With the accelerated pace of urban development, underground utility networks are being laid ever more densely, resulting in a complex and interwoven web of pipelines that crisscross and tangle beneath city streets. Traditional trenching-and-burial methods are characterized by long construction cycles, significant environmental impacts, and high safety risks. To ensure the efficiency and safety of urban operations and to maximize the utilization of vertical underground space, an increasing number of trenchless construction techniques—such as pipe jacking, microtunneling, and directional drilling—are being deployed in engineering projects. This, in turn, has placed new demands and challenges on the detection technologies for deeply buried trenchless pipelines.

I. Advantages of Trenchless Pipeline Detection Technology

1. Reduced pollution at the construction site and its surrounding environment. Traditional construction sites often leave a dirty, messy, and substandard impression, whereas trenchless pipeline detection technology significantly minimizes the pollution associated with construction activities.

2. During the construction of trenchless pipeline detection technology, the degree of damage and impact on the ground surface and surface facilities is relatively minor.

3. Rapid construction progress and high efficiency. Trenchless pipeline detection technology allows for flexible equipment mobilization and demobilization, and the drilling rig’s advance rate during construction is significantly higher than that of traditional open-cut methods.

4. Trenchless construction methods significantly reduce earthwork excavation and fill costs, as well as labor expenses and associated costs such as dewatering during construction, thereby delivering substantial benefits in cost control and enhanced economic efficiency.

5. Trenchless pipeline detection technology boasts high safety and reliability. Because construction personnel work on the ground rather than in hazardous environments such as deep excavations, construction safety is significantly enhanced. Moreover, many related tasks, such as pipeline welding, are also performed at ground level, which facilitates inspection and improves the quality of pipeline welds.

II. Common Pipeline Detection Methods

1. Electromagnetic Induction Method

Metallic pipelines generally exhibit good electrical and magnetic conductivity, and when buried underground they display distinct electrical and magnetic contrasts relative to the surrounding soil and other subsurface media. Consequently, underground pipeline detectors based on the principle of electromagnetic induction can accurately map the spatial distribution of subsurface metallic pipelines, thereby satisfying the essential geophysical prerequisites for such detection.

By applying an alternating electromagnetic field of a specific frequency and appropriate intensity to the target pipeline, an alternating current will flow between the pipeline and the earth. This alternating current, in turn, generates an alternating electromagnetic field of the same frequency in the surrounding space, thereby creating a secondary alternating electromagnetic-field anomaly around the pipeline. By detecting this anomaly with a receiving device, the location of the target pipeline can be determined, thus achieving the purpose of underground pipeline detection.

Electromagnetic induction methods are further classified into active-source and passive-source techniques. The active-source methods include the direct method, clamp-on method, and induction method. The appropriate method should be selected based on the characteristics of each type of pipeline. For example, the passive-source method is suitable for power cables; whereas, when tracing the alignment of underground pipelines or distinguishing between different underground pipelines, active-source methods—namely the direct method and the clamp-on method—are preferred, as they offer higher detection accuracy than passive-source methods.

The electromagnetic method demonstrates excellent performance in both detection accuracy and efficiency, and is now widely used for underground pipeline detection in many cities—particularly for metallic pipelines such as water supply and drainage systems and gas pipelines, where it offers distinct advantages. However, its effectiveness is limited when applied to non-metallic pipelines.

2. Tracer Electromagnetic Method

For non-metallic pipelines with access points, a cable-pulling device can be used to thread a fixed-frequency sensor into the pipeline. A receiver on the ground then detects the electromagnetic signals emitted by the sensor, enabling determination of the sensor’s depth below ground and its planar location, thereby identifying the pipeline’s location and characteristics.

3. Inertial Gyroscope Method

A gyroscope is a device designed based on the principle of conservation of angular momentum and consists primarily of a rotor mounted on an axis that can rotate. Once the gyroscope begins to spin, the rotor’s angular momentum causes it to resist any change in its orientation.

