Which statement about underground joint requirements is accurate?

• A. Gasketed joints are optional for underground pipes.
• B. Threaded joints are required for underground pipes.
• C. Underground pipes must use gasketed joints.
• D. Welded joints are prohibited underground.

Answer: (C)

Underground sprinkler piping needs a reliable, watertight seal that can withstand soil movement and the challenges of burial. Gasketed joints provide that through mechanical or push-on connections with rubber gaskets, creating a leak-tight seal that remains serviceable underground. Because of these suitability factors, NFPA 13R requires gasketed joints for underground sections, making this statement the correct one. Threaded or welded joints aren’t specified as the preferred or required approach for underground piping: threaded joints can loosen under soil conditions and are harder to seal reliably underground, and welding underground is impractical for fieldwork and maintenance.