What type of joint is primarily used for steel piping?

The correct choice is the welded joint. Welded joints are commonly employed in steel piping systems due to their ability to create strong, permanent connections. This type of joint involves the melting and fusing of the steel edges, which results in minimal leakage and excellent structural integrity. Welded joints are particularly advantageous in high-pressure situations as they provide greater resistance to stress and environmental factors.

While rubber gasket joints are often used in applications requiring flexibility and easy disassembly, they are not the primary choice for steel piping where strength and durability are critical. Slip joints allow for easy assembly and disassembly of pipes but do not provide the secure, rigid connection needed for steel piping under pressure. Expansion joints are designed to accommodate thermal expansion or contraction and are typically used in conjunction with other types of joints, but they are not predominantly utilized for the main connections in steel piping systems.