An apparatus for venting an annular space between a liner and a pipeline of a subsea riser used for conveying hydrocarbons, the apparatus comprising a permeate recovery device for recovering permeate passing through the liner into the annular space. The permeate recovery device includes a first vent port in a wall of the pipeline at or adjacent a lower region of the pipeline and communicating with a permeate recovery line defining a flow path between the annular space and a permeate collection vessel. A one-way valve is associated with the permeate recovery line for preventing flow from the permeate recovery line into the annular space. A gaseous permeate recovery line connected to a second vent port at an upper region of the pipeline defining a flow of gaseous permeate from the annular space.