Understanding Copper Pipe
Copper pipe is commonly used in many parts of the country for water supply lines in homes. The sizes most commonly encountered are 3/8 inch, 1/2 inch, 3/4 inch, 1 inch and 1-1/2 inch pipe. These common sizes of copper pipe comes in three main grades, two of which you can probably find at your local home center. The third, and strongest grade, is not generally available.
M grade copper pipe has the thinnest walls and is found in standard home plumbing across the United States. L grade, also called extra strong, has thicker walls and can also be found in homes, especially for pipe that runs through concrete and sometimes underground. K grade is double extra strong and has limited residential use.
Grades K,L and M are hard temper pipe and their sizing is Nominal Pipe Size, or NPS. In the smaller sizes already mentioned, the outside diameter of the pipe is typically 1/8 inch larger than the specified pipe size. For example, grade L 3/8 inch pipe has an Outside Diameter of 1/2 inch. 1/2 inch pipe has an O.D. of 5/8 inch.
Copper pipe differs from copper tubing in several ways. Copper tubing is typically used in air conditioning and refrigeration. The temper is soft and the tubing is easily bent and shaped, although repeated cold forming (bending, forming, straightening, etc.) it will cause the temper to shift to hard and the tubing becomes brittle and easily kinked. Copper tubing has a true O.D. relationship to its size. 1/2 inch tubing will have an outside diameter of 1/2 inch. The wall thickness is greater than M grade pipe and less than L grade pipe.
Copper fittings are extruded much like copper pipe and are hard tempered. The hub where the pipe fits into for brazing is slightly larger than the outside diameter of the same size pipe. Brazing is accomplished with a propane or mapp gas torch and solder wire. The heated copper draws the liquid solder via a capillary action into the space between the pipe and the fitting. Flux is used to enhance the capillary action between the pipe and the solder.