Selection of threaded fittings and Series A and Series B pipes
Thread Content
I’ve been having some trouble lately with Series A and Series B pipes; flanges are easy to handle – just buy those corresponding to the appropriate series. But what about loose connections with threaded fittings, ball valves, and the like? The pipe ends are threaded using a threading machine on site; should the pipes be chosen from series A or B? In some cases the difference isn’t significant, but in others it is quite substantial. For example, for DN50: Series A has an outer diameter of 60.3 mm, while Series B has an outer diameter of 57 mm. The inner-threaded ball valves or union-type valves seem to have an outer diameter of around 54 mm. If a 60-mm pipe is chosen and a wall thickness of 3.5 mm is selected, there will be no wall thickness left after threading is done. With so many standards available – European standards, American standards, Chinese standards, those set by the Ministry of Chemicals, petroleum standards – it’s easy to end up not meeting any of them. For threaded standard components such as ball valves and slip joints, which standard should be used for the piping? Are there any guiding materials available?
Normally, choosing all the A-series models will ensure a good synergy in use； Many threaded fittings are only available in Series A; Series B is custom-made
Pipes should be arranged in a series. It’s either all A, or all B – procurement and installation are both simplified.
Most products available on the market are of National Standard Series A, so for ordinary pipes, Series A is sufficient, unless special requirements apply.
Series B are metric pipes, and there are currently no thread standards for metric pipes
Choose Series A; NPT or BSP are both acceptable, though some pipe diameters are not suitable – DN65 and DN125