The new, portable, reliable, state-of-the-art Remote Methane Leak Detector (RMLD) is changing the way natural gas (methane) leak surveys are conducted. Instead of having to walk the entire length of the service line to check for natural gas leaks, the RMLD can quickly and efficiently detect leaks up to one hundred (100) feet or thirty (30) meters away, allowing for remote detection of hard-to-reach areas and difficult terrains. Remote detection allows the user to safely survey areas that may be difficult to reach, such as busy roadways, yards with large dogs, locked gates, pipes suspended under a bridge, indoor commercial piping, compressor stations, gas plants and other hard to access places.
For utilities and their employees, this new time-saving method represents the potential for significant productivity gains, reduced maintenance costs, and a safer survey. Surveying gas gathering, distribution and transmission lines for leaks has been an on-going effort in the natural gas industry ever since natural gas piping was first buried in the ground. Due to the nature of natural gas, utilities, with the support of safety regulators, periodically survey their system to assure its safe operation. Today, every company periodically performs walking and mobile type surveys on all mains and services with particular interest to those located in congested or densely populated areas. Tools of the trade have improved over the years, beginning with early combustible gas indicators (CGI). In the late 1950s, flame ionization detectors (FID) were introduced providing improved leak surveying productivity and accuracy. In recent years, optical methane detection (OMD) has come on the scene, and has proven to be an effective tool, thereby further improving both portable and mobile survey operations.
All of these leak detection devices have something in common in that they require the instrument sample system to be physically located in the gas leak plume to get a reading or indication. To accomplish this, the operator generally must walk or ride directly over the pipeline during the survey of which can be a costly and at times a difficult process.
Benefits Natural gas utility companies continually survey gas pipelines to detect small leaks and correct them before they become dangerous. Routine surveys are scheduled at 1, 3, or 5-year intervals for each pipe segment, and more frequent surveys are required during the winter for some segments. These surveys are conducted by utility in-house crews or by professional survey companies.
Currently, this process is labor intensive requiring an individual to either drive or walk over the pipeline. Gas leaks are sensed with either the FID or OMD instrumentation.
The prospect of replacing an FID with a laser-based device that can rapidly survey off-road pipelines (such as service lines) has great appeal to these utilities. The laser beam would be projected from the road or sidewalk above the path of the pipeline to the home, and the instrument would indicate the presence or absence of gas. If gas is detected, the survey crew would then walk the length of the pipeline to localize the leak. The time to make each measurement would be only seconds. Since most of the services surveyed do not produce a leak response, the use of RMLD would eliminate the need to walk along services and buildings, thereby reducing survey time and enabling more efficient use of manpower. Preliminary estimates for walking survey operations have shown savings in the range of 25% to 40%.
Another major benefit to survey and leak investigators is that the RMLD can be used to remotely determine the presence of natural gas inside a building or confined space with clear access, and also in difficult-to-reach areas, such as gas pipelines under bridges, backyard mains and fenced-in areas. The RMLD could also be a valuable tool for use by first responders to determine if an area or building is safe for occupation or to localize the source of a leak after a pipeline disturbance has occurred.
The RMLD can also be used to survey both gas gathering and transmission pipelines where exact location of the buried lines is difficult. Use of the RMLD can also be used in those hard-to-reach locations in compressor stations and gas processing plants where large volume leaks are quite common in vents, valves and rod packing.
RMLD components
The RMLD consists of two interactive components: a transceiver sub-system and a signal processing/user interface controller. The transceiver has two lasers. One is an infrared laser beam that is non-visible and is continuously on while the unit is turned on. The other is a green spotter laser which is similar to those used for presentation pointers. It is turned on by the operator by depressing the trigger button.
How it works
When the infrared laser beam is transmitted from the launch port, some of the laser light is reflected by a normal background such as brick, concrete, grass, etc., to the detector. This reflected light is collected and converted to an electrical signal that carries the information needed to deduce the relative methane concentration. This signal is processed so that methane can be reported in parts-per-million meter of ppm-m. The laser has a maximum distance of up to 100 feet and is selective to methane only. It will not false alarm on other hydrocarbons.
Measurement difference
The standard FID unit uses part-per-million (ppm) as a measurement value. Simply put, PPM is the amount of methane actually measured at a given point or within a specific sample. The RMLD uses part-per-million meter (ppm-m) which is the total accumulation of methane in the path of the laser light being from the RMLD transceiver to the reflective background, and back to the collection mirror on the transceiver.
Another advantage of the RMLD over the FID is that the FID detects total combustible hydrocarbon while the RMLD only detects methane. This eliminates many false positives on vehicle exhaust, gasoline vapors and any other hydrocarbons that may be in the inspection path. The standoff detection ability permits the wide area coverage and greater flexibility in surveying a given area. A typical example shows that the FID will indicate natural background levels of methane (at about 2 ppm – a level often zeroed out by the operator) at one meter steps along the path from the street to the structure, except at the location of the plume indicated, where suddenly the FID will detect 100 ppm.
In contrast, the RMLD measures the accumulated signal from methane present along the 12-meter path from the transceiver to the reflective background level (2 ppm for 11 meters = 22 ppm-m) and the contribution from the leak of 100 ppm for a one meter leak plume. The total RMLD reading is 122 ppm-m. This dramatic change in signal when a leak plume is encountered will enable an operator to verify the leak. Because the laser beam can be easily scanned over the survey area, the presence of leaks can be quickly determined.
The RMLD has been proven to be a reliable and effective leak detection survey tool. It has been used on the market for a little over three years and has been accepted worldwide for use in gas gathering, transmission and distribution applications. The simple ease of use and low-end sensitivity has increased productivity and reduced survey costs throughout the natural gas industry, while providing improved safety to the general public and the reduction of natural gas emissions to the environment.
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