Study reveals soil moisture plays the biggest role in underground spread of natural gas leaking from pipelines
Peer-Reviewed Publication DALLAS (SMU) – Soil moisture content is the main factor that controls how far and at what concentration natural gas spreads from a leaked pipeline underground, a new study has found.
Pipeline operators need to factor how the amount of water found in surrounding soil affects gas movement when trying to determine the potential hazards posed by a pipeline leak, said SMU’s Kathleen M. Smits, who led the study recently published in the journal Elementa that examined soil properties from 77 locations around the country where a gas leakage had occurred.
“We don’t need to look any further than Dallas or Georgetown, Texas to see where underground pipeline leaks have the potential to result in catastrophic outcomes,” said Smits, SMU Lyle School of Engineering Chair of Civil and Environmental Engineering and Solomon Professor for Global Development. “We often see that such incidents are the result of a lack of clear protocols to detect the leaks or assess damage. That’s why there should be more focus on the importance of environmental factors such as soil moisture and how to properly account for them in leak scenarios.”
In general the team, co-led by Younki Cho, a research scientist at Colorado State University’s Energy Institute, found that methane gas leaking from a pipeline does not spread as far when the soil moisture content increases. That results in a higher concentration of methane gas close to the leak site in more moist soil, the study revealed.
The opposite was true with drier soil.
But Smits stressed that simply knowing how wet the ground is at the time of the leak is not enough to make conclusions about how soil moisture content impacts gas movement. The moistness of the soil – or lack thereof – at the time of leak triggers different complex behaviors in the soil when methane gas seeps into the same spaces as water and oxygen in the pores of the soil. Soil moisture content can also change over time because of weather and other factors such as seasonal water table levels.
“You have to understand how the moisture controls both the movement and concentration together,” Smits said. “This is something we can assist [pipeline owners] with going forward in addressing leak incidents.”
The research team looked at more than 300 soil samples from leak sites around the country. The samples – which were taken at the time of the leak and again after the leak was repaired – were weighed when they were wet. They were also weighed a second time after they had been dried out in an oven.
“The difference in the dry and wet weights, linked with knowledge of the volume of the soil sample, allowed us to calculate the soil moisture,” Smits explained.
Other soil qualities like its texture and permeability were also examined by the team, but did not demonstrate as much impact on how natural gas moved belowground.
Other co-authors were Nathaniel L. Steadman, from the Department of Civil Engineering at the University of Texas at Arlington; Bridget A. Ulrich, from the Natural Resources Research Institute at the University of Minnesota Duluth; Clay S. Bell, from the CSU Energy Institute; and Daniel J. Zimmerle, Director and Principal Director of the Methane Emissions Technology Evaluation Center at CSU.
Walking surveys better at finding pipeline leaks than mobile detection under certain circumstances
In another study aimed at improving gas leak detection, Smits and researchers from CSU’s Energy Institute found that there are instances where operating a mobile detection unit from the front or roof of a car were not as effective as walkers carrying a handheld detection instrument.
In a mobile survey, the detection unit measures for elevated levels of methane gas in the air as the car is driving. A higher traveling speed or wind speed outside the car resulted in a lowered probability of leak detection when compared to a foot patrol.
“For example, if you just isolated the speed of travel – comparing a person walking at 2 to 3 miles per hour versus a car driving at a slow speed of 20 to 30 mph – the probability of detecting a leak drops from 85 percent for a walking survey to 25 percent for a car,” Smits said.
The study, published in the journal Environmental Pollution, showed that atmospheric stability also had an effect on mobile surveys.
Atmospheric stability essentially determines whether air will rise, sink, or do nothing. Warm, less dense air rises (unstable), while cooler, more dense air sinks (stable). Air staying at the same altitude is considered neutral.
Researchers found that mobile surveys conducted at speeds between 2 to 11 miles per hour got progressively less effective (from 85 percent to 60 percent) at finding a leak as the atmospheric stability went from extremely unstable conditions to extremely stable. Walking surveys conducted under these same conditions did not reflect variability.
“Walking surveys find the most leaks, by far, but they are labor intensive and cost a lot of money,” Smits noted. “This study shows that if operators want to use another method such as a mobile survey, they need to thoughtfully choose a suitable survey speed under different weather conditions to achieve a detection probability equivalent to the traditional walking survey.”
The findings could apply to any type of buried pipeline, Smits said.
Cho, Bell, Cho and Zimmerle from CSU assisted with this study, as did Stuart N. Riddick, a research scientist from the Energy Institute. Shanru Tian, a Ph.D. student in the Department of Civil Engineering at the University of Texas at Arlington, was the lead author of this study.
