MME Lecture: Stainless Steel Corrosion

Wednesday, Tatiana Reyes spoke for a materials science seminar in Hill Hall. Entitled, “Corrosion of Supermartenstic Stainless Steel Under Alternating Current” her discussion attracted both MME and EE students.

Supermartenistic stainless steel works well for offshore pipelines, except for one problem. Corrosion builds up at the site where the pipes are welded together. Reyes, who received her bachelor’s degree in Venezula, and is now working on her doctorate, is studying this very problem. The welding process creates impurities and weaknesses in the stainless steel. Her team aims to pinpoint what exactly is causing the corrosion at these points, and how to reduce it.

Reyes began her discussion with by explaining the purpose of her experiments. “The goal of this research is first to achieve an accurate understanding of the mechanisms and severity of applied alternating currents on corrosion of 13 Chrome stainless steel in artificial sea water. We want to address also the change in flexibility to localize corrosion with and without alternating currents.”

Reyes and her colleagues designed and performed various experiments to gather data about how different variables will affect the rate of corrosion. The oil company funding her research is looking for a better way to protect their pipes. “What they wanted to prevent is the formation of the obstruction of the pipeline,” Reyes explained. “These are problems they know how to live with, but it is not quite solved.”

One of the variables examined was the effect of the changing magnetic field with the current. So Reyes tested the corrosion levels at various strengths of electromagnets. “First try, we got fake currents from the electromagnet. Second try, there was electric noise from the electromagnetic magnet. So that’s being adjusted, we’ve been working on that.” As with many tests, she had to make various adjustments along the way to ensure she was measuring the data with as much accuracy as possible. Reyes explained her adjustments, “I coated the electromagnet in epoxy and silicon to prevent stray currents. I also used thicker magnetic wire to prevent excessive heat generation, that would be another variable I’m not interested in.” Despite some remaining corruption in the experiment, the data is still useful for drawing conclusions.

Reyes described the results of the experiment, saying, “The samples [that] pitted under higher magnetic field were more densely pitted than those corresponding to a lower magnetic field.” The presence of pitting, depressions, and cracks on the surface of the metal indicates corrosion. Reyes’ team then determined that “overall the magnetic field increases the corrosion rate.”

Reyes also added that “alternating current densities of 40 amps per square meter would produce pitting.” Her team plans to continue their research to answer what is really happening to these pipes in sea water.