The PASS Coupling adopts flat-mouth type design and it meets the requirement on passing with the gap between the coupling key shoulder and the pipeline. Under the prerequisite of guaranteed strength, the coupling with this type of structure is not necessary to complete clamp the pipeline and partial axial and radical shift are allowable. 
This coupling is suitable for flexibility-required pipelines. In the coupling structure the deviation of outside diameter of pipeline and elimination of the disadvantageous factors resulted from the said deviation are considered. The pass design can completely adapt the pipeline deviation and the coupling performances are not impacted.