Posted by Hydrographic Catalogue on 06/26/2017

Oil and gas pipeline leak detection industry - A growing business and what this mean to surveyors

Oil and gas pipeline leak detection industry - A growing business and what this mean to surveyors

According to Business Wire, most of the oil and gas pipelines around the world are between 30 to 100 years old. The chance of corrosion and leaks gets higher as the subsea structures get older and older. The frequency of leaks reported in recent years is almost more than twice of the rate it used to be.

Due to local and international environmental policies, many advanced and under development countries have been putting standards in place for leak detection and consequent pollution of the environment. Some of these regulations mandate all hazardous liquid pipelines such as oil and gas to have a leak detection system in place. Some of the pipeline leak regulations enforce compliance with international and industry standards such as DNV, API and TRFL.

As a surveyor or hydrographer what does this mean to us? In addition to the traditional leak detection which all works based on internally based leak detection systems (LDS) to monitor internal pipeline parameters, the growth of externally based systems is significant. The externally based leak detection systems are highly sensitive and accurate, but the system cost and complexity of installation are usually very high. A Survey by Gerhard Geiger, University of Applied Sciences Gelsenkirchen, Faculty of Electrical Engineering, provides more information if you are interested to know more about this. However, the recent developments show that the externally based systems are becoming more cost efficient.

Here is a list of externally based LDS systems available in the market:

  • Digital Oil Leak Detection Cable

  • Infrared Radiometric Pipeline Testing

  • Acoustic emission detectors

  • Vapour-sensing tubes

  • Fibre-optic leak detection

  • Pipeline Fly Overs

  • Biological leak detection

Survey industry become an important player when it comes to active acoustic sonar detectors and pipeline fly overs which is usually by an AUV or ROV.

Acoustic emission detectors

There are two methods to detect a leak via acoustic sensors. we categorize them as passive and active acoustic sensors and will try to explain how they work.

Passive acoustic systems

Escaping liquids creates an acoustic signal as they pass 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 analyzed. 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 easier 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 to 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 different range of sounds when leaving the pipe.

Active acoustic systems

Modern active acoustic multibeam sonars have the last 1.5 years achieved a major breakthrough in terms of performance, physical size, power consumption, uplink flexibility, processing and not least price. This now allows the tool to be used in a much wider context during subsea hydro carbonate (Oil/gas) detection, quantification and visualization. As the new generation sonar is so flexible it will easily integrate to any platform, AUV, ROV, Gliders, permanent installation, ship borne etc.

Active sonar works by projecting a short-duration high-bandwidth ultrasonic pulse into the water and listening for echoes from any objects such as subsea structures, ROVs or hydrocarbon leaks. A software is then capable of detecting and localizing a potential leak from all the other sonar targets. This way the characteristics and position of leaks could be shown on the sonar display.

Active sonar does not just passively listen for leaks. Compared to a hydrophone solution, the sonar does not need to discriminate the different sounds that could be made from a leaking flange or valve stem from background noise; it is monitoring the actual leak directly.

Here are some of the companies who provide active sonar products:

Sonardyne

One of the leading product is the market is Sentry integrity monitoring sonar developed by Sonardyne. Sentry IMS (Integrity Monitoring Sonar) has been developed to automatically warn of integrity breaches around subsea oil and gas assets. The system is capable of monitoring more than one billion cubic feet of seawater, with 360° of coverage from a single sensor location, operating without the need for skilled sonar operators to monitor the system. Sentry IMS is designed to be very sensitive and can detect leaks below 1 barrel per day at ranges more than 500 metres.

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Figure 2: Sentry IMS (Integrity Monitoring Sonar)

The Sentry IMS software is based on the proven architecture and detailed design of Sonardyne’s Sentinel IDS, the world’s best-selling Intruder Detection Sonar, offering both high reliability detection and classification algorithms, which are field proven andbest in class. Very importantly, Sentry does not require a trained sonar expert to adjust the sonar parameters. It has been designed to provide robust, reliable detection in all conditions without constant tweaking. The software is intuitive, simple to understand and automatically advises status/capability in real-time.

If hydrocarbons (or indeed other gases/fluids) are detected, Sentry produces an audible and visible alarm. Data on the leak position is displayed and can also be automatically transmitted to remote monitoring stations via an Ethernet link. The systemconstantly records any gas or oil detections, thus providing a log of events which cansubsequently be played back.

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Figure 3: remote monitoring stations

Sentry can support a secure external interface allowing alerts and monitoring status to be distributed globally as required. The same interface can also allow remote support by experienced Sonardyne engineers.

MEATAS

METAS new AALD, Active Acoustic Leak Detection Sensor System for Oil and Gas, is our latest development in our suit of products for subsea acoustic monitoring. The system is designed for subsea installation, detecting even tiny amounts of oil and gas at ranges up to 700+ meters. Various alternative hardware applications and sensors are available with horizontal scanning selectable from 0 to 360 degrees and 0 to 90 degrees vertical for monitoring one or more potential locations in same area to fulfill customers need. For analyzing detected leakages, an in house developed software system are used. The software is tuned for alarms on detected leakages and its location as well as trend indications for small leakages. The software was developed in cooperation with Codelab Bergen.

Video showing CO2 leakage detection at 270 meter distance from the sensor. Left part presents the raw echo-sounder data, while on the right side the processed and scrutinized data is presented in 3D. The leakage is highlighted in red.

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Figure 4: METAS AALD, Active Acoustic Leak Detection Sensor System

The sonar could be either deployed with a tripod including subsea power supply unit and acoustic modems for communication on directly on a subsea structure. pictures below show how a leak detection sonar could be deployed and used subsea.

