2. REMOVAL OF WORN-OUT TUBES.
The tubes are taken out independently of one another through the front tube-plate, after an incision has been made with a chisel through the part of the tube that is fixed into the back plate. When the holes in the front tube-plate are not greater in diameter than the external diameter of the tube, and the latter is incrusted, this process becomes very difficult, and the use of it often completely spoils the tube. In fact, we can only remove the tube by live force, and for this purpose we either use the shock of a heavy body or mechanical apparatus upon whose arrangement I shall not dwell.
In all cases the holes of the tube-plate are injured. The edge of these must, in fact, detach the scale from the tube before the latter can be removed from the boiler, and, when a little of this scale remains adherent, it produces grooves in the hole, which render it very difficult later on to make the new tube tight. It is consequently preferable to cut the tubes immediately back of the plates by means of a special apparatus consisting of a cone provided with a small circular steel saw.
This operation should be begun at the bottom of the boiler near the blow-off plug, and be continued in advancing toward the top. The cut tubes fall to the bottom of the boiler, and are removed through the blow-off hole of the front tube-plate. The pieces of tube that remain in the plate are afterward easily removed by cutting them with a chisel.
If there are but few tubes to be removed, a passage is made for them toward the blow-off plug by removing a few of the tubes beneath. When the tubes to be removed are not too far from the plug, this method is very satisfactory. Even though there were a few more tubes removed, the cost of such removal would be more than compensated for, because this method is cheaper, and preserves the tubes and plates, and because the boiler, by receiving a larger number of clean tubes, will afterward utilize the fuel better.