Standard Threaded Black Pipe Dimensions

Definition

• Black metal pipe receives its color during the forging process. The black is an oxide scale that forms on the metal's surface when it is exposed to high heat. Manufacturers coat the black steel pipe with a protective oil to prevent corrosion or rust. Threaded black pipe purchased from a supplier or directly from the manufacturer follows the requirements regarding threading dimensions as stated in publication numbered B1.20.1 written by the American National Standards Institute.

Dimensions

• Threads on black pipe are tapered according to national standards referred to as the American National Pipe Tapered Thread and referenced using the acronym NPT. The standard requires the thread to taper, becoming smaller toward the end of the pipe, to help seal the pipe and its fitting tightly. Black threaded pipe will be sized using two sets of numbers. The first number identifies the inside diameter of the pipe, also called its flow size. Off the shelf pipe, the type purchased in home remodeling or hardware stores, has an inside diameter of 1/2 to 4 inches; industrial and plumbing supply houses may stock larger diameter pipe. The second identifying dimension is threads per inch which identifies the number of turns in the thread. For example, a threaded black pipe labeled 1/2-14 NPT is a 1/2-inch diameter pipe with 14 threads per inch and follows the NPT standard.

Uses

• Black pipe is used in oil or gas applications and also may be found as a conduit for circulating hot water in boiler systems. The pipe can be used in interior and exterior applications and is typically found transporting gas from its source into the home. However, the pipe is not for use with potable water, vent lines or drain waste. Black pipe without threads is purchased in lengths of 10 to 21 feet and can be cut and threaded on site. Cutting black pipe requires a hacksaw, tube cutter or a cutoff saw. Threading is accomplished using a threader set that contains various sized die heads that fit a variety of pipe diameters.

Connections

• Fittings used with black pipe, such as elbows and adapters, are typically a soft or malleable black, cast iron. The connection between the fitting and the black pipe is made by applying pipe joint compound to the threads before screwing the fitting to the pipe. Larger sized black pipe may require welding instead of threading. Smaller lengths of black pipe called nipples are sold for use in repairing or making an extension from an existing pipe or a fitting. Nipples are pre-threaded and come in lengths ranging from 2 to 12 inches and diameters of 1/2 to 1 inch.