Which conditions must be suitable for the type of metallic piping joint used?

The correct choice focuses on the critical factors of pressure and temperature, which are essential for ensuring the integrity and reliability of metallic piping joints.

In piping systems, especially those carrying fluids or gases, both pressure and temperature can significantly affect the performance and safety of the joints. Higher pressures can lead to increased stress on the joint, which could result in leaks or failures if the joint is not rated for such conditions. Similarly, temperature influences the material properties of metals; for instance, at elevated temperatures, metals can become more ductile, while at low temperatures, they might become brittle. Understanding both of these parameters is crucial when selecting the appropriate type of joint and ensuring it can withstand operational conditions without compromising the system's integrity.

While factors like humidity, length, width, weight, and strength may play a role in specific contexts, they do not directly address the fundamental requirements for metallic piping joints under service conditions, which primarily revolve around the pressure exerted by the fluid and the temperature of the environment.