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Drain, waste, and vent (DWV) piping is thinner (Type M). In the HVAC industry, most copper is Type L (medium thickness) hard (tempered) copper, although underground soft (annealed) copper is often Type K (thick). Also, copper is generally more noble and corrosion-resistant than steel or galvanized steel. Copper is an expensive material but has the advantage of weighing less than steel and may require fewer employees to install, depending on weight and union restrictions. However, some contractors propose replacing galvanized steel domestic-water pipe with copper up to 6-in. (More information is available via the American Galvanizers Association.)Ĭopper pipe often is used in both hydronic and domestic applications, especially for 2-in. If the interior needs a continuous galvanized layer, consider mechanical couplings. Repairing galvanizing on the inside of the pipe is difficult or impossible. If galvanized pipe is being welded, the welder needs to be careful to grind down to the raw steel. It can fail in environments with high sodium (e.g., softened water that started out very hard) because the sodium makes the adherent oxide film detach and react more like steel pipe where the oxide flakes off. Galvanizing works almost perfectly in applications where it is wetted and dried periodically (e.g., road signs and guard rails).

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Galvanized steel pipe has all the advantages of steel pipe, plus improved corrosion resistance in most environments, although at a slightly higher cost. It provides a sacrificial anode (zinc) to receive corrosion instead of the steel corroding.

It coats the surface like paint, and under most circumstances it forms a very adherent oxide layer like aluminum and SS.Galvanizing has two methods of corrosion reduction: Galvanized steel pipe is steel pipe that is dipped into a pool of zinc (see Figure 1). However, the high rigidity of steel means that although it expands less, it exerts very high forces on anchors. Consult ANSI/MSS SP-58: Pipe Hangers and Supports – Materials, Design, Manufacture, Selection, Application, and Installation for details about hangers and hanger spacing.Ī low coefficient of thermal expansion minimizes the need for expansion loops and expansion joints. More flexible materials, however, may require hangers on as close as 4-ft centers or even continuously. Steel pipe is manufactured in 21-ft lengths, and the hangers can be spaced that widely for large-diameter pipe. Rigidity is important because it determines the distance between hangers. Some building owners do not want these chemicals in steam that may be used for humidification because of health concerns however, not using these amines might require a change to stainless steel (SS) piping or adding a separate “clean steam” system for humidification and for sterilization of medical instruments. If amines (commonly cyclohexylamine, morpholine, or diethylethanolamine (DEAE) are fed properly to neutralize condensate pipe pH, condensate pipes can last the life of the building. However, corrosion is an issue in steam-condensate pipes, and many engineers specify schedule 80 steel pipe simply because it takes about twice as long to rust through as schedule 40 pipe. It also is a good choice for steam and steam-condensate systems because it handles high temperatures and pressures well, and corrosion is normally not an issue in steam pipes. Steel often is used for closed hydronic systems because it is inexpensive, especially when compared with other materials in systems with high pressures, and corrosion is relatively easily controlled in these systems.

All steel, by definition, contains carbon. Sometimes it is called carbon steel or black steel to differentiate from stainless and galvanized steel. It is also heavy (multiple workers may be needed to transport it) and is subject to corrosion. Steel is strong, rigid, and has a low coefficient of thermal expansion. For example, heating systems often employ steel pipe because of its low cost, strength, and resistance to heat-while pure water systems are likely to use virgin polypropylene (PP) or polyvinylidene fluoride (PVDF) pipe. The piping material chosen depends on the application and the water quality. Just as the properties of different pipe materials vary widely (see Table 1), the importance of these properties varies widely between projects.

Learn about corrosion issues in hydronic and domestic piping systems.

Become familiar with some issues related to materials compatibility.

Understand the pros and cons of various piping materials.

Designers should approach these decisions and identify strengths and weaknesses of various pipe materials and connection methods. Selecting pipe and piping materials involves many factors.

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