Brazilian Steam Vehicle Update

Wood fired vehicle -- still worried about boiler

I've been pondering the safety of this myself. Air tanks like this are usually made using 1/8in mild steel. The ASME boiler code wall thickness calculation for 100psi produces a wall thickness requirement of around 0.080in thick depending on how you run the numbers, giving a reasonable safety margin for a 0.125in thick wall. Except there's a special callout in the code that shell walls should be a minimum thickness of 1/4in.

This air tank from McMaster has a 1/8in wall and is rated for 200psi at 400F.

Other than that special minimum thickness requirement, the requirements for boilers and the requirements for air tanks are pretty much identical as far as wall thickness goes.

I'm sure the additional wall thickness requirement is due to increased corrosion risk in a tank holding boiling water.

I'm considering trying out one of these tanks for my lamont boiler. I want a capacity of 2-4 gallons. I only want a working pressure of 60-100psi. The decreased wall thickness mostly means that I wouldn't use it for more than a few years. However that will give me plenty of time to get something working, and then save up for a custom made boiler tank that would likely be different anyways. Then again, I won't be directly exposing the tank to fire like this person.

At roughly 700 to 750 degrees F, a large number of steel alloys begin to lose strength. By about 1000 degrees we can see the strength drop by half. When applying heat directly to the drum, as in this device, we can see very elevated temperatures should the boiler drum run low on water (Note this machine has no feed pump or even sight glass --so it's not user friendly in regard to feed). Better yet, when the water level is low, it can only cool a small portion of the drum. So, as the drum gets hotter, the steam pressure rises to match saturation temperature. I would argue that, in such circumstances, the drum could fail. Since it contains a large volume of hot, pressurized steam (and even worse -- some hot and pressurized water), this seems like a bad idea...

That’s why there are pressure vessel laws. The ASME code. Even the head plates on a Stanley boiler does not pass the code.

Ken would you know if the Nimitz aircraft carries have heat exchanges between the reactor and a pressure vessel that feeds steam to the four turbines?

Rolly

Hi Rolly,

I can only talk in vague generalities because of security issues -- although I am sure the Soviets knew a lot more about the power plant than I did, 40 years ago.

The two ship's reactors are of two-loop, pressurized water design -- hot, pressurized water is withdrawn from the reactor housing by circulating pumps and passed through heat exchangers residing inside in the steam generator drums before returning to the reactor. Feed water entering the steam generator drums is heated by the pressurized hot water in the primary loop and converted to steam. All water from the main condensers, turbo generator condensers, and aux. drains returns to the steam generators -- ensuring that the primary reactor loop and the secondary steam loop are always separated. We had two reactors which could be cross-connected for redundancy and each reactor has multiple circulating pumps and steam generators for the same reason.

I always found it funny that cutaway drawings of the power plants, appearing in magazines, looked so little like the real thing. The artists worked from photos of steam electrical generating plants and ignored all the books on naval propulsion that are in the public domain -- it was just laziness and not secrecy.

Regards,

Ken

Thanks Ken
I was one of six project managers renovating the 20-year shut down of the Pilgrim power plant now closed. One of the most radioactive jobs was repairing and replacing the circulation pumps around the reactor core. I don’t remember any work being done on the heat exchanger before the turbine, but one can’t be everywhere with such a large construction job. The turbine room was very low radioactive area.

Rolly