A group of experts from Shell and BP recently released a report in Offshore Magazine that details the dangers of pitting and crevice corrosion that can occur in the steel of offshore oil rigs, providing examples of such instances and the results of the degradation.
According to the news source, stainless steel tubing is often used for instrumentation and sensing in the oil and gas industry, among a number of other functions, but corrosion of 316 stainless steel tubing has been increasingly reported at facilities.
“Corrosion is a serious development that can lead to perforations of the tubing wall and the escape, under pressure, of highly flammable chemicals,” the experts warned.
The media outlet stated that the experts noted the two most prevalent forms of corrosion found in offshore rigs are pitting – which is easy to see with the naked eye – and crevice corrosion, which is harder to identify. The panel asserted that around the world, experts agree that the 316 stainless steel tubing made today “may more readily corrode than the more generously alloyed 316 tubing products produced decades ago.”
According to the news source, the experts also noted contamination as one of the leading problems for stainless steel tubing found in offshore facilities. This contamination, which leads to surface degradation, can be caused by particles emitted during welding operations, drilling, handling and blasting procedures and because of diesel exhaust, which has extremely high sulfur levels.
The most concerning, though, are the pitting and crevice corrosion problems. Pitting has been linked with higher chloride concentrations, which cause shallow pits to form in the beginning. This can give way to larger, more dangerous pits later on, which are easily recognized. What’s worse about crevices, according to the news source, is that they are sometimes impossible to avoid when installing new tubing.
Crevices form the tubes and their supports, within clamps, between two tubes and near contamination sites.
“Relatively tight crevices pose the greatest danger,” the group warned.
One example of unchecked corrosion that could potentially have led to a catastrophe is BP’s Ula operation in Norway. According to Bloomberg, country regulators recently discovered what they called “serious breaches” that could have caused an explosion with deadly consequences. The incident was limited to 125 barrels of oil being leaked into the North Sea, which was the result of corroded bolts in a valve.
“The incident had the potential to become a major accident,” the Petroleum Safety Authority said. “A number of lives might have been lost and substantial material damage caused.”
Focusing on metal testing can not only bring maintenance costs down, but also ensure the safety of the operation.