Collar (10; 20; 30) intended to encircle a fluid pipe, suitable for either closing off an orifice in the pipe or creating a bypass on the pipe, or repairing a crack in said pipe, said collar (10; 20; 30) comprising: - a flexible flange intended to encircle said pipe, - screwing means cooperating with said flexible flange in order to clamp said collar on said pipe, characterised in that: - said screwing means comprise a screw and a nut, or alternatively a threaded rod and two nuts (5, 42), the screwing of the screw on the nut or of said nuts (5, 42) on said threaded rod clamping the collar on the pipe, - said collar (10; 20; 30) has an attachment body having a bore through which said screwing means pass, provided with attachment means intended to cooperate with at least one reception zone (9, 11; 12, 13, 14, 15, 91 to 96) of the flexible flange in order to removably attach said flexible flange, so as to make it possible to open the collar without completely unscrewing said screwing means, - said collar (10; 20; 30) has means for adjusting the effective length of said flexible flange comprising a plurality of adjustment openings (16; 17, 18) distributed over the length of said flexible flange, intended for adjusting the position of the screwing means, said screw or alternatively said threaded rod being intended to be inserted in the adjustment opening most suited to the diameter of the pipe, and wherein, when said attachment means grip the reception zone of the flexible flange, said collar (10; 20; 30) makes it possible to encircle the pipe in a position of said attachment body where said attachment body does not bear on the pipe, the attachment body cooperating in abutment with the head of the screw or alternatively with one of the of the two nuts (4, 42) screwed on the threaded rod, and wherein the nut cooperating with the screw or alternatively the other one of the two nuts (5, 42) screwed onto said threaded rod being intended to engage in abutment on the external surface of the flexible flange. - a flexible flange intended to encircle said pipe, - screwing means cooperating with said flexible flange in order to clamp said collar on said pipe, - said screwing means comprise a screw and a nut, or alternatively a threaded rod and two nuts (5, 42), the screwing of the screw on the nut or of said nuts (5, 42) on said threaded rod clamping the collar on the pipe, - said collar (10; 20; 30) has an attachment body having a bore through which said screwing means pass, provided with attachment means intended to cooperate with at least one reception zone (9, 11; 12, 13, 14, 15, 91 to 96) of the flexible flange in order to removably attach said flexible flange, so as to make it possible to open the collar without completely unscrewing said screwing means, - said collar (10; 20; 30) has means for adjusting the effective length of said flexible flange comprising a plurality of adjustment openings (16; 17, 18) distributed over the length of said flexible flange, intended for adjusting the position of the screwing means, said screw or alternatively said threaded rod being intended to be inserted in the adjustment opening most suited to the diameter of the pipe,