The oil pipeline leak that fouled a stretch of California coastline this week reflects a troubling trend in the nation's infrastructure: As U.S. oil production has soared, so has the number of pipeline accidents.
Since 2009, the annual number of significant accidents on oil and petroleum pipelines has shot up by almost 60 percent, roughly matching the rise in U.S. crude oil production, according to an analysis of federal data by The Associated Press.
Nearly two-thirds of the leaks during that time have been linked to corrosion or material, welding and equipment failures, problems often associated with older pipelines, although they also can occur in newer ones, too. Other leaks were blamed on natural disasters or human error, such as a backhoe striking a pipeline.
Industry officials and federal regulators say they have adequate means of gauging the safety of pipelines, but the aging infrastructure is a source of lingering concern for outside experts.
"Tick, tick, tick," said Robert Bea, a professor emeritus in civil engineering at the University of California, Berkeley. "Things get older. They don't get stronger."
Since 1995, there have been more than 2,000 significant accidents involving pipelines carrying crude oil and refined petroleum products that have caused about $3 billion in property damage, according to data from the federal office that oversees pipeline safety, the Pipeline and Hazardous Materials Safety Administration. That's an average of a little over 100 per year. But after dipping to 77 in 2009, that figure has spiked to at least 121 in each of the past two years.
No cause has yet been determined for the pipeline failure northwest of Santa Barbara that spilled up to 105,000 gallons of crude oil, making it among the largest spills in the U.S. over the past two decades.
The leak covered sand and rocks with a thick, tar-like goo and forced two state beaches to close ahead of the Memorial Day weekend. About a fifth of the oil reached the Pacific Ocean. Federal regulators on Friday barred the pipeline from reopening until a series of corrective actions are taken.
Plains All American Pipeline LP, which operates the pipeline, and its subsidiaries have reported 223 accidents along their lines since 2006. Those accidents resulted in a combined 864,300 gallons of spilled hazardous liquids, damages topping $32 million and 25 enforcement actions by federal regulators.
Corrosion was determined to be the cause in 76 of those accidents. Failures in materials, welds and other equipment were cited more than 80 times.
The company and its affiliates have had the fifth highest number of significant pipeline accidents among all of the nation's pipeline operators since 2006.
The 2-foot-wide pipe at issue in California had no previous problems and was thoroughly inspected in 2012, according to the company. It underwent similar tests about two weeks ago, although the results had not been analyzed.
Federal regulators said Friday that the 2012 inspection identified 41 "anomalies" along the pipeline, mostly due to external corrosion that frequently was found near welds.
At 28 years old, the pipeline is just half the age of many pipes that were installed during the industrial boom of the 1950s and 1960s, some of them with a structurally flawed welding technology that regulators say is prone to failure.
"The takeaway from it is that even though the technology is getting better and pipeline companies are spending a lot more money on inspecting pipelines, there's been an uptick in failures over the last decade," said Carl Weimer, executive director of the Pipeline Safety Trust, a Bellingham, Washington-based watchdog group.
"Age isn't the only consideration," he said "but it's an issue."
Federal officials and industry leaders have long maintained that a pipeline can live for decades, as long as it is properly maintained.
"Age alone doesn't necessarily make a pipeline safe, or unsafe," said Brigham McCown, who served as an acting administrator and interim chief executive of the pipeline safety administration under President George W. Bush.
Pipelines undergo regular checks at least every five years, said John Stoody, a spokesman for the Association of Oil Pipelines, an industry lobbying group. Overall, the industry spent $2.1 billion to evaluate, inspect and improve pipelines in 2013, the most recent year his organization had compiled information, he said.
About 170 industry officials are gathering this week in New Orleans for a previously scheduled meeting of the Pipeline Research Council International. Their goal is determine how to use as much as $20 million in annual research funding to improve pipeline designs and make them more resistant to problems such as corrosion, council spokeswoman Natalie Tessel said.
Outside of inspections, there's no sure-fire way to guarantee an aging pipeline's integrity.
Safety advocates say they would like to see the federal government take a stronger role in regulating older pipelines. Some older systems do not have the same quality of steel or the same coatings to protect from corrosion. And lines welded with a low-frequency electric-resistance bonds are particularly concerning because studies show they are much more likely to fail, said the watchdog group's Weimer.
Older oil pipelines have been a factor in some of the most costly pipeline failures in recent years.
A 2013 rupture in Mayflower, Arkansas, spilled 504,000 gallons of crude oil that sloshed into suburban cul de sacs and the town's lawns. The pipeline was built during the 1940s. In 2010, a pipeline that was more than 40 years old ruptured in Michigan, leaking nearly 850,000 gallons of crude oil.
With new drilling techniques such as hydraulic fracturing, the U.S. is in a period of sustained growth in oil production. New frontiers, such as parts of North Dakota, Oklahoma, Texas and Pennsylvania, have lifted domestic output to near historic highs.