Abstract: Pipeline apparatus comprising a housing (2) including a riser (2a) and a pipeline connector (2b) and a device (3) configured to interact with fluid flowing through the pipeline connector, a mounting means (25) for releasably mounting the device in the riser and seal means (50) situated between an inner surface of the riser and an outer surface of the mounting means, the seal means configured to seal against egress of fluid from the apparatus, the mounting means and the riser each including a part of a locking means (27, 28) for releasably locking the device in the riser, the device situated in the pipeline connector.