The tightness test is to fill the whole process system with nitrogen, air or water with a certain pressure, so that the inner wall of the pipe wall equipment is under pressure, so as to check whether there is any leakage in the joints, flanges, pipes and equipment after installation. Water pressure test is generally used for strength test and leak test of pipeline system. If water pressure test cannot be used due to design structure or other reasons, air pressure test can be used.