Wiped joints on copper pipes are longer than wiped joints on lead or composition pipes. Copper pipes 2 in. or more in diameter have joints from 2 1/2 in. to 3 in. long; 4-in. pipes have joints about 4in. long; but it must be remembered that whilst reasonable length and thickness of joint are necessary to enable the copper pipe to withstand pressure and strain, the maximum time of service does not depend on the length or thickness ot the joint as in lead-pipe work. That which determines practically the life of the joint is the extent of pipe which is carefully tinned before forming the wiped joint. If the interiors of the two pipe ends are tinned, say, tor 6 in or 8in., on cutting open the joint in a few years time, it is found that the tinning has diminished to 2in. or 3 in., a corroding action having taken place at the end of the tinning; for this reason it is advisable that the tinning be fairly thick, so as to retard the separation and ultimate failure of the joint. In tinning copper, first thoroughly clean it with dilute sulphuric acid or scour with sand and water, and then rinse it with chloride or zinc known as killed spirit.

Melt some pure tin, throw in sal-ammoniac as a flux, and dip the copper in the tin, or pour or rub the latter over the copper, in pipes forming a portion of a distillery plant it is especially important that no untinned spots are left on the interiors of the pipe ends, as at such spots the destruction of the tinning commences at once. In Iig. 1, which is a part sectional view of the two pipe ends prepared for jointing, A shows the extent of the tinning, which is on the exterior and interior of the pipe ends and on the edges also. Fig. 2 shows the tinned ends slipped together ready for wiping, the form of the required joint being shown by the dotted lines. The pipe is strengthened by putting one pipe within the other and the corrosion of the tinning is arrested when it reaches the lap. If sufficient lap is given, the pipe may be handled before the joint is wiped - a great convenience. The pipe ends are placed together, when practicable, over the iron pot containing the molten solder, which is then poured continuously over the joint until a heat is got up. This practice is not possible with lead or brass pipes, because in the one case the lead would melt, and in the other the molten zinc would leave the brass and ruin the solder. When the pipes cannot be moved, a grain scoop (a kind of shovel) is placed beneath the joint and the solder poured on rapidly. When a thorough heat has been obtained, the joint can be wiped, with the aid of a cloth and of the mushy solder from the scoop, in much the same way as a joint on a lead pipe is wiped, the latter operation being described on p. 88.

Wiping Joints on Copper Pipes.