This standard specifies the test equipment, sample preparation, test conditions, test procedures, test result evaluation and test report for the test method of cathodic disbonding resistance of anti-rust paint. This standard is applicable to the test method of cathodic disbonding resistance of single-layer or multi-layer protective coatings of ships and marine structures under cathodic protection in marine environments. GB/T 7790-1996 Test method for cathodic disbonding resistance of anti-rust paint GB/T7790-1996 Standard download decompression password: www.bzxz.net

National Standard of the People's Republic of China
Test method for the resistance of cathodic disbondment of anticorrosive paint1 Subject content and scope of application
GB/T7790-1996
Replaces GB7790-87
This standard specifies the test device, sample preparation, test conditions, test procedures, test result evaluation and test report for the test method of cathodic disbondment resistance of anticorrosive paint.
This standard is applicable to the test method for the resistance of cathodic disbondment of single-layer or multi-layer protective coatings of ships and marine structures under cathodic protection in marine environments.
2 Reference standards
GB712 Structural steel for hull
GB8923 Rust grade and rust removal grade of steel surface before painting GB9277.2 Evaluation of aging of paint coating Part II: Evaluation of blister grade GB/T13288 Evaluation of surface roughness grade of steel before painting (comparison sample method) GB/T13452.2 Determination of film thickness of paint and varnish SY J19 Technical standard for application of magnesium alloy sacrificial anode 3 Terminology
3.1 Cathodic stripping
Due to the action of cathode products, the adhesion between the coating and the substrate is destroyed. 3.2 Test potential
The potential of the sample coated with anti-rust paint under cathodic protection relative to the reference electrode. 3.3 Sample edge effect area
The area within 10mm of the sample edge.
3.4 ​​Sample effective area
The test area excluding the sample edge effect area. 4 Test capacity
The schematic diagram of the test device is shown in Figure 1. The test container is a circular plastic trough with a diameter of not less than 500 mm and a height of not less than 400 mm, equipped with a cover, a sample holder, etc. Approved by the State Administration of Technical Supervision on January 25, 1996 and implemented on October 1, 1996
5 Sample preparation
GB/T7790—1996
Figure 1 Schematic diagram of the test apparatus
1--Circular plastic tank+2-Test sample; 3-Reference electrode (SCE)+4-Terminal; 5-Pocket digital multimeter, 6-Bolt connector, 7-Slot cover, 8-Overflow, 9-Magnesium anode, 10-Sea water, 11-Drain 5.1 Unless otherwise specified, the base material of the sample shall be hot-rolled ordinary carbon steel as specified in GB712, with a size of 250mm×150mm×2mm. The edges shall be free of burrs and rounded corners. A connecting hole with a diameter of 5mm shall be drilled on the center line of any of the two short sides at a distance of 6mm from the edge, as shown in Figure 2.
GB/T7790—1996
Figure 2 Test specimen
5.2 Unless otherwise specified, the test specimen shall be prepared according to the rust removal grade requirements of Sa? special wire grade in GB 8923. The surface roughness shall be in accordance with GB/T13288, R, 40~70μm.
5.3 Use M5, 10mm long screws, copper nuts and copper washers to fix a copper wire with a length of 600mm and a core diameter of 1mm with plastic insulation to the connection hole of the test specimen base. After connection, use a multimeter to measure the conductivity of the connection between the wire and the base, and the resistance value should be less than 0.01Ω. After checking the connection between the wire and the base, use epoxy adhesive or other equivalent adhesive to coat the connection point for insulation and sealing.
