Prudhoe Bay Pipeline Corrosion
In 2006, a British Petroleum (BP) worker in Prudhoe Bay, Alaska discovered a leak in its transit, or feeder pipelines (which deliver the crude oil drilled by BP to the main Trans-Alaskan Pipeline, which transports the oil to Valdez, in the southern part of Alaska. The oil is taken from there in ships to the lower 48.) Approximately 5,000 barrels (more than 200,000 gallons) of oil were spilled, adversely affecting almost 2 acres of permafrost (continually frozen soil). During inspections performed as a result of the spill, severe corrosion (and another, smaller spill) was discovered in 16 miles of pipeline. BP decided to replace all 16 miles of affected pipeline, at a cost of $260 million. Additionally, BP paid $20 million in fines, restitution to the State of Alaska, and a payment for environmental research. Some people believe this is the largest fine ever paid in the state for what was legally considered an “environmental misdemeanor.”
A thorough root cause analysis built as a Cause Map can capture all of the causes in a simple, intuitive format that fits on one page (see attached pdf). First we will look at the impact to the goals. For the BP pipeline the environmental goal was impacted because 5,000 barrels of crude oil spilled, which affect on 1.9 acres of permafrost. The impact on the two environmental goals was caused by the leak of crude oil. The customer service goal was impact due to an increase in oil prices to consumers. This occurred because of the loss of barrels during the production shutdown, which is an impact to our production goal. The loss of oil is due to the shutdown, which occurred in order to replace the affected lines, which is also an impact to the material goals. The lines had to be replaced because a loss of pipe integrity was discovered, which led to the fine and restitution, which is also an impact to the material goal.
The loss of pipe integrity was due to severe corrosion product buildup. The corrosion product buildup also resulted in a hole in the pipeline, which caused the leak.
The permafrost that was affected by the oil because of the leak, but also because the leak was not contained promptly. The next question is “Why was the leak not contained promptly?” (And also, “Why did the leak occur?” which was due to a hole, but we’ll get to that later.) The leak was not contained promptly because the the leaked oil was not visible, the location of the leak was inaccessible, and the leak detection program was ineffective.
The severe corrosion product buildup resulted from three things. First, there was corrosion in the pipe. Second, the corrosion went undetected (we’ll go into both of these in more detail). And third, the pipes were used beyond their design life (25 years vs. the 29 years they had been in service.
There was corrosion in the pipes because there were microbes in the pipe protected by a layer of sediment, and microbes produce corrosive substances (this is known as internal microbiological corrosion). This layer of sediment was due to an ineffective maintenance program. It settled to the bottom of the pipe because there were low spots in the pipe, and because the velocity of the oil was too low to remove sediment because the pipe diameter was too large.
The corrosion went undetected because of an ineffective inspection program. The inspection progrm was ineffective because there was not a regular internal inspection schedule. The ultrasonic testing used was not effective because it did not cover 100% of the line and the damage was very localized (thus the ultrasonic testing was missing the spots with the worst corrosion). Additionally, a “smart pig”, which is used internally to measure the wall thickness of a line, was never run through the line, because BP did not believe it was necessary as they performed ultrasonic testing.
Once the Cause Map is build to a sufficient level of detail with supporting evidence the solutions step can be started. The Cause Map is used to identify all the possible solutions for given issue so that the best solutions can be selected. On the Cause Map you can see some solutions derived from the causes (in the green boxes). Looking through news reports or BP press releases regarding their Prudhoe Bay pipeline, you’ll see that almost all of the actions listed have been or are being taken to prevent this problem from happening again.