Apparatus and techniques for coating pipeline field joints

An injection moulding apparatus for coating a field joint of a pipeline, the apparatus comprising:

• a mould tool positionable around the field joint to define a mould cavity;
• first and second pumping chambers communicating with the mould tool, each chamber being reciprocally expansible in an induction stroke for drawing molten polymer into that chamber from a melt supply and reciprocally contractible in a compression stroke for driving molten polymer out of that chamber into the mould cavity in use;
• and
• first and second injection valves, each of those injection valves being associated with a respective one of the pumping chambers and being interposed in a flow path between that pumping chamber and an injection gate of the mould tool with which both of the pumping chambers communicate via the respective associated injection valves;
• wherein expansion of one of said chambers is synchronised with contraction of the other of said chambers such that the induction stroke of one of said chambers coincides with the compression stroke of the other of said chambers;
• and
• the apparatus is arranged for sequential injection of shots of molten polymer into the mould cavity through the shared injection gate, those shots being output in alternation from the first and second pumping chambers.