The gyroscope and accelerometer are used to measure, respectively, the three angular rates of the positioning device relative to the inertial space and the three components of linear acceleration along the positioning device’s coordinate system. Through coordinate transformation, the acceleration data are converted into acceleration components expressed in the navigation coordinate system, and the positioning device’s position, velocity, heading, and horizontal attitude are then computed. As a novel underground pipeline localization method, three-dimensional high-precision positioning technology based on gyroscopes exhibits the following technical characteristics:

(1) The measurement is not limited by terrain, depth, or electromagnetic interference;
(2) High positioning accuracy;
(3) Suitable for underground pipelines made of any material;
(4) Automatically generates 3D spatial curve plots and ensures seamless compatibility with GIS;
(5) Can be used to detect large-depth, trenchless pipelines made of various materials, including those for electricity, gas, water supply, and drainage.

4. Crosshole CT Method for Well-Bore Resistivity

The resistivity method is an electrical prospecting technique that exploits the differences in electrical conductivity—expressed as resistivity—among various rock types in the Earth’s crust. By observing and analyzing the distribution patterns of a stable, artificially generated electric current field underground, this method aims to address geologic problems.

High-density electrical prospecting and ultra-high-density electrical prospecting refer to resistivity methods that observe the distribution patterns of an artificially established steady subsurface current field by means of specific electrode array configurations, thereby enabling the detection of subsurface targets.

Ultra-high-density electrical prospecting overcomes the limitations of conventional electrical surveying in terms of data acquisition methods by employing a flexible, unconstrained combination of survey configurations. This approach can acquire data volumes that are dozens of times greater than those obtained with conventional methods, thereby significantly enhancing the accuracy and reliability of inversion results. Moreover, it eliminates the shortcomings inherent in conventional data acquisition—such as a tendency to favor either lateral or vertical resolution—that often lead to divergent inversion outcomes.

In addition, this method employs modern inversion techniques to directly invert the large volume of measured data into true resistivity profiles, which can be used directly for analyzing and interpreting subsurface geologic structures and anomalous bodies. Utilizing a 64-channel system, whereas conventional methods would require three days to acquire 60,000 data points, the 64-channel system can accomplish the same task in just one hour.

5. Industrial Endoscope Visual Imaging Method

An endoscope is a multidisciplinary, versatile tool designed to inspect the deep, curved lumen of tubular structures, visualize areas that are otherwise inaccessible to direct line-of-sight observation, examine the internal architecture and condition of sealed cavities, and enable remote visualization and manipulation.

The operating principle of an industrial endoscope relies on relay lens optical technology to transmit images, with light delivery and illumination provided by optical fibers. To ensure the transmission of sharp, high-quality images, the endoscope’s effective stainless-steel insertion section is equipped with a relay lens system comprising several optical elements. Built-in optical fibers convey the illumination required for imaging directly from a separate cold-light source to the working location, where the objective lens forms an image that is focused onto the CCD sensor surface. The CCD then converts this optical image into an electrical signal, which is transmitted to the video endoscope control unit. From there, the control unit outputs the image to a monitor or computer. As a highly intuitive method for visualizing internal pipeline conditions, the endoscope offers advantages such as high precision and accurate detection.

6. Ground Penetrating Radar Method

Ground-penetrating radar (GPR) detection is a method that exploits the principle of electromagnetic wave reflection to identify subsurface targets by exploiting the electromagnetic contrast between the target and the surrounding medium. In urban utility mapping, it is common to encounter underground pipelines made of special materials, such as concrete, plastic, PVC, and PE—nonmetallic materials. These types of pipelines cannot be detected using conventional pipeline locators; however, GPR can effectively locate and characterize such underground infrastructure.

Based on the principle that electromagnetic waves are reflected when they encounter different geological interfaces during propagation underground, a wideband, high-frequency, short-pulse electromagnetic signal is transmitted into the subsurface via a transmitting antenna. Since different subsurface media typically exhibit distinct physical properties and, consequently, varying acoustic impedances, the electromagnetic wave undergoes reflection and refraction at each interface it traverses—whether passing through successive stratigraphic layers or encountering a specific target body. The reflected pulse returning to the surface has a propagation path, electromagnetic field strength, and waveform that vary in accordance with the electrical properties and geometric configuration of the intervening medium. Therefore, by analyzing the travel time, amplitude, and waveform of the received radar echoes, it is possible to infer the structural characteristics of the subsurface media.

Each of the aforementioned detection methods has its own characteristics and is suitable for trenchless pipeline surveys. Depending on factors such as pipeline type, terrain, surface features, and burial depth, different methods or combinations thereof should be selected to enhance the accuracy of pipeline detection.

