20# and 20G refer to the steel grade of seamless steel pipe. 20G seamless steel tube and 20# seamless steel pipe adopt different technical standards and have different application.

20# seamless steel pipe has high cold deformation plasticity and is suitable for bending, calendering and hammer arch processing. The welding performance of arc welding and contact welding of 20# seamless steel pipe is good. During gas welding, cracks are easy to occur on the 20# steel parts with small thickness, strict shape requirements or complex shape. 20# seamless steel pipe is generally used to manufacture pipe fittings with low stress and high toughness requirements.

20G seamless steel tube is mainly used to manufacture high-pressure and higher parameter boiler pipe fittings, low-temperature section superheater, reheater, economizer and water-cooled wall, etc.. For example, small-diameter 20G seamless steel tube is used as heating surface pipe with wall temperature ≤ 500 ℃, water-cooled wall pipe and economizer pipe; large-diameter 20G seamless steel tube is used as steam pipe with wall temperature ≤ 450 ℃, pipeline accessories, etc.