Thanks to their high strength, durability and corrosion resistance, copper pipes have been used in plumbing systems since the days of ancient Egypt. ASTM International, formerly known as American Society for Testing and Materials, sets standards for various materials to help installers quickly identify and choose the right pipe for the job. Type L and type K copper pipes share many characteristics, but these two products are quite different, with each designed for specific applications.
Type L and type K copper pipes both come in hard, tempered, straight sections or soft, flexible coils. The straight sections of both types are quite hard, and installers use tools to cut and bend these pipes. The rolls of Type L and K copper are soft, and installers can often bend these sections by hand to fit around obstacles. While hard lengths of pipe allow for a neater installation, coils work better for renovation work, where other pipes or beams may prevent straight runs of pipe. Coils are also used in many cooling and specialty plumbing systems.
Both Type L and type K copper pipes are sold in standard sizes set by ASTM International. The outer diameter of a type L and a type K pipe of the same size designation is identical. Where these pipes differ is their wall thickness. Type K pipes have thicker walls then type L, so the inner diameter of type K pipes will also be smaller than the inner diameter of a type L pipe.
Copper pipes manufactured to ASTM International standards feature color-coded labeling for easy identification. Type K copper pipes feature labels with green lettering, while type L pipes feature blue lettering. Each of these pipes also includes incised, or carved identification marks to help installers identify pipes if the label is removed.
The thicker walls of type K pipes allow these pipes to handle greater pressure than the thinner walled type L pipes. Each of these pipes can be used to transport water, waste, air, fuel, refrigerant or gas, according to the Copper Development Association, Inc, but high-pressure applications, such as medical gas, often require type K copper piping. When choosing between these two types of pipe, always refer to local building codes to learn which type is required in your area.
ASTM International also provides standards for type M copper pipe, which features thinner walls than both type L and type K pipes. This material features labels with red lettering, and comes in rigid lengths only. Copper piping also comes in three specialty varieties, which are designed for air conditioning, medical gas, and drainage and waste venting.