Pipe leak detection is used to determine whether and in some cases where leaks have occurred in systems containing liquids and gases. Detection methods include hydrostatic testing, infrared, and laser technology after pipeline erection and leak detection during service.
Pipelines are the most economical and safe mode of transportation for oil, gas and other liquid products. As a means of long-distance transport, pipelines must meet the demands of safety, reliability, and high efficiency. If properly maintained, pipelines can survive indefinitely without leaks. The most significant leak that occurred caused by damage from nearby digging. If the pipe is not maintained properly, it can corrode, especially at construction joints, low points where moisture is accumulated, or locations with imperfections in the pipe. However, these defects can be identified by checking devices and corrected before they leak. Other reasons for leaks include accidents, earth movements, or sabotage.
The main purpose of a leak detection system (LDS) is to assist the pipeline controller to detect and localize leaks. LDS provides alarm and displays other related data to the pipeline controller to assist decision making. Pipe leak detection systems can also improve system productivity and reliability thanks to shorter downtime and inspection times.
According to the API document "RP 1130", LDS is divided into internal-based LDS and external-based LDS. Internal based systems use field instrumentation (eg flow, pressure or fluid temperature sensor) to monitor internal pipe parameters. External-based systems use different sets of field instrumentation (eg infrared radiometer or thermal camera, steam sensor, acoustic microphone or fiber-optic cable) to monitor external pipe parameters.
Video Leak detection
Aturan dan peraturan
Some countries officially regulate pipeline operations.
API RP 1130 "Monitoring Compute Pipe Channels for Liquid" ( AS)
This recommended practice (RP) focuses on the design, implementation, testing, and operation of LDS using an algorithmic approach. The purpose of this recommended practice is to assist the Pipe Line Operator in identifying issues relevant to the selection, implementation, testing and operation of LDS. TRFL (Germany)
TRFL stands for "Technische Regel fÃÆ'¼r Fernleitungsanlagen" (Technical Rules for Pipeline System). TRFL summarizes the requirements for pipelines that are subject to official regulation. This includes pipelines that carry flammable liquids, pipelines carrying liquids that are harmful to water, and most of the pipelines carry gas. Five different OSZA or LDS functions are required:
- Two independent LDS for continuous leak detection during steady-state operation. One of these systems or additional ones should also be able to detect leaks during a temporary operation, eg. during the start-up of the pipeline
- One LDS for leak detection during shut-in operation
- One LDS for leaking propagation
- One LDS for fast leak location
Maps Leak detection
Requirements
API 1155 (replaced by API RP 1130) defines the following essential requirements for LDS:
- Sensitivity: LDS should ensure that fluid loss as a result of leakage is as small as possible. This places two requirements on the system: it must detect a small leak, and should detect them quickly.
- Reliability: Users should be able to trust LDS. This means that it has to properly report every actual alarm, but it is also important that it does not generate false alarms.
- Accuracy: Some LDS can calculate leakage flow and leak location. This should be done accurately.
- Sharpness: LDS should continue to operate in a state that is not ideal. For example, in case of a transducer failure, the system must detect failure and continue to operate (perhaps with the necessary compromises such as reducing sensitivity).
Steady conditions and transient conditions
During steady-state conditions, flow, pressure, etc. In pipes are (more or less) constant over time. During transient conditions, these variables can change rapidly. Changes spread like waves through pipes with the speed of sound of fluid. Temporary conditions occur in the pipeline for example at start-up, if the pressure on the inlet or outlet changes (even if the change is small), and when the batch changes, or when some product is in the pipeline. Gas pipes are almost always in transient conditions, because the gas is very compressible. Even in liquid pipelines, temporary effects can not be ignored most of the time. LDS should allow to detect leaks for both conditions to provide leak detection during the entire operation time of the pipe.
Internal LDS
Internal based systems use field instrumentation (eg for fluid flow, pressure and temperature) to monitor internal pipe parameters used to detect possible leaks. The cost and complexity of moderate internal based LDS systems because they use existing field instrumentation. This type of LDS is used for standard security requirements.
Pressure/flow monitoring
Leakage alters the hydraulics of the pipe, and thereby changes the pressure or flow of readings over time. Local monitoring of pressure or flow only at one point can provide simple leak detection. As is done locally in principle there is no telemetry. This is only useful in steady conditions, and its ability to handle limited gas pipelines.
Acoustic pressure waves
The acoustic pressure wave method analyzes the resulting wave of smoothing when the leak occurs. When pipe wall damage occurs, liquids or gases escape in the form of high-speed jets. This produces negative pressure waves that spread in both directions in the pipe and can be detected and analyzed. The operating principles of this method are based on a very important characteristic of pressure waves to travel long distances at the speed of sound guided by the pipe wall. The amplitude of the pressure wave increases with the size of the leak. The complex mathematical algorithm analyzes data from the pressure sensor and is capable of within seconds to show the location of the leak with an accuracy of less than 50 m (164 ft). Experimental data have demonstrated the ability of a method to detect leaks less than 3mm (0.1 inches) in diameter and operate with the lowest false alarm rate in the industry - less than 1 false alarm per year.
