Aerial Pipeline Surveillance
using the Airwave Environmental Technologies
Model AE2420 Flame Ionization Hydrocarbon Analyzer
Airwave Environmental Technologies has designed and manufactured ambient air monitoring systems since its beginnings in 1984. Since this time Airwave has developed the model AE2420 Flame Ionization Hydrocarbon Analyzer and the model AE2430 Sulfur Analyzer for ground environmental monitoring stations.
There has been increased interest in developing a method for rapid aerial surveying of oil and gas pipelines. Conventional surveys usually involve visual surveillance by pilots as they routinely fly the pipeline right-of-way. Visual sightings rely on the recognition of dead vegetation to identify a leak source. As can be imagined, this technique is rather limited to the summer season and areas that are covered with sufficient green vegetation (i.e. not a desert climate). The use of Infrared technology has been applied to pipeline leak detection. This technique utilizes the thermal differences of a pipeline oil/gas leak compared to the surrounding area. However, this technique is limited due to the length of time needed to develop an image. As well, it is difficult to apply Infrared technology where the climate is cold or where there is a significant vegetation canopy.
Since 1992, Airwave has been interested in applying its Flame Ionization technology to the detection of pipeline leaks. An airborne instrument platform has been developed, incorporating the model AE2420 Hydrocarbon Analyzer, Global Positioning System, data collection system and video recording. The platform is mounted in a Piper Seneca or Navajo fixed wing aircraft and during the aerial surveillance the aircraft is flown at 100 – 200 feet above ground at a speed of approximately 100 knots.
The purpose of this document is to describe the system that Airwave Environmental Technologies has developed and give details as to its current operation and detection capabilities.
2.0 AERIAL PIPELINE LEAK DETECTION SYSTEM OVERVIEW
An excellent reference regarding the problems associated with airborne monitoring is as follows:
Proceedings of the Specialty Conference on: In-Situ Air Quality Monitoring from Moving Platforms, sponsored by The Air Pollution Control Association’s TP-9 Moving & Remote Monitoring Committee and the U.S. Environmental Protection Agency, January 18-21, 1982
2.1 Aircraft and Operations Crew
A Piper Seneca or Navajo twin engine aircraft is the preferred method for aerial monitoring. The nose baggage compartment of these fixed wing aircraft allows for easy location of the aerial sampling probe and video camera. There is ample room to carry the a pilot, co-pilot, system operator and instrument platform. With respect to the use of a helicopter (Bell 206 Long Ranger Version or larger), Airwave would only use this aircraft when the pipeline terrain is to difficult to negotiate using a fixed wing aircraft, for example in a mountainous area.
The lower maintenance and operating costs favour the use of fixed wing aircraft to that of helicopters. In addition , use of helicopters would require fuel dumps be placed every 200 miles compared to the Navajo and Seneca aircraft with an operating range of over 500 miles.
The operation of the aircraft requires 3 personnel : pilot, co-pilot and system operator. Due to the stresses of low level flying the pilot and co-pilot change roles every 2 hours.
2.2 Instrument Platform Components
Figure I is a block diagram illustrating the components of the instrument platform:
Figure I Block Diagram of the Instrument Platform for the Airwave Environmental Technologies Airborne Pipeline Surveillance System
The aircraft nose/baggage compartment houses the sample probe/manifold assembly and video camera. The sample probe (0.5 inch i.d. stainless steel) extends 18 inches into the undisturbed air sample beyond the aircraft nose. The video camera is mounted such that it monitors about a 30 degree view of the flight path.
The instrument platform less video camera, sample probe/manifold assembly measures only 3.5’ wide by 2.5’ high by 2.5’ deep and weighs less than 200 lbs. The components of the platform are as follows:
2.2.1 Airwave Electronics model AE2420 Flame Ionization Hydrocarbon Analyzer
The model AE2420 analyzer is the heart of the airborne surveillance system. The AE2420 used in this system has improved temperature stability and radio frequency interference reduction to make this proven ground-based analyzer reliable in an airborne setting.
The Flame Ionization mode can be either set for Total Hydrocarbon (for liquid pipelines) or Methane (for natural gas pipelines) through the use of a built-in oxidizer.
Please refer to the Airwave Electronics literature for the overall operating specifications of the model AE2420 analyzer.
In order to obtain the fastest response as possible, the analyzer is operated without a time constant. Figure II gives the response of the model AE2420 to methane gas during an airborne calibration under operating conditions.
Figure II Response Time for the Airwave Model AE2420 Flame Ionization Analyzer
2.2.2 Global Positioning System (GPS)
The location (Longitude/Latitude), air speed and altitude of the aircraft, along with the time of day (expressed as UTC – Greenwich Mean Time) are determined using a Garmin GPS 95 AVD Personal Navigator. This data during flight is updated every 2 seconds and is outputted to both the video recorder and data acquisition for a permanent record of the test run.
