During the last few decades, a number of leak detection methods have been applied to assess a pipeline’s integrity. There are many leak detection systems, all of which uniquely apply to individual pipeline applications. However, it’s possible to classify leak detection technologies based on the physical principles of leak detection. In essence, leak detection technologies are classified into three groups: software-based methods, hardware-based methods, and biological methods.
To constantly monitor data of flow rate, temperature, and pressure for detecting leaks in a pipeline, software-based methods use computer software packages. However, the reliability and complexity of these packages differ greatly. Some examples of these methods include pressure point analysis, dynamic-model-based systems, mass-volume balance, and flow and pressure change detection.
In contrast, hardware-based methods detect the occurrence of leaks directly using hardware sensors, assisting the leak’s localization. Some common devices used for this purpose are infrared thermography, ultrasonic technologies, negative pressure detectors, fiber optic sensors, and acoustic emission detectors.
Biological methods use trained dogs and experienced personnel to locate and detect a leak via sound, odor, or visual inspection. These methods are conventional leak detection methods that use experienced professionals who manually inspect the pipeline to find unusual patterns near it. These professionals listen to noises produced by a product escaping from a pipeline hole and smell substances that may release from the pipeline. The outcomes of biological leak detection methods depend on the experience of individuals and whether a leak has developed before/after the inspection. However, doing this with a deep-water pipeline or a pipeline with H2S is challenging.
The leak detection methods can be broadly classified into two main categories, which are internal-based detection systems and external-based detection systems. Internal-based methods are similar to software-based methods and use instruments for monitoring internal pipeline parameters like flow rate, density, temperature, and pressure, which are inputs for inferring the release of a product. On the other hand, external-based methods use traditional methods like hydrocarbon sensing (via fiber optics) along with right-of-way inspection by line patrols for detecting leaking products outside the pipeline. The internal-based and external-based leak detection systems are described below.
Internal-based leak detection systems
To monitor internal pipeline parameters for detecting potential leaks, internal-based leak detection systems use field instruments, such as fluid temperature, pressure, and flow. Since internal-based leak detection systems use existing field instrumentation, their complexity and system cost is moderate. This type of leak detection system is used for standard safety requirements.
Infrared radiometric pipeline testing
This method is efficient and accurate when it comes to locating and detecting poor backfill, deteriorated pipeline insulation, voids caused by erosion, and subsurface pipeline leaks. When a pipeline leak has enabled a fluid, for example, water, to produce a plume near a pipeline, the fluid has a different thermal conductance than one may expect from backfill or dry soil. The difference in surface temperature patterns above the location of the leak will reflect it. Thanks to a high-resolution infrared radiometer, every area can be scanned. Now, the data obtained can be displayed as pictures with different grey tones representing areas of different temperatures on a black and white image (or different colors on a color image). While this system measures just the surface patterns, patterns measured on the ground’s surface above a buried pipeline can help identify where resulting erosion voids and pipeline leaks are forming. It’s useful in detecting issues as deep as 30 meters below the surface of the ground.
These methods are based on the principle of conservation of mass. During a steady-state, the mass flow M0 leaving a leak-free pipeline will be balanced by the mass flow M1 entering it. If there’s any mass imbalance M1-M0, that is, if the mass drops when leaving the pipeline, a leak is indicated. These methods use flowmeters to measure M0 and M1 for computing the imbalance – an estimate of the true, unknown leak flow. Better balancing methods also consider the change rate of the pipeline’s mass inventory. Compensated mass balance, modified volume balance, and volume balance are some names used for improved line balancing techniques.
Acoustic pressure waves
When a leak occurs, some rarefaction waves are produced – this method analysis these. During a pipeline wall breakdown, fluid/gas escapes like a high-velocity jet. Because this leads to the production of negative pressure waves that propagate in both directions, their detection and analysis are possible. This method’s operating principles are based on one of the most important characteristics of pressure waves – traveling over long distances at the speed of sound with pipeline walls guiding them. With the increase in leak size, the amplitude of a pressure wave increases. The pressure sensors produce data, which is analyzed by a complex mathematical algorithm, pinpointing the exact location of the leak in a matter of seconds.
However, this method fails to detect an ongoing leak after the initial event—that is—after the pipeline wall rupture (or breakdown), no further pressure waves are produced once the initial pressure waves subside. Therefore, if the system is not able to detect the leak, for example, an operational event like valve switching or a change in pumping pressure may cause transient pressure waves that can mask the pressure waves, the system will fail to detect the ongoing leak.
Even a single leak can change the hydraulics of the pipeline, thereby changing flow or pressure readings after some time. Local monitoring or flow/pressure at any single point can, therefore, offer simple leak detection. Since it’s carried out locally, it doesn’t require any telemetry. Its usefulness is limited to steady-state conditions. Plus, it doesn’t have enough capacity to deal with gas pipelines.
External-based leak detection systems
These systems use dedicated, local sensors. While such systems are very precise and sensitive, their complexity of installation and system cost is quite high; therefore, applications are limited to some high-risk areas, for example, near nature-protection areas.
Digital oil leak detection cable
These cables include a braid of semi-permeable internal conductors, and a permeable insulating molded braid is used to protect them. An inbuilt microprocessor within the cable connector monitors an electrical signal that passes through the internal conductors. The escaping fluids come in contact with the internal semi-permeable conductors after passing through the external permeable braid. This changes the cable’s electrical properties, which the microprocessor detects. Besides locating the fluid within a 1-meter resolution along its length, the microprocessor offers a decent signal to operators or monitoring systems. The sense cables can either be installed as a pipe-in-pipe configuration, buried sub-surface with pipelines, and wrapped around pipelines.
Analytic thermal leak detector for pipelines located above the ground
Currently, uncooled microbolometer infrared sensors are used by thermal imaging and video analytics to detect, visualize, and generate alerts of hydrocarbon gas liquids and unplanned surface emissions of liquids. Detection to alarm generation doesn’t take more than half a minute. This technology is ideal for piping facilities located above the ground, for example, water treatment plants, water crossings, chemical plants, mines, storage sites, refineries, and pump stations. Since over half of pipeline leaks occur at facilities, it’s important to introduce new solutions in this area.
High-quality thermographic technology precisely visualizes and measures the infrared radiation (thermal heat) or emissivity of objects into grayscale imagery – and ambient lighting isn’t needed. This heat difference distinguishes monitored petroleum products, for example, oil, from background objects. With the integration of an analytics software component, dependency on manpower can be reduced through validation, reporting, and automated onsite leak analysis. A leak emerging within an analytic region is instantly analyzed for its attributes, including behavior (for example, spilling, pooling, and spraying), size, and thermal temperature. If a leak is considered valid depending on some parameters, a leak video and an alarm notification are sent to a monitoring station.
Optimal detection distance isn’t constant and is impacted by leak size, and camera’s sensitivity, thermal detection range, field of view, resolution, and lens size. The layers of filters of the system as well as immunity to environmental aspects like glare, fog, rain, ice, and snow. The existing leak detection and repair can use video monitoring architecture, including surveillance systems like SCADA networks.
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While the technologies described above are effective, they don’t deliver as much as PermAlert. Our smart leak detection systems aren’t just effective but are built to detect leaks with fast response time and pinpoint accuracy. Our systems are versatile and highly scalable and can be deployed both indoors and outdoors along with environments rated for hazardous locations.
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