ALMA provides smarter gas pipeline aerial survey.

Author:Horn, Boris
Position::Tech Notes: Product Development
 
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Gas transportation companies have a wide variety of choices to make concerning pipeline inspections. Aerial technologies that include measurement of gas concentration and recording capabilities are gaining ground in this regard; one of the conventional systems is called aerial laser methane assessment, or ALMA for short, but how does it work?

Dead, brown vegetation that has been starved of oxygen is a reliable sign of a gas leak. It is generally observed by an inspector viewing the corridor from a helicopter. This method can become more sensitive and comprehensive with the attachment of a small piece of technology to the helicopter.

With the inclusion of such a device, gas leaks that rise only a few parts per million (ppm) can be detected reliably on both aboveground and buried pipelines. In addition to earlier detection of leakage, the corridor can be filmed during the same flight.

"This detailed reporting tool became an important component of our inspection efforts and provided us with valuable historical data," a representative of a large U.S. gas grid operating company said. "The leak data was shared with our integrity management group. The right-of-way (ROW) video was enormously important to our encroachment control department."

In fact, a video documentation of the ROW is a vital instrument to identify erosion, landslides or external threats well in advance.

There are essentially three different concepts for aerial gas leak detections available. One suctions air samples, allowing a multi-pass system to detect the smallest amounts of gas. The sensitivity of this system is high, but the helicopter must fly at a very low altitude to obtain the air samples. This flight altitude is dangerous from a safety standpoint and not considered acceptable by many grid operators.

The second procedure relies on the absorption of gases at different wave lengths and is based on reflected sunlight. A number of gases can be detected but the system is dependent on precise weather conditions. Multiple research projects testing this approach can be expected within the next few years.

The most frequently used model involves a laser in the spectral range at which methane has a high absorption of about 1,650 nanometers (nm). A laser beam is emitted from the equipment on the helicopter and hits the surface, regardless of whether it is soil, grass, concrete, asphalt or the pipeline.

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The laser light is reflected back to the unit and the system uses the...

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