III. Pipeline Leak Detection Technology

During long-term operation, underground pipelines can fail due to corrosion, welding defects, third-party damage, and other factors, leading to leakage incidents. Such leaks not only disrupt the normal operation of the pipeline but also pose threats to the environment and human safety. Therefore, the effective implementation of pipeline leak detection has become a critical issue that urgently needs to be addressed for the safe operation and integrity management of gas pipelines and similar infrastructure.

Based on the intelligent characteristics of detection technologies, pipeline leak detection can be classified into automatic, semi-automatic, and manual methods; based on the correlation among detection data features, it can be categorized into direct and indirect detection.

1. Based on chemical composition analysis

The principle of the sniffing instrument method is to use specialized equipment to detect leaked gas and analyze its concentration. To enhance efficiency, airborne or vehicle-mounted devices are typically deployed to conduct inspections along pipeline routes, such as gas inspection vehicles.

The advantages of this method are rapid detection, high accuracy, and precise localization of leak locations. Its main limitations are relatively high operational costs and susceptibility of the detection results to environmental factors such as wind speed.

2. Acoustic Analysis Method

The principle of acoustic emission testing is to use acoustic sensors pre-installed on the outer surface of the pipe wall to capture and amplify the sound signals generated by the medium inside the pipe as it jets outward through a leak opening. These received sound signals are then processed by a detection system into usable full-waveform acoustic records, thereby enabling the monitoring of pipeline leakage conditions and the localization of leak points.

The advantage of this method is that acoustic emission technology can more accurately locate leak sources in buried pipelines online, with high detection sensitivity. Its main limitation is the need for trenching to install sensors, and in certain cases, pipeline gas supply must be temporarily shut off.

3. Optical Measurement Method

1. LiDAR System Method

The lidar-based method for natural gas pipelines operates on the principle of spectral absorption: a laser emitter generates light waves that are strongly absorbed by methane, and an absorption-spectroscopy sensor detects the returned laser echo. By measuring the attenuation of the laser beam and its power, the concentration of methane in the atmosphere can be determined.

The advantages of this method are rapid detection and accurate localization of leaks. Its main limitation is the high operational cost.

2. Thermal Imaging Method

The principle of thermal imaging is to detect gas leaks by capturing infrared radiation emitted by the gas being monitored. Thermal imaging cameras use thermal imaging technology to analyze changes in thermal radiation around pipelines. For example, when a natural gas pipeline leaks, the soil temperature in the surrounding area decreases due to the throttling effect. This method can be deployed using mobile vehicles, helicopters, or portable systems.

The advantage of this method is its relatively fast detection speed. Its main limitations, however, are the high cost of the equipment, the elevated detection expenses, and the susceptibility of the results to inaccuracies caused by variations in gas temperature and ambient soil temperature.

3. Spectral Imaging

The principle of spectral imaging is to scan space spectrally, acquiring spectral radiometric information distributed across wavelengths, and then processing the resulting data to derive the target’s three-dimensional characteristics and internal property information. It can be further categorized into multi-wavelength imaging and hyperspectral imaging.

Spectral imaging can be implemented in either absorption or emission modes. When using multi-wavelength emission techniques to measure the concentration of gaseous media such as natural gas, the prerequisite is that the temperature of the leaked medium is significantly higher than that of the surrounding air. Even in the absence of a temperature difference, multi-wavelength absorption imaging can still directly quantify the medium’s concentration by leveraging multi-wavelength background radiation.

The advantage of spectral imaging is its low false-positive rate. Its main limitations are the high cost of the equipment and the complexity of data analysis.

4. Distributed Fiber Optic Sensor Method

The principle of the distributed fiber-optic sensor method relies on the capability of distributed optical fibers to detect strain and temperature anomalies, thereby enabling real-time monitoring of pipeline leaks. Due to the significant pressure differential between the inside and outside of the pipeline, leakage events induce vibrations in the pipe wall and the surrounding soil, creating localized temperature variation zones. These abnormal conditions result in changes in the fiber’s temperature, alterations in its optical transmission properties, and induced bending and tensile (or compressive) strain.

Distributed fiber-optic sensing can be categorized into reflective, interferometric, and quasi-distributed fiber Bragg grating–based methods. The advantages of this approach include not only online monitoring of pipeline leaks but also strong anti-interference capability, long measurement spans, and high sensitivity to minor leaks. Its main limitations, however, lie in multi-point detection, resistance to environmental interference, improvement of localization accuracy, and automatic identification of vibration source types—areas that still require further refinement.

