Copper pipe has specific limits on the amount of pressure the fluid or gas it carries may exert on the pipe. The limits, which are higher than the pressures found in a normal residential application, are determined by the thickness of the pipe wall and by the diameter of the pipe.
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Copper Pipe Types
There are three main types of copper pipe used in residential applications. Type K copper pipe has the thickest walls and withstands the most pressure in any given size. Type L pipe walls are not as thick as type K, but are thicker than type M. Type K is the only copper pipe suitable for burial and is used mainly as the underground pipe that supplies water to a home. For comparison, at 100 degrees Fahrenheit, a 3/4-inch type K pipe has a working pressure of 1,466 pounds per square inch, type L 1,002 pounds per square inch and type M 701 pounds per square inch.
Copper pipes fit inside the ends of fittings. For this reason, the outside diameter of copper pipes of the same size stay the same regardless of the type of pipe. The inside diameter varies according to the wall thickness.
As the pipe diameter increases, the working pressure rating decreases for the same size copper pipe. Using type L copper pipe at 100 degrees Fahrenheit as an example, 1/2-inch copper pipe has a maximum working pressure of 1,242 pounds per square inch, the maximum pressure of 3/4 inch is 1,002 pounds per square inch and 1-inch pipe is 850 pounds per square inch.
Copper pipe is manufactured using two different methods. Drawn pipe is the most familiar and is the most widely used. It is not easily bent and most connections are made by soldering or brazing copper fittings. Annealed pipe is a flexible tubing that routes easily around corners. The fittings used are compression or flare type threaded fittings. The copper in annealed pipe is softer than the copper in drawn pipe and withstands less pressure. Type M, 3/4-inch drawn copper pipe handles a maximum of 701 pounds per square inch at 100 degrees. The same size and type of annealed copper pipe has a maximum pressure rating of just 337 pounds per square inch.
Both drawn and annealed copper pipe are suitable for use in residential plumbing for water and for some types of gas plumbing. The gas lines inside a residential home carry gas at 1/4 pounds per square inch or less according to the American Gas Association. Residential water lines range in pressure from a low 40 pounds per square inch to a high of 80 pounds per square inch. The Copper Development Association website provides tables that list the maximum allowed working pressures in copper pipe.