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Figure 5: AALD Installation

Christian Michelsen Research

CMR have broad experience with acoustic simulations, instruments and data analysis. While benefitting from this experience, CMR have contributed to developing leakage detection technology by data analysis of both active and passive acoustic data, modelling acoustic scattering of oil and gas plumes, flow simulations, acoustic design and selection of material.

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Figure 6: Christian Michelsen Research Leak Detection System

Advantages of using active sonar

Early Warning

Early warnings of small leaks can allow operators to schedule investigations and take control actions in a timely manner. The system can detect gas outflows at the seafloor which may never surface near the platform because the gas has beenabsorbed into the seawater as it rises. It can also alert an operator to oil that may only break surface many miles from the hydrocarbon source due to a combination of greater water depth and local currents.

Wide Area Coverage

Unlike single point chemical sensors, Sentry is not dependent on being ‘in the flow’ of gas or oil. Similarly, it does not need to be within visual range as would be the case for video inspection using an ROV. When compared to passive systems, Sentry candetect low differential pressure leaks that are silent and which can’t be picked up with passive hydrophones. This allows the system to monitor the seabed for natural seeps, as well as leaks arising during drilling, production or decommissioning activities. Thesonar has a user configurable detection radius of up to 1,500 metres (5,000 feet).

High Performance

Indicative performance predictions for both oil and gas detection, at a typical deep water installation, are shown in the graphs to the right. In practice many leaks will be a dual-phase mixture of oil and gas, which will make any oil leak more detectable than it

might appear from the data presented. At a gas/oil ratio of 1,000, a tiny dual-phase oil leak of 0.1 barrels per day would then be detectable at a leak-to-sonar range more than 500 metres.

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.

There are ultrasonic and light sensors that could be mounted on an ROV to deter the leakages in short distance up to 10 meters.

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Figure 7: Pipeline Fly over

Here are some of them listed with a bit of description of their technology and applications.

Neptune Acoustic Leak Detection (APLD)

Ultrasonic leak detection is a method of pipeline leak detection that uses a directional hydrophone that ‘listens’ for ultrasounds generated by leaking fluids passing through an orifice under pressure. The acoustic signals generated by a leak tend to be at frequencies above 30kHz. The software uses techniques that determine the difference between leak generated sound and lower frequency noise such as that caused by the attendantROVand surface vessels.

Hydrophones are effectively underwater microphones that ‘listen’ for ultrasound generated by leaking fluids under pressure. For small leaks, the acoustic signals generated tend to be at frequencies well above the audible range thus requiring sophisticated sensors and software to reliably determine the difference between ‘leak’ generated sounds and ambient sounds. The major problems with this method are the sounds caused by the attendant (ROV) and other vessels in the vicinity. However, modern data handling and spectral analysis techniques have improved the method sufficiently such that the method can be highly successful.

Neptune Oceanographics’ acoustic leak detection sensor may be diver-held or mounted on a ROV,AUV, orPIG. It incorporates a directional hydrophone with the system featuring noise filters to remove the effects of ambient noise, including mechanical noise from anROVor support vessel.

The detected acoustic signals are sent, via theROVumbilical or diver cable, to the on-board PC where acoustic intensity may be displayed either alongside fluorometer readings in dual capacity mode or as a single channel. In common with the fluorometer system, the sensitivity is controlled by the data logger to obtain the maximum dynamic range.

Neptune Fluorescent Leak Detection

Neptune’s fluorescent leak detection system is based around a family of submersible long-range fluorometers. The sensors respond to a range of fluorescent leak detection dyes and liquid hydrocarbons at low concentrations. The advantage of Neptune’s fluorescence detector system is the ability to detect very low concentrations in turbid conditions with a high spatial coverage using the new family of long range remote sensing fluorometers.

The submersible fluorometers are very sensitive and will detect fluorescent leak detection dye at concentrations so low as to be invisible to the naked eye or underwater camera.

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Figure 8: fluorescent leak detection dyes and liquid

Neptune Oceanographics has recently and successfully introduced a new range of long-range fluorometers. The long-range fluorescent detector has a forward facing ‘tuned’ light source (like a torch) producing a beam of excitation light spreading to about 40cm diameter at 3m. Fluoresced light signals generated in the leaked fluid are detected by the sensor and converted for transmission to the surface via theROVumbilical for display and recording.

By mounting the fluorescence detector on theROVmanipulator and because the sensors have high spatial coverage, quick and easy scanning for leaks is achieved without needing to consider tidal flow direction to ‘capture’ dye as is necessary with most fluorometers.

Other major advantages of the long-range fluorescent detection include the detection of leaks from risers while working at safe distances and detecting leaks within confined structures whereROVaccess is not possible or too hazardous.

OceanSENSE Subsea leak and dye detection systems

A single OceanSENSE unit may be used both to detect leaks from subsea infrastructure and detect cement dye during cementing operations.When deployed in a commissioning role, OceanSENSE can be used to prove the structural integrity of spool tie-ins and subsea structures beyond the capability of the human eye to see trace dye in water.

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Figure 9: OceanSENSE Subsea leak and dye detection systems

Dive Works 2 Channel ‘Long Ranger’ Subsea Leak Detection System - MKII

The system comprises a two channel unit that can be used with two fluorometers or one fluorometer plus an acoustic sensor operating simultaneously. One or more sensors are connected to a two channel pressure housed processor board that is mounted on the ROV and wired through the MUX to the umbilical for data transmission to the surface. The processor produces data in operator selected RS232 or RS485 format for transmission to the surface via the ROV umbilical. Power is supplied by the ROV at 24vdc.

The on­board PC displays data as colour time series plots in real time, allowing the operator to easily see changes in signal that indicate the presence of a leak. The software also allows the user to set alarm levels that will provide an immediate response when a leak has been detected and to record data.

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Figure 10: Camera view of excited dye using the Long Ranger

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