Which type of copper tubing does not require a protective coating when installed underground?

Type K copper tubing is designed to withstand the pressures and conditions associated with underground installations without requiring a protective coating. This type of tubing has the thickest walls among the common types of copper tubing, making it more resistant to physical damage, corrosion, and environmental factors that might be present when buried underground.

Due to its durability and resistance properties, Type K is often used for underground water service lines and other applications where protection from external elements is crucial. The thickness of the walls provides added strength and reduces the risks of leaks or breaks in the tubing over time, which is essential in buried applications where repairs can be challenging.

In contrast, other types of copper tubing, such as Type L, Type M, and Type T, have thinner walls and may not offer the same level of protection against the corrosive effects of soil or potential mechanical damage when installed underground. Therefore, they typically require a protective coating to ensure their longevity and reliable performance in such environments.