An in-line accessory structure for a subsea pipeline has an elongate pipe section arranged to be integrated into the pipeline, hence defining a flow axis through the structure. A branch has a lower end in fluid communication with the pipe section and an upper end in fluid communication with a connector hub. The structure further has a subsea foundation such as a mudmat, arranged to support the structure installed orientation. When the structure is in that orientation, the branch inclines inwardly from its lower end toward its upper end in a transverse direction, toward an upright longitudinal plane containing the flow axis.