Pipeline connecting device, pipeline element coupling piece and coupling method therefor

Disclosed are a pipeline connecting device, a pipeline element coupling piece (8100, 8100A, 8100B, 100) and a coupling method therefor. The pipeline element coupling piece (8100, 8100A, 8100B, 100) comprises a plurality of coupling units (10, 10A, 10B, 10C, 810, 811, 812), a gasket (40, 840A, 840B) arranged at the coupling unit (10, 10A, 10B, 10C, 810, 811, 812), and a fastening element (30, 830, 830A, 830B). Each coupling unit (10, 10A, 10B, 10C, 810, 811, 812) comprises two engaging keys (12, 12A, 12B, 12C, 81114, 81214) located at two coupling ends (100a, 100b) thereof, each engaging key (12, 12A, 12B, 12C, 81114, 81214) has an engaging surface (121, 121A, 121B, 121C, 81111, 81211), and each engaging surface (121, 121A, 121B, 121C, 81111, 81211) has a variable curvature radius. The fastening element (30, 830, 830A, 830B) is coupled to the coupling unit (10, 10A, 10B, 10C, 810, 811, 812), wherein the pipeline element coupling piece (8100, 8100A, 8100B, 100) is adapted to be pre-mounted onto two pipeline elements (200, 210, 220, 8200, 8210, 8220) and be aligned with the engagement keys (12, 12A, 12B, 12C, 81114, 81214) and corresponding grooves (201, 8201) of the pipeline elements (200, 210, 220, 8200, 8210, 8220). When the fastening element (30, 830, 830A, 830B) is operated to fasten together the coupling units (10, 10A, 10B, 10C, 810, 811, 812), each engaging surface (121, 121A, 121B, 121C, 81111, 81211) is deformed to change the curvature radius to substantially match the curvature radius of the groove circumference (203) of the bottom of the groove (201, 8201) of the pipeline element (200, 210, 220, 8200, 8210, 8220).