The Steamboating Forum

The only time I've encountered these external sleeves was, as noted here, on a 1929 locomotive, a 90 ton geared Shay locomotive. I don't know what the original intent was but I was very thankful as they allowed me to get the scale encrusted tubes out through the tube sheets with much less hassle.

Mike

One of the things I'd be concerned about is the thermal expansion rates of different metals. It's obviously a non- issue. Don't fix what ain't broke, as they say.

Ron

One thought has to be that the copper sleeve will expand both inwards and outwards so possibly tightens the seal?

"Why do you think that the tube sheets will deform more when pressurized from the inside of the gas path?"

I do not know that this will occur, I was just entering a cautionary comment.

The stress condition when the furnace is pressurized, and test pressure tends to put the tubes in tension is far different than when pressurized in the opposite direction. I would think that there may only be minor variations, but since the geometry of the subject boiler's furnace/tubesheets/stack would be very difficult to analyse (compared to typical boiler configurations), I believe caution here is prudent.

Boiler tube to tubesheet joints generally experience tube tension when pressurized in typical firetube boilers, as well as tube to boiler drum joints in typical watertube boilers. The tube rolling process generally expands the end of the tube with a slight taper, and pressure forces of normal operation (tube in tension) tend to pull this taper toward the tube, into the tubesheet. This wedge process usually gives a "self tightening" property.

The boiler of this forum thread is unusual in that the normal operating pressure forces tend to put the tubes in compression, with the tendency to force the tubes out of the tubesheet in the direction where the taper formed during tube rolling would not be the same as typical.

If a high test pressure in the furnace is used, loading joints in the opposite of normal loadings, then the tube joint might displace slightly, tightening the seal due to this taper geometry. Then when normal pressure loads force the joint in the opposite direction, an opposite displacement could be imagined, and thus increasing the probability of a leak.

I am not saying this will occur, but experience dictates the testing a component with all loads generally reversed is tempting fate, so avoiding heavy loads in the opposite direction is prudent.