Pipeline Leak Detection

Pipeline leak detection is used to determine if and in some cases where a leak has occurred in systems which contain liquids and gases. Methods of detection include hydrostatic testing, infrared, and laser technology after pipeline erection and leak detection during service.

Pipeline networks are the most economic and safest mode of transportation for oil, gases and other fluid products. As a means of long-distance transport, pipelines have to fulfill high demands of safety, reliability and efficiency. If properly maintained, pipelines can last indefinitely without leaks. Most significant leaks that do occur are caused by damage from nearby excavation. If a pipeline is not properly maintained, it can corrode, particularly at construction joints, low points where moisture collects, or locations with imperfections in the pipe. However, these defects can be identified by inspection tools and corrected before they progress to a leak. Other reasons for leaks include accidents, earth movement, or sabotage.

The primary purpose of leak detection systems (LDS) is to help pipeline controllers to detect and localize leaks. LDS provide alarms and display other related data to the pipeline controllers to assist decision-making. Pipeline leak detection systems can also enhance productivity and system reliability thanks to reduced downtime and inspection time.

According to the API document “RP 1130”, LDS are divided into internally based LDS and externally based LDS. Internally based systems use field instrumentation (for example flow, pressure or fluid temperature sensors) to monitor internal pipeline parameters. Externally based systems use a different set of field instrumentation (for example infrared radiometers or thermal cameras, vapor sensors, acoustic microphones or fiber-optic cables) to monitor external pipeline parameters.

API 1155 (replaced by API RP 1130) defines the following important requirements for an LDS:

• Sensitivity: An LDS must ensure that the loss of fluid as a result of a leak is as small as possible. This places two requirements on the system: it must detect small leaks, and it must detect them quickly.
• Reliability: The user must be able to trust the LDS. This means that it must correctly report any real alarms, but it is equally important that it does not generate false alarms.
• Accuracy: Some LDS are able to calculate leak flow and leak location. This must be done accurately.
• Robustness: The LDS should continue to operate in non-ideal circumstances. For example, in case of a transducer failure, the system should detect the failure and continue to operate (possibly with necessary compromises such as reduced sensitivity).

Externally based LDS

Externally based systems use local, dedicated sensors. Such LDS are highly sensitive and accurate, but system cost and complexity of installation are usually very high; applications are therefore limited to special high-risk areas, e.g. near rivers or nature-protection areas.

Analytic Thermal Leak Detector for Above Ground Pipelines

Video analytics driven thermal imaging using uncooled microbolometer infrared sensors is emerging as a new and effective method of visualizing, detecting and generating alerts of unplanned surface emissions of liquids and hydrocarbon gas liquids. Detection to alarm generation takes less than 30 seconds. This technology is suitable for above-ground piping facilities, such as pump stations, refineries, storage sites, mines, chemical plants, water crossings, and water treatment plants. The need for new solutions in this area is driven by the fact that more than half of pipeline leaks occur at facilities.

High quality thermographic technology accurately measures and visualizes emissivity or infrared radiation (thermal heat) of objects into gray scale imagery without the need for ambient lighting. The monitored petroleum product (e.g. oil) is distinguished from background objects by this heat difference. The addition of an analytic software component, typically optimizable to better address a specific application or environment, enables automated onsite leak analysis, validation and reporting, thereby reducing reliance on man power. A leak appearing within an analytic region (a rule added to the camera) is immediately analyzed for its attributes, including thermal temperature, size, and behaviour (e.g. spraying, pooling, spilling). When a leak is determined to be valid based on set parameters, an alarm notification with leak video is generated and sent to a monitoring station.

Optimal detection distance varies and is influenced by camera lens size, resolution, field of view, thermal detection range and sensitivity, leak size, and other factors. The system’s layers of filters and immunity to environmental elements, such as snow, ice, rain, fog and glare, contribute to false alarms reduction. The video monitoring architecture can be integrated onto existing leak detection and repair (LDAR) systems, including SCADA networks, as well as other surveillance systems

Thermal camera system with video analysis software detecting an oil leak from a valve at 50 feet and 150 feet in heavy rain.

Digital Oil Leak Detection Cable

Digital Sense Cables consist of a braid of semi-permeable internal conductors protected by a permeable insulating moulded braid. An electrical signal is passed though the internal conductors and is monitored by an inbuilt microprocessor inside the cable connector. Escaping fluids pass through the external permeable braid and make contact with the internal semi-permeable conductors. This causes a change in the electrical properties of the cable that is detected by the microprocessor. The microprocessor can locate the fluid to within a 1-metre resolution along its length and provide an appropriate signal to monitoring systems or operators. The sense cables can be wrapped around pipelines, buried sub-surface with pipelines or installed as a pipe-in-pipe configuration.

Infrared Radiometric Pipeline Testing

Infrared thermographic pipeline testing has shown itself to be both accurate and efficient in detecting and locating subsurface pipeline leaks, voids caused by erosion, deteriorated pipeline insulation, and poor backfill. When a pipeline leak has allowed a fluid, such as water, to form a plume near a pipeline, the fluid has a thermal conductance different from the dry soil or backfill. This will be reflected in different surface temperature patterns above the leak location. A high-resolution infrared radiometer allows entire areas to be scanned and the resulting data to be displayed as pictures with areas of differing temperatures designated by differing grey tones on a black & white image or by various colours on a colour image. This system measures surface energy patterns only, but the patterns that are measured on the surface of the ground above a buried pipeline can help show where pipeline leaks and resulting erosion voids are forming; it detects problems as deep as 30 meters below the ground surface.

Aerial thermogram of buried cross country oil pipeline revealing subsurface contamination caused by a leak.

