Pipelines

HGI provides innovative deployment of geophysical techniques to detect and locate leaks in subsurface pipelines.  Subsurface pipes can exist in almost any environment; from water and sewage pipes in residential and commercial areas to material transfer pipes in industrial settings. Leaks can occur due to a multitude of reasons, including pipe and joint defects, unreported damage, and failure of infrastructure being used past the designed lifespan. Geophysical techniques rely on detecting a contrast in soil properties caused by the leaking fluid from the pipeline, as compared to non-leak areas. Being non-invasive these techniques can be deployed in almost any environment, roadways, parking lots, and industrial sites for example, and at sites where hazardous wastes may be encountered.

Geophysical techniques, such as Time Domain Electromagnetics can detect contrasts in soil properties caused by the leaking fluid from the pipeline, as compared to non-leak areas. 

HGI developed a multi-channel Time Domain Electromagnetic (TDEM) system which can be towed behind an ATV, allowing for the rapid and efficient coverage of large scale surveys. The TDEM technique provides a measure of the electrical conductivity of the subsurface. The presence of a leak will increase or decrease (depending on pipe contents) the electrical conductivity of the subsurface materials compared to surrounding areas where no leak is present. The TDEM system can detect the resulting contrast and provide spatial and depth information on the extent of the leak.

Cartoon representation of the multi-channel TDEM system mounted behind an ATV. In the absence of a leak the TDEM signal displays only the pipe response (red dots) on the left image, the effect of a leak on the TDEM signal is displayed on the right image (white dots).

In addition, HGI also utilizes a suite of traditional geophysical tools to detect subsurface leaks from pipelines, including electrical resistivity and ground penetrating radar.

Example:

Historical leak detection using a multi-channel TDEM system at an industrial pipeline site.

Click here to read the full paper.

The following example displays the results from a multi-channel TDEM survey over a pipeline at an industrial site. The aim of the investigation was to identify the locations of conductive plumes of liquid known to have leaked from the pipeline in the past. The pipeline was constructed of stainless steel, buried approximately 0.6m below the ground surface.

The Hanford Site Is Home to over 200 Miles of Abandoned Pipelines Used From 1943 to 1995 to Transfer Waste Generated from the production of uranium and plutonium for the United States military.

Over the last 60 years several leaks have been found along waste transfer pipelines which could pose significant short-term risk to workers and long-term risk to groundwater.  These pipelines were used to transfer multiple waste streams from the reprocessing facilities, between waste tank farms, and from tank to tank.    A review of these failures showed corrosion attacking from the outside of the pipe as one of the primary factors in pipeline leaks.

These pipelines were used to transfer multiple waste streams from the reprocessing facilities, between waste tank farms, and from tank to tank.

Historical records from the Department of Energy Hanford Nuclear Reservation (in eastern WA) indicate that ruptures in buried waste transfer pipelines were common between the 1940 and 1980s, which resulted in unplanned releases (UPRs) of tank waste at numerous locations.  Current methods used to detect leaks on the Hanford Site have included visual observation of liquid waste on the ground surface, discrepancies in mass balance between input and output locations, and encountering subsurface waste material near a pipeline through excavation or drilling.  Since these detection methods are so limited in resolution and effectiveness, it is likely that a significant number of pipeline leaks have not been detected.  Therefore, a technology was needed to detect specific locations of unknown pipeline leaks so characterization technologies can be used to identify any risks to groundwater.

A proof-of-concept electromagnetic geophysical survey was conducted at a Hanford test site in order to image a historical leak from a waste transfer pipeline.  Extensive surface-based geophysical characterization has already demonstrated that geophysical technologies have the capability to provide an efficient and cost effective tool for leak detection.

Survey area of Leak Detection & Leak Location test area.

The geophysical method used for pipeline leak location is based on the transient electromagnetic (TEM) technique that is sensitive to electrically conductive features buried beneath the ground, including high moisture, salt content, and metal.  Although, electromagnetic methods have been demonstrated successfully at mapping the location of buried metal pipes it has never been applied specifically as a leak mapping tool due to the potential of the more conductive pipeline metal interfering with the ability to see the less conductive ionic plume resulting from the leak.  HGI demonstrate the success of the method by comparing the TEM results with the more familiar electrical resistivity plume mapping technology.

Using the more familiar electrical resistivity plume mapping technology for conformation of the TEM results.

The fundamental principle behind TEM is mutual inductance between a loop transmitter (Tx) and a loop receiver (Rx), with a two-loop configuration commonly employed.  Each loop consists of a number of windings of copper wire of a given size; from centimeters to meters. The number of windings and the physical size of the loop controls sensitivity and depth of investigation.  An alternating-current waveform is injected into the transmitter loop.  Faraday’s Law suggests that, conceptually, an image of the transmitter loop is propagated into the earth during each pulse.  The amplitude of the pulse immediately begins to decay and generates eddy currents that, in turn, propagate downward and outward into the subsurface like a series of smoke rings.  The amplitude of the secondary field is then recorded at the receiver after the transmitter is turned off.  The amplitude is digitally sampled and recorded for a few milliseconds, and these data are used to assess subsurface conditions.

The test site contained two 7.6 cm diameter stainless steel pipes buried approximately 0.6 m below ground surface that transported process effluent when they were in use (see image above).   The electrically conductive stainless steel pipelines were expected to dominate the TEM dataset.  Therefore, the subtle variations parallel and orthogonal to the pipeline would possibly indicate the presence of historical leaks.   To maximize the data coverage, many receiver loop locations were occupied relative to a single Tx loop.  The individual Rx loop measurements were then spatially related and contoured to provide a graphical visualization in order to detect subtle changes that may be indicative of a leak plume.  The key conclusions from this project provide confidence that TEM successfully mapped high-conductivity soils in close proximity to the pipeline in areas of known soil contamination.

TEM successfully mapped high-conductivity soils in close proximity to the pipeline in areas of known soil contamination.

The below figure shows results from the multi-channel TDEM pipeline survey.  Each numbered transect represents a single measurement swath using the multiple receiver channels along the pipeline. Purple and blue colors represent a high amplitude response, indicating the presence of a leak plume. The green, yellow, and red colors represent a low amplitude response, indicating no leak occurred.

Results from the multi-channel TDEM pipeline survey.

The multi-channel TDEM results were confirmed by a more traditional electrical resistivity survey shown in the below figure. The low resistivity areas highlighted in red correspond well to the high amplitude response areas in the TDEM survey. The pipeline is represented by the red line in the figure, with the 10 TDEM survey lines running perpendicular to the pipeline, and the 4 electrical resistivity line running parallel to the pipeline. The blue and purple lines indicate the locations of additional infrastructure in the survey area.

Electrical resistivity survey.