1. Field of the Invention
The present invention generally relates to detection and monitoring systems and, more particularly, to a real-time method and system for detecting leaks and inventory loss and for managing information corresponding thereto. The present invention may be employed with respect to, for example, gas and liquid pipeline network systems, storage tanks of process systems, blood vessels and stroke management.
2. Background of the Invention
Most conventional pipeline leak detection systems have failed in terms of response time, sensitivity, robustness and cost. Pipeline leaks can be detected by observation of the external effects of the spill, or by monitoring and analysis of the internal hydraulics of the pipeline. One of the objectives of a pipeline leak detection system is to alert operators so that the size of the spill can be limited, which argues for speedy detection as well as reliability and sensitivity.
In choosing the optimum model, a leak detection system that provides continuous monitoring of pressures, temperatures, and flow at points along the pipeline, supported by automated analysis of the data is most ideal. A conventional leak detection system is based on several models. One of the oldest techniques, over short analysis is based on the application of the principle of conservation of mass using flow meters to establish whether the flow in the pipeline is balanced by the flow out. The existence of flow transients makes this method for leak detection a slow response technique, since it is necessary to either average flow over a long time period to filter out the effect of line pack changes due to transients. For long transmission pipelines, the response time is usually very long. Such long response time is unsatisfactory, and has the additional problem of significant data loss during the averaging time. This model cannot detect leak location, but can be used to establish commodity release and the volume spilled. Another model for leak detection is the Pressure Point Analysis. The basic idea of this model is that a leak initiation event produces a pressure drop that propagates in both directions from the leak site. Pressure changes can be detected with great sensitivity, and so it should be possible to detect the onset of small leaks. Pressure surges or operational changes can mask leaks if they are positive or cause false alarms if they are negative. It is applicable to pipelines operating under steady flow.
The dynamic model based real time leak detection system compares measurements collected by the Supervisory Control & Data Acquisition (SCADA) System, with a simulated model of the flow in the pipeline in lock step with actual operations. The results of simulation can be used to provide accurate line pack changes that, in combination with measured flow, give fast volume response. They can be used to support deviation analysis such as pressure drop or flow deviations, by correcting for changes not caused by leaks. This dynamic system model can be used to establish a leak location through a set of statistical and probability mathematical models. The major draw back to this model is the cost of installing the software and instrumentation. Another draw back is the incidence of false alarms due to fluctuating threshold setting, model complexity and poor instrumentation. Automatic threshold adjustment to optimize the sensitivity/false alarm/response time trade off and various means of coping with data problems would reduce the incidence of false alarms, but significantly increase the cost. Other leak detection system models are wave alert, acoustic and statistical pipeline leak detection models.
Most conventional systems are computer assisted to conform to Application Programming Interface (API) documentation on leak detection, which mandate all operators of U.S. hazardous Liquid pipelines to engage in pipeline leak detection known as Computational Pipeline Monitoring (CPM). For example, CPM must use, by reference the document API 11.30, the newest technology for pipeline monitoring for leaks. API 11.30 defines CPM as “an algorithmic monitoring tool” as it allows the pipeline controller to respond to a pipeline-operating anomaly that may indicate product release. As a system therefore, CPM is computer based.
As can be appreciated, because of inherent shortcomings of previous leak detection system models, a need exists for better models, methods, and systems for leak detection that have a fast response time and produce no false alarms, and that are obtained at optimal cost preferably in range of conventional leak detection systems. Also, the model should be capable of being employed with any kind of fluid system, locating leaks precisely, detecting small leaks, and predicting and assessing inventory loss precisely in any pipeline network system.
Current thresholds of false alarms reported by operators of most commonly used conventional leak detection systems create serious concerns for the need of more robust and optimal leak detection systems. Moreover, the slow level of response time and false alarm thresholds have led to serious revenue loss translating in millions of dollars in some cases, resulting from commodity, operational and asset lost, couple with penalties for spillage to the environment and lost man hours. There is a need for a more robust leak detection system that is error proof and has a fast response feedback time, which is enabled by a web based interactive platform for expert leak detection that reduces the feed back time between detection and control.
