Pressure calculations for NPT threads

Muhammad Ijaz · Jun 3, 2023

Dear Sir,

1" NPT threaded carbon steel elbows (3000#) and piping are installed at downstream of control valve drain. Service is hot compressed air (P = 7.5 bar and Temp = 350 deg C).
Control valve is passing.
Now it is required to install NPT valve at open end (drain end) of piping to contain compressed air. it will result in increase in pressure at outlet piping and threaded connections may leak.
Please let me know calculation procedure for NPT threads against pressure and leakage.

Regards,
Ijaz

3DDave · Jun 3, 2023

NPT leaks. NPT + thread sealant doesn't. Either find and use a suitable sealant or use NPTF (dryseal) threads. Finding a suitable sealant for that temperature may be difficult - more difficult is making sure that the selected sealant is used. It is likely to be expensive and assemblers will substitute what they can find more readily.

Example:

https://www.jetlube.com/deacon-thread-sealants

Nothing with PTFE (Teflon) will be suitable.

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Pressure calculations for NPT threads

Muhammad Ijaz

Mechanical

3DDave

Aerospace

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