Input on boiler design

[mtnman]

I am currently working on a 16' Thayer hull in which I am installing a Ray Hasbroucks #1 engine. The boiler, I am building from stainless steel tubing. I'm using a 7"x21" schedule 80 SS pipe with both ends welded and standing vertical(it was part of a steam system and rated at 700lbs). Then there are 5, 20' lengths of 1/2" SS tubing coiled around the lower half of the 7" pipe. Each tube will began and end in the lower half of the 7" pipe. “Water In” will be introduced to the lower side of the 7" pipe, “Sight Glass” will be on the upper half of the 7" pipe above the ½” tubing, “Steam Out” and “Safety Valve” will exit the top of the 7" pipe. “Blow Down” will exit the bottom of the 7” pipe. Propane will be the heat source. This is still in the design stage and I am looking for input. Will it work or am I going to blow myself sky-high!

[fredrosse]

The ASME Boiler Code specifically prohibits use of stainless steel for wetted parts of a power boiler. There can be exceptions to this rule, but it would be prudent for you to use materials acceptable to the Code.

[mcandrew1894]

What Fred said.....
I would start with a tried and true boiler design.


Additionally, and I know I will take heat for this....don't use propane MHO

If it leaks and collects in the bottom of the boat, your sitting in it....and your passengers too.

try wood......much safer

Dave

[dhic001]

Why bother with the large stainles pipe, why not just build a true monotube? Simple to build, simple to steam, no hassles with code design, light in weight and very efficent.
Daniel

[mtnman]

OK, scrap the stainless idea. But I have to wonder why ASME frowns on stainless?

[mcandrew1894]

I believe its much more sensitive to stress corrosion cracking than mild steel.....

Dave

[fredrosse]

That is correct, the stainless steel is sensitive to stress corrosion cracking, and unless you have very very clean feedwater (chloride impurities measured in "parts per billion") the use of stainless steel is not allowed. Very low carbon steel is ideal for low pressure (under 600 psi) steam launch boilers, and should be used. In the USA, this is A-53 or better yet, A-106 pipe. Boiler tubes are usually A-178 material in low carbon steel.

[mcandrew1894]

That is correct, the stainless steel is sensitive to stress corrosion cracking, and unless you have very very clean feedwater (chloride impurities measured in "parts per billion") the use of stainless steel is not allowed. Very low carbon steel is ideal for low pressure (under 600 psi) steam launch boilers, and should be used. In the USA, this is A-53 or better yet, A-106 pipe. Boiler tubes are usually A-178 material in low carbon steel.

A106 on all three drums of my boiler...schedule 80 on the steam drum and schedule 40 on the smaller mud drums......good stuff.

[87gn@tahoe]

Why bother with the large stainles pipe, why not just build a true monotube? Simple to build, simple to steam, no hassles with code design, light in weight and very efficent.
Daniel

Controls can become an issue with monotubes.

[dhic001]

Controls can become an issue with monotubes.

Nope, been mastered here on oil fired ones, not so easy if solid fuel is used. Totally safe too, so little water in them that they can't explode, they only go fizz, believe me, I saw it happen. A friend here in New Zealand has built a number of monotubes using stainless tubing. Superb steamers, and once set up are virtually automatic steamers.
Daniel