Pipe corrosion is a recipe for disaster in Alaska's Prudhoe Bay

By Wesley Loy

07-12-03 In late May a North Slope oil field worker made an alarming discovery: an oily sheen in melting snow alongside large pipelines moving a mix of crude oil, natural gas and water. The sighting set off a massive and expensive operation to stop the flow and investigate how the 24-inch carbon steel pipe had sprung a leak.
The pipeline operator, BP Exploration (Alaska), shut down the line carrying 8,000 to 10,000 barrels of oil worth some $ 277,000 a day. Eighty cleanup workers took up shovels to clear away oily snow and dig to the source of the leak, which occurred where the otherwise unburied pipes passed under a gravel mound where caribou can cross over. Within a few days, investigators had the answer: Corrosion.

It had eaten three pinholes into the bottom of a pipe wall, perhaps months before the spill was detected, letting about 6,000 gallons of oil and oily water trickle over about half an acre of tundra. Corrosion, triggered by water touching steel, is an insidious and potentially disastrous problem in Prudhoe Bay and other North Slope oil fields, especially as they get older. Stopping it is a $ 100 mm industry within an industry in the oil patch, employing hundreds of oil company engineers and contractors.
In recent years, BP and the Slope's other operator, ConocoPhillips Alaska, have maintained big budgets for corrosion detection and prevention. And regulators have increased their scrutiny of the oil companies, sometimes meting out fines.
"It's a constant battle," said Bruce Weiler, a BP field supervisor, during a visit to the spill site on a windy, 33-degree day in late August. "I wish corrosion didn't exist."

Finding corrosion is a huge and tedious task. A visitor to the Slope might shake his head and say it's hopeless -- some 1,690 miles of pipeline, more than enough to link Anchorage to Portland, Oregon, spider web across the North Slope. In many places, bundles of pipe wind over the tundra like eight-lane freeways.
The search for potential leaks is greatly complicated by the 3 inches of hard foam insulation wrapped around each line, nearly all of which are elevated a few feet off the ground. The insulation keeps the hot oil flowing inside from melting the permafrost and the oil from cooling into a gel.

The oil companies use all manner of tricks -- from X-rays to ultrasound to big, bullet-shaped magnets called "smart pigs" -- to probe the lines outside and inside. It's not just the cross-country pipelines that bear watching. The many processing plants on the Slope are themselves jam-packed with piping, holding tanks and other equipment that can corrode.
Prudhoe Bay, the largest oil field in North America, has been producing oil since 1977. Operator BP wants another half-century of use out of Prudhoe's pipes, but getting there will take a lot of money and attention, said field manager George Blankenship.
"A piece of steel, maintained, will last forever," he said.

Corrosion is something that dogs all kinds of industry, not just oil and gas. It can bite manufacturers, shippers, utilities, even the military. A 2001 study prepared for the Federal Highway Administration estimated the total cost of corrosion for US industry and government agencies at $ 276 bn a year. For oil and gas exploration and production, the cost is almost $ 1.4 bn, according to the study.
On the North Slope, BP is now spending about $ 50 mm a year to find and control corrosion and fix damaged pipe, Blankenship said. Conoco, which operates the large Kuparuk and Alpine oil fields, spends more than $ 20 mm. Alyeska Pipeline Service, operator of the trans-Alaska pipeline, which carries North Slope oil 800 miles south to the tanker port at Valdez, spends about $ 50 mm annually on corrosion.

Spills aren't the only consequence of corrosion. It can kill. Corrosion has been known to sink ships and bring down airplanes, killing their crews. In one of the most famous of corrosion disasters, a weakened Silver Bridge spanning the Ohio River at Point Pleasant, West Virginia, collapsed in 1967, killing 46 people.
On the North Slope, a corrosion cousin, abrasion, nearly proved deadly in October 1998 when sand and grit cut a small hole in a pipe at a Prudhoe production site called Z Pad. Natural gas leaked inside a building and exploded. Luckily, no workers were nearby. It seems hard to believe that water is much of a threat to heavy North Slope pipelines whose walls are a third of an inch thick. But it is.

Corrosion is a natural, electrochemical process that can break down steel and produce a by-product, rust. It needs water and oxygen to work. With the water serving to complete a circuit, electrons move from negative to positive points in the steel -- from anode to cathode. The steel dissolves as electrons flow away from the anodes. The same thing is at work in flashlight batteries, which use a corrosive reaction to power the bulb.
North Slope water is also infested with bacteria, hydrogen sulphide and carbon dioxide that can form an acidic and corrosive environment inside pipes. Corrosion can thin down the pipe wall, or create little pits that can grow like potholes on the streets of Anchorage during break-up. Depending on the type of metal, the way it's used or the environment it's in, serious corrosion damage can develop in only a few hours or many years, according to corrosion experts.

Hundreds of spills usually occur on the North Slope every year, but most are small, and corrosion is to blame for only a handful. Since mid-1995, the state has cited corrosion as the cause of 72 spills involving a total of about 176,000 gallons of crude oil, oily water, chemicals and other oil industry liquids. But these spills tend to be larger than spills caused by other factors such as valve failure, overflows or human error, state records show.
In one of the biggest spills ever seen on the Slope, 92,400 gallons of water spilled from a pipeline onto the tundra in April 2001. State regulators say the water, which often is salty and comes out of the ground mixed with oil, can be about as deadly to tundra plant life as dousing it with oil. Investigators determined that corrosion attacked the outside of the pipe at an insulated weld joint and ate into the steel.

