Four branches are measured in inches, so four branches are 1/2 inches (4/8= 1/2) and one inch is =25.4mm, so the inner diameter of four branches is 25.4/2= 12.7mm, that is, DN1. Four points are the names of the diameter and length of British pipelines, that is, 1/2 inches equals 15 mm. 1 metric, while 1 inch equals eight points, which is 25.4 mm in metric. 6 pounds =3/4 inch = 20 mm. ?
Classification of national standard steel pipes
Seamless steel tubes are divided into two categories: hot-rolled and cold-rolled (drawn) seamless steel tubes.
Hot rolled seamless steel pipes are divided into ordinary steel pipes, medium and low pressure boiler steel pipes, high pressure boiler steel pipes, alloy steel pipes, stainless steel pipes, petroleum cracking pipes, geological steel pipes and other steel pipes.
Cold rolled (drawn) seamless steel pipes include carbon thin-walled steel pipes, alloy thin-walled steel pipes, stainless steel thin-walled steel pipes and special-shaped steel pipes in addition to ordinary steel pipes, medium and low pressure boiler steel pipes, high pressure boiler steel pipes, alloy steel pipes and other steel pipes. Generally, hot-rolled seamless pipes have an outer diameter greater than 32mm and a wall thickness of 2.5-75 mm; The diameter of cold-rolled seamless pipe can reach 6mm, the wall thickness can reach 0.25mm, the outer diameter of thin-walled pipe can reach 5mm, and the wall thickness is less than 0.25mm, so the dimensional accuracy of cold-rolled seamless pipe is higher than that of hot-rolled.