The Pipeline and Hazardous Materials Safety Administration (PHMSA) has issued an advisory to the industry warning that reversing a pipeline's flow or changing the product it carries can lead to degradation and heighten the possibility of failure. PHMSA's report comes as a reaction to an increase in these practices, which may have contributed to at least two incidents last year.
On March 29, an ExxonMobil pipeline ruptured in Mayflower, Arkansas, spilling 5,000-7,000 barrels of oil sands from the Wabasca oil field in Alberta. In October, a leak was discovered in a Tesoro pipe in Tioga, North Dakota, and authorities believe it could take two to three years to clean up the oil. In both cases, the pipelines had been reversed, and PHMSA believes that exacerbated existing corrosion and cracking.
PHMSA has not issued any new regulations, but has made recommendations to pipeline operators on what integrity tests to conduct before reversing the flow. The most common is a hydrostatic test, which involves filling the pipeline with water to observe whether there is any loss of pressure which would signal a leak.
In most cases, a flow reversal changes the pipeline's contents. In the Mayflower case, it was switched to Canadian oil sands, which are heavier than the crude it carried before. The presence of oil sands in North American pipelines is fairly recent and growing fast, often in pipes that were designed for lighter oils. Changes in flow and content are up amid uncertainty over the construction of the Keystone XL Pipeline.
Pipeline safety training helps reduce the risk of accidents and ensure compliance with Department of Transportation and PHMSA regulations.