2.2.3 Data Acquisition System
The data acquisition system consists of a 386 laptop computer with an internal 8 channel 12 bit A/D board, a 240 megabyte hard drive and external VGA color monitor.
The information is collected using the Airwave “Leak Tracker” software. This custom package collects data at a rate of every 0.5 seconds. The information is displayed graphically and digitally in real time on the computer monitor. By this means, the operator has the ability to immediately alert personnel if a major leak has been located. This is especially important in emergency response situations where rapid identification of a leak source is necessary. Following a test run the information can be immediately processed for presentation in a spreadsheet format for further analysis and graphing.
2.2.4 Video Recording
The information from the video camera located in the nose of the aircraft, along with the digital information from the Garmin GPS 95 AVD, is displayed on the TV monitor and permanently stored using the onboard video recorder.
The TV monitor allows the system operator to view the pipeline as it is traveled and identify (using the “Leak Tracker” software) any obvious hydrocarbon sources such as farming feedlots, compressor stations, valves…..etc. The video is later reviewed to try to identify any hydrocarbon anomalies that were revealed by the analysis of the data but not readily apparent during the survey. As well, the video is useful when planning the logistics of responding to maintenance/remediation of the leak site.
This information is presented to the client along with the data from the survey and is a permanent visual record of the status of the pipeline right-of-way at the time of the survey.
2.2.5 Calibration (Zero/Span Gases)
With respect to the location of oil/gas pipeline leaks, the actual concentration of the gas measured is not of critical concern. The tests are conducted at only 100-200 feet above ground. Hence the aircraft is only in the leak plume for about 1 to 3 seconds. There is not enough time to achieve 100% instrument response to the elevated hydrocarbon levels. However, it is only necessary to qualitatively identify a larger than background hydrocarbon anomaly to determine the presence of a potential leak source. As a result the purpose of calibrating the FID instrument is simply to set the instrument up to a suitable sensitivity and verify that it is operating properly.
The operation of the FID analyzer is verified prior to each test run. Typically a span gas of about 20 ppm methane/balance air is chosen with the analyzer on the 0 – 25 ppm range. It is important that the analyzer be zero/spanned before each test run as experience has shown that the response of model AE2420 Flame Ionization Detector will vary with altitude above sealevel.
3.0 Types of Aerial Pipeline Surveys and Survey Requirements
3.1 Types of Aerial Pipeline Surveys
Airwave Environmental Technologies offers three types of aerial pipeline surveys:
3.1.1 EMERGENCY RESPONSE – LEAK LOCATING SURVEILLANCE
The purpose of this survey is to rapidly identify the point of rupture in a pipeline. Airwave has a Seneca Twin Engine aircraft available on 24 hour standby for these emergencies. In addition to identifying the point(s) of leakage, Airwave is also available as an option to assist in the ground surveillance to pinpoint the exact location of the event.
3.1.2 SCHEDULED ROUTINE PIPELINE SURVEILLANCE
On an annual or semi-annual basis, a single pass aerial survey would be conducted to identify hydrocarbon anomalies and determine if any of this occurrences relate to leaks in the oil or gas pipeline. Airwave would maintain a database of each survey and comparisons would be made between past surveys to identify changes in the magnitude of the anomalies.
3.1.3 COMPREHENSIVE PIPELINE SURVEILLANCE
This type of survey would involve a detailed hydrocarbon emission profile of a pipeline, showing all potential leakage sites. The length of the pipeline would be flown about four times at different distances parallel to the pipeline to confirm each anomaly and result in a 3 dimensional profile being developed. Ground assistance would also be available at an option to collect samples for analysis to confirm suspected sites. An example of this type of survey request would occur perhaps prior to a purchase of an existing pipeline.
3.2 Pipeline Survey Requirements
3.2.1 Weather Requirements
In general the preferred weather conditions necessary to conduct a satisfactory aerial pipeline leak survey would be as follows:
Temperature : greater than 0o C (32o F)
Wind Speed : Less than 10 knots (11.5 MPH)
Precipitation : Nil
Under these conditions the plume due to the pipeline leakage has an opportunity to become well established even at very low leakage rates (eg. natural gas leak at 1 ft3/ min (28.3 litres/ min) or liquid spill of about 25 gallons over a 100 square foot area).
With respect to routine surveys of liquid pipelines it is preferable to operate at ground temperatures of over 0o C (32o F). Warmer temperatures are required to promote a suitable evaporation rate in order to yield a well defined plume. However, with respect to natural gas leakage, a temperature as low as -200 C (-40 F) can be tolerated before flying the aircraft becomes a hazard. Similarly, while winds of less than 10 knots are preferred, where the suspected leakage rate is high (for example during an emergency response situation) winds of up to 20 knots can be tolerated.