About SMU
SMU is the nationally ranked global research university in the dynamic city of Dallas. SMU’s alumni, faculty and more than 12,000 students in eight degree-granting schools demonstrate an entrepreneurial spirit as they lead change in their professions, communities and the world.
DALLAS (SMU) – Soil moisture content is the main factor that controls how far and at what concentration natural gas spreads from a leaked pipeline underground, a new study has found.
Pipeline operators need to factor how the amount of water found in surrounding soil affects gas movement when trying to determine the potential hazards posed by a pipeline leak, said SMU’s Kathleen M. Smits, who led the study recently published in the journal Elementa that examined soil properties from 77 locations around the country where a gas leakage had occurred.
“We don’t need to look any further than Dallas or Georgetown, Texas to see where underground pipeline leaks have the potential to result in catastrophic outcomes,” said Smits, SMU Lyle School of Engineering Chair of Civil and Environmental Engineering and Solomon Professor for Global Development. “We often see that such incidents are the result of a lack of clear protocols to detect the leaks or assess damage. That’s why there should be more focus on the importance of environmental factors such as soil moisture and how to properly account for them in leak scenarios.”
In general the team, co-led by Younki Cho, a research scientist at Colorado State University’s Energy Institute, found that methane gas leaking from a pipeline does not spread as far when the soil moisture content increases. That results in a higher concentration of methane gas close to the leak site in more moist soil, the study revealed.
The opposite was true with drier soil.
But Smits stressed that simply knowing how wet the ground is at the time of the leak is not enough to make conclusions about how soil moisture content impacts gas movement. The moistness of the soil – or lack thereof – at the time of leak triggers different complex behaviors in the soil when methane gas seeps into the same spaces as water and oxygen in the pores of the soil. Soil moisture content can also change over time because of weather and other factors such as seasonal water table levels.
“You have to understand how the moisture controls both the movement and concentration together,” Smits said. “This is something we can assist [pipeline owners] with going forward in addressing leak incidents.”
The research team looked at more than 300 soil samples from leak sites around the country. The samples – which were taken at the time of the leak and again after the leak was repaired – were weighed when they were wet. They were also weighed a second time after they had been dried out in an oven.
“The difference in the dry and wet weights, linked with knowledge of the volume of the soil sample, allowed us to calculate the soil moisture,” Smits explained.
Other soil qualities like its texture and permeability were also examined by the team, but did not demonstrate as much impact on how natural gas moved belowground.
Other co-authors were Nathaniel L. Steadman, from the Department of Civil Engineering at the University of Texas at Arlington; Bridget A. Ulrich, from the Natural Resources Research Institute at the University of Minnesota Duluth; Clay S. Bell, from the CSU Energy Institute; and Daniel J. Zimmerle, Director and Principal Director of the Methane Emissions Technology Evaluation Center at CSU.
Walking surveys better at finding pipeline leaks than mobile detection under certain circumstances
In another study aimed at improving gas leak detection, Smits and researchers from CSU’s Energy Institute found that there are instances where operating a mobile detection unit from the front or roof of a car were not as effective as walkers carrying a handheld detection instrument.
In a mobile survey, the detection unit measures for elevated levels of methane gas in the air as the car is driving. A higher traveling speed or wind speed outside the car resulted in a lowered probability of leak detection when compared to a foot patrol.
“For example, if you just isolated the speed of travel – comparing a person walking at 2 to 3 miles per hour versus a car driving at a slow speed of 20 to 30 mph – the probability of detecting a leak drops from 85 percent for a walking survey to 25 percent for a car,” Smits said.
The study, published in the journal Environmental Pollution, showed that atmospheric stability also had an effect on mobile surveys.
Atmospheric stability essentially determines whether air will rise, sink, or do nothing. Warm, less dense air rises (unstable), while cooler, more dense air sinks (stable). Air staying at the same altitude is considered neutral.
Researchers found that mobile surveys conducted at speeds between 2 to 11 miles per hour got progressively less effective (from 85 percent to 60 percent) at finding a leak as the atmospheric stability went from extremely unstable conditions to extremely stable. Walking surveys conducted under these same conditions did not reflect variability.
“Walking surveys find the most leaks, by far, but they are labor intensive and cost a lot of money,” Smits noted. “This study shows that if operators want to use another method such as a mobile survey, they need to thoughtfully choose a suitable survey speed under different weather conditions to achieve a detection probability equivalent to the traditional walking survey.”
The findings could apply to any type of buried pipeline, Smits said.
Cho, Bell, Cho and Zimmerle from CSU assisted with this study, as did Stuart N. Riddick, a research scientist from the Energy Institute. Shanru Tian, a Ph.D. student in the Department of Civil Engineering at the University of Texas at Arlington, was the lead author of this study.
