Which of the following methods is not allowed for modifying or repairing sprinkler systems?

Torch cutting and welding is not an acceptable method for modifying or repairing sprinkler systems due to the potential hazards it introduces, particularly the risks of fire and damage to system components. Sprinkler systems are designed to operate under specific pressure and temperature conditions, and the application of heat can compromise the integrity of pipes and fittings, potentially leading to failures or leaks.

In contrast, methods such as pipe replacement, using couplings, and sealing joints are standard practices within the industry. Pipe replacement allows for the introduction of new materials that meet current codes and standards, ensuring reliability. Using couplings provides a means to connect sections of pipe securely, while sealing joints effectively prevents leaks and maintains system pressure. These processes comply with safety regulations and ensure the effective operation of the system without risking the safety of occupants or the property.