Question by a novice on Model M boiler

[CannonFodder]

Can copper tubing replace the 5/8th steel seamless tubing called for on the a model M blueprints for superheater and water heater? What are the trade offs in doing this?

Thanks,

Robert

[barts]

Can copper tubing replace the 5/8th steel seamless tubing called for on the a model M blueprints for superheater and water heater? What are the trade offs in doing this?

Thanks,

Robert

You should use copper pipe in a superheater; it will fail very quickly if overheated as happens when the engine is not running and the fire is going.
^^^^ EDIT SHOULD NOT
Copper loses strength very quickly above 400 F. For a economizer, copper works fine since it has water in it.

- Bart

[CannonFodder]

Thanks Bart!

CannonFodder

[TahoeSteam]

I believe Bart meant to type "SHOULDN'T" in regards to copper in superheater use.

[DetroiTug]

Wes,

Bart surely mistyped on that and it is "shouldn't" use copper. Copper would not last long which he wrote in the next sentence.

I use 1/2" Schedule80 black iron for my superheater on the kerosene fired Ofeldt and no issues to report. It works, but doesn't overdo it. One of the area steamfolk said he used thin stainless for his bolsover with fuel oil gun burner, he said it burned all the paint of the cylinder. Can't be good for the rings.

I have the throttle before the superheater and every once in a while I run the water a bit high and get a little carry over, it reminds me of the old 2 cycle dirt bikes with expansion chamber. Sudden burst of power.

-Ron

[barts]

Note that Ron's superheater is directly exposed to radiant heat. This means that it can get quite warm quickly if the fire is roaring and there's no steam flow to cool the superheater from the inside. Other superheaters are installed so they're protected from the radiant heat of the fire behind a few tubes, but still get enough hot gasses to provide ample superheat. The latter type of superheater will produce much less heat at low fire settings; the radiant type tends to produce a most constant amount of heat input; this can make operation at part throttle produce very hot steam temperatures.

Sometimes the two types are both used and the result is a more even amount of superheat.

Another approach is to use a desuperheater. In large sizes this is done with water injection, but for our small plants it might well suffice to pass a portion of the superheated steam back through a pipe that runs through the steam drum below the water level. A thermostatic mixing valve could then produce a more constant superheat automatically as boiler fire and engine throttle varied.

- Bart