No.20 seamless pipe is 20# steel seamless pipe, which is the most common type of seamless pipe. If there is no special requirement for seamless pipe, No.20 seamless pipe is generally used.

Q235B seamless pipe is an ordinary carbon structure pipe. It is named according to the yield strength. Q is the initial letter of yield strength, 235 is the yield strength value is 235, B represents impact at room temperature, and Q235B seamless pipe stock is less than No.20 seamless pipe. Basically, Q235B steel is generally applied to welded pipe, steel plate and section steel. And it is also used for seamless pipe, but not as common as No.20 seamless pipe.

From the chemical composition point of view:
No.20 seamless pipe: C 0.17-0.23%, Si 0.17-0.37%, Mn 0.35-0.65%, S≤ 0.035%, P ≤ 0.035%, Cr ≤ 0.20%, Ni ≤ 0.30%, Cu 0.20%.

Q235B seamless pipe: C: ≤ 0.20; Si: ≤ 0.35; Mn: ≤ 1.40; S: ≤ 0.045; P: ≤ 0.045.