GB/T 24596-2021Ductile iron pipes and fittings—Polyurethane coatings (English PDF)

3.1 Polyurethanelining

Polyurethane coating applied to the inner surface of pipes and fittings.

3.2 Externalpolyurethanecoating

Polyurethane coating applied to the outer surface of pipes and fittings.

3.3 Missing point detection holidaytest

Under specified conditions, the electrical breakdown test of the coating.

3.4 Indirect impact resistance

Under the specified conditions, the inner coating can withstand the impact energy applied from the outer surface of the tube without being damaged.

3.5 Impact resistance

Under the specified conditions, the coating can withstand impact energy without being damaged.

3.6 Specificelectricalinsulationresistance

The surface resistance of the coating perpendicular to the tube wall.

3.7 Abrasionresistance

Under specified conditions, the ability of the coating to resist wear.

3.8 Resistancetoovalization

Under specified conditions, the ability of the coating to not be damaged when deformed with the radial deformation of the tube.

3.9 Indentation resistance

Under the specified conditions, the ability of the coating to withstand the intrusion of the pressure head.

4.1 Substrate surface treatment

The surface of pipes and fittings should be sandblasted or shot blasted. Before processing, remove grease or other soluble contaminants on the surface of the substrate Quality, the surface temperature of the substrate should be greater than (dew point temperature 3) °C, and the relative humidity of the environment should be less than 85%; after treatment, the rust removal level of the surface should meet Meet the requirements of Sa2 1/2  level in GB/T 8923.1-2011; use the method in GB/T 13288.1 for surface roughness inspection, surface Roughness Ra>=12.5µm, Rz>=63µm.

4.2 Coating material requirements

4.2.1 The polyurethane coating should be a two-component solvent-free coating, one of which contains isocyanate resin and the other contains polyol Resin or polyamine resin or their mixture.

4.2.2 When the polyurethane inner coating is used to transport drinking water, it should meet the requirements of GB/T 17219 or related specifications. Qualitatively produce harmful effects.

4.3 Polyurethane coating

4.3.1 Appearance quality

4.3.1.1 The polyurethane coating shall meet the following requirements.

---The color of the coating should be uniform, and the socket can be coated with different colors;

---The coating surface should be uniform and smooth, except for repaired parts;

---The coating should have no visible defects such as pinholes, bubbles, wrinkles, cracks, etc.

4.3.1.2 Due to repair or long-term exposure to sunlight, the color or gloss of the coating surface may change slightly.

4.3.2 Thickness

The average thickness of the coating should not be less than 1000µm, and the local thickness should not be less than 900µm. If there are other requirements, it should be negotiated by the supplier and the buyer

5.1 Substrate surface treatment

5.1.1 Derusting grade

According to the requirements of GB/T 8923.1-2011.

5.1.2 Surface roughness

According to the requirements of GB/T 13288.1.

5.2 Polyurethane coating

5.2.1 Appearance quality

Visually inspect the appearance quality of the coating.

5.2.2 Thickness

5.2.2.1 A magnetic thickness gauge shall be used for testing, and the accuracy of the instrument shall be ±1%.

5.2.2.2 Randomly select 3 cross-sections from the straight pipe part of the pipe, and measure the coating thickness at 4 points spaced 90° apart from each other on each cross-section. In control Take 10 points uniformly on the surface of the part to measure the thickness of the coating.

5.2.3 Leak point detection

5.2.3.1 Use an electric spark leak detector to detect the leakage point of the coating according to the voltage required by 4.3.3. The leak detector should be equipped with a copper wire brush or other The detection electrode, the audio signal generator, the ground wire connected to the pipe wall, and the peak voltmeter are composed of conductive materials.

5.2.3.2 During the detection process, move the detection electrode along the surface of the coating, and always keep the detection electrode in close contact with the coating surface, and the moving speed Should not be greater than 300mm/s. When the detection electrode passes through the coating leakage point or the position where the thickness is too thin, the defect can be determined according to the electric spark emitted by the instrument Mark the position of the trap.

5.2.3.3 During the testing process, ensure that the coating surface is dry, and the distance between the detection electrode and the end of the pipe and the pipe fitting or its exposed surface should not be less than 13mm.

5.2.4 Adhesion

According to the requirements of GB/T 5210.

5.2.5 Hardness

The hardness measurement is carried out at 10°C~30°C, according to the requirements of GB/T 2411.

5.3 Port coating

Use a suitable measuring tool to inspect the coating thickness of the socket end, the end face of the socket and the inner surface of the socket, on each section of the pipe port Take 4 points separated by 90° to measure the coating thickness, and evenly extract 10 points from each section of the pipe fitting port to measure the coating thickness.

5.4 Type test

5.4.1 Indirect impact resistance

5.4.1.1 The sample (using a tube, pipe section or tube sheet coated with polyurethane internal coating) should be well supported and fixed to eliminate the gravity of the sample.

The impact generated by the elastic deformation caused by the action absorbs energy.

5.4.1.2 The contact part of the drop weight used in the test with the sample should be a spherical surface with a diameter of 25mm.

5.4.1.3 A 5000g drop hammer is used, the drop height is 1000mm, and the impact energy can fluctuate within 5%. Ensure that the impact energy is guaranteed.

Keep it at a stable level and try to eliminate or reduce the resistance encountered during the fall of heavy objects. The ambient temperature during inspection should be (23±2)°C, Perform at least 10 impacts on the sample, and the distance between each impact point should not be less than 30mm.

5.4.1.4 After each impact test, the internal coating shall be tested for leaks immediately in accordance with the requirements of 4.3.3.

5.4.1.5 The test report shall record the nominal diameter, wall thickness grade (or pressure grade) and impact absorption energy of the test tube.

