What is the allowable method of joining joints in NH3 that are 1-1/4 inches or smaller?

The correct answer is the method of joining joints in NH3 (ammonia) that are 1-1/4 inches or smaller is through welded or threaded connections.

This is because welding offers a strong, permanent joint that can withstand the pressures and conditions typically associated with ammonia service. The integrity of a welded joint is crucial in preventing leaks, especially considering the potential hazards of ammonia.

Threaded joints are also widely accepted for smaller piping. They allow for easier disassembly when maintenance or repairs are needed, which is important in scenarios involving ammonia. The threaded design ensures a secure fit while maintaining the necessary seal to prevent leaks.

In contrast, other joining methods like flanging or riveting may not provide the same level of security and integrity needed for high-pressure ammonia systems, particularly at smaller diameters. Flanged joints are typically used for larger piping configurations where disassembly and maintenance are frequent, while riveted joints are less common in modern high-pressure applications due to advancements in welding and threading technologies.