Costain has already done the front end engineering design (FEED) and has now been given the detailed design, decommissioning, build and re-commissioning of the two compressor stations.
The work is part of National Grid's emissions reduction project and will take until 2021 to complete.
The work will ensure both compressor stations comply with the Industrial Emissions Directive and Pollution Prevention & Control regulations. The modernisation will also increase system resilience and reduce overall risk on the national transmission system.
Costain chief executive Andrew Wyllie said: “This is another example of Costain's strategy in action. From design and delivery to programme management, we are providing a full range of engineering solutions to National Grid to help them meet national needs by providing a secure and sustainable energy supply.”