A T-piece preformer for forming a T-piece in a pipe-in-pipe (PIP) pipeline for a marine environment, the PIP pipeline has at least inner and outer pipes having an annular space thereinbetween, and one or more cables extending along the annular space. The T-piece preformer includes at least: (a) inner and outer longitudinal collars; (b) annular walls between the inner and outer collars; (c) cable apertures through each annular wall; and (d) one or more guide points on the outer collar radially offset from the or each cable apertures, to guidance for a hole into the T-piece performer. The T-piece preformer can be assembled into a PIP pipeline, and requires a final hole during laying. The T-piece preformer has cable apertures through each annular wall, for allowing continuation of cables in the annular space through the PIP pipeline and T-piece preformer, and the T-piece.