A computer model that tests automobile components for crashworthiness also could be of use to the oil and gas industry, according to researchers at MIT's Impact and Crashworthiness Laboratory, who now are 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 the 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
Wierzbicki, professor of applied mechanics at MIT, says that 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.
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 explains. "For that, you need technology to
predict the limits of a material's behavior."
has 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
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.
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 especially is important for offshore
drilling, he says, where pipes continually are subjected to tremendous
pressures at great depths.
and graduate students Kirki Kofiani and Evangelos Koutsolelos used the same
principles to predict the strength and breaking points of the Deepwater
Horizon's drill riser.
researchers were unable to obtain a sample from the actual collapsed riser,
they consulted an offshore-drilling handbook, finding that the riser was likely
made from X70, a grade of steel commonly used in such risers. The material's
mechanical properties closely matched those of TRIP 690, a grade of steel the
team had previously tested in the lab.
researchers drew up a computer model of the drill riser - a large-diameter pipe
attached at one end to a large rectangle, representing the surface drilling
platform. The team then ran a simulation that partially reconstructed the
Deepwater Horizon accident: After methane gas erupted and shot to the surface,
setting the entire platform on fire, the oil rig began to list and sink. The
researchers simulated the sinking by slowly angling the rectangular platform
result, the attached drill riser began to bend. A color-coded simulation showed
points along the pipe where it was likely to crack: Green and blue meant the
material was intact; yellow and red indicated it was at its breaking point. The
group found four red areas where cracks - and oil leaks - especially were likely
had one point of comparison: an image, taken by an underwater robot shortly
after the accident, of the ruined pipe. When the researchers compared their
model with the real-life image, they found an almost perfect match.
sees the results as an encouraging first step in applying the model to
materials for offshore drilling.
unlikely that any pipe material could have remained intact during the Deepwater
Horizon disaster, Wierzbicki says that there are many improvements that can be
made to shore up existing oil and gas pipelines. He and his group, whose
research partly is sponsored by Royal Dutch Shell, will be analyzing samples
from retired offshore pipes in the next few months.
you go in the ocean, two or three miles down, the stronger material you need to
withstand the pressure," Wierzbicki says. "But stronger materials are
more brittle and break more easily. So there's a difficult problem for the
offshore industry, and I think they can learn a lot from us."
MIT: Forecasting and Preventing Pipe Fractures
August 23, 2011