Which practice ensures a gas-tight 2 1/2-8 NPT joint in natural gas installations?

• A. Use Thread Sealant Appropriate For Gas Service And Proper Tightening
• B. Use Only Straight Threads
• C. No Sealant Or Sealant Not Rated For Gas
• D. Use Gasket Only

Answer: (A)

Gas-tight NPT joints rely on the seal created by a material that is approved for gas service and the correct tightening of the connection. NPT threads are tapered, so the seal comes from compressing a suitable sealant into the threads rather than from the metal threads themselves. Using a thread sealant that is specifically rated for gas service (such as gas-rated pipe dope or PTFE tape) fills the tiny gaps and prevents leaks, while simply relying on straight threads won’t seal a tapered connection. No sealant or a sealant not rated for gas increases the risk of a leak, and gaskets are used with flanged joints, not threaded NPT joints. Therefore, applying a gas-rated thread sealant and tightening to the proper specification is the correct practice to ensure a gas-tight 2 1/2-8 NPT joint.