512 ISSN 1392−1207. MECHANIKA. 2014 Volume 20(5): 512−515 Functioning analysis of cathode protection of pipelines for transporting of natural gas through fuzzy logic V. Rafa*, E. Teutan** *Technical University of Cluj-Napoca, C. Daicoviciu no. 15, 400020, Cluj-Napoca, Romania, E-mail: raffavasile@yahoo.com ** Technical University of Cluj-Napoca, C. Daicoviciu no. 15, 400020, Cluj-Napoca, Romania, E-mail: emilteutan@yahoo.com http://dx.doi.org/10.5755/j01.mech.20.5.6144 1. Introduction Once with development of oil and gases indus- tries, it was conditioning also the necessity to create a hy- drocarbons which to be performed in safety conditions and with the possibility to seize, detect damage, respectively of accidental leakages. Especially for long pipelines which pass near to urban areas or through farmlands is necessary to exist a cathode protection system and/or an analysis method both of cathode protection parameters as of trans- porting, by following the parameters: pressure, flow, densi- ty, temperature, transporting speed etc. The purpose of this controlling and informational acquisition system – through which is following the electrical potential pipeline – sol, flows evolutions of the receiving-deliveries process is to ensure, in safety conditions, the transporting process of natural gases to consumers [1]. To prevent any accidental leakages of natural gas- es, and thus occurrence of certain corrosions, cracks on the pipeline route have developed numerous monitoring meth- ods, analysis, in by dispatching as meticulous of transport- ing parameters. In this sense was search a procedure, an algorithm through would increase the detection accuracy of the defect, and no least to reduce the detection time of the defect. In practice it is a very delicate issue to diagnose the corrosion defects and also their location in the field [2]. They are different available methods to detect and locate the leakages at the pipelines, which we propose is about the analysis of electrical potential of the pipeline beside the ground. This method is conditioned by the ne- cessity to install potential sockets along to the pipeline. It is a method through which are sequentially following the evolution of cathode protection parameters, following that by notification an anomaly – decreasing the electrical po- tential under the value to which ensure the cathode protec- tion – to determine the defect location. Because of complexity of diagnose of operation of cathode protection, on the long pipelines, a one method is not enough to analyse of qualitative operation of cathode protection. However, was a result in a combination of meth- ods, heuristic, to solve this issue. This paper proposes a monitoring method of cathode protection by using of fuzzy decision theory. 2. Control of pipe protection by DVG method With direct current voltage gradient (DCVG) equipment can be make an inspection concerning the integ- rity of cathode protection grounded. The technology of this method is characterised by investing the wide applications on the inspection activity and quality analysis of cathode protection of pipelines. This is one of the newest and more precise to detect the insulation defects. This method meas- ure with accuracy continuous current potential gradients in the mode ON – OFF being capable to determine the loca- tion, severity, the corrosive character or non-corrosive of the defects and also the possible presence of stray currents [3]. The method is based on measurement of differ- ence of potential between two points along of the pipeline, measured potential at the ground surface. When a continu- ous current is applied to a metallic pipeline grounded in a same way as the cathode protection, this current pass through the ground in the places where exist direct contact, meaning without insulation or damaged. In the defect pla- ces, as the current is higher, as the defect is much higher [4]. The current is injected on the pipeline and can be supplied by the cathode protection station or by a mobile station. The signal of continuous current is pulsating, achieving of this signal performing by installation on the electrical circuit of cathode protection station of one cyclic switch with a period of 0.3 s on the ON position and 0.7 s on the OFF position. To evidence the potential gradient on the ground, this method use a special voltmeter, ultrasensitive, which measure the potential difference between two un-polarized electrodes of Cu/CuSO 4 placed over the pipeline on the ground at a distance of approximately by 1,5 – 2 m one side by other along of the pipeline. As the operator is passing along of the pipeline, in the moment when occur a potential difference between the two electrodes, this is associated on the device’s scale with a regular motion of needle (from the analogical voltmeter from equipment configuration) which correspond with the current’s pulse. The short motion of the needle the direc- tion towards which the defect is finds. The operator motion is continuous, and when is exceeding the defect area, the needle will change its direc- tion [4]. The withdrawal of two electrodes can touch the place where the needle of the voltmeter is no longer move. In this case the defect is positioned at the middle of dis- tance between the two electrodes. The location where are intersected the medians of the segments between of two electrodes after the two direc- tions, is the exactly positioning of the defect on the pipe-