What type of copper tubing is acceptable for underground service?

For underground service, the use of copper tubing is subject to specific standards to ensure durability and safety. Type K and Type L copper tubing are both acceptable because they possess thicker walls compared to other types, which makes them more resilient to external pressures and potential physical damage that might occur underground. Additionally, the term "coated" indicates that these types of copper tubing can be covered with protective materials to further enhance their resistance to corrosion caused by soil or moisture, thus ensuring a longer lifespan for the piping system.

Type G coated piping is also included in this answer choice, as it can be suitable for certain underground applications, depending on the specific environmental factors present. In contrast, other types of copper tubing that are not as thick or lacking protective coatings would not provide the necessary durability for underground installation, leading to increased risks of failure or leakage. This understanding of the characteristics of various copper tubing types highlights the importance of selecting the appropriate material for safe and effective underground service.