Under favourable conditions, one should be able to locate the source of a pipeline leak within 150 to 300 meters using the data obtained from this test.
3.2.2 Customer Requirements (Survey Preplanning)
Prior to commencing an aerial pipeline leak survey, an in depth survey preplanning session is held with each client. During this meeting the client should provide detailed maps showing the pipeline right-of-way and its longitude/latitude co-ordinates. When the pipeline right-of-way is not clearly defined, or where there may be confusion due to a parallel pipeline being close by, it may be necessary to have a company observer available on the first traverse of the pipeline, The observer would not be necessary on subsequent surveys as accurate pipeline co-ordinates would be obtained from the observer flight.
From this information and the proposed schedule for the survey, a detailed proposal would be provided to the client outlining the costs, survey schedule and alternative scheduling arrangements in the event of inclement weather for their approval.
4.0 Examples of Data from Natural Gas Leaks and Liquid Hydrocarbon Spills
A common question from clients, interested in using this technique for pipeline leak detection, is
“How does the response of the Airwave Aerial Pipeline Surveillance System relate to the size of the natural gas leak or liquid hydrocarbon spill on the ground?”
In attempt to answer this question two test situations were created.
4.1 Natural Gas Leakage Test
A site, west of Crossfield, Alberta, was chosen for this test. A cylinder of 100% Natural Gas was discharged from a 1/8″ ID SS tube about 4 feet off the ground at a flow rate of 29.5 LPM (about 1 CFM) with a bottle pressure of 1000 psig. A temperature compensated dry gas meter was used to determine the gas output. The gas leak was created about 25 minutes prior to conducting the test flight. A slight wind of about 5 knots at ground level was blowing toward the aircraft during the test. The ambient temperature at ground level was about 30C.
Table I Test Data – Natural Gas Leakage Test – February 17, 1995
Figure III Natural Gas Leakage Test – February 17, 1995
The preceding test demonstrates the sensitivity of the Airwave Aerial Pipeline Surveillance System. The peak corresponding to the 29.5 LPM discharge of 100% natural gas is clearly visible above the background readings. In a real pipeline situation, one would expect the greater response to a natural gas leak of this magnitude, as the plume would be much stronger due to a continuous discharge rather than 25 minutes as was used in this test.
4.2 Liquid Hydrocarbon Spill Test
In order to determine the response of the Airwave Aerial Pipeline Surveillance system to liquid hydrocarbon spills, a test was created whereby about 20 gallons of a mixture of diesel, jet B, gasoline and aviation fuel in equal proportions was placed in a 100 square foot shallow pan. The air temperature was approximately 00 C and the mixture was allowed to evaporate for about 2 hours prior to being tested. There was a wind of about 10 – 12 knots blowing toward aircraft during the aerial test.
Table II Test Data – Liquid Hydrocarbon Spill Test – February 8, 1995
Figure IV Liquid Hydrocarbon Spill Test – February 8, 1995
The conditions of this test were much less than ideal and would be considered a worst case situation with respect to detecting a liquid hydrocarbon spills. Unfortunately the test was conducted at a higher altitude than is normally flown. This combined with the low temperature and wind, caused the measured peak to be much broader than normal and detected at a distance much further than is desirable.
However, in a positive light, this data does indicate the system’s capability to detect very small hydrocarbon spills under difficult conditions. Airwave intends to rerun this test in summer conditions at a temperature of 200C to demonstrate the detection capability under a more favorable climate.
The preceding discussion and data is a detailed description of the Airwave Environmental Technologies Aerial Pipeline Surveillance system. From the data shown in section 4.0 it is clear that this system is a viable method of pipeline monitoring. Conducting our surveys at speeds of 100 knots allows us to complete a pipeline survey or emergency response situation in a very short time frame. This system has been successfully employed over about 10,000 miles of pipeline in the past year.
Airwave Environmental Technologies is in the process of applying this airborne instrument platform to other instruments in their product line, specifically the model AE2430 Flame Photometric Sulfur Analyzer. This instrument can be configured to respond to Sulfur Dioxide or Total Reduced Sulfur gases (TRS). Due to the fast response of this instrument, it is possible using selective scrubbers and solenoid switching to monitor both Sulfur Dioxide and TRS from the same analyzer in a sequential mode with 60 second updates on each parameter.
Airwave Environmental Technologies is also adapting this proven airborne instrument platform to mobile ground based monitors for use in downwind surveillance studies of oil and gas operations.
Please contact us for more information on any of these applications.