Forecasting pipe fractures

MIT News
Aug 16, 2011

A computer model that tests automobile components for crashworthiness could also be of use to the oil and gas industry, according to researchers at MIT’s Impact and Crashworthiness Laboratory, who are now using their simulations of material deformation in car crashes to predict how pipes may fracture in offshore drilling accidents.

As a case study, the team simulated the forces involved in the 2010 Deepwater Horizon explosion in the Gulf of Mexico, finding that their model accurately predicted the location and propagation of cracks in the oil rig’s drill riser — the portion of pipe connecting the surface drilling platform to the seafloor. In a side-by-side comparison, the researchers found that their model’s reconstruction closely resembled an image of the actual fractured pipe taken by a remotely operated vehicle shortly after the accident occurred. The group presented their results at the International Offshore and Polar Engineering Conference in June.

Tomasz Wierzbicki, professor of applied mechanics at MIT, says such a simulation could help oil and gas companies identify stronger or more flexible pipe materials that could help minimize the impact of a future large-scale accident.

“We are looking at what would happen during a severe accident, and we’re trying to determine what should be the material that would not fail under those conditions,” Wierzbicki says. “For that, you need technology to predict the limits of a material’s behavior.”

Wierzbicki has already laid much of the foundation for what he calls Fracture Predictive Technology through his work in car-crash safety testing. Over the years, he’s fine-tuned a testing method that combines physical experiments with computer simulations to predict the strength and behavior of materials under severe impacts.

For example, to safety-test materials used in automobile bodies, Wierzbicki first cuts small samples from a candidate such as steel, using a high-pressure water jet. He then sprays the sample with a fine pattern of speckles, covering the surface with tiny dots. After the spray dries, Wierzbicki clamps the cutout into a machine, which subjects specimens to different types of loading. A motion-capture camera, set up in front of the sample, takes images as it crumples, sending the images to a computer, which plots the image’s dots along a grid to show exactly when and where deformations occur.

By testing different shapes and sizes of materials under various pressures, Wierzbicki can determine a material’s overall mechanical properties, such as its strength and ductility. Knowing this, he says, it’s possible to create a simulation to predict a material’s behavior in any configuration, under any conditions. Determining the exact limits for materials is especially important for offshore drilling, he says, where pipes are continually subjected to tremendous pressures at great depths.
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