What type of joint is specifically used for steel piping?

The correct answer is the expansion joint. Expansion joints are specifically designed to absorb the thermal expansion and contraction that occurs in piping systems, particularly those constructed from materials like steel, which can significantly expand and contract with temperature changes. These joints allow for movement in the piping, thus preventing stress and potential failure in the system.

While restrained joints are used in situations where pipes need to be held in place to prevent movement and pressure build-up, expansion joints serve a different purpose by accommodating the changes in length that occur due to temperature variations. Coupling joints are connectors that allow two lengths of pipe to be joined together, but they do not address the thermal expansion aspect. Socket joints, on the other hand, are used for connecting pipes with a diametrical interface but also do not accommodate movement caused by temperature fluctuations.

In scenarios involving steel piping, utilizing expansion joints is crucial to maintaining the integrity and longevity of the piping system by allowing for safe and reliable movement.