How do you stop an oil pipe from rusting e.g. the Siberian one?

Our teacher told us that two scientists in a helicopter got off every 5 miles from a helicopter, did something to the pipe got back on and continued. I want to know what they did to stop the pipe from rusting.How do you stop an oil pipe from rusting e.g. the Siberian one?
Jaysfan has one of the answers. You would think that anything carying oil would not rust. Unfortunately, the crude oil usually has sulfur compounds in it and contact with water forms sulfuric acid, an eater of pipe. Pipe in earth will naturally rust when it comes into contact with acid rain or suffer from something called galvanic corosion which is caused by the formation of a localized battery. The pipe will act just like a battery and eat itself up while making a little bit of electricity. Protecting the pipe with coverings works well but keeping the thousands of little batteries from doing harm and creating pinholes is the chalange. They only have to charge the pipeline with a 1-2 volt DC charge to keep the pipe from corroding. One company actually used to construct the equivilant of a carbon-zinc battery in a hole and hook it to the pipeline and repeat at frequent intervals. These had to be replaced frequently. Modern systems can be done using photocells or connections to powerlines. Systems using higher activity sacrificial metals sometimes are used much like boats in saltwater use a piece of sacrificial zinc alloy to create a battery to protect steel or aluminum hulls. This forms a battery with the sea water and stops the corrosion.How do you stop an oil pipe from rusting e.g. the Siberian one?
The pipe is made from special steel that contains molybdenum. This strengthens and prevents rust from forming. The outer layer of the pipe is coated with a ';tar' or resin and then is wrapped in a material that prevents rusting and scratching of the metal. The investigators were probably inspecting the outer casing of the pipe for damage to the casing. On some piping, but not all, a small electrical current is passed along the metal to prevent rust.
It has been proposed that since the majority of leaks occur where the pipes are joined, that a ring of sensors be placed over each weld. Use the link to get more details.