About SMU
SMU is the nationally ranked global research university in the dynamic city of Dallas. SMU’s alumni, faculty and more than 12,000 students in eight degree-granting schools demonstrate an entrepreneurial spirit as they lead change in their professions, communities and the world.
JOURNAL
Elementa Science of the Anthropocene
Elementa Science of the Anthropocene
DOI
METHOD OF RESEARCH
Observational study
Observational study
SUBJECT OF RESEARCH
Not applicable
Not applicable
ARTICLE TITLE
A closer look at underground natural gas pipeline leaks across the United States
A closer look at underground natural gas pipeline leaks across the United States
WHY IS THIS NOT IN USE ON ALL PIPELINES
SwRI improves corrosion-detecting technology that detects leaks in pipes before they occur
New generation of Magnetostrictive Transducer Collar is more accurate, flexible and efficient
Reports and ProceedingsIMAGE: SOUTHWEST RESEARCH INSTITUTE (SWRI) HAS CREATED THE NEXT GENERATION OF TRANSDUCERS THAT USE ULTRASONIC GUIDED WAVE TECHNOLOGY TO DETECT ANOMALIES IN PIPES, ENABLING USERS TO PREVENT LEAKS BEFORE THEY START. THE DEVICE, WHICH UTILIZES THE SWRI-DEVELOPED MAGNETOSTRICTIVE SENSOR (MSS®) TECHNOLOGY, WILL BE SHOWCASED AT THE AMERICAN SOCIETY FOR NONDESTRUCTIVE TESTING’S (ASNT) ANNUAL CONFERENCE IN NASHVILLE, TENNESSEE, FROM OCTOBER 31 TO NOVEMBER 3. view more
CREDIT: SOUTHWEST RESEARCH INSTITUTE
SAN ANTONIO — Oct. 25, 2022 — Southwest Research Institute (SwRI) has created the next generation of transducers that use ultrasonic guided wave technology to detect anomalies in pipes, enabling users to prevent leaks before they start. The device, which utilizes the SwRI-developed Magnetostrictive Sensor® (MsS®) technology, will be showcased at the American Society for Nondestructive Testing’s (ASNT) Annual Conference in Nashville, Tennessee, from October 31 to November 3.
“Pipeline corrosion resulting in leaks is very common,” said SwRI Staff Engineer Sergey Vinogradov, who developed the technology with Staff Engineer Keith Bartels and other SwRI staff members. “There are only a few current methods to detect defects before they cause leaks. Quite often, the pipe is repaired and re-inspected after a leak occurs. We’ve developed a technology that can consistently monitor the pipe’s condition, hopefully preventing leaks from happening in the first place.”
The technology is known as a Magnetostrictive Transducer (MsT) Collar. It was originally developed by SwRI in 2002. The updated version has a flat, thin design allowing it to be used on pipes in tight spaces. In custom configurations, it can withstand heat up to 400 degrees Fahrenheit. The new, segmented MsT design also features eight sensors that give the transducer the ability to more accurately identify where in the pipe corrosion is occurring.
The MsT Collar utilizes magnetostrictive sensors, which generate and receive guided waves that propagate along an elongated structure, guided by its boundaries. This technique allows the waves to travel long distances with little loss in energy. In some cases, hundreds of meters can be inspected from a single location, though obstacles such as couplings would require an additional sensor.
“Instead of using one sensor to cover an entire pipe circumference, allowing only the axial location of an anomaly to be measured, we now have eight sensors in the transducer,” Vinogradov said. “Each of the sensors are independently connected to the electronics so that all possible guided wave signals can be acquired. Algorithms combine this information to better detect and locate the anomaly both axially and circumferentially, and the growth of the corrosion can be monitored by examining data sets acquired over time.”
The MsS system can send data to a remote terminal via a wireless transmitter unit or by means of a wired connection. It is designed primarily for oil and gas transmission pipelines to prevent costly and damaging leaks before they begin. However, the technology is versatile and has been used for other industrial pipes such as those used for water, heating, or in chemical plants.
Vinogradov and Bartels will demonstrate the MsT Collar at the ASNT Annual Conference in Nashville, Tennessee, from October 31 to November 3 at booth 1219.
SwRI’s Nondestructive Evaluation and Sensor Systems Section develops tools and techniques for nondestructive inspection, evaluation and testing featuring guided waves, computed tomography, ultrasonics, electromagnetics and other techniques.
To learn more, visit https://www.swri.org/magnetostrictive-sensor-based-guided-waves or https://www.swri.org/industries/sensor-systems-nondestructive-evaluation-nde.
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