5.4.2 Impact resistance

5.4.2.1 The sample (tubes, pipe sections or segments coated with polyurethane internal coating) should be well supported to eliminate the influence caused by the gravity of the sample. The shock generated by the elastic deformation absorbs energy.

5.4.2.2 The contact part of the drop weight used in the test with the sample should be a spherical surface with a diameter of 25mm.

5.4.2.3 A 1000g drop weight is used, and the drop height is 1000mm. Different quality drop weights and drop heights can also be selected, but they should be guaranteed The impact absorption energy reaches the requirement of 10J/mm. The impact energy can fluctuate within a range of 5%, and it should be ensured that the impact energy remains at a stable level.

At a certain level, try to eliminate or reduce the resistance encountered during the fall of the falling hammer. The ambient temperature during the test should be (23±2)°C, and the temperature should be up to Make 10 less impacts, and the distance between each impact point should not be less than 30mm.

5.4.2.4 After each impact test, the coating shall be tested for leaks immediately in accordance with the requirements of 4.3.3.

5.4.2.5 The weight and drop height of the falling weight shall be recorded in the test report.

5.4.3 Chemical resistance

5.4.3.1 Water absorption

5.4.3.1.1 The sample should be stripped coating, and its preparation method and maintenance process are consistent with the coating on the pipe and fittings. The sample size should be 40mm×125mm×(1±0.2)mm.

5.4.3.1.2 Put the sample in an oven at (50±2)°C to dry for (24±1)h, then cool to room temperature in a desiccator, weigh the sample and record, Accurate to 0.1mg; then put the samples into different containers filled with distilled water, so that they are completely immersed in distilled water, and the temperature is controlled at (50±2)°C, soak for 100d, take out the sample, quickly wipe off the water on the surface of the sample with a clean dry cloth or filter paper, weigh each sample and record, Accurate to 0.1mg, the sample should be taken out from the water to the completion of weighing should be completed within 1min. Calculate the mass change according to formula (1). C1=(m2-m1)/m1×100% (1) Where.

C1---The quality change after soaking, %; m1---The initial mass of the test, in milligrams (mg); m2---The mass of the sample after the immersion test, in milligrams (mg).

5.4.3.1.3 Then place the sample in an oven at (50±2)°C to dry for (24±1)h, then cool it to room temperature in a desiccator, and weigh each Sample and record, accurate to 0.1mg, repeat drying to constant weight of sample. Calculate the mass reduction value according to formula (2). C2=(m3-m1)/m1×100% (2) Where.

C2---The quality change after drying, %; m1---The initial mass of the test, in milligrams (mg); m3---The mass of the sample after drying, in milligrams (mg).

5.4.3.1.4 Take 3 samples and calculate the average value of the mass change as the test result of the test.

5.4.3.2 Corrosion resistance to dilute sulfuric acid

5.4.3.2.1 The sample should be peeled off coating, and its preparation method and maintenance process are consistent with the coating on the pipe and fittings. The sample size should be 40mm×125mm×(1±0.2)mm.

5.4.3.2.2 Put the sample in an oven at (50±2)°C to dry for (24±1)h, then cool to room temperature in a desiccator, weigh the sample and record, Confirm to 0.1mg; then immerse the sample in different containers containing 10% sulfuric acid solution, the temperature is controlled at (50 ± 2) °C, soak Soak for 100 days, take out the sample, quickly wipe off the solution on the surface of the sample with a clean dry cloth or filter paper, weigh each sample and record, accurate to 0.1mg, the sample is taken out from the solution to the completion of weighing should be completed within 1min. Calculate the mass change according to formula (1).

5.4.3.2.3 Then place the sample in an oven at (50±2)°C to dry for (24±1) h, then cool to room temperature in a desiccator, and weigh each Sample and record, accurate to 0.1mg, repeat drying to constant weight of sample. Calculate the mass reduction value according to formula (2).

5.4.3.2.4 Take 3 samples and calculate the average value of the mass change as the test result of the test.

5.4.3.3 Alkali corrosion resistance

According to the requirements of GB/T 26081.

5.4.4 Indentation hardness

5.4.4.1 The sample should be a polyurethane coating with a thickness of (1000 ± 90) µm on the steel plate. The preparation method and maintenance process are the same as those of the tube and tube. The coating on the parts is consistent.

5.4.4.2 The indenter used by the indenter is a metal rod with a bottom diameter of 1.8mm, with a total mass of 2.5kg, and the reading accuracy of the scale indicator is 0.05mm. The temperature control accuracy of the thermostat should be ±2°C.

5.4.4.3 After the sample is placed at (23±2)°C and adjusted for at least 1h, the indenter (without load) is slowly dropped on the sample, and the scale is adjusted within 5s.

Adjust the indicator to zero, then increase the load, and read after 24h. This value is the indentation depth of the sample.

5.4.4.4 The ratio of the average value of the indentation depth of the three samples to the average value of the coating thickness of the original sample is taken as the test result of the sample.

5.4.5 Insulation resistance

5.4.5.1 General

Cut a coated sample with an area not less than 0.03m² on each of 5 different tubes for inspection. The sample shall be in accordance with 4.3.3 A leak detection is required. Testing equipment includes electrodes with a surface area of not less than 0.001m² (such as copper electrodes), and an output voltage of not less than 50V DC power supply, ammeter and voltmeter; the detection medium is 0.1mol/L sodium chloride solution; at a temperature of (23±2)°C, the The sample is immersed in the medium for 100d.

5.4.5.2 Test device

The insulation resistance test of the polyurethane inner coating can be selected as the test device in Figure 2 a) or b), and the insulation resistance test of the polyurethane outer coating can be selected.

Figure 3 a) or b) test device.