U.S. Pat. No. 5,548,530 (hereinafter the “'530 patent”), entitled “High-Precision Leak Detector and Locator”, issued on Aug. 20, 1996, the disclosure of which is incorporated by reference herein, describes a method and apparatus for leak detection which involves creating site stations at the beginning and the end of a pipeline, and dividing each pipeline segment into a plurality of hypothetical pipeline sections, each section having the same nominal volume, measuring the liquid flow into the first section and determining a volume of liquid that has passed the first section and determining a volume of liquid that has passed the first site station for a defined period, measuring the temperature of the liquid entering the first section of the first site station, measuring the liquid flow out of the last pipeline section of the segment and determining a volume of liquid that has passed the second site station for a defined period, measuring the temperature of the liquid leaving the last section at the second site stations, measuring the ambient temperature of the pipeline at the first station or that representative of the topography of the segment, measuring the ambient temperature of the pipeline at the second site station or that representative of the topography of the segment. The invention of the '530 patent computes changes in one segment relative to the penultimate, correcting the difference in measured volume of all sections during the defined period, comparing the corrected difference in measured volume between the first and second site stations and generating an alarm signal if the difference exceeds the threshold level.
U.S. Published Patent Application No. 2002/0124633 (hereinafter the “'633 application”), entitled “Method and Apparatus for Pattern Match Filtering for Real Time Acoustic Pipeline Leak Detection and Location”, filed on Sep. 12, 2002, the disclosure of which is incorporated by reference herein, describes a pattern match filter that includes using previously recorded leak profiles that benchmark pressure waveforms suggesting leaks against previous data. At site processes located at multiple points along a pipeline, a series of previously recorded signature leak profiles are continuously compared in real-time against pipeline pressure signals. The '633 application acknowledges that multiple transients on the pipeline from normal operating procedures can produce pressure disturbances (similar to an expansion wave generated by leak event), which are located on the monitored segment of pipeline and thus cause false leak alarms. The '633 application further acknowledge that previous techniques such as moving average, repetitive filter, dynamic threshold and band pass filters have only been successful in removing a certain type of noise, but has little effect on other types of transient noise such as pumps, compressors and valve operation, which produce signals with amplitudes similar to the amplitudes of signals produced by leaks, which has led to a high false alarm rate and reduced sensitivity. The '633 application further states that knowing the exact time of arrival of the expansion pressure wave at each monitor is critical for precisely locating the leak on the pipeline. Precise measurement by each monitor of arrival times is critical. However, the low frequency content of the expansion pressure wave produces a wavelength from a few hundred meters to 100,000 meters or more. Due to the length of the wave front and other factors, an uncertainty in the time tag between monitors occur, which in the past has limited leak location accuracy to typically +/−500 or more meters out of 10,000 meters. This has led to the inability to accurately locate leaks. Furthermore, this system uses a real-time acoustic pipeline leak detection technique that requires placing permanent monitors on a pipeline for detecting expansion pressure waves associated with a sudden breakdown in pressure boundary due to a rupture in a pipe wall. The '633 application discloses that in the past it was the amplitude of the signal that was of concern. The source of the pressure waves was located between the monitors by recording the times when the expansion pressure waves arrived at the monitors. Using these times (t2 and t1) and knowing the fluid sound velocity (V) and the length of the pipe between the monitors (D) the leak event could be located. Denoting the leak event location (distance from sensors number I) as “X”, the leak event location is computed as follows:X=D/2+V(t2−t1)/2  (1)
In U.S. Published Patent Application 2002/0134140, entitled “Leak Locator For Pipe Systems”, filed on Sep. 26, 2002, the disclosure of which is incorporated by reference herein, describes a system and method for determining a time of occurrence of a pressure wave in a pipe that provides a first sonic transducer and a second sonic transducer at each of a plurality of site locations along a pipe, with sonic waves being generated through a pipe wall at a particular rate. At each of the plurality of site locations, the sonic waves travel from the first sonic transducer to the second sonic transducer through a liquid flow in the pipe, with a measure of travel time set for the sonic waves. The measure is compared to each of the successive travel times for the sonic waves as the sonic waves arrive at respective second transducers. A string of counts is output at each second transducer. Each count includes a first count value if a present sonic wave has a travel time that is late as compared to the measure. A time of occurrence of the pressure wave is determined based on a reference clock when the string of counts includes a string of first count values longer than a threshold value. The time of occurrence of a pressure transient is indicated by a first count in the string of first count values.
As can be appreciated, a need exists for a dynamic facile, voice and virtual automated system for the representation, sorting and management of information about leaks and inventory loss in pipeline network systems through assessable web based stations.
Accordingly, it would be desirable and highly advantageous to have a real-time, computer-assisted, leak detection/location reporting and inventory loss monitoring system that overcomes the above-identified problems of the prior art.