Boiler Materials

A special section just for steam engines and boilers, as without these you may as well fit a sail.
SL Ethel
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Boiler Materials

Post by SL Ethel » Thu Jun 16, 2011 1:27 am

Can anyone point me in the right direction for coils of stainless tubing for flash boiler construction? So far the best I've found for small quantities is McMaster Carr or the odd coil listed on ebay. McMaster only sells 50' coils, and I'd like to be able to have a 100' or longer primary coil without having to have a fitting or welded joint.

Also, has anyone tried carbon steel tubing (vs. pipe) for the cooler portions of a flash boiler? I believe the Lamont that George Nutz built had a carbon steel coil, but I've never seen any mention of what the tube or pipe spec was. I haven't been able to find carbon steel tubing coiled in long lengths anywhere - not sure that such stuff exists.

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Re: Boiler Materials

Post by fredrosse » Thu Jun 16, 2011 10:40 am

In the ASME Boiler and Pressure Vessel Code, stainless steel is specifically prohibited for the wetted parts of a power boiler. This is because stainless steel suffers from chloride stress corrosion cracking, and there is virtually no way you can keep your boiler water free of small amounts of chlorides (in the PPB range), inless you use distilled water exclusively, or have a sophisticated demineralization system.

Look into the coils made for pressure washer "hot box" technology, these are carbon steel, and usually designed for 3000 - 5000 psi.

As far a having a coil joint midway in the coil, Swagelok compression fittings are reliable in this service. Wrapping the fitting with a few layers of stainless steel foil will provide sufficient insulation to protect it from furnace heat. Alternately you can arrange the coil to exit the case, have the connection, then re-enter the case. I used a Swagelok fitting (3/4 tube, carbon steel) directly in the furnace coil of my domestic heat-power system, it never gave trouble. Other than Swagelok is risky business.
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Re: Boiler Materials

Post by SL Ethel » Tue Jun 21, 2011 1:43 am

Thanks for the guidance, but it also leaves me confused in some respects. I've seen articles on flash boilers with stainless tube in small boats going back to the 60's, but never any mention of failures, versus plenty of references to conventional boilers rusting out. Is this mostly luck, or is chloride stress corrosion less of an issue at lower temperatures and pressures (150 psi saturated steam in my case)?

As far as alternatives, I have looked into hot box coils. The problem is that they are quite costly to have fabricated, and not particularly efficient as far as having proper counter-flow heat transfer. I found a company here in Chicago that would make one up (just the coil itself) for around $1,000, which is a cheap boiler, but it a lot to pay for what is essentially 100' of 1/2" schedule 40 or 80 black pipe.

You mention using Swagelok fittings on 3/4" carbon steel tube. Where were you able to find tube that small in carbon steel? The smallest boiler tube I've been able to find is 2". If possible, I'd like to find 1/2" carbon tube in long lengths or coils so that I could fabricate the boiler coils myself.
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Re: Boiler Materials

Post by fredrosse » Tue Jun 21, 2011 4:15 pm

As far as the stainless steel issue goes, I only mention it because the ASME Code is quite clear in its directive prohibiting its use in the wetted parts of the boiler. I believe the problem is worse where there are high stresses, and, while the pressures we use are generally low, stress can come from bending of tubes due to thermal expansion, tubing hanger attachments (plenty of them in a large coil) or numerous other causes. I think most steamboaters don’t have the technical skills to address these issues.

I have actually seen stainless steel which developed corrosion pits about 1/2 inch deep in 30 days time, on a poorly specified sea water intake system. Carbon steel is much more predictable.

Carbon steel does not have the stress-corrosion issue, and is a very ductile material, and hence forgiving with respect to many stress related issues. Rust is a potential problem, but a few simple layup practices can virtually eliminate the rust issues for many years. My boiler for a domestic heat power module was built in 1979, and I recently hydro-tested it at 550 PSI. It uses 1-1/2 inch boiler tubes, 0.125 wall. The shell is 12 inch Sch 20 pipe (0.25 inch wall).

On e-bay, you can buy a new Hot Box, with casing, a 350,000 BTU oil burner, fuel tank, mounted on a metal dolly with wheels, with automatic controls and connections for $1400. I know the burner itself is a $500 plus wholesale item, so I would think the coil alone would be less than $500 probably. It is always easy to find someone who will make something for a high price, and they are often being fair, because they are not experienced in that specific type of work, and don’t want to take a risk of losing money on a small order. If you find the people who manufacture the coils for hot boxes, the prices will be much lower I am sure.

Carbon steel boiler tubes are the norm for typical low pressure boilers. ASME SA-178A boiler tubes are readily available, the smallest my supplier has is 3/4 inch OD x 0.085 wall. 3/4”, 1”, 1-1/4” , 1-1/2” , 2” , 3” and 4” boiler tubes are the standard inventory at Anderson Tube Inc., with wall thickness typically ranging from 0.095” to 0.135”.

Smaller tubing in carbon steel is available as heat exchanger and hydraulic tubing, ranging from 1/16” OD and up.

