Abstract: Disclosed are apparatus, systems and methods for maintaining desired thermal properties of a flowing hydrocarbon fluid in a subsea pipeline. An insulating layer including a plurality of elongated hollow elements containing an insulation material can surround the pipeline. The apparatus can be located on a seabed and connected to a source of hydrocarbon fluid at one end and to a facility for processing hydrocarbon fluid at another end. One method includes spirally winding an elongated hollow element containing an insulation material around the subsea pipeline. One method includes wrapping the subsea pipeline with a connecting layer which includes surface protrusions protruding radially outwards. An insulating layer having surface features reversibly engageable with the surface protrusions of the connecting layer can be reversibly attached to the connecting layer by engaging the surface features of the at least one elongated hollow element with the surface protrusions of the connecting layer.