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Re: Scorched Boilers
Posted by: Mark Drake (62.189.28.---)
Date: May 26, 2009 11:44AM


Like Les, a few of years ago I nearly got caught out on a long hill (also in the Cotswolds!). Luckily I spotted the problem early – no damage. The problem was twofold: firstly my engine exhaust feedwater heater decided to spring a leak just before the hill and secondly the water level ‘kidney’ gauge had been installed rather low relative to the boiler.

These two conditions conspired to cause the water level to drop sharply as steam demand was reasonably high for the hill. I was surprised quite how fast the water disappeared and, worrying that I could damage the boiler, I stopped to investigate; that’s when I discovered the feedwater heater problem. Luckily I had made provision to easily bypass the heater in just such an event and I was soon on my way again.

The following weekend I decided to check the relative heights of the kidney gauge and water automatic expansion tube. The results were revealing – the kidney gauge mid point was above the mid point of the expansion tube (it always read a little low), and in my opinion the tube was set far too low, barely half way up the boiler. This meant that on a steep hill the front end of the bottom tubeplate could have less water over it than one would like.

I repositioned the expansion tube so that it resulted in a nominal 4” steam space. This now means that the water gauge reads several inches high, I can live with that. Another interesting effect is that heat transfer to the water is much improved as more of the area of the firetubes is covered by water. This is definitely noticeable in the hilly area where I live – pressure variations are less and the burner cycles off more often. There’s such a marked difference in the way the boiler behaves with a high water level that I’m confident(ish!) that I would spot a problem if I suffered another water system failure.

I’m convinced that the relatively small steam space is the best way to set these boilers up, and I’ve set my 740 water automatic the same. As to the reliability of the kidney gauge, mmmm….

I hope this is useful to someone,


Re: Scorched Boilers
Posted by: Old timer (86.112.218.---)
Date: May 27, 2009 01:43AM

I have a questions to ask. With the condensing cars oil can get inyo the boiler. Can that be another way of scorching your boiler? I know some people turn their cars from condensing to Non-condensing.Old Timer

Re: Scorched Boilers
Posted by: Mark Drake (62.189.28.---)
Date: May 27, 2009 06:44AM

Hi Old Timer,

It certainly seems that oil contamination can result in damage to our boilers, certainly the copper firetubes. The mechanism seems to be that the oil gathers at the surface of the water and the oil in contact with the tubes gets hot enough to break down resulting in a tough carbon deposit around the tube. This deposit has a thermal conductivity far lower than the copper tube and results in local overheating which in turn leads to early failure of the tube.

Another mechanism for failure is that tiny amounts of oil seek into the joints of the copper firetubes where they are expanded into the lower tubeplate. Here two things can happen. The oil literally lubricates this area and results in the tubeplate shifting dramatically resulting in substantial leakage (all those tubes double as stays too); or the oil turns into a carbon deposit as above causing the expanded tube ends to overheat as the heat can’t conduct away quickly enough; big leakage again – this can spoil your afternoon too.

I used to run my 735 condensing with a home cooked oil separator which had an average performance. I was still getting oil in the boiler, so in the last few years I have run the car non-condensing. I have had no problems finding water every 20 miles or so, in fact people are always delighted to provide!

I am working on a much better considered oil separator at the moment involving a baffle plate separator in the exhaust steam and a coalescing tank for the condensate to pass through before returning to the main tank. I have become very much of the opinion that multiple separation stages in a steam car will give the best results. I am under no illusion that it is a difficult trick to come up with a satisfactory oil separation system for a car; space is always at a premium.


Mark Drake

Re: Scorched Boilers
Posted by: (
Date: May 28, 2009 07:17AM

Did not Stanley's go over to steel tubes welded in (at the bottom only?) for the Condensing cars to get round this problem?

Re: Scorched Boilers
Posted by: Rolly (
Date: May 28, 2009 09:06AM

Yes they did Peter. Exactly when I’m not sure. It was an interesting way in how they prepared the tube sheet for the welding. They milled a recessed grove around the hole for the tube to form a false tube. Then when the tube passed through it looked like one tube inside another. They then gas welded the edge of the tubes together. This was only done on the bottom, the top was rolled in.
I am attaching a PDF drawing as well as a photo.

Attachments: boiler tube weld Model (1).pdf (2kB)   P1010002a.JPG (123kB)  
Re: Scorched Boilers
Posted by: Mike Clark (
Date: May 28, 2009 10:24AM

Interesting welding technique - I suppose it was gas welding and forming the ring of steel around the tube end reduced the heat input needed to fuse the metal, also both bits were of similar thickness which would help to get uniform penetration. Impressively even beads of weld in your picture Rolly.


Re: Scorched Boilers
Posted by: johnhennessy (
Date: June 1, 2009 07:16AM

The welding described is fairly standard for welding thin tube into a plate - nowadays more with TIG.

But can any one out there give me sound reasions why we should not use stainless steel tubes?

Re: Scorched Boilers
Posted by: Rolly (
Date: June 1, 2009 09:55AM

Look up the proprieties of stainless steel. You will find that stainless steels need oxygen to remain corrosion free. Another reason is its high coefficient of expansion.

The only use in a boiler for stainless is in a supper heater coil, and using the right alloy hear is also important. 316L is about all I can afford but Tp-347H is what is mostly used today in power plant design. Or at this time.

Re: Scorched Boilers
Posted by: (81.168.70.---)
Date: June 1, 2009 11:18AM


I'm afraid I haven't grasped your message.

As a first cut, Wikipedia gave me 17.3 ppm/°Kelvin for stainless, 17 for copper - linear expansion coefficient. If stainless is good for super heat, I can't see the problems at lower temperatures.

Thermal conductivity is about 12 for stainless, 380 for copper (Watts/metre/°Kelvin).

Although yield strength of stainless is much better than copper - even more so as it gets hotter, so wall thickness can come down, reducing the effective deficit for stainless. But that tends to be offset by availability of thinner walled tubes - back to welding difficulties.

Re: Scorched Boilers
Posted by: Rolly (
Date: June 1, 2009 12:43PM

Stainless needs oxygen to stay corrosion resistance, deny it oxygen and it corrodes.
In a boiler full of water like a Stanley the only place there is an oxygen environment is at the water line as this is the boundary between the steam and the water where oxygen and hydrogen are separated from the water. Pinholes develop at the water line with steel tubes. They can develop any where in the water area with a stainless tube. Chlorine is another detriment to stainless and all the foreign chemicals remain in the water as steam is given off in a drum boiler, unlike a mono tube boiler.
Supper heaters only have clean oxygen free gas passing through them and tend to last with only burnout from heat deterioration.

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