Johns Hopkins Magazine - June 1995 Issue

A "goopless" way to detect oil leaks

By Melissa Hendricks

In the oil business, small leaks can mean big losses. Not only can a leak cause an explosion, if it occurs in a high temperature reaction vessel or piping, it can force a plant shutdown, as workers search for and mend the leak. Unplanned shutdowns due to leaks and other incidents cost the petrochemical industry more than $1 billion per year in lost revenue, according to Chia-Pin Hsiao, a lead engineer with Chevron oil company.

Now PhD candidate Doug Oursler and his advisor, James Wagner, chairman of Materials Science and Engineering, have developed a laser device that can detect minute cracks in 3/4-inch-thick carbon-steel, the material from which pipes and tanks are made. In laboratory tests, their instrument detected cracks that were thinner than a strand of hair.

In practice, a technician could use such a device to scan the outside surface of a vessel for incipient cracks forming on the inside surface. "The idea is to find the defect before it penetrates all the way through" and causes a leak, says Oursler. "It's a preventive measure."

Oursler and Wagner, who are conducting their research through the School of Engineering's Center for Nondestructive Evaluation (CNDE), get support for their project from Exxon, Chevron, and Shell oil companies. These companies have a vested interest in finding a way to detect leaks, since many of the nation's refineries - - particularly older refineries that were build before high-grade carbon-steel came into use - - are at risk for corrosion. Petroleum processing can gradually oxidize carbon-steel.

The problem will only get worse as the United States depletes its sweeter crudes and relies more on crudes with high sulfur content, which are more corrosive.

Oil refineries currently have a variety of methods to probe for leaks, but each has its limitations. Many companies use ultrasound techniques similar to those used on pregnant women, in which sound waves are bounced off the fetus and translated into an image. In the oil industry, says Oursler, a technician smears a "goop" of polymer couplant on the tank's outer surface. The goop seals the contact and provides a medium through which sound waves can travel. But it also melts at high temperatures. Since reaction vessels and some piping operate at around 800°ree; F, oil companies need to cool their tanks to ambient temperature before probing for leaks with ultrasound.

With the laser technique developed at Hopkins, "we don't need goop," says Oursler. The instrument consists of two parts: a pulsed laser beam and a device called an electro-magnetic acoustic transducer, or EMAT. The laser beam is pulsed onto the surface of a material, where it heats and agitates the molecules. The jiggling generates sound waves.

Then the EMAT takes over. It detects the sound waves and transduces them into radio waves. Since radio waves travel freely through air, the device does not require goop. A large radio wave signal indicates the material has a crack, pit, or other flaw.

This summer, Oursler will work with Idaho National Laboratories, in Idaho Falls, to refine the laser/EMAT for testing under 800°ree; F. (He and Wagner have also discussed the possibility of planting the instrument in a robotic cart to search for cracks in nuclear power plants.) Since the laser/EMAT theoretically can be used at high temperatures, "it might enable oil companies to do more maintenance on a regular basis," says Oursler.

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