5.4 The coating of the test specimen shall be applied and dried according to the technical requirements of the coating product. 5.5 The coating thickness of the sample shall be measured and recorded in accordance with the provisions of GB/T13452.2, and the integrity of the coating shall be checked at low voltage (67.5V) using a wet sponge pinhole detector. If the coating has defects such as pinholes, it shall be repaired. 5.6 Before starting the test, an artificial coating leakage hole shall be opened in the center of each sample (as shown in Figure 2). The hole is a circular hole with a coating diameter of 6mm removed. A flat-head drill with a diameter of 6mm shall be used to make the hole smooth and the hole shall not penetrate the metal base plate. All coatings in the hole shall be removed to expose the bright metal. 5.7 For each single-layer or multi-layer protective coating, a sufficient number of samples shall be prepared, at least three, and three control samples of the same coating shall also be prepared. They are not connected to the cathodic protection system during the test. 6 Test conditions
6.1 The test medium is filtered natural seawater or artificial seawater. The formula of artificial seawater is shown in Appendix A (reference). 6.2 The test temperature is 23±2℃. If it is not possible to adjust the seawater temperature to 23 ± 2℃, it can be determined according to environmental conditions, but the temperature of the electrolyte in the container should be measured and recorded regularly. GB/T7790-1996
6.3 The test potential is determined by the magnesium alloy sacrificial anode, and the performance should comply with the provisions of SYJ19. The magnesium anode is a round rod with a diameter of 52mm and a length of 240mm, and weighs about 1kg (including an M12×30mm steel bolt buried in the anode). 7 Test procedure
7.1 Check, record and take photos of the sample before the test. 7.2 Inject natural seawater or artificial seawater into the plastic tank, adjust the water temperature to the test temperature, and add tap water every day to maintain the original liquid level in the container.
7.3 Suspend the magnesium anode in the center of the container, and the samples are arranged equidistantly from the anode along the four sides of the container, and the artificial leakage hole in the sample faces the anode. Each sample is not less than 150mm away from the anode and not less than 50mm away from the bottom of the container. Make sure that the sample is completely soaked and that the samples do not touch each other or the container wall.
7.4 If the space in the container allows, place the control sample in an appropriate position, but do not connect the control sample to the anode. If the space in the container is limited, place the control sample in another container whose test medium and environmental conditions are consistent with those of the test container, and explain it in the test report.
7.5 Place the reference electrode near the sample, but do not block the artificial leakage hole. 7.6 Use a bolt connector to connect the wire of each sample to the anode wire. Measure the potential between the sample and the reference electrode as the test potential, and keep the potential stable during the test.
7.7 The test cycle is 30 days. The test potential and the coating of the sample should be checked once a day in the first week of the test, and twice a week from the second week onwards. Detailed records should be made after each inspection. During the inspection, take out the sample, rinse it carefully with tap water, wipe it gently with filter paper or soft cloth, check the coating for blistering, peeling and other damage, and then put it back into the plastic tank. If the coating surface changes significantly, additional photos should be taken. 7.8 After the test, rinse each sample thoroughly with tap water and handle carefully without damaging the coating. 8 Evaluation of test results
8.1 First, make a visual inspection of the sample. Record the density, size and distance of the bubbles from the artificial leak hole, and evaluate according to the requirements of GB9277.2. If the back of the sample is also coated with the same coating, the same inspection is also carried out. 8.2 Check the situation of reduced adhesion of the coating around the artificial leak hole (i.e. cathodic peeling): Use a sharp and small force to gently peel off all loose coatings or peeled coatings along the bottom of the coating at the edge of the artificial leak hole, calculate the peeling area of ​​the effective area of ​​the sample, and take photos of each sample after inspection.
8.3 Make the same inspection on the control sample according to the requirements of Articles 8.1 and 8.2. 9 Test report
The test report shall include at least the following contents:
Standard number used in the test,
Type, name and code of the test coating, test conditions,
Average thickness of the coating of each sample;
Condition and degree of blistering of the coating of each sample; Area of ​​coating peeling around the artificial coating hole of each sample, Photographs of each sample after visual inspection and coating peeling, h.
Condition of the coating of the control sample after the test;
Inspection date and inspector.
A1 Formula 1
GB/T7790-1996bzxz.net
Appendix A
Artificial seawater formula
(reference)
Use 10g of each industrial grade salt of sodium chloride, sodium sulfate and sodium carbonate calculated in anhydrous state, dissolve in tap water and dilute to a total of 1L.
Formula 2
23g sodium nitride (NaCl), 8.9g sodium sulfate 10H2O (NazSO4·10H2O), 9.8g magnesium chloride 6H2O (MgCl26H2O) and 1.2g calcium chloride anhydrous (CaCl2) are dissolved in tap water and diluted to a total of 1L. Additional remarks:
This standard is proposed by China State Shipbuilding Corporation. This standard is under the jurisdiction of the National Technical Committee for Standardization of Marine Ships, Marine Materials Application Technology Subcommittee. This standard was drafted by Luoyang Marine Materials Research Institute. The main drafter of this standard is Jin Xiaohong.
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