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All About Pipe

There are hundreds of varieties of pipe. Each is designed to carry specific types of fluids and gases under varying conditions. We sell pipe for residential water systems, and for natural gas.

Water pipe generally falls into one of two categories, Pressure pipe that delivers the water, and Drain, Waste, and Vent pipe (DWV), which carries it away.

Both categories are sold in metal and plastic; however metal (copper) dominates the pressure category, and plastic is most common for DWV.

Pressure Pipe
Pressure pipe must be heavy enough to hold continuous pressure without rupture, and all connections must be leak proof.

This pipe tends to be of a smaller diameter, and it must be made of material that will not react with the chemicals or minerals in the water.

Drain, Waste, Vent Pipe (DWV)
DWV, on the other hand essentially provides a pathway for waste materials to flow freely by force of gravity away from the fixtures and the home.

They may be lighter weight with thinner walls than pressure pipe, and joints need not be as tightly sealed because there is no pressure exerted on them. This pipe is larger in size than pressure pipe to allow for free flow, and it must not react to common household chemicals that might be poured down a drain.

The standard sizes used in residential plumbing are 1-1/2, 2, 3 and 4 in.

As a general rule, 3-in. pipe is soil pipe (used for carrying solids), while 1-1/2- and 2-in. pipe carry gray water (waste water) from sinks, laundries, showers and tubs.

4 in. soil pipe offers a more efficient way to dispose of solid material, but the introduction of low-volume toilets and other water-conserving measures, significantly reduces the level (height) of water in the pipe, resulting in significant clogging within the soil pipe. In new construction, the 4-in. pipe is now too wide for long, horizontal runs (especially between the home's main vertical drain, or stack, and the street).

3-in. soil pipes raise the flow level in horizontal runs and, as a result, suffer fewer clogs.

General
Pipe was originally sized based on the inside diameter of the pipe that was typical of the period, which was cast iron. A half inch cast iron pipe was exactly one half inch inside diameter. The thickness of its wall determined the outside diameter. In order to insure that all pipes and fittings would go together, the standard was established based on that specific outside diameter.

Today, that size remains the standard by which pipe is measured, but since materials have changed, wall thicknesses of pipe, and therefore the inside diameters vary. Consequently, a half inch pipe is neither a half inch on the inside nor the outside, but it is still called a half inch pipe based on the Nominal size established by Iron Pipe of yesteryear. Hence the terms NPS for "Nominal Pipe Size" or IPS (Iron Pipe Size). The terms are interchangeable.

Pipe is distinguished from tubing by the standard by which it is measured. Pipe is thick walled, and in standard IPS sizes. When copper tubing was developed, the walls were much thinner than cast iron or steel. Because of copper's unique characteristics, it was deemed not necessary that it be made in IPS sizes. A new standard was developed called CTS or "Copper Tube Size" that was much smaller. The actual size of CTS is much closer to its nominal size than that of pipe.

The standard has evolved so that any product made in IPS sizes is called pipe and any product made in CTS sizes is called tubing, without regard to any differences in material or manufacturing process. CPVC is an exception, being called "pipe" but being sold in CTS.

Pipe is available in a number of different thicknesses or "schedules." The American Society for Testing Meterials (ASTM) establishes the standards by which they are graded. The ASTM has assigned standards to each schedule of pipe made, and those standards dictate their use.

Pipe size is determined by its inside diameter (ID). Its outside diameter (OD) will vary with the thickness of its walls.

Three different weights designations are used for pipe: Standard wall (Std.), extra strong wall (XS) and double extra strong wall (XXS). These last two designations are sometines referred to as extra heavy wall (XH) and double extra heavy wall (XXH), respectively.

On steel pipe,for sizes thru 12-inch, wall thicknesses are assigned schedule numbers from schedule 10 (S.10) thru schedule 160 (S.160), which represent approximate values for 1000 times the pressure-stress ratios. Wrought iron pipe is referred to as Std, XS, and XXS and not by schedule numbers.

Pipe is normally supplied in 3 end styles; PE or plain end, BE, or beveled end for welding, or T&C for threaded and supplied with one coupling per length. Steel pipe can be cut to any length and sold threaded both ends (TBE) or threaded on one end only (TOE). Copper and PVC are sold PE only.

For detailed information on the type of pipe, its use, available sizes, etc. see the above links in the left column.

See Also:

Other:
    ASTM Reference Library (material and manufacturing specifications)

Links to Related Websites:
ASTM Reference Library

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