Thwarting Oil-Pipeline Corrosion by Identifying a Nanoscale Villain 6 June 2019

Thwarting oil-pipeline corrosion by identifying a nanoscale villain 6 June 2019

Using transmission electron microscopes, which shoot electrons through targets to take pictures, the researchers were able to pin the root of the problem on a triple junction formed by a grain of cementite—a compound of carbon and iron—and two grains of ferrite, a type of iron. This junction forms frequently during most methods of fashioning steel pipe.

Iron atoms slip-sliding away

The researchers found that interfacial disorder in the atomic structure of those triple junctions made it easier for the corrosive solution to remove iron atoms along that interface.

In the experiment, the corrosive process stopped when the triple junction had been consumed by corrosion, but the crevice left behind allowed the corrosive solution to attack the interior of the steel.

A Sandia National Laboratories transmission electron "We thought of a possible solution for forming new microscope helped create this phase equilibrium map pipe, based on changing the microstructure of the showing areas where corrosion of steel was observed at steel surface during forging, but it still needs to be the triple junction formed where one cementite grain tested and have a patent filed if it works," said abuts two ferrite grains. Credit: Katherine Jungjohann Sandia's principle investigator Katherine Jungjohann, a paper author and lead microscopist. "But now we think we know where the major problem is." Steel pipes rust and eventually fail. To preempt disasters, oil companies and others have created Aramco senior research scientist Steven Hayden computer models to predict when replacement is added, "This was the world's first real-time needed. But if the models themselves go wrong, observation of nanoscale corrosion in a real-world they can be modified only through experience, a material—carbon steel—which is the most prevalent costly problem if detection comes too late. type of steel used in infrastructure worldwide. Through it, we identified the types of interfaces and Now, researchers at Sandia National Laboratories, mechanisms that play a role in the initiation and the Department of Energy's Center for Integrated progression of localized steel corrosion. The work Nanotechnologies and the Aramco Research is already being translated into models used to Center in Boston, have found that a particular form prevent corrosion-related catastrophes like of nanoscale corrosion is responsible for infrastructure collapse and pipeline breaks." unpredictably decreasing the working life of steel pipes, according to a paper recently published in To mimic the chemical exposure of pipe in the field, Nature's Materials Degradation journal. where the expensive, delicate microscopes could

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not be moved, very thin pipe samples were exposedcorrosion. The latter occurs in bulk form and is at Sandia to a variety of chemicals known to pass highly predictable. The former is invisible, creating through oil pipelines. a pathway observable only at its endpoint and increasing bulk corrosion rates by making it easier Sandia researcher and paper author Khalid Hattar for corrosion to spread. put a dry sample in a vacuum and used a transmission electron microscope to create maps of "A better understanding of the mechanisms by the steel grain types and their orientation, much as which corrosion initiates and progresses at these a pilot in a plane might use a camera to create area types of interfaces in steel will be key to mitigating maps of farmland and roads, except that Hattar's corrosion-related losses," according to the paper. maps had approximately 6 nanometers resolution. More information: Steven C. Hayden et al. "By comparing these maps before and after the Localized corrosion of low-carbon steel at the liquid corrosion experiments, a direct identification nanoscale, npj Materials Degradation (2019). DOI: of the first phase that fell out of the samples could 10.1038/s41529-019-0078-1 be identified, essentially identifying the weakest link in the internal microstructure," Hattar said.

Sandia researcher and paper author Paul Kotula Provided by Sandia National Laboratories said, "The sample we analyzed was considered a low-carbon steel, but it has relatively high-carbon inclusions of cementite which are the sites of localized corrosion attacks.

"Our transmission electron microscopes were a key piece of this work, allowing us to image the sample, observe the corrosion process, and do microanalysis before and after the corrosion occurred to identify the part played by the ferrite and cementite grains and the corrosion product."

When Hayden first started working in corrosion research, he said, "I was daunted at how complex and poorly understood corrosion is. This is largely because realistic experiments would involve observing complex materials like steel in liquid environments and with nanoscale resolution, and the technology to accomplish such a feat had only recently been developed and yet to be applied to corrosion. Now we are optimistic that further work at Sandia and the Center for Integrated Nanotechnologies will allow us to rethink manufacturing processes to minimize the expression of the susceptible nanostructures that render the steel vulnerable to accelerated decay mechanisms."

Invisible path of localized corrosion

Localized corrosion is different from uniform

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APA citation: Thwarting oil-pipeline corrosion by identifying a nanoscale villain (2019, June 6) retrieved 29 September 2021 from https://phys.org/news/2019-06-thwarting-oil-pipeline-corrosion-nanoscale- villain.html

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