5. Intelligent Ball Method

The smart ball comprises acoustic sensors, accelerometers, magnetometers, ultrasonic transmitters, temperature sensors, and other components. It is a self-drifting, spherical device that can move within pipelines along with the flow of media such as gas, and is suitable for pipelines with a nominal diameter greater than 100 mm.

The intelligent ball can be launched and retrieved using a pigging device, requiring no additional auxiliary equipment. It is capable of overcoming pipeline geometry constraints and delivering the highest response sensitivity to small leaks. As it traverses the pipeline, the device records all acoustic events; with the exception of ambient noise that shares similar characteristics with small-leak sounds—such as those from pressure regulators and valves—pipeline leak signatures can be clearly distinguished from other types of environmental noise.

The advantage of this method is its applicability to online pipeline inspection for various materials and its high leak detection sensitivity. Its main limitation, however, is that the accuracy of the measurement results is significantly influenced by the pressure differential between the inside and outside of the leak location.

IV. The market size of pipeline monitoring systems continues to grow

The pipeline monitoring system, also known as the water distribution network monitoring system, leverages modern computer communication and sensing technologies to enable unmanned, remote, real-time monitoring of water supply pipelines. It continuously tracks key parameters such as pipeline pressure and flow rate, providing an accurate assessment of the network’s operational status, enhancing the visualization of comprehensive data, facilitating the timely detection of network faults, improving maintenance efficiency, reducing losses, and ultimately achieving scientific early warning, cost reduction, and operational efficiency gains.

In recent years, the global smart water industry has experienced robust growth. As the cost of trenching for pipeline installation continues to rise, the demand for pipeline monitoring has increased accordingly. Coupled with continuous advancements in sensor technology and other innovations, the market for pipeline monitoring systems has been expanding steadily.

According to the “2022 Global and China Pipeline Monitoring Systems Industry In-Depth Research Report” published by the New Thought Industry Research Center, the global pipeline monitoring systems market is projected to grow from US$13.7 billion in 2021 to US$20.5 billion in 2026, representing a compound annual growth rate of 8.4%.

1. The demand for pipeline monitoring systems in the metal piping sector will account for the largest share.

Metallic pipelines will account for the largest share of the overall market for pipeline monitoring systems. Ductile iron pipes, stainless steel pipes, aluminum pipes, and other types—such as cast iron pipes, corrugated pipes, and copper pipes—all classified as metallic pipes—can corrode when exposed to high-temperature, oxygen-rich steam; consequently, the downstream application sector exhibits a stronger demand for steel-based metallic pipelines. Moreover, metallic pipes offer superior heat dissipation and lower corrosion resistance compared with non-metallic pipes, while also boasting a broader range of applications—factors that are among the primary reasons why metallic pipeline monitoring systems command the largest market share.

2. Leak detection services are the fastest-growing segment in the pipeline monitoring systems market.

During the forecast period, the leak detection subsegment is expected to register the highest compound annual growth rate. This is primarily attributable to the increasing focus among companies in various application sectors on enhancing control over pipeline infrastructure and optimizing automation processes to boost productivity, thereby enabling continuous monitoring of asset conditions and timely alerts in the event of unauthorized incidents. Additional drivers of growth in leak detection applications include increased investment by oil and gas companies in pipeline monitoring infrastructure and in ensuring the safe transportation of materials via pipelines.

3. The Asia-Pacific region will become the fastest-growing regional market in the global pipeline monitoring systems market.

During the forecast period, the Asia-Pacific region is expected to register the fastest growth in both value and volume in the global pipeline monitoring systems market. Driven by rapid economic expansion, the Asia-Pacific region also boasts the highest pipeline installation rates, resulting in the strongest demand for pipeline monitoring systems. The expansion of existing pipelines and the development of new ones have led to an increase in oil and gas leakage incidents from production facility pipelines and storage tanks. In addition, stringent regulations on leak detection technologies and system implementation enacted by governments across the Asia-Pacific region, coupled with rapidly growing industrial market demand, will further propel market growth in the region.

The major players in the global pipeline monitoring systems market include Siemens AG (U.S.), Honeywell International Inc. (U.S.), Huawei Technologies Co., Ltd. (China), BAE Systems (U.K.), and TransCanada PipeLines Limited (Canada), among others.

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