Abstract: Pipeline apparatus comprising a housing including a riser and a pipeline connector and a device configured to interact with fluid flowing through the pipeline connector, a mounting structure for releasably mounting the device in the riser and seal situated between an inner surface of the riser and an outer surface of the mounting structure, the seal configured to seal against egress of fluid from the apparatus, the mounting structure and the riser each including a part of a locking structure for releasably locking the device in the riser, the device situated in the pipeline connector.