hydroforming a boiler from sheet metal

A special section just for steam engines and boilers, as without these you may as well fit a sail.
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lostintime
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hydroforming a boiler from sheet metal

Post by lostintime » Wed Aug 01, 2018 9:55 pm

Okay, I know this thought is a bit out there, but with local shops that will lazer cut sheet stock cheap ive been toying with the idea of cutting a series of "harp?" Shaped sheets, weld the edges together, hook up a 2400psi pressure washer to one of the bungs welded to it, and "inflate" it to shape. My thoughts are that surviving the forming process would prove its strength for a 100-150 psi boiler, it opens more options on shape, and its cheaper/easier than machining, reaming, rolling, and welding in a bunch of expensive tubes. Ive seen it done for one off exhaust pipes,, but i dont want to waste time or money on it if im overlooking something
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marinesteam
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Re: hydroforming a boiler from sheet metal

Post by marinesteam » Thu Aug 02, 2018 4:19 am

Proper Hydroforming is done in a enclosed die, not just blown up like a balloon. The tool will cost a fortune not to mention the need for FEA FEM to simulate the forming to predict that it doen't thin out too much in areas. Take two sheets of paper, tape two opposite edges together and blow in-between then to spread them apart. You'll see that the shape you now get is kind if a mess. You could form halves and weld them together but you still have the cost of the tool and welding to deal with. Tube is cheap and it's already the proper shape. Exhaust pipes don't need to hold pressure to any real extent so much more lenient in where this processes that can be used.

Sorry, if I rained on your parade. But it is pretty out there.

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Ken
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DetroiTug
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Re: hydroforming a boiler from sheet metal

Post by DetroiTug » Thu Aug 02, 2018 5:28 pm

Any vessel that could be formed in that manner with only 2400 psi would not be safe for a boiler. Much of the tubing we use, larger shell material, smaller pipe etc has working ratings that high, the actual burst pressure can be many times that. For instance, 1/4" schedule 40 pipe if memory serves me correct has a 2400 working psi rating, but the burst pressure is over 10,000 psi, again if I remember correctly, but I'm not far off.

I see people doing this on youtube making ramjets etc, but keep in mind, any air trapped between the sheets when hydroforming will store energy and can expel components at high speed if there is a failure. It's essentially a bomb.

I found a chart, have a look for comparison.



-Ron
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lostintime
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Re: hydroforming a boiler from sheet metal

Post by lostintime » Thu Aug 02, 2018 10:16 pm

Okay, idea officially scrapped. Though I guess I never really though about saftey margins to ultimate fail as high as >100/1. Im more use to 1.5/1 or 2/1 on life critical parts in my other hobby (experimental class aircraft) but weight is much more of an issue there.
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