All types of tubing will typically have a fine finish on the OD and ID, which is what you need to use Swagelok fittings. Pipe usually has a rough mill finish on the ID and OD, so the surfaces would have to be cleaned up with emery paper before using Swagelok fittings.
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PeteThePen1
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Re: Boiler Materials

Post by PeteThePen1 » Mon Aug 08, 2011 2:00 pm

Hi Folks

I hope you will not mind me chipping in at this point, but given the title of the thread it seemed silly to start a new one.

My question relates to funnel materials. What do people generally use for their funnel? I have been talking to the wood stove dealer in my local town as a potential handly local supplier. However, he suggested that one could only use vitreous enamel coated flue pipe. His argument was that coal and wood will release tars and sulphur that will quickly eat away mild steel and even stainless steel. His examples had a really nice finish but were pretty thick steel and quite heavy which is something I would wish to avoid.

I am not wholly convinced by his argument as our wood stove flue of 13 years is either mild or stainless steel and is in no way corroded.

As ever your collective wisdom would be appreciated.

Regards

Pete
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Re: Boiler Materials

Post by artemis » Mon Aug 08, 2011 5:58 pm

PeteThePen1 wrote:Hi Folks

I hope you will not mind me chipping in at this point, but given the title of the thread it seemed silly to start a new one.

My question relates to funnel materials. What do people generally use for their funnel? I have been talking to the wood stove dealer in my local town as a potential handly local supplier. However, he suggested that one could only use vitreous enamel coated flue pipe. His argument was that coal and wood will release tars and sulphur that will quickly eat away mild steel and even stainless steel. His examples had a really nice finish but were pretty thick steel and quite heavy which is something I would wish to avoid.

I am not wholly convinced by his argument as our wood stove flue of 13 years is either mild or stainless steel and is in no way corroded.

As ever your collective wisdom would be appreciated.

Regards

Pete
Hi Pete,

In the States the building code specifies that wood stove/fireplace chimneys in a hazardous fire area of the structure (I'm not going to list them but building inspectors know) must be double walled and stainless steel is the material used. The older style (sheet metal) pipes are still used, but the double walled, stainless steel are considered to be safer. Even if the chimney "catches fire" (due to creosote buildup), the double wall construction will usually contain the fire. The double wall also prevents accidental burns. I know many steamboaters who have used this quick and easy solution and have heard of no "stack fires" resulting from using the stainless. But plenty from not keeping the stack clean. :lol:
Ron Fossum
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http://www.steamboating.org
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Re: Boiler Materials

Post by fredrosse » Tue Aug 09, 2011 4:23 am

My last two steamboats, gas fired, used ordinary light weight galvanized “snap together” ducts for stacks (0.014 inch metal thickness), with no problems. My domestic heat power system (a coal fired automatic unattended steam – electric cogeneration system) used the same stuff for a stack, burned coal 24/7 for 4 seasons, and had no problems with the stack.

I heated a farmhouse with a wood stove for years, with a heavy wall “snap together” chimney (0.028 inch metal thickness), with no problems. This chimney even had a creosote fire, and survived with virtually no damage.

Based on these experiences, ordinary light wall steel is OK, provided it is adequately supported. Be sure to use steel rivets to join sections together, not aluminum rivets.

My latest stack is painted buff white with Krylon High Heat Spray paint, it has been holding up well, with 1200 F rated temperature. If you use paint on a galvanized stack, heat up the metal (I used a propane weed burner) until the glaze turns to a flat color/texture, this allows good adhesion of the paint.
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Re: Boiler Materials

Post by PeteThePen1 » Tue Aug 09, 2011 11:03 am

Thanks Everybody for your suggestions.

All I need to do now is to find a source that can do me a 2m length. All the domestic focused suppliers in the UK appear to limit the size to 1.2m. So, do any UK colleagues have a good source of longer lengths (or two) to share?

Regards

Pete
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Re: Boiler Materials

Post by dhic001 » Wed Aug 10, 2011 10:21 am

The funnel on Zeltic has a inner made of stainless, just a couple of sheets rolled up and rivetted together, and an outer casepipe of aluminium. The casepipe was made in sections and rivetted to look like a proper steam ships funnel. Despite being 6 feet high (and in the case of the outer, 1 foot in diameter), both sections are quite light. The outer sits on flanged plate on the cabin top, and is stayed to the cabin top, while the inner fits over the uptake and has brackets at the top to hold it centrally in the casepipe. Despite many years use, neither section seems to have suffered from either the gasses carried by them, or the marine environment.
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Re: Boiler Materials

Post by Johnlanark » Sat Aug 13, 2011 4:10 pm

Pete, I have a funnel in progress for my 20ft boat, which is made much as Daniel describes. (Click thumbnail to open)
Image

The inner funnel is standard 6" stainless flue pipe - there are two pieces but the joint is hidden. Mine are intended to pull apart, but you could fix yours permanently with self tapping screws or similar. The outer is 3mm aluminium alloy that was supplied by an ebay fabricator ready rolled to 7" diameter and with a 1" overlap that I then pop riveted together. It will be held together with bolts and half inch spacers. A brass ring provides a bit of bling at the top. John.
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