The Steamboating Forum

Hi all,

I have a 60 sq/ft Roberts style (all steel) water tube boiler. I have removed the casing to inspect and clean the boiler and found the inner liner severely deteriorated. When originally built, the inner liner was one sheet (0.030" thick stainless), wrapped athwartship around the boiler (the top is rounded). I plan to cut and replace the side walls with new material.

What type of stainless steel should be used/recommended for the fireside?

What would you recommend for insulation? My boiler currently has 2 layers of Kaowool. Are there any new materials out there that may work better? I would like to research different types of board and blanket as the current insulation on the boiler was marginal at best.

Recommendations for refractory? The boiler's current 1/4" ceramic refractory has crumbled due to a design error joining the sheets together (the metal strip joining the ceramic tiles together warped and cracked the refractory).

Alex

Most Stanley Car owners now use 310S stainless as a liner inside the burner. It can handle more heat and no oxidize like otehr stainless alloys. I would think this should give good service for you as well.

You might look into 321 stainless steel. It is a little more expensive than 310 but with better long term performance. Commonly used in aircraft applications for heat exchangers and shielding. Good stuff for direct flame impingement.

Does anyone have reasonable sources for 310 and 321 stainless? The prices I've seen are hair-raising.

2" of Kaowool should be plenty for a steamboat boiler, so long as the metal outside is exposed to air. I've had no issues with 1" of Kaowool with inner and outer stainless jackets of 304/316 stainless in the areas exposed to just hot gases. If you insulate the outside of the metal jacket with wood, this will cause the temperature of the metal liner to climb higher - wood is a good insulator.

For direct exposure to fire, I feel that refractories remain the best choice. I recently poured a new firebox liner of Mizzou castable refractory in Otter, and have been quite happy. It' very strong even at 1" thickness, it laughs off the direct impingment of an oil fire, and was not difficult to install. It does hold more heat; if I shut the fire off and cap the stack, boiler pressure rises perhaps 10 psi before starting to slowly drop. When restarting after sitting, it also appears to take no damage from the spurts of water and steam from the burner while it warms up. The only real downside of this material is that it is heavy, so thin sections are important for smaller boats.

- Bart

The former refractory ran 24" up the side of my 40" tall boiler. If I install the new the refractory higher, could I get away with using 304 ss as in inner liner behind it?

Bart, is the Mizzou castable very brittle?

Alex

The Mizzou is not really brittle... think concrete, from a strength, weight and brittleness aspect. It's quite heavy, so I'd use it only when the walls of the combustion chamber is directly exposed to flame impingment or intense radiant heat. IIRC the boiler on your boat is a Roberts boiler with a kerosene vaporizer; the inner walls behind the vertical tubes are subject to radiant heat from the fire where they are not masked by those tubes. I've never looked at the fire underway, however; I have no idea how much flame reaches the walls of the boiler.

Note that the Mizzou will cast very nicely; I think it's worth making some forms from 3/4" ply and casting some tiles that can be used in the boiler; necessary ledges or holes for securing the tiles can be cast in place.

There are also rigidifiers that can be applied to Kaowool/Fiberfrax to render them more stable and to prevent fiber shedding. I'd suggest reading what the folks building propane blacksmithing forges are doing.

- Bart

I have never found "reasonably" priced 321 SS. And, yes, the price of that stuff is ridiculous in my opinion. 304 is a good substitute.

Bart,

You recall correctly, the burner is a kerosene vaporizer. While the flame is fairly large, most of it is directed upward, not really reaching the walls of the boiler. The old 1/4" refractory cracked away leading to the deterioration of the inner liner and charring of the wood lagging on top of the boiler.

Thank you all for your responses.

FYI

A source for 310 SS is onlinemetals.com

$300 for a 36 x 36" sheet.

Alex

Doesn't sound cheap. What thickness?