Oil companies like BP generally conduct constant checks on pipelines, which are key assets that they cannot afford to idle, a leading international pipeline engineer said Tuesday, according to dpa. This week's shutdown of the Prudhoe Bay pipeline in Alaska because of corrosion is an "utter exception," said Lars Bangert, director of pipeline systems at ILF, a Munich-based consulting engineering firm. "I don't know one other case in the past 15 years where a pipeline had to shut down because of corrosion," he told Deutsche Presse- Agentur dpa in an interview. Records show most shutdowns are caused by third-party damage, such as being rammed by bulldozers. Generally, oil companies spend heavily to maintain their pipelines, said Bangert. Robotic devices, so-called pipeline pigs, float through the pipes, checking wall thickness and hunting for corrosion and cracks. "An oil company knows every square centimetre of its pipelines," he said. "They are key capital assets." Most companies subject pipelines to a major check-up every 10 years or so. Pipelines are also equipped with sensors to monitor pressure, temperature and flow rates. Crude oil contains some water as well as corrosive gases such as hydrogen sulphide. Without specific knowledge, Bangert speculated that the BP pipeline could have been corroded by an accumulation of salty water at a low point in the line. Corrosive components in crude oil vary among fields and can be reduced by filtration before the oil is pumped. But even tiny, residual quantities of some substances can cause corrosion. Water is denser than oil, so it settles in the bottom of a pipe. Pipeline pigs can clean the pipe and suck up accumulated water. If corrosion does set in, repair crews can put a metal sleeve up to 2 metres long on the outside of the pipe, Bangert said. If a pipeline is badly rusted, as appears to have happened in Alaska, whole sections have to be replaced. The rust threat increases with age. BP says that its northern Alaska line is nearly 30 years old and much more badly rusted than originally believed. Bangert, whose firm designs modern pipelines, said that Arctic temperatures could be a factor, because long periods of extreme cold make steel brittle and more likely to crack. The outsides of modern pipelines are generally protected from corrosion by rust-proof coatings and cathodic protection systems that fight rust electrically.
