A sleeve is provided with an upstream end a downstream end each fitted with inflatable bladders. Rigid rings are provided inboard of these inflatable bladders to keep the sleeve open when the bladders are expanded against a surface of a fluid transport line. The ends of the sleeve preferably include cuffs thereon with the rings residing within these cuffs. Spreader bars can be provided between the rings at the upstream and downstream ends of the sleeves, to keep the sleeve in an elongated form. Sleeve support trolleys can be provided for supporting the sleeve and resisting sagging thereof at points between ends of the sleeve. Portions of the rings and sleeve support trolley can be collapsible to facilitate placement through limited size entry ports into the fluid transport line. Flow thus continues through the sleeve while maintenance is done on portions of the fluid line adjacent to the sleeve.