Acoustic emission detectors

Escaping liquids creates an acoustic signal as they passes through a hole in the pipe. Acoustic sensors affixed to the outside of the pipeline create a baseline acoustic “fingerprint” of the line from the internal noise of the pipeline in its undamaged state. When a leak occurs, a resulting low frequency acoustic signal is detected and analysed. Deviations from the baseline “fingerprint” signal an alarm. Now sensors are having better arrangement with frequency band selection, time delay range selection etc. This makes the graphs more distinct and easy to analyse.There are other ways to detect leakage. Ground geo-phones with filter arrangement are very useful to pinpoint the leakage location. It saves the excavation cost. The water jet in the soil hits the inner wall of soil or concrete. This will create a feeble noise. This noise will decay while coming up on the surface. But the maximum sound can be picked up only over the leakage position. Amplifiers and filter helps to get clear noise. Some types of gases entered into the pipe line will create a range of sounds when leaving the pipe.

Vapour-sensing tubes

The vapour-sensing tube leak detection method involves the installation of a tube along the entire length of the pipeline. This tube - in cable form - is highly permeable to the substances to be detected in the particular application. If a leak occurs, the substances to be measured come into contact with the tube in the form of vapour, gas or dissolved in water. In the event of a leak, some of the leaking substance diffuses into the tube. After a certain period of time, the inside of the tube produces an accurate image of the substances surrounding the tube. In order to analyse the concentration distribution present in the sensor tube, a pump pushes the column of air in the tube past a detection unit at a constant speed. The detector unit at the end of the sensor tube is equipped with gas sensors. Every increase in gas concentration results in a pronounced "leak peak"

Fibre-optic leak detection

At least two fibr-optic leak detection methods are being commercialized: Distributed Temperature Sensing (DTS) and Distributed Acoustic Sensing (DAS). The DTS method involves the installation of a fibre-optic cable along the length of pipeline being monitored. The substances to be measured come into contact with the cable when a leak occurs, changing the temperature of the cable and changing the reflection of the laser beam pulse, signalling a leak. The location is known by measuring the time delay between when the laser pulse was emitted and when the reflection is detected. This only works if the substance is at a temperature different from the ambient environment. In addition, the distributed fibre-optical temperature-sensing technique offers the possibility to measure temperature along the pipeline. Scanning the entire length of the fibre, the temperature profile along the fibre is determined, leading to leak detection.

The DAS method involves a similar installation of fiber-optic cable along the length of pipeline being monitored. Vibrations caused by a substance leaving the pipeline via a leak changes the reflection of the laser beam pulse, signaling a leak. The location is known by measuring the time delay between when the laser pulse was emitted and when the reflection is detected. This technique can also be combined with the Distributed Temperature Sensing method to provide a temperature profile of the pipeline.

Pipeline Fly Overs

Fly overs of the pipeline are frequently carried out to either confirm the location or to detect and locate small releases that cannot be identified by other methods. Typically the flyover of the right of way is recorded by video which may have some image filtering, such as thermal imaging. Larger spills will typically be identified by a "sheen" in wetland or an area of dead vegetation around the release location.

Flyovers are typically scheduled and not recommended as a primary leak detection method. They may be used to rapidly confirm the presence and location of a leak.

Biological leak detection

Biological methods of leak detection includes the use of dogs, which are more likely to be used once a release has been identified but not located due to its small size; or by landscapers who keep the pipeline right of way clear.

There are several companies who can provide dogs trained to identify the scent of release. Typically a technician injects a fluid into the pipeline that the scent dogs are trained to track. The dogs will then direct handlers towards a pipeline leak. It typically takes 24 to 48 hours to mobilise a team, and may take several days to actually locate a release depending on the remoteness of the area.

Pipeline rights of way are kept clear by landscapers who are also trained to look for signs of pipeline releases. This is typically a scheduled process and should not be considered a primary form of leak detection

Pipeline pre-commissioning

Pipeline pre-commissioning is the process of proving the ability of a pipeline and piping systems to contain product without leaking. This product may be liquid, gaseous or multiphase hydrocarbons, water, steam, CO2, N2, petrol, aviation fuel etc.

Pre-commissioning is the series of processes carried out on the pipeline before the final product is introduced. The process during which the pipeline is made "live" i.e. the product is put in the pipeline, is called pipeline commissioning or start-up.

Despite being seen as an offshoot, or minor part of the business for the larger oil service companies, the pipeline pre-commissioning industry possesses quite a large portfolio of services including, but not limited to the following services:

Pipeline Cleaning - this is carried out by pushing pigs or gel pigs through the pipeline to remove any debris buildup or corrosion.

Pipeline Gauging - this is carried out to prove the dimensional quality of the internal diameter of the pipeline.

Pipeline Filling (Flooding) - which can be carried out by propelling pigs through the pipeline with water or free flooding with water (normally for smaller or unpiggable pipelines).

Hydrotesting - this is a process by which the pipeline in question is pressure tested to a predefined pressure above the operating design pressure of the pipeline.

Dewatering - this involves pushing pigs through the pipeline propelled by a gas to remove the water prior to start-up.

Other services include vacuum drying, degassing, pneumatic testing, barrier testing, leak testing, decommissioning to mention but a few.

On the pipeline process pre-commissioning side, there are various services such as chemical cleaning, helium leak detection, bolting, hot oil flushing, pipe freezing, foam inerting etc...

Other services include valve testing, umbilical testing, hot tapping, leak metering, riser annulus testing.

Flow Assurance

Dynamic Simulation

Computational Fluid Dynamics

Surge Analysis

& More...