However, this method can not detect the ongoing leak after the initial incident: after the pipe wall damage (or break), the initial pressure wave subsides and no subsequent pressure wave is generated. Therefore, if the system fails to detect leakage (for example, because pressure waves are obscured by transient pressure waves caused by operational occurrences such as changes in pumping pressure or valve replacement), the system will not detect any leakage in progress.
Balancing method
This method is based on a state observer designed from a mathematical model of liquid expressed in a space-state representation. These methods can be classified into two types: unlimited observers and by-dimensional observers. The first type is based on some quasi-linear hyperbolic partial differential equations: the momentum and continuity equations that represent fluid dynamics in the pipeline. The limited-dimensional observer is constructed from the paralyzed version of the momentum and the continuity equation. Several types of observers have been used to detect leaks, such as Kalman filters, high-gain observers, observers of shear modes and observers of the Luenberger type.
Statistical methods
LDS statistics use statistical methods (eg from decision-making fields) to analyze pressure/flow only at one point or the imbalance for detecting leakage. This leads to the opportunity to optimize the leaked decision if some statistical assumptions apply. The general approach is the use of hypothesis testing procedures
This is a classic detection problem, and there are various known solutions from statistics.
RTTM Method
RTTM means "Real Time Transient Model". RTTM LDS uses a flow mathematical model in the pipeline using basic physical laws such as mass conservation, momentum conservation, and energy conservation. The RTTM method can be seen as an improved balancing method because they also use the principles of momentum and energy conservation. An RTTM makes it possible to calculate mass flow, pressure, density and temperature at each point along the pipeline in real-time with the help of a mathematical algorithm. RTTM LDS can easily model steady state and transient flow in a pipeline. Using RTTM technology, leaks can be detected during steady conditions and transient conditions. With well-functioning instrumentation, leakage levels can be estimated functionally using the available formulas.
E-RTTM Method
E-RTTM stands for "Extended Real-Time Transient Model", using RTTM technology with statistical methods. Thus, leak detection is possible during steady state and temporary conditions with high sensitivity, and false alarms will be avoided using statistical methods.
External based systems use dedicated local sensors. Such LDSs are very sensitive and accurate, but system costs and complexity of installation are usually very high; Therefore, the app is limited to specific high-risk areas, e.g. near a river or a natural protection area.
Analytical thermal leak detector for above ground pipelines
Video thermal imaging driven by sensors using infrared sensors microbolometer does not emerge as a new and effective method of visualizing, detecting and generating warnings of unplanned surface emissions from liquids and hydrocarbon gas liquids. Detection of alarm making takes less than 30 seconds. This technology is suitable for above ground pipe facilities, such as pumping stations, refineries, storage areas, mines, chemical plants, water crossings, and water treatment plants. The need for new solutions in this field is driven by the fact that more than half of the pipeline leaks occur at the facility.
High quality thermographic technology accurately measures and visualizes the emissivity or infrared radiation (hot heat) objects into a gray scale image without the need for ambient lighting. Monitored oil products (eg oil) are distinguished from background objects with this heat difference. The addition of an analytics software component, usually optimized to better address a particular application or environment, enables automatic leak analysis, validation and reporting of leaks in locations, thereby reducing dependence on manpower. Leaks that appear in the analytic region (rules added to the camera) are immediately analyzed for their attributes, including temperature, size, and thermal behavior (eg spraying, collection, spillage). When the leak is determined to be valid based on the parameters set, the alarm notification with the leaked video is generated and sent to the monitoring station.
The optimal detection range varies and is affected by the size of the camera lens, resolution, field of view, thermal detection range and sensitivity, leakage size, and other factors. Layers of filter systems and immunity to environmental elements, such as snow, ice, rain, fog and glare, contribute to the reduction of false alarms. The video monitoring architecture can be integrated into existing leak detection and repair (LDAR) systems, including SCADA networks, as well as other surveillance systems.
Digital oil leakage detection cable
Digital sensory cables consist of a network of semi-permeable internal conductors protected by braids formed from translucent insulation. Electrical signals are passed through an internal conductor and monitored by an inbuilt microprocessor inside the cable connector. The runaway fluid passes through the external permeable braid and makes contact with the internal semi-permeable conductor. This causes a change in the electrical properties of the cable detected by the microprocessor. The microprocessor can place the liquid into a resolution of 1 meter along its length and provide the correct signal for the system or monitoring operator. Sensory cables can be wound around pipelines, buried sub-surfaces with pipes or installed as pipeline-in-pipe configurations.
