Which is a type of joint used for ductile iron piping?

A restrained joint is a specific type of joint used in ductile iron piping systems that provides resistance against the movement of the pipe under various conditions, such as changes in pressure or temperature. This type of joint is particularly important in applications where the piping is subjected to external forces, such as water flow or ground movement, which could potentially cause the pipes to shift or dislocate.

In restrained joints, additional mechanisms, such as locking devices or additional components, are utilized to secure the pipes together and prevent separation, thereby maintaining the integrity of the system. This ensures that the joints remain tight and leak-free, which is crucial for maintaining water pressure and preventing contamination in water distribution systems.

A welded joint, while strong, is not typically used for ductile iron piping due to the material's propensity for brittleness at high temperatures involved in welding. An expansion joint is used to accommodate movement due to thermal expansion but does not inherently provide the same restraint against movement as a restrained joint. A rubber gasket joint is commonly used for sealing but also does not offer the same level of structural integrity against pipe movement as a restrained joint does. Therefore, the restrained joint stands out as the most effective choice for ensuring stability in ductile iron piping systems.