Galvanized steel pipes used for domestic water supply are uniformly connected by threading, also known as screwed connections. Typically, water supply pipes with a nominal diameter not exceeding 100 millimeters and a nominal pressure not exceeding 1 MPa can adopt screwed connections.
The pipe threads used for connecting pipes are similar to pipe fittings, and are divided into two types: conical and cylindrical. Generally, pipes that are manually threaded are usually equipped with conical pipe threads.
The pitch and other technical requirements of cylindrical pipe threads are the same as those of conical pipe threads.
Pipe threads can be formed using a pipe threading machine or by lathe turning.
There are several different ways to connect pipe threads. For instance, cylindrical internal threads can be inserted into cylindrical external threads; cylindrical internal threads can be inserted into conical external threads; and conical internal threads can be inserted into conical external threads. The latter two methods can achieve a tighter connection and are thus the most commonly used.
When connecting pipes with threads, it is necessary to add appropriate packing material between the external threads of the pipe and the internal threads of the fitting. Commonly used packing materials are hemp fibers and white lead paint. The specific method is as follows: Wrap a thin and even layer of hemp fibers along the direction of the threads on the externally threaded pipe (or fitting), then apply a coat of white lead paint over the hemp fibers, and finally screw on the connecting piece. It is essential to avoid allowing the hemp fibers and white lead paint to enter the pipe, as this could cause clogging.
After tightening the connecting piece, to ensure a clean and aesthetically pleasing interface, excess hemp fibers and white lead paint should be removed and wiped clean.
The use of hemp fibers and white lead paint not only serves to seal the medium but also provides rust protection for the machined pipe threads.
