The TUBE algorithm: Discovering trends in time series for the early detection of fuel leaks from underground storage tanks

Abstract

Abstract Leaks and spills of hazardous fluids like petroleum endanger the environment, while remediation costs and penalties imposed when petroleum contaminates the ecosystem affect economics heavily. Therefore, it is crucial to detect any possible symptoms of a leak as soon as possible. Most of existing leak detection techniques require specialized equipment to be used, while purely software-based methods rely solely on data analysis and are very desirable since they can be deployed on petrol stations without any changes to the existing infrastructure. Moreover, such techniques can be considered as complementary to the hardware leak detection systems, as they provide additional security level. In this paper we present the TUBE algorithm, which detects fuel leaks from underground storage tanks, using only standard measurements that are normally registered on petrol stations, i.e. the amount of stored, sold, and delivered fuel. The TUBE algorithm is an autonomous solution capable of making decisions independently as well as supporting human-made decisions and thus can be considered as an expert leak detection system. The TUBE algorithm introduces a new data mining technique for trend detection and cleaning data over time series, which can be easily adapted to any other problem domain. A trend detection technique, called tubes , created for the TUBE algorithm is a novel data analysis method that allows to envelop uncertainties and oscillations in data and produce stable trends. Trend interpretation technique described in this paper has been designed especially for fuel leak detection purposes using our industrial experience. This paper includes a step-by-step usage example of the TUBE algorithm and its evaluation according to the United States Environmental Protection Agency requirements for leakage detection systems (the EPA SIR standard). Such an evaluation involves calculating the probability of detection and the probability of false alarm. The TUBE algorithm has obtained 98.84% probability of detection and 0.07% probability of false alarm while rejecting 42.22% of analyzed datasets due to their uncertainty. Rejecting datasets from analysis is compliant with the EPA SIR standard; however, rejection rate higher than 20% is not acceptable. Therefore we have evaluated the two-phase filtering stage of the algorithm in order to find the best combination of filters as means of data cleaning. Moreover, we have discussed the results pointing at the overall data quality problem, since it is the main cause of rejecting some datasets from the analysis. Finally, the TUBE algorithm has obtained 93.11% probability of detection and 0.73% probability of false alarm for the best combination of all parameters with 15.56% rejection rate, which is acceptable by the EPA SIR standard. The value of probability of detection is not fully compliant with the EPA SIR standard where 95% probability of detection with probability of false alarm lower than 5% is required. We have found that the requirements for the aforementioned probabilities have been completely fulfilled for datasets representing manifolded tank systems but not for single tank datasets. Such a situation was unexpected since manifolded tank systems are generally claimed to be more complex for analysis as they are in fact systems of multiple single tanks directly connected. In this paper we have also measured the time and memory complexity of the TUBE algorithm as well as discussed the issues connected to the TUBE algorithm deployment on petrol stations using our industrial experience in the topic.