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fugitive emissions from its cargo tanks. "Before entering into a va- por recovery zone (which varies with each locale) we must eliminate any fugitive emissions from entering into the atmosphere," said Lou

Lanza, senior marine superintendant for Chevron. "Fre- quently, a representative from an air quality board will board a vessel and check for fugitive emissions.

The inspector checks us with a de- vice that measures hydrocarbons.

If fugitive emissions are found which are in excess of what is al- lowed, the board can shut down the operation until the problem is cor- rected." "We want to avoid unnecessary delays and we also want to be sure that we're in compliance with the requirements," continued Mr.

Lanza. "So before entering into a restricted zone we use ultrasonics to routinely check any potential area where we might have leakage.

We want to detect all leaks and repair them before we enter into a restricted area."

According to Mr. Lanza, ultra- sonic testing provides Chevron with a quick and easy way to check for almost any leak. "If, for example, our maintenance person is testing a circular Butterworth plate about a foot and a half in diameter, he points the probe of the ultrasonic instrument about two inches from the plate and slowly moves along the perimeter, listening for leakage along the gasket. In a very short time, he can walk from location to location along the deck and check the problem areas. "We're continu- ally looking for ways to comply with the vapor recovery laws in the West

Coast area, and ultrasonic detec- tion is helping us meet our obliga- tions," said Mr. Lanza.

The Technology

The theory of airborne ultrasonic detection is relatively simple. Ul- trasonic instruments are sensitive to sounds beyond the limits of nor- mal human hearing. An ultrasonic detector translates ultrasound to the range of human hearing. Fre- quency, the number of times a sound wave cycles from trough to crest, is expressed in "cycles per second" and measured in "hertz." One kilo- hertz (kHz), for example, is one thousand cycles per second. The best human ears can hear noises in the range of 20 hertz to about 20,000 hertz.

Many ultrasonic detectors start at approximately 20 kHz and work upv/ard to sounds as high as 100 kHz.

Thus inspectors using the ultra- sound equipment can tune into and "hear" faults in electrical systems, operating machinery, and leaks in vacuum or pressurized systems.

Fluid and gas systems, electrical systems, and working machinery all produce consistent ultrasound patterns. Changes in the sonic sig- natures can be readily recognized as loose connections, faulty equip- ment, wear in components or leak- age. An ultrasonic detector senses subtle changes in the ultrasonic sig- nature of a component and pinpoints potential sources of failure before they can cause costly damage. Ul- trasound detectors are ideal for iso- lating machinery leaks.

For years, ultrasonic inspection has been a cornerstone of predictive and preventive maintenance pro- grams in a wide range of industries.

As the maritime industry begins to embrace this technology, engineers and senior management are already recognizing substantial savings and doing their part to create a safer environment.

The perceding is based on an ar- ticle by Alan S. Bandes, vice presi- dent of UE Systems, Inc., Elmsford,

N.Y.

For more information on ultrasonic testing

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