The contract, which covers a three year programme of work between April 2010 and March 2013, is divided into three geographical lots – North Wales, South Wales and South-west England.
Elements to be installed include pipelines, pig traps, filters, meters, pre heaters, heat exchangers, slam shuts, regulators, control panels, pipework, valves and actuators; buildings.
The utility company is seeking bids from contractors able to manage and work across all installations in the regional lots.
It suggests that specialist firms may be considered by the main contractor as second tier contractors.
Firms have until 7 September to register their interest.