The Steamboating Forum

Also, there is no way to isolate that pipe at the boiler if it were to rupture. Every pipe except the relief valve on the boiler needs a shutoff valve where it is connected.

The water in the boiler when steaming at the top is probably more steam than water. Boil a pot water on the stove, it's more steam bubbles than water at the top.

I've been on and around quite a few small steamers in the last few years, never seen any steam traps, and never heard of anyone having issue with water in the main steam line, other than at start up, and that is due to steam condensing back to water in the cold lines and engine.

-Ron

OK, I'm going to buy the shell tomorrow, WOOO progress. I'll post pictures on Monday

Have a good weekend everybody

Josh

You're moving quickly Josh. I think I speak for everyone in asking for pictures once the meat meats the metal...

You could/should put a stay tube or just a solid stay where you had that main steam line drawn in.

Good luck on your endeavor.

wes

Do you have a picture of such a stay tube? I've seen pictures of stay bolts, just a length of rod threaded on one end and bolted on the fire side surface with a tell tale hole drilled in. The other end being attached to two welded in tabs in the waterside of the bottom plate? I'll try to find a picture...

Also just requested a quote from Anderson Tube Co. for the cost of my 8 8' tubes... Here's hoping for something reasonable

Josh

Edit: after scouring google images for a good five minutes I could not find a picture. Gee dang it.

The Stanley boilers had a wire wound shell, so they could have no connections anywhere on the shell. All connections were on the tubesheets, and this can work OK.

The boiler for Margaret S. is similar, and has all feedwater, blowdown, and steam connections on the tubesheets, and this has worked OK (see picture posted 02 Mar 2012 in this forum thread). The connections on the bottom tubesheet need to be insulated against flame impingement, and are wrapped with several layers of stainless steel foil, which can take the heat from the firebox. The bottom blowdown connections are also fitted with Field Tubes. The top tubesheet has much lower temperature, and can use aluminum foil to insulate connections, but since the flue gas temperature is much lower there, no insulation is needed on this boiler. This boiler also has shell connections, for the washout plugs and water column connections.

Having said that, in hindsight I would have eliminated all piping connections on the bottom (fireside) tubesheet, and put them all on the shell. This would avoid all the high temperature protection issues, stainless steel insulating wrap, Field Tubes, etc.

So, in summary, mounting your steam pipe either way has worked OK. Tubesheet connections from the late 19th century Stanley Boilers up to the, 21st century boilers can be fitted and give reasonable service. However, since your shell is fairly heavy wall thickness, and you will be using welded construction, I would recommend you use all shell connections and keep the threaded piping out of the firebox and out of the smokebox.



Some ASME Code rules, which I recommend you follow:

The Safety Valve connection must only connect to the Safety Valve, nothing else, and be as short as possible. The valve must be mounted with its stem vertical.

An 18 inch diameter VFT shell requires four washout connections that allow inspection of the bottom tubesheet on the waterside of the boiler, 1-1/2 inch minimum nominal pipe size. These connections may not be used for blowdown or feedwater connections if the shell is greater than 16 inch diameter.

These four inspection plugs should be spaced 90 degrees from each other I assume? A bit off topic but this also seems like a good time to ask about how often should a boiler be blown down and how often it should be flushed completely and the waterside of the tubes washed off?

Josh

A stay tube is simply a tube that is attached to the tubesheets to support open areas of the tubesheet that are NOT supported by by the normal firetubes. The boiler design you are developing would not require any stay tubes.

“These four inspection plugs should be spaced 90 degrees from each other I assume?”

ANS: The code is silent on this, however they should be placed to allow maximum inspection coverage. The Margaret S. Boiler has them at 90 degree intervals, and I have seen them on other boilers oriented so you can look down the free space between tube rows, perhaps to allow a washing lance to be manipulated inside the tube rows. I think your boiler tube spacing would not allow enough clearance to feed a lance between the tube rows?

“A bit off topic but this also seems like a good time to ask about how often should a boiler be blown down and how often it should be flushed completely and the waterside of the tubes washed off?”

ANS; This is highly variable, and I am sure you can get all kinds of answers to this, I blowdown the boiler about 50% of the total water level at the end of every days outing, and fully washout the boiler at the end of each season. With this plan I end up with a total dissolved solids concentration (Parts Per Million, ppm) at about 10x the input feedwater ppm. I fill my feedwater tanks with 200 ppm city water, and approach 2000 ppm at the end of the season. The ABMA (American Boiler Manufacturers Association) recommends 3500 ppm maximum for a 100 psi boiler, and lower values for higher pressure boilers. These numbers are based on evaporating about 5 boiler water volumes on each outing, obviously if you evaporate more boiler water inventories between blowdowns, the ppm concentration goes up, etc. You can buy a TDS meter for about $30 USD.

I doubt it. The tubes are 1/2" wall to wall so there is about a 1/4" space for something to go down the rows. I could maybe fit our pressure washer down the rows though.

Josh

On my VFT, which is 24" in diameter, there are about six 3/4" diameter solid stays welded spaced evenly from tubesheet to tubesheet. They are imperative. In time the tubes will corrode and you wouldn't want to rely on them for any sort of boiler strength. A failed tube or tubes should result in a leak, not the tube sheet bulging

-Ron