We have two complete power plants at our station. As you have learned in elementary school, power is generated by boiling water and directing the steam over something like a fan, and that turns a generator producing electricity. It is a little more complicated that that. The turbine is actually a bunch of sections of fan like blade, but it is more like a jet engine than anything else that you might be familiar with.
The steam goes through the turbine and has to go somewhere. The turbine is enclosed in a big steel box that would quickly fill up with steam if it remained as steam. We work pretty hard to make the boiler water really, really pure, so we don't want to just shoot it into the ditch, or blow it off into the atmosphere, so we cool it down and make the steam back into water and pump it back into the boiler.
But there is a lot of energy that has to be absorbed, even from the spent steam before it turns back into water. You have probably noticed how badly you can be burned from just a little bit of steam leaking out of a microwaved potato. Your skin is providing cooling for the steam from the potato and condensing it back into water. We have a LOT of little pipes that run through the steel box - tens of thousands - that the steam can condense on. What keeps them from getting as hot as the steam? We have huge pipes connected to some of the worlds biggest swamp coolers, and we circulate the water from the swamp cooler (cooling tower) to the big hot steel box with tens of thousands of cool tubes (condenser). The steam comes off the turbine and comes in contact with the outside of the small pipes. Water from the cooling tower is on the inside of the pipes (condenser tubes) and keeps them cool enough to condense the steam.
The pipes that carry the water from the cooling tower to the condenser are the circulating water lines. They look like they are made of concrete, but there is a steel liner in the concrete and around the liner is something like a rebar mat. Each section of pipe has a steel end that hooks to the liner. Each of the steel ends of all the sections should have been welded together with little straps to make sure that they are connected electrically. We put a little bit of current into buried steel structures. This is called cathodic protection. During construction these rings should have been connected, but they weren't and consequently they got rusty and weak.
Annie has been working with a company that has been reinforcing these pipes. They are about 9 feet in diameter, and are buried about 20 feet underground. The workers have been pasting sections of cloth soaked with epoxy into the pipes, forming hoops. It is kind of like paper-maché on steroids. The carbon fiber is extremely strong, and when saturated with epoxy and glued into multiple layers, it is unbelievably strong and tough. We hope that it keeps the pipes from collapsing.
The rebar-like mat that corroded provided most of the structural strength that the pipe had. The rings, on the interior of the pipe will help prevent the pipe from failing. Even though this is a pretty expensive repair, it is very cheap if you consider the alternative. To dig up a 9 foot in diameter pipe buried 20 feet deep in the ground - two of them (one to bring the water and one to return it to the cooling tower) - and about 2000 feet long would have been a gargantuan job. Pipe like this will cost hundreds of dollars per foot, and even to lay new lines and then just tie in during an outage would be like installing the Panama canal. So this is a better plan.