| 摘要 |
This invention, which pertains to the field of testing of the corrosion-resistance of materials, includes devices (a probe formed by a permanent reference electrode with corrosion coupons and an electronic switch) and a measurement method for evaluating the probability of corrosion of buried ducts due to alternating current (AC), and aims at providing a methodology that eliminates ohmic losses and allows the desired measurement to be obtained. For that purpose, a probe formed by a permanent copper or copper sulphate reference electrode (ECSC) with four corrosion coupons was developed, and an electronic switch which was also developed within the scope of this invention is coupled to this probe. This assembly (probe and switch), associated with a preferably portable digital oscilloscope or a data acquisition device with digital signal processing (DSP), makes it possible to obtain the waveform of the pipe/ground potential AC+DC off, and hence the peak potential of this waveform, this value being used to predict the corrosion of buried, cathode-protected ducts due to alternating current, on the basis of the criterion that corrosion due to alternating current will not occur or will be insignificant if the peak of the waveform of the pipe/ground potential AC+DC off is more negative than −0.85 VECSC. The present invention can also be directly used for monitoring external corrosion of ground ducts and to verify the real cathode protection potential of these ducts. In order to ensure the integrity of the ducts, this equipment can be installed at test points, at valve boxes and cathode protection rectifiers, as well as in zones where corrosion is suspected. |
| 主权项 |
1. “METHOD FOR IDENTIFICATION AND MEASUREMENT OF INTERFERENCE OF ALTERNATING CURRENTS IN BURIED DUCTS”, characterized in that it comprises the steps of selection of parts for installation of the probes, installation of equipment in the field; measurement procedure; Obtaining of results and analysis, in which each one consists of:
Selection of parts for installation of the probes a) Ducts in existing tracks (consolidated facilities) 1. Finding the lines of high voltage transmission and electricity distribution systems throughout range duct, and identify the operating voltage of each line, emphasizing the parallels and intersections of lines with ducts; 2. Lifting the history of external corrosion of the duct based on the results of carried out inspections correlation (indications of loss of external thicknesses indicated by instrumented PIG); 3. Raising the profile of the DC potential pipe/soil on over the entire length of the duct, using a voltmeter register and at each measurement point, raising the minimum, maximum and predominant potential and concomitantly to the records of DC potential pipe/soil on, measuring the CA effective potential pipe/soil, using a conventional multimeter, 4. Selecting the sections for installation of the probes, prioritizing data points where the largest effective potential pipe/soil on CA were obtained, in agreement with corrosion history and proximity to electric power systems (transmission lines and distribution); 5. Installing the probes in the selected regions.b) Ducts under implementation:
1. Finding the lines of high voltage transmission and electric power distribution systems throughout the track of the duct, identifying the proximity of the duct to track with electrified lines and other possible sources of interference and operating voltage of each of the lines, emphasizing the parallels and intersections of lines with ducts; 2. Installing the probes at points of intersection with the range of ducts with high voltage transmission lines.
Installation of the equipment in field 1. Identify the point of installation of the equipment (test point, valve box, rectifier, and others); 2. Checking the amount of products present on the strip, locate them and flag them indicating the position of the upper generatrix of each one and check the depth of burial; 3. Installing the probe at approximately 50 cm from the upper generatrix of the pipe, making a mark to approximately 50 cm to the right or left of signaling the upper generatrix of the duct, which opens a trench to the depth of burial of the duct, so that the probe is installed at the same level of the pipe. 4. Starting the installation procedure of the probe soon after the opening of the trench, with two corrosion coupons that must be orthogonal and two should be parallel to the duct, it is recommended that the cables from corrosion coupons and the reference electrode are housed within a flexible conduit toward the testing point, which should be taken to be connected to the duct. 5. Connecting the cables of the four corrosion coupons to the duct through the test point, and the reference electrode cable must remain isolated. 6. Ensuring the maximum degree of soil compaction in the vicinity of the probe and the electrical contact with the soil corrosion coupons and metallic titanium base. 7. Continuing the installation of the electronic switching device (DCE) putting it in series with the duct and the four corrosion coupons, already interconnected, assuring the synchronized switching of the current in the four corrosion coupons. Measurement Procedure 1. After installing the DCE, connecting the oscilloscope or a data acquisition device with digital signal processing (DSP—digital signal processing), the DCE for data acquisition, so that the “COM” terminal of the multimeter is connected to cable of the permanent reference electrode and the other end connected to the corrosion coupons. 2. Turning on the oscilloscope or the DSP, and adjusting the scale of the apparatus according to the levels of AC interference on measurement point, ensuring that at least one complete waveform of the potential AC+DC on is obtained. 3. Adjusting the scale of the device according to the levels of AC interference in the measuring point, ensuring that at least one complete waveform of the potential AC+DC off is obtained, and results should be saved and stored in the equipment.
Getting Results and analysis 1. The probes should be installed in the field for a minimum of 12 months and the electrical measurements must be performed in time intervals of up to 3 months to give the waveforms of the potentials pipe/soil AC+DC on and off, as well as the AC current circulating in each of corrosion coupons. 2. After 12 months of installing the probe, removing it to inspect and review the coupons making photographic records, and the soil adhering to the corrosion coupons should not be removed in order to avoid a distortion of the coupons and the loss of corrosion products. 3. Evaluation of corrosion coupons
After removing the coupons from the probe, they must be properly inspected and made photographic records.The soil adhering on the coupons should be removed with washing in running water, using a soft bristle brush.Making a new visual analysis with photographic records, reporting any damage to the corrosion coupon.Determining the weight loss per unit area of the coupons and the corrosion rate, and the mass loss due to corrosion obtained by the difference of the initial mass of the Coupon and the final mass after removal of the corrosion products and the corrosion rate determined by etching in Clarke solution.If it is verified the occurrence of pitting corrosion, determining the depth of pits by metallographic technique according to ASTM G 46-94 or alternatively, specially designed for the analysis of corroded surfaces, capable of providing the density and depth microscopes each of the pits. |