The state fined Conoco $ 10,000, with half of it suspended. The fine might have been stiffer, but the company's cleanup response was excellent, said Leslie Pearson, spill response manager for the state Department of Environmental Conservation. BP also is expecting a state fine for its May spill.
Richard Woollam, BP's corrosion manager, sounds a little like a big league pitcher, always looking for another "save." Woollam, 43, a corrosion engineer who grew up north of London, manages a team of 150 people, most of them contractors, who fight corrosion in Prudhoe Bay's maze of pipes and plants.
"Neil Young was right -- rust never sleeps," said Woollam, wincing at himself for conjuring up the rock singer's cliche.

Yet it's true. Woollam and his team are in an endless contest with corrosion, and it promises to get tougher. As oil fields age, producers pump more and more seawater underground to flush out residual oil. That means more corrosive water is coming up wells with the oil and flowing down the pipelines to cause mischief. Woollam's job is to find and prevent corrosion that assaults the pipes from inside and out.
His best stuff includes inhibitors, chemicals that coat the inner walls against water. BP injects inhibitors by the train car into its pipelines, about 3 mm gallons or $ 20 mm worth annually. The company also injects bacteria-killing biocide.

Sometimes design and construction of the pipelines can encourage corrosion, such as in elbows where the rush of oil, gas and water can create turbulence that wears the steel, or at welded joints, called weld packs, where outside water can seep under insulation that was applied in the field, not in a factory.
The Slope seems a crazy quilt of pipes -- pipes ranging from 2 to 60 inches in diameter, pipes running from wells to processing plants, pipes runningfrom the plants back to drill sites, huge trunk lines crossing miles of lonely tundra. Collectively, the pipelines work to drain about 1 mm bpd of crude oil off the North Slope.

To find every weak spot along so many miles of tubing, nearly all of it jacketed with thick insulation plus a metal outer jacket, seems like a pipe dream. But that's Woollam's game.
To make a save -- that is, to find and fix a corroded spot -- technicians take thousands of X-rays. They launch pigs through the larger pipes to detect thin spots. They stand in the cold for hours with hand-held ultrasonic scanners, hunting for deformities in pipeline walls. Sometimes they just hop in the truck and go look.

Steam rises off flowline 9-E, connecting Flow Station 2 and Drill Site 9, as Charlotte Foley runs an ultrasound sensor over the warm steel and eyes spiky lines on a video screen. The sensor looks like the head off a cassette tape deck. It's the same as checking a woman's unborn baby, except Foley is testing for signs of corrosion.
"It could be anything from a lump to a crack," said Foley, who works for Canspec, a Canadian contractor for BP. Her aim is "finding the big one, what somebody else didn't find."

Actually replacing pipe these days is rare on the Slope, though BP was forced to put in many new sections during a corrosion crisis in the early 1990s. Workers are more likely to weld a sleeve over a bad section to reinforce it and to avoid interrupting the lucrative flow of oil.
One of Woollam's key corrosion assets is a long, dark room packed with a hospital's worth of X-ray negatives. These pictures, plus thousands more digital images stored on computer, show pipeline trouble spots that crews can revisit time and again to see if the corrosion is worsening.

BP's overall goal is to keep each of Prudhoe's pipes from losing more than a hair of its wall thickness each year. To measure the corrosion rate, engineers annually examine about 10,000 weight-loss coupons, small slips of metal stuck inside pipelines. Thecoupons wear down measurably as oil and water stream by.
Keep the walls thick and the oil stays where it belongs -- inside the pipes, Woollam said. He's aiming to keep Prudhoe's pipes in the game till 2050.
"Yes, the field is older and there is some damage out there," he said. "The question is how much wall is left, and how fast is it going away?"

So, how good have the oil companies been at striking out corrosion? The state has no one regularly inspecting most pipelines in the field. But independent reviews of corrosion reports that BP and Conoco file annually with the Department of Environmental Conservation are pretty positive.
The two companies agreed to file the reports under a charter agreement signed with the state in December 1999. The charter contains a slew of environmental and other commitments the companies made to the state when former North Slope major Atlantic Richfield sold out to BP and Phillips.

The charter requires BP and Conoco to develop corrosion-monitoring programs and to pay up to $ 500,000 annually for corrosion experts to advise DEC. That's where Tim Bieri comes in. He's an Anchorage corrosion engineer for Seattle-based Coffman Engineers. For three years, the DEC has hired his firm to analyse the BP and Conoco corrosion reports.
"Overall, both companies have a complex task and do very well at managing the infrastructure that they have," Bieri said. "They've come a long way in managing the internal corrosion of the systems. I would say external corrosion is where they're focusing a lot attention now, at places like animal crossings or road crossings, or where there are weld packs."

Bieri concedes that Coffman has counted not only the state but BP and Conoco as clients. Also, neither Bieri nor state employees actually go to the Slope to inspect for corrosion problems in pipelines.
Sam Saengsudham, an DEC environmental engineer, agrees with Bieri, however, that the companies seem to have a good grip on corrosion. "Oh, yeah," he said, when asked whether he had faith in the numbers in BP's report.
The data show a pronounced and steady decline in pipeline wall thinning since the early 1990s, when the rash of pipe replacements prompted BP to launch a corrosion-management program. Prudhoe pipelines can, and should, last as long as the oil lasts, Saengsudham said.
"You see people driving a 1965 car, and it's fine," he said. "Good maintenance."

 

Source: Anchorage Daily News