Piping is the bread and butter of the plumbing industry. Let’s face it, if there were no way to get fluids from one place to another, there would be no plumbers and we’d all be unimaginably thirsty.    
    Pipe materials have come a long way since the earliest forms of piping. Hollowed-out logs, clay tubes, cast iron and lead have all been used in water distribution systems at various times. Today’s most popular choice, by far, is copper. But a recent bumper crop of pricey copper thefts, among other developments, has opened up the field to plastics.
    The choices in the World of Plastics are many, so here’s a primer on the most common types a plumber may run into over the course of a day.

Polyethylene

Polyethylene, or 'PE,' is categorized by density. Photo courtesy of PPFA.

“PE” stands for polyethylene, a generic description for a certain type of polymer. Tony Radoszewski, executive director of the Plastics Pipe Institute, a D.C.- based trade association that represents the pipe industry, broke it down further.    
    “There’s low density polyethylene, there’s limited density polyethylene, medium density polyethylene and high density polyethylene,” Radoszewski said. “The difference is what the structure is of carbon molecules, so if you go up in density, it means you’re packing more molecules—in this case it’s more hydrogen molecules—in a given area. It’s just simple physics.”   
    The higher the density, the stiffer the product will be; low density is soft and pliable, high density can withstand more pressure. PE is used for everything from milk bottles to plastic bags. Popular pipe applications include municipal water systems and outdoor storm drains.   
    According to PPI, polyethylene is structurally better suited to withstand impact than PVC, especially in cold weather installations and where other pipes would be more prone to cracks and breaks.

PEX

PEX or 'cross-linked polyethylene' is popular for its flexibility and multiple uses. Reeves Journal photo.

Even though PEX is technically a type of polyethylene, it’s kind of a breakout star all its own.    
    PEX is polyethylene that has been chemically cross-linked. Cross-linking is a process using chemicals, heat or heat and pressure to form links between polyethylene molecules resulting in bridges, creating a thermoset material that will not melt.    
    PEX’s structure lends itself to many uses and is, arguably, the biggest competitor to copper. Its meshlike properties make it very flexible and easily coiled. The smooth inner surface assures resistance to corrosion. And the pipe’s durability in extreme temperatures makes it quite versatile.    
    PEX tubing is typically joined with metal fittings and doesn’t require soldering or special threaded connections. It’s particularly suited to hot and cold indoor or underground applications. It is also the current material of choice for hydronic radiant heating, snow melting systems and ice rinks. Because sunlight exposure should be limited, a PEX system is not recommended for outdoor use except underground.    
    Proponents point out that PEX is easier to install because there are fewer joints and fewer directional fittings required. PEX is an approved material in current model plumbing codes but there’s a caveat from the Plastic Pipe and Fittings Association, a manufacturers’ trade group in Glen Ellyn, Ill. The PPFA cautions that some jurisdictions may not have amended their codes to include PEX tubing.    The founder of Advanced Radiant Technology in Seattle is already sold. Paul Pollets made the switch from copper three years ago.    
    “We’ve converted PEX tubing for all domestic water piping and PEX-Al-PEX [a composite of layered PEX with an aluminum core] for distribution piping on closed loop systems,” Pollets said, adding he uses press fittings for all piping, whether PEX or copper.

PVC

PVC (polyvinyl chloride) piping has been around since the 1960s. Photo courtesy of PPFA.

Polyvinyl chloride pipe has been around since the 1960s, a time when people were still suspicious of plastic. But, PPI’s Radoszewski said, it began to gain market share once people became more familiar with it.    
    PVC is known for its white color and stiffness and is corrosion-proof. “It can take pressure,” Radoszewski said. “A lot of times people will also perforate it for subsurface drainage applications. It’s a very versatile material.”   
    PVC joints require a special primer before they are “welded” with a chemical solvent. Systems can be pressure and non-pressure (gravity flow) and always use pipe in a bell or socket.PVC’s primary use is in drainage, waste, and vent systems, according to the Uni-bell PVC Pipe Association. Uni-bell is a Dallas-based organization, partially funded by the Vinyl Institute, that promotes the use of PVC systems, particularly in DWV applications.    
    Technical director Craig Fisher said PVC is well suited to municipal projects. “It doesn’t corrode the water main and is less prone to damage.” He added that PVC pipe accounts for 80 percent of the footage installed in the sanitary sewer market.

CPVC

Chlorinated polyvinyl chloride, or CPVC, is often used in sprinkler systems. Photo courtesy of PPFA.

CPVC is chlorinated polyvinyl chloride, a variety of PVC. The usually beige-colored pipe can be used in both hot and cold water  distribution systems and meets potable water piping requirements in typical residential, hotel/motel and light commercial systems. Its reputation for compatibility comes from the design—the outside diameter of CPVC tubing is sized the same as copper pipe, so the grip-style mechanical fittings can be used with both copper and CPVC. It is very quiet and handles short term pressure and temperature extremes particularly well.    
    Like PVC, CPVC tubing is joined with solvent cement fittings. A straight square cut is recommended and can be achieved with a circular tubing cutter or fine-tooth wood or hacksaw.     
    Lubrizol Corporation, manufacturer of Corzan-brand CPVC and Flowguard Gold cement, advises applying a heavy even coat to the pipe end and a thin coat inside the fitting. Garry Gage, a technical support manager with Lubrizol, cautioned applicators, “One of the biggest problems is using too big of a dauber on too small of a pipe. If it doesn’t look right, it’s probably not.”   
    Gage also has a tip about using CPVC with joints under slab: “Pressure test the system before pouring and use 1-inch foam insulation pipe sleeve at changes in direction, construction joints, and where the pipe comes out of the slab.”   
    The tubing comes in diameters ranging from ½- to 2 inches. CPVC is popular in fire sprinkler systems for a number of reasons. It cannot support combustion, is corrosion resistant, and boasts low flame spread and low smoke emission levels. CPVC was probably the earliest serious competition to copper.

Why Plastic?

Recent price and sustainability concerns have turned people on to the wonders of plastic—previously synonymous with environmental unfriendliness.   
    “Plastic piping is not only less costly than alternatives, but corrosion proof to various qualities of gray and reclaimed water, and is a natural for subsurface irrigation,” said Mike Cudahy, who does codes and training for the PPFA. “Plastic pipes are a vital component for the structured, manifold and other engineered piping layouts that minimize the ‘dead’ hot water pipe volume and the associated water and energy waste traditional layouts produce.”   
     In a plastic pipe, hot water is delivered more quickly, because heat isn’t absorbed on the way.     “The other aspect is in installation because you don’t have to solder all the joints,” PPI’s Radoszewski said. “You basically pull PEX off of a reel and pull it through your house or your plumbing system, much like you pull an electrical cable.”   
    What’s next? Hybrids systems, said Gage of Lubrizol. “All the engineers and architects and designers are finding that particular system on a multi-family unit is the most cost effective way to plumb,” Gage said. “We have basements on podiums where it’s all Corzan going up, feeding CPVC risers, and then branching off to PEX.”  He predicted that combined systems would get a push as design costs rise.   
    So plastics may be a train you want to board, if you haven’t already. “Piping systems that save water and energy really should lay the groundwork for these buildings,” Cudahy said, “as these are the most difficult, if not impossible, systems to attempt to retrofit later on.”