According to the oil and gas industry standard SY/T 0315-97, the cathodic disbonding resistance test of the coating is carried out as follows.
(1) Equipment required for the test
①Adjustable DC stable speed power supply;
②Hot plate or oven, the temperature accuracy is ±3°C;
③Steel platter filled with quartz sand;
④ calomel electrode;
⑤ Platinum wire into carbon electrode;
⑥Plastic cylinder with an inner diameter of 75mm ± 3mm;
⑦3% NaCl solution;
⑧Universal pocket knife.
(2) Test piece
The size of the test piece painted in the laboratory is about 100mmX100mm. The size of the pipe section test piece is 100mmX100mmxpipe wall thickness. The number of test pieces in each group is 2 pieces.
(3) Test procedure
① This test should use the test piece that has been confirmed to have no leaks, and the minimum leak detection voltage of the electric spark leak Detector should be 1800V.
② Drill a blind hole with a diameter of 3.2 mm in the center of the test piece, through the coating, to expose the steel substrate.
③Place the center of the plastic cylinder on the test piece with the alignment hole, and glue it with sealing glue, so there should be no water leakage.
④ Inject at least 300mL of NaCl solution into the cylinder, and draw the liquid level position mark on the cylinder. Insert the electrode into the solution and connect it to the positive pole of the DC power supply, and then connect the test piece with the exposed blind hole to the negative pole.
⑤ Apply voltage to the test piece (apply voltage to the calomel reference electrode), and keep the temperature constant under one or more of the following test conditions.
a.1.5V, 20℃±3℃, 28d;
b.1.5V, 65℃±3℃, 48h;
c. 3.5V, 65℃±3℃, 24h.
During the test, distilled water was added directly to maintain the liquid level.
⑥After the above test is completed, dismantle the electrolytic cell, remove the test piece, and cool it to 20°C ± 3°C in the air. Within 1h of starting to remove the power supply, test the resistance to cathodic disbonding of the specimen.
⑦ With the blind hole as the center, use a knife to draw the radial line, as shown in Figure 6-26. The line shall penetrate the coating to the substrate and extend at least 20 mm from the blind hole.
⑧Use the tip of the knife to start from the mouth hole, insert it under the coating, and use horizontal force to pry the coating along the radial direction until the coating shows obvious prying resistance.
⑨Starting from the center of the hole, measure the distances of each prying strip, and calculate the average value, which is the cathodic stripping distance of the test piece.
(4) Result representation
Use the arithmetic mean of the bright pole peeling values of two parallel test specimens as the cathodic peeling value of this group of test pieces.
