Laser leak detection: Past, present and future

Airborne laser leak-detection surveys are conducted by trained crews using turbine-powered Bell helicopters.

All over the world, gas pipelines crisscross vast lands. Most are underground and undetected by the general public. Out of sight, out of mind, 99% of the time.

Yet, with international attention on the BP Plc oil spill in the Gulf of Mexico over the past few months, every roustabout to chief executive in the energy industry is acutely aware of the impact a leak can have on families, environments, their company’s financial solidity and even a nation’s economy.

Numerous airborne surveys show that more than 80% of methane releases occur around pipeline and production surface equipment. Yet, although there are as many leak-detection systems on the market as there have ever been, one size does not fit all.

Specifically, sometimes vegetation and hostile terrain make it impossible to apply a ground-based leak-survey program to the gas pipeline right-of-way. The bygone visual airborne patrols are useless to quantify as a leak-detection survey program. Other aging low-tech leak-detection programs require time-consuming operating procedures, maintenance and continuous training, which deflate the true impact. What is the value of a technologically advanced leak-detection program that by simply driving or flying near a pipeline can allow a company chief executive to have a good night’s sleep knowing the pipeline is secure?

Laser leak-detection devices have quietly been in service all over the world since the early 1990s, sampling the air for the smallest of target-gas releases. Numerous leaks have been identified and repaired, thus preventing a possibly catastrophic loss of life or property.

Open and closed

An ATS airborne laser system can identify and pinpoint leaks as low as 1.8 s/cfh in wind speeds up to 15 knots, according to testing at the Rocky Mountain Oil Field Testing Center.

Several different laser leak-detection systems are available. Generally, all operate using basically the same laser technology. They are capable of identifying specific gasses such as CH4, CO2, H2S, HF, CO and NH3 while offering incredible sensitivity to the target gas and speed of processing.

Also, leak-detection lasers operate in open- and closed-path applications, each having specific advantages. Open-path lasers use higher-powered lasers and are primarily used to survey perimeter fence lines and smoke stacks at refineries, gas plants and smelters. The access to the laser path can be harmful to human soft tissues and must be controlled.

Others can fly higher and faster while surveying a larger area for the target gas. However, the drawback to this type of system is that, because it uses the ground as a reflective media, ground conditions may disrupt the return laser‘s energy to the receiver, thus limiting sensitivity. Closed-path airborne lasers use a lower-powered harmless class-2 laser. These have hyper sensitivity of the target gas by controlling the laser’s environment and directing all of the laser energy back to the receiver for analyzing the target gas. This requires the laser be deployed closer and fly slower to the proposed survey path. The limitations to any laser technology are similar to other leak-detection devices—high winds and falling precipitation.

The Boreal laser, by Denver-based Aviation Technology Services LLC (ATS), also samples the air near gas pipelines. The closed-path leak-detection system uses a tunable diode laser absorption spectroscopy (TDLAS) laser, which frequency is tuned to the absorption wave length of the methane molecule firing inside a sensor cell attached near the bottom of the helicopter or above the roof of a vehicle. Air passing through the sensor cell is sampled by the laser over 300 times per second, accurately monitoring methane levels to less than one part per million.

Elevated methane plumes with specific wave-form signatures pin point minute leaks and filter out methane producers like landfills and feed lots. Laser accuracy is maintained by a patented, self-calibration system that refers to a contained methane sample every 3 to 6 seconds, which increases stability and accuracy and eliminates background drift and interference.

Temperature, terrain, ground and cloud conditions do not affect performance of the Boreal laser leak-detection system. An optional video service can enhance the leak survey and be used for post-survey reviewing, training and archiving for future reference. The ability to visually review a section of pipeline right-of–way on a computer, analyze a known potential problem or locate possible future facilities has multi-level value.

In 2006, the Boreal laser technology was proven at a Department of Energy (DOE) testing facility where it outperformed all previously tested land or airborne leak-detection systems. During the controlled evaluation at Rocky Mountain Oil Field Testing Center (RMOTC), which sets the standards for ground and airborne leak-detection devices, ATS identified and pinpointed leaks as low as 1.8 s/cfh in wind speeds up to 15 knots. A direct quote from the DOE/RMOTC publication 41006, working under CRADA 2006-075, reported:

“In summary, the ATS leak-detection system proved to be a reliable, rapid, and efficient leak-detection system. The performance of the system substantially exceeded prior evaluated detection systems at RMOTC. The test demonstrated the system’s strengths in measuring minute levels of methane in the air. And, the client demonstrated their ability to interpret the collected data and determine when the conditions were not conducive for accurate measurements.

“With new federally mandated leak detection for pipeline networks, this system could provide companies with an effective, rapid, accurate and cost effective option.”

ATS’ airborne laser leak surveys are conducted by a trained crew using turbine-powered helicopters flying at 50 miles per hour at roughly 75 feet above ground level. The pilot follows directions from the operator’s onboard ride-along lineman. As back-up, a known accurate pipeline right-of-way route can be preloaded in the onboard GPS-mapping display computer. The pipeline survey record is encoded and stored on the laser technician’s laptop computer in real time displaying date, GPS position, airspeed and altitude and methane levels.

The final report has a map depicting the pipeline, analyzed data identifying points of interest with exact location, methane level and possible source for further investigation. Typically, the process allows the operator to accurately survey up to 200 miles of pipeline per day.

A safety advantage of the system is that the operator is removed from elevated methane levels, potential hazardous conditions and right-of-way encroachments. Yet, exposed pipe or dead vegetation can be noted and immediately communicated to the operator using an on board satellite phone.

This is in contrast to a ground leak survey of the same 200 miles of pipeline. An operator might risk the safety of multiple line crews for several weeks as they leap frog over hazardous terrain, wild animals, fences and land owners.

By air, by ground

By truck, operators survey accessible drill rig sites, pipeline surface facilities and rights-of-way.

For less hazardous terrain, a ground laser leak survey is possible by mounting the airborne system to an all terrain field vehicle. By simply driving around a site, operators can quickly survey accessible pipeline surface facilities and rights-of-way, eliminating the area for further time-consuming leak-detection measures. If an elevated methane level is detected, a more in depth investigation can be initiated to locate the source with a hand-held methane detector.

Operators with confidentiality and access issues can lease the Boreal laser leak-detection system to mount on company vehicles operated by their company pipeline corrosion, integrity and environmental employees.

The devices can be priced by the mile for operators who require a cost-effective leak survey alternative with documented verification and conformation to the federally mandated leak quantification of their pipeline networks. Also, leasing terms are available for training, operating and maintenance exchange programs, allowing larger operators to manage their own advanced laser leak-detection program.

Conclusion
Given the current sensitivity to pipeline and drill rig gas leaks, each operation must carefully choose an appropriate leak-detection system suitable to its operations and environment. While cost is always a factor, cost-saving measures can include reliable and durable leak-detection methods to ensure adherence to environmental and regulatory standards, be it by air or ground.

Richard Westra is president of Aviation Technology Services LLC. Photos courtesy of ATS.