LITTLE P.ENG. FOR ENGINEERS TRAINING / Engineering Consultant

Pressure tight joints for low pressure service are sometimes made with straight internal threads and the American standard taper external threads. The ductility of the coupling enables the straight thread to conform to the taper of the pipe thread. In commercial practice, straight-tapped couplings are furnished for standard- weight (schedule 40) pipe NPS 2 (DN 50) and smaller. If taper-tapped couplings are required for standard-weight pipe sizes NPS 2 (DN 50) and smaller, lin

Threaded joints are normally used in low-pressure small-bore, nonflammable service, although threaded iron pipe is commonly used in domestic gas piping and threaded joints up to NPS 12 (DN 300) have been used in low-pressure liquid service. For quality joints, it is essential to have smooth, clean threads. Because cut-thread surfaces are somewhat imperfect, thread sealants (pipe dope) and lubricants are often used to ensure a leak-tight joint. Lubricants such as linseed oil o