20# and 20G are the material of seamless steel pipe. 20G steel pipe uses GB5310 national standard steel grade, and 20# steel pipe uses GBT 699-1999&GBT 3639-2008. The national standard numbers of the two steel pipes are different, and their uses, characteristics, and prices are also different.

1. The difference in usage.

20# seamless steel pipes are structural pipes, fluid pipes, and low and medium pressure boiler pipes. 20G seamless steel pipes are used to manufacture high-pressure and higher-parameter boiler pipe fittings. Both of them contain carbon content, but 20G seamless steel pipes also have some trace elements, which are better for make boiler pressure vessels. 

2. The difference in characteristics.

The characteristic strength of 20# seamless steel pipe is higher than 15# steel. It is rarely quenched and has no temper brittleness. Cold deformation has high plasticity and able to bending, rolling and hammer arching. The welding performance of arc welding and contact welding is good. The thickness is small during gas welding, and cracks are easy to occur on parts with strict requirements or complex shapes. The cold drawn or normalized state of machinability is better than the annealed state.

20G seamless steel pipes have strict requirements on the steel grades used in the manufacture of steel pipes. It is required to have high endurance strength, high oxidation and corrosion resistance, and good structural stability.

3. The difference in price.

Due to the manufacturing process and composition of 20G seamless steel pipe, the price of it will be higher than 20# seamless steel pipe.