These are part of the network of overhead lines, underground cables and substations that carry high voltage electricity across the country. The investment will keep the lines in good working order to ensure that everyone has the power they need, safely, and at the touch of a button.
Engineers will be replacing existing wires and repairing or renewing steelwork, foundations and other equipment on 30 pylons.
Another 14 pylons will be dismantled and new ones built to replace them.
Work is already underway with over 60 workers mobilized and is expected to take until the end of 2013 to complete. The bulk of the work will be carried out between March and October this year and next. There will be no interruption to electricity supplies during the work.
National Grid, which is the UKs largest utility, has been working with local authorities, the Environment Agency and Natural England, amongst others, in planning the works on the lines which cross industrial areas, roads, railways and waterways.
During the project, 14 pylons will be totally dismantled and new ones built to replace them. This will allow National Grid to divert the overhead line which runs between Saltholme substation and Lakenby substation away from its current route through a chemical plant. This phase of the work will see two new 145 meters high towers build to carry the line across the River Tees.
Mark Brennan, Project Manager said: "Our purpose is to connect people to the energy they use. This £50m investment will help ensure we can all continue to rely on having energy at our finger tips. Our society is built on the warmth and light we rely on at home, and the power which keeps our factories and offices going."
National Grid is writing to homes and liaising with businesses directly affected by its work on the lines in the area. Advance notice will be given of any road and footpath closures. A special contact number has been set up for people to ring if they have questions about the work. The number is 0800 319 6162.
National Grid is an electricity and gas company that connects consumers to energy sources through its networks.