Abstract: A safety device for protecting a fluid pipeline (1) from an excessive flow of the fluid running through it. The device includes a body (2) delimited by a tubular wall (20), having an upstream end (21) and a downstream end (22) and being selectively inserted into the pipeline (1). A valve (3), which is sensitive to a pressure loss, is supported by the body (2) and disposed between the upstream and downstream ends. A retaining means (4a, 4b) holds the body (2) in place inside the pipeline (1). An inflatable envelope (5) is provided outside the body for impermeably encasing a section of effective length of the tubular wall (20) into which at least one first opening (231) is cut.