They should be hand tightened and then another 1 or 2 turns, but no more. More turns will put to much pressure on the fitting and may crack it and cause a leak. The Tensile Stress created by tightening the fitting beyond hand tight and 1 or 2 more turns will crack the female fittings.
A sealant should be used that is compatible with the material of the fittings. Teflon paste, pipe dope, and too much Teflon tape should not be used as this creates bulk which will create more stress and may lubricate fittings causing you to over tighten them. If Teflon tape is used it should not be more then 2.5 mil thick and care should be taken not to over tighten threaded joints.
The smaller the pipe size the easier it is to crack it. It is easy to over-torque smaller diameter fittings because their resistance to torque is less.
Title: How tight do you have to tighten National Pipe Thread?
Description: Information on tightening NPT fittings
Last Edited: 10/3/2013
The information contained in this article is for general information purposes only. The information is provided by
United States Plastic Corp. and while we endeavor to keep the information up to date and correct, we make no representations or
warranties of any kind, express or implied, about the completeness, accuracy, reliability, suitability or availability with
respect to the website or the information, products, services, or related graphics contained on the website for any purpose.
Any reliance you place on such information is therefore strictly at your own risk.
In no event will we be liable for any loss or damage including without limitation, indirect or consequential loss
or damage, or any loss or damage whatsoever arising from loss of materials, time or profits arising out of,
or in connection with, the use of this information.