A protection system for a pipeline comprises a hydraulically actuated valve operable to switchably prevent a flow of fluid from a first section of the pipeline to a second section of the pipeline, a hydraulic fluid source for supplying hydraulic fluid to said hydraulically actuated valve to enable actuation thereof, a vent for venting hydraulic fluid from the hydraulically actuated valve, the hydraulically actuated valve being connected to the vent via a differential pressure valve to control venting of the hydraulically actuated valve, a pressure transfer barrier with a first port connected to the first section of the pipeline and a second port connected to said differential pressure valve, said differential pressure valve being supplied with hydraulic fluid at a reference pressure. If the pressure of fluid in the first section of pipeline exceeds the reference pressure of the hydraulic fluid supplied to the differential pressure valve, the differential pressure valve is caused to be in an open state, thereby causing the hydraulic pressure in the hydraulically actuated valve to be released via the vent. The protection system is of particular application to sub-sea hydrocarbon extraction wells.