Specially made casing is set when the pipe passes through the basement and other buildings and structures with waterproof requirements.  Commonly used rigid waterproof casing.  For rigid waterproof casing, it is necessary to weld the sealing ring wing outside the casing, which has strict requirements on the wall thickness of the casing and the ring wing, and should ensure the quality of the weld.  

New elongated waterproof casing, customized for thickened wall, can meet the requirements of ultra-thick wall pipe.  Anti-corrosion waterproof casing, waterproof casing with special treatment of anti-corrosion coating, effectively prevent the oxidation and corrosion of waterproof casing.  

Common bushing, mostly welded pipe, both ends of the bushing should be mechanical cutting (for example, with toothless saw, etc.), the wall thickness requirements are not strict.