What is the requirement for joints in refrigerant piping installed in the field?

The appropriate requirement for joints in refrigerant piping installed in the field is that they must be sealed completely. Sealing joints is crucial to prevent refrigerant leaks, which can lead to system inefficiency, environmental harm, and safety hazards. Proper sealing ensures that the refrigerant remains contained within the system, allowing for optimal performance and reducing the risk of exposure to harmful substances.

Leaving the joints open for visual inspection, as indicated in the provided choice, would compromise the integrity of the refrigerant system and potentially lead to leaks. Thus, it is essential that field-installed joints be properly sealed to maintain both functionality and safety standards in accordance with the mechanical code.