clean one out.

Of course all of this has more to do with the design with which we are familiar. The rest is mostly enjoyable wrangling.
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Re: Flex pipe

Post by barts » Fri Sep 15, 2017 4:21 am

With proper practice and joint preparation, welding pipe joints (NOT longitudinal seams) is relatively easily mastered w/ a AC/DC welder of sufficient capacity. On our small boilers and relatively open designs, it's possible to reposition the boiler so that welding is done 'down hand' in almost all cases. A root pass of 6010 EP on a properly beveled 45 degree & gapped (1/8")seam, thoroughly ground out and subsequent filler passes of 7018 EP with any interpass inclusions ground out makes for a very strong weld indeed. You can practice these welds w/ 3/8" steel plate and then saw/grind the welds in half to look for quality problems.

[Before our cousins in other parts of the world gasp in horror, in most US states small steamboat boilers need not be ASME stamped, so welding your own boiler is not a legal issue, just as welding your own trailer or indeed, automobile, is permitted.]

I'd rather weld my own boiler than race in the Isle of Mann TT :), but to each his own perceived risks.

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