Infrared radiometric pipe testing
Infrared heat pipe testing has shown itself to be both accurate and efficient in detecting and locating sub-pipe leaks, cavities caused by erosion, worsening pipe insulation, and poor deterioration. When pipeline leaks have allowed liquids, such as water, to form clumps near the pipelines, the liquid has a different thermal conductance than dry soil or backfill. This will be reflected in the pattern of different surface temperatures above the location of the leak. The high resolution infrared radiometer allows the entire area to be scanned and the resulting data is displayed as an image with a different temperature area marked by a gray tone difference in black & amp; white images or with various colors on the color image. This system measures only the pattern of surface energy, but the measured pattern on the ground surface above the buried tube can help indicate where the pipe leaks and result in the erosion vacuum formed; detecting problems as deep as 30 meters below ground level.
Acoustic emission detector
The exit fluid creates an acoustic signal as they pass through the hole in the pipe. The acoustic sensors pinned outside the pipe make the baseline acoustic "fingerprint" of the line from the internal noise of the pipe in an undamaged state. When a leak occurs, the resulting low-frequency acoustic signal is detected and analyzed. Deviations from the initial "fingerprint" signal alarm. Now the sensor has better settings with frequency band selection, snap time delay selection, etc. This makes the charts more different and easy to analyze. There are other ways to detect leaks. Geo-mobile landline with filter settings is very useful for determining the location of the leak. This saves the cost of excavation. Water jets on the ground touch the inner walls of the soil or concrete. This will create a weak sound. This noise will rot when it appears on the surface. But the maximum sound can only be taken above the leak position. Amplifiers and filters help to get a clear sound. Some types of gas that is inserted into the pipeline will create various sounds when leaving the pipe.
Steam sensing tube
The leak detection method of the steam sensing tube involves mounting the tube along the entire length of the pipeline. This tube - in the form of a cable - is highly permeable to the substance to be detected in a particular application. If a leak occurs, the substance to be measured comes in contact with the tube in the form of steam, gas or soluble in water. In case of leakage, some leaking substance diffuses into the tube. After a period of time, the inside of the tube produces an accurate picture of the substance surrounding the tube. To analyze the distribution of concentrations present in the sensor tube, the pump pushes the air column in the tube through the detection unit at a constant speed. The detector unit at the end of the sensor tube is equipped with a gas sensor. Any increase in gas concentration produces a real "peak leak".
Fiber optic leak detection
At least two optical fiber leak detection methods are being commercialized: Distributed Temperature Sensing (DTS) and Distributed Acoustic Sensing (DAS). The DTS method involves the installation of fiber optic cables along the monitored pipe. Substance to be measured in contact with the cable when a leak occurs, change the cable temperature and change the reflection of laser light, signaling leakage. This location is known as measuring the time delay between when the laser pulse is emitted and when its reflection is detected. This only works if the substance is at a different temperature than the surrounding environment. In addition, the distributed fiber optic sensing technique offers the possibility to measure the temperature along the pipe. Scans the entire fiber length, the temperature profile along the fiber is determined, leading to leak detection.
The DAS method involves the installation of similar fiber optic cables along the monitored pipeline. The vibrations caused by a substance leaving the pipe through a leak change the reflection of a laser light, which signifies a leak. This location is known as measuring the time delay between when the laser pulse is emitted and when its reflection is detected. This technique can also be combined with the Distributed Temperature Sensing method to provide a pipe temperature profile.
overpass pipeline
Overpasses from pipes are often done to confirm the location or to detect and find small releases that can not be identified by other methods. Usually the overpass on the right is recorded by video, which may have some image filtering, such as thermal imaging. Larger spills will usually be identified with "sheen" in wetlands or dead vegetation areas around the release site.
Overpass is usually scheduled and is not recommended as a major leak detection method. They can be used to quickly confirm the presence and location of leaks.
Detection of biological leakage
Biological methods of leak detection include the use of dogs, which are more likely to be used after release has been identified but not located due to their small size; or by landscapers that maintain the pipeline properly.
There are several companies that can provide trained dogs to identify the scent of release. Usually a technician injects fluid into a pipe that the fragrant dogs are trained to track. The dogs will then direct the handler towards the pipe leak. They are trained to be indicated at the strongest concentrations therefore their ability to determine them is usually within a meter. It usually takes 24 to 48 hours to mobilize the team, and it may take a few days to actually find the release depending on the remoteness of the area.
Pipeline rights are clearly guarded by landscapers that are also trained to look for signs of pipeline release. This is usually a scheduled process and should not be considered a major form of leak detection.
See also
- Pre-commissioning pipes
- Air leak detection
References
Source of the article : Wikipedia
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