Copper Pipes

Copper Pipes are commonly used in the plumbing industry for water supply lines and refrigerant lines to HVAC systems. Copper offers excellent corrosion resistance and is on the more expensive side of plumbing supplies. Repiping plumbers prefer to use copper over PEX when the homeowner can afford it.

Before we get into the types of copper pipes, let’s take a moment to understand how they are measured. The size of copper tubing is defined by the outside diameter (OD) x wall thickness x length. When describing different sizes of copper tubing, the dimensions are noted as “pipe size/pipe type/pipe material” followed by its OD, average wall thickness, and length in inches. For example 1/2 inch Type L-X PVC Sch 40 Pipe – this measurement would be read as one-half inch, type L copper tubing with an average wall thickness of 1/8 inch.

Here are the types of copper piping:

• Type K Copper Pipe (1/4 – 6 inches)
• Type L Copper Pipe (1/2 to 2 inches)
• Type M Copper Pipe (3/4 to 24 inches)
• Copper DWV Piping (1 1/2 or 2 inches)

Type K Copper Pipe

Type K is the smallest in diameter of copper tubing and has a thinner wall than either L or M pipe. It is used in residential water supply systems for general purposes. The outside diameter (OD) of type K copper tubing ranges from 1/4 inch to 6 inches, with the most common being 3/8 inch. Its wall thickness ranges from 0.015 to 0.035 inches depending on the size of the OD (thinner walls for smaller sizes).

Type L Copper Pipe

This type of piping is larger than type K but smaller than all other types. Wall thickness ranges between 1/16-1/2 inch thick depending on size, with average wall thicknesses ranging around .025 inches. The outside diameter (OD) of type L copper piping ranges from 1/2 to 2 inches, with its length usually between 4-8 feet.

Type M Copper Pipe

Although type M is larger than both types K and L, its wall thickness stays the same as that of L pipe at .025 inches. The OD of type M copper tubing is 3/4 to 24 inches long, ranging in average wall thicknesses around .035 inches for all sizes.

Copper DWV Piping

This should be used for drain waste vent lines only. It has a thicker exterior wall because it will need to withstand higher pressure, although the interior walls are still thin compared to other materials like PVC or CPVC. Drain waste vent copper piping is available in 1 1/2 inch and 2 inch OD.

Copper Pipes Connections

Now that we know about copper pipes, let’s look into the different ways they can be connected to one another.

• Sweated Joint: Used for joining copper tubing without solder. A sweat fitting uses a metal ring or sleeve called a sweat ring, which has an unthreaded inside diameter (ID). The copper pipe is inserted through this ring and supported while it is heated with a torch until the surface of the fitting and tube turn bright red and solder flow freely onto the connection. Sweat fittings come in different types: barbed, compression, flare, coupling or reducing, solvent cementing, or soldering.
• Soldered Joint: Soft soldered joints are known as “sweated” joints, and use solder to fill any gaps that may exist between two copper pieces. The first step is to clean the copper surfaces and apply flux. Once the flux has dried, the copper should be reheated to allow the solder to flow into seams formed by other metals or minerals in each piece.
• Mechanical Joint: These fittings use a gasket material instead of solder to make a watertight connection. While it’s not as common today as soldered or sweated joints, many older plumbing systems around the country still rely on mechanical fittings for their supply lines.

Types of Mechanical Joints

There are three main types of mechanical pipe fittings – compression ells (or ferules), threaded connectors, and compression couplings.

• Compression Els: Compression ells use a ferrule that is pushed onto the tube, then compressed into a groove on the fitting by either a ring or screw cap device. The compression force from this tool forms a barrier between the tube and fitting to prevent water from escaping. Threaded connectors are used for joining pipes of dissimilar materials, such as copper tubing to plastic pipes. They consist of two separate pieces – an insert and a nut – with indented threads inside each piece’s end cap. A rubber O-ring within each end stops leaks at its connection point between the two pieces during normal operation of the plumbing system.
• Compression Coupling: Compression couplings work in much the same way as compression ells. A ferrule is attached to the tube and then the entire assembly is inserted into the fitting, which has an interior thread. The coupling nut screws onto this internal thread, compressing the ferrule between itself and the fitting body to create a watertight seal.
• Threaded Fittings: Threaded fittings are used when joining copper tubing to another material with threaded ends, such as plastic or galvanized steel pipe. The copper tubing simply screws directly onto these types of plumbing parts.