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Welding issues major cause of pipeline failures

April 22, 2013
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Researchers have analyzed 280 cases of electric-welded pipe failures between 1950 and 2005, including 55 instances of rupture while the pipe was in use.

The question of efficiency and safety of pipes produced decades ago and in use almost as many years has recently caused much debate, following a number of pipeline ruptures that have caused problems across the United States. The most serious of them occurred last month, when an ExxonMobil pipeline rupture caused a huge oil spill in Arkansas.

One of the biggest problems is the controversial welding technique used in the 1970s, known as low-frequency, electric-resistance welding. The technique has not been used since then but federal data from 2011 shows that it is still to be found in about a quarter of the 182,500 miles of liquid fuel pipelines across the country, Hydrocarbon Processing reported.

In the ExxonMobil incident, 5,000 bbl of crude leaked through an incision-like hole into a residential area. According to Rick Kuprewicz, a pipeline-safety consultant who has examined photographs of the pipes, it is very likely that the spill was caused by a seam-type failure. Meanwhile, Exxon spokesman Alan Jeffers noted that the company had not reached any conclusions regarding what caused the rupture and was awaiting a third-party review of the failed section.

Currently, federal regulators are looking into the ability of up-to-date inspection methods to detect weak spots and flaws in the old pipes. A study has been launched to investigate outdated and substandard pipes, so that new rules can be laid down. Doubts have been raised about the efficacy of inspection methods, as federal regulatory bodies found that inspection failed to notice problems with pipes prior to big explosions, including one in Mississippi in 2007 which killed two people.

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The study was commissioned by pipeline regulator the Pipeline and Hazardous Materials Safety Administration (PHMSA) to Battelle Memorial Institute in 2011 and is still being conducted. So far, researchers have analyzed 280 cases of electric-welded pipe failures between 1950 and 2005, including 55 instances of rupture while the pipe was in use. The research group explained that the best way to tell if a weld is defective is to pump water through the pipe at high pressure. Carrying out such tests is expensive because pipelines operators have to shut down the line. Moreover, accidents have occurred in several instances when the pipes have been put back into service, Battelle said.

Another testing method involves running a robotic device through the inside of the pipe to detect any anomalies. This machinery, known as a "smart pig," is also known to have failed to identify flaws that later resulted in a rupture. Neither of these methods is foolproof, noted Brian Leis, a researcher leading Battelle's study.

According to the PHMSA, most incidents either cause very small spills or are not related to pipe welds, which means that operators are not required to submit detailed information about them. However, the total number of pipeline accidents has been on the rise and in 2012 there were 364 accidents on liquids pipelines recorded -- the highest number since 2008. A spokesman for the Association of Oil Pipe Lines claimed that an old pipe is safe provided that it has been maintained up to standards, and that spills occur quite rarely.
 

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