Wrought pipes* are made in various sizes and weights and may be had plain, tar coated or galvanized. The weights of wrought pipe are designated as standard, extra strong and double extra strong; standard weight pipe being the weight most commonly used in plumbing installations. Wrought pipe is sometimes classified as butt-welded and lap-welded. In the manufacture of butt-welded pipe the edges of the metal that forms the pipe are butted together and welded. In the manufacture of lap-welded pipe the edges are first beveled and then lapped and welded to smooth interior and exterior finishes. Butt-welded pipes are not as strong in the seam as lap-welded pipes and are made only in small sizes of standard weight.

Wrought pipes are galvanized by cleaning them with acid and then immersing them in a bath of molten zinc or tin and zinc. This process makes the pipe a little more brittle than plain pipe but it lengthens its life by preserving it from corrosion. Furthermore, galvanizing protects the water that flows through the pipe from rust discoloration which would render the water unfit for domestic and for most manufacturing purposes.

Table XXXI - Size And Weight Of Lead Pipes - Continued

*The term wrought pipe is here used to indicate either wrought iron or steel pipe.

The safe working pressure for wrought pipe does not depend altogether upon the thickness of the walls of the pipe and the tensile strength of the metal, but is governed by the strength of the seams and the method of connecting different lengths of pipe. For instance, a 1 1/2 inch butt-weld standard pipe is tested to a pressure of 600 pounds and will safely sustain a working pressure of 300 pounds to the square inch, while a 1 1/2-inch lap-weld standard pipe is tested to a pressure of 1000 pounds and will safely withstand a working pressure of 500 pounds per square inch.

The rule may be broadly stated that small sizes of standard weight pipe, ranging from 1/8 to 1 1/2-inch diameters, are butt-welded and tested to 600 pounds pressure. Such pipes will safely sustain a working pressure of 300 pounds per square inch. All larger sizes of standard weight pipes are lap-welded. They are tested to 1000 pounds, and will safely sustain a working pressure of 500 pounds per square inch. Extra strong lap-welded pipes when joined with extra heavy couplings will safely sustain a working pressure of 1000 pounds per square inch.

Most of the pipe now sold as wrought iron is in fact made of steel. It cannot easily be distinguished from wrought iron pipe, and for most purposes is equally as good.

In Tables XXXII, XXXIII and XXXIV the weights and dimensions of standard, extra strong and double extra strong pipes can be found.

These tables of dimensions and capacity of pipes are from 1/8 to 6 inches inclusive. Larger sizes are so seldom used by plumbers that they have been omitted. The number of threads to the lineal inch can be found in table of standard wrought pipe. The number of threads is the same in the corresponding sizes of extra strong and double extra strong pipe.