Pipe, Tubing, and Fittings Pipe, Tubing, and Fittings Machinery's Handbook, 31st Edition
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Design of pipe systems must be undertaken with great care. Safety, performance, reliability, and cost are all significantly affected by selection of appropriate pipe sizes, materials, and connection methods. For many applications, the design must comply with codes and standards. Organizations such as ISO, ASTM, NSF, NFPA, AWWA, AFSA, and IAPMO should be consulted when working with pipe. Tubing systems are also covered by standards in cases of sanitary, food, medical, and high pressure applications. Metal Pipe.— Metal pipe is ideal for applications where structural strength is needed. Metal pipe is also resistant to high temperatures and is non-combustible. Extremely low temperatures should be avoided. Metal pipe systems may need proper grounding to pre vent shocks and accelerated corrosion. A wide range of materials is available. Materials: Steel is the most commonly used metal pipe material for general use. Steel pipe is highly resistant to shock and vibration from water hammer or external sources. To carry a given pressure, steel pipe can be made with a thinner wall than pipes made from other materials, and as a result the pipe will have a larger flow capacity. Carbon steel pipes are susceptible to corrosion and oxidation, so additional allowance should be made when calculating flow capacity. Galvanized steel can inhibit atmospheric corrosion to some extent, but the coating can break down when exposed to constant moisture. Stainless steel pipes cost more, but are resistant to corrosion and oxidation. Stainless steel is also compatible with a wide variety of chemicals. Ductile iron pipe is commonly used for water and sewer applications. It combines the physical strength of mild steel with the long life of gray cast iron. It has superseded cast iron pipe in the water handling industry. In addition to the benefits of long life, corrosion resistance, high structural strength, and tight joints, ductile iron is also readily machin- able. Although somewhat corrosion resistant when in contact with water, these pipes are often internally lined or coated to inhibit corrosion further. Copper pipe is commonly used in household and industrial supply lines for both liquids and gases. It costs more than steel pipe, but is much easier to join. It is extremely thermally conductive, which makes it a top choice for heat exchangers and other thermal applica tions. Copper resists corrosion, is unaffected by UV radiation, and inhibits the growth of bacteria. It will corrode in the presence of high or low pH liquids. Connecting pipes and fittings of different metals is not recommended because galvanic corrosion to occur. Protective coatings should be employed where necessary to prevent contamination or failure of the joint. Schedules and Classes: Schedule number designations for steel pipe, previously called “Iron Pipe Sizes (IPS)” are an indicator of wall thickness. Schedules range from 10 to 160, with higher numbers designating thicker walls. Schedules 40 and 80 are the most commonly used. From the IPS system, designations like STD, XS or XHY (extra heavy or strong), and XXS or XXHY (double extra strong or heavy) are still used. For a given pipe size, all schedules have the same outside diameter. Higher schedule pipes of the same diameter have smaller flow areas. The nominal pipe size (NPS) is given, along with the schedule or IPS designation to indicate the full dimen sional characteristics of the pipe. Ductile iron pipe ranges in size from 3 to 64 inches and in pressure classes from 150 psi to 350 psi, although custom sizes and pressure ratings can be obtained. Copper pipe is classified as copper tube. Information on copper tube can be found in the section Metal Tube starting on page 2771. Copper pipe is suitable for water and steam service at pressures up to 250 psi (1750 kPa) and temperatures up to 406°F (208°C). Sizes: Nominal sizes for commercial steel pipe are generally given in inches. Actual diameter of the pipe can be different from the nominal designation, so refer to Table 7 for actual dimensions of common pipe sizes up to 6 inches in diameter. This is the Nominal
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