GB 5776-1986 Test method for conventional corrosion of metallic materials exposed to surface seawater
Some standard content:
National Standard of the People's Republic of China
Method for surface seawater exposure corrosion tests of metallic materialsUDC 669:620.19
GB 5776 --86
This standard applies to corrosion tests of metallic materials (including ferrous and non-ferrous metals) in surface seawater (within 10m of seawater depth) under full immersion, tidal range and splash conditions. It is the general procedure to be followed in seawater corrosion tests to unify test conditions and evaluation indicators. 1 Preparation and requirements of test specimens
1.1 Original records of test materials
The test materials must have complete original records, such as smelting, processing technology, chemical composition, mechanical properties and heat treatment status. 1.2 Surface requirements of test materials
The surface requirements of test materials are free of obvious defects, such as pitting, cracks, scratches, delamination, etc. 1.3 Specimen size
The specimen size is shown in Figure 1. Depending on the material and test cycle, the thickness can be 1.5 to 10 mm. All edges of the sample must be free of burrs. A
1.4 Sampling method
Figure 1 Sample size
8 ±1.5 ~10
Sampling can be done by shearing and gas cutting, and the heat affected zone of 20 to 30 mm should be removed from the gas cutting edge. The edge of the sheared sample should retain a processing allowance of 5 to 10 mm. When sampling, the longitudinal direction of the sample should be perpendicular to the rolling direction. All samples should be temporarily marked according to the material grade classification. 1.5 Sample processing
The surface roughness of carbon steel and low alloy steel samples is generally Ra 3.2um, and the original surface or other surface conditions can be maintained as needed. Non-ferrous metals and stainless steel generally maintain the original surface, and the surface roughness of the four sides is Ra 3.2μm. 1.6 Sample marking
National Bureau of Standards 1986-01-14 Issued
198611-01 Implementation
GB 5776-86
General metal materials use the coordinate punching method to indicate the material grade, test location, test cycle, test conditions and parallel sample serial number of the sample. The samples of corrosion-resistant materials with a short cycle can also be printed and marked. 2 Test equipment
2.1 Gold immersion and tidal range tests can use the following facilities on the premise of meeting the requirements of 4.1 and 4.2. 2.1.1 Fixed type: such as full immersion cage, tidal range platform and dock pier hanging, etc. 2.1.2 Floating type: such as floating rafts, floating tubes, etc. 2.1.3 Sample frame: The sample frame should be sturdy and durable, and can be made of metal materials, equipped with plastic spacers for insulation, and shall not be replaced during the entire test period. Copper alloy frames shall not be used to hang aluminum samples. 2.2 For splash tests, it is recommended to use a fence-type hanging rack. 2.3 Long-rule electrical connection (short specimens are connected with wires instead of long rulers) specimen rack, which can be fixed on the lifting frame or dock, dam, etc. 2.4 Specimen state determination
2.4.1' For tests without exposure requirements, such as full immersion and tidal range, the string hanging method can be adopted, as shown in Figure 2. The spacing of the string hanging specimens is determined according to different sea areas and cycles, generally between 20 and 100 mm. Figure 2 Schematic diagram of the specimen string hanging method
1 Frame, 2-Specimen, 3 Plastic spacer
4 Screw, 5-Nut
2.4.2 Splash and electrical connection specimens are single-hanging, as shown in Figure 3. 666
3 Test site requirements
GB 5776—86
Figure 3 Schematic diagram of single sample hanging method
1 Sample rack, 2 Sample, 3-Plastic spacer; 4 Plastic gasket, 5-Nut, 6-Screw cabinet
3.1 The water quality must be clean and meet the requirements of GB3097-82 "Seawater Quality Standard". 3.2 Prevent the impact of large waves, and the wave height at mid-tide is less than 0.5m. There are natural sea currents caused by tides, and the general flow rate is less than 1m/s. 3.3 There is a certain temperature difference with seasonal changes, there is a growing season for marine organisms, and there is no freezing period. 3.4 There is no large estuary nearby to prevent a large amount of fresh water from entering. 3.5 There are conditions for conducting different corrosion tests such as full immersion, tidal range, splashing and long ruler. 4
Test conditions
4.1 Full immersion test
4.1.1 Fixed full immersion: the specimen is not less than 0.8m from the seabed, and not less than 0.2m from the water surface at the lowest tide. 4.1.2 Floating full immersion: the specimen is 0.2~2m below the water surface. 4.2 Tidal range test
±0.30m of semi-average mid-tide level.
4.3 Splash zone test
0~0.6m above the average highest tide level, with sunlight exposure. 4.4 Long-ruler electrical connection test
4.4.1 There are five corrosion zones: mud, full immersion, tidal range,
splash and atmosphere.
4.4.2 The specimens are fixed on the long-ruler specimen rack at a spacing of 200mm. According to the test requirements, determine the number of parallel specimens. 667
GB5776-86
4.4.3 The specimens are connected by waterproof (multi-core) wires, and the welding points are sealed with waterproof adhesive. 4.5 Test cycle
4.5.1 The test cycle of conventional corrosion test shall not be less than 11 years. 4.5.2 For finalized materials or large-scale tests, the recommended test cycle is 1, 2, 5, 10, and 20 years. 4.6 Regularly measure the seawater temperature, dissolved oxygen, salinity, and pH value at the test point. The determination method refers to the seawater element analysis determination method in the marine survey specification.
5 Test procedure
5.1 Test preparation
5.1.1 Mark the sample after adding 1 according to 1.6. 5.1.2 Clean the surface of the sample according to Appendix A. 5.1.3 Weigh the sample, and the accuracy of ordinary carbon steel and low-gold steel is 10mg, and the accuracy of corrosion-resistant materials is 1mg. 5.1.4 Measure the dimensions with an accuracy of 0.05mm. 5.1.5 Fix the specimens in the frame according to 2.4, and strictly ensure the insulation between the specimens and the frames. 5.1.6 Record the specimen markings, weights, dimensions and the location of the specimens in detail. 5.2 Exposure test
5.2.1 The specimens are perpendicular to the sea surface and parallel to the direction of the water flow. For aluminum and aluminum alloy tests, it is strictly forbidden to hang them together with copper specimens. They should be kept at a certain distance so as not to affect the test results. 5.2.2
5.2.3 For the intermediate inspection of non-ferrous metal and stainless steel specimens, the time for the initial inspection and the intermediate inspection can be determined according to the test requirements. During the inspection process, the time of the metal out of water shall not exceed 30 minutes. 5.3 Post-test processing
5.3.1 Take out the specimens at the scheduled time, observe and record the corrosion products and marine organisms attached, and take photos as needed. 5.3.2 Remove the corrosion products mechanically (do not damage the substrate), and then treat according to Appendix B. 5.3.3
Weighing is the same as 5.1.3.
Observe and record the corrosion morphology in detail, and take photos of typical samples. 5.3.5 Calculate the corrosion rate and measure the local corrosion depth in accordance with the provisions of Appendix C. 5.3.6 Non-ferrous metal materials and stainless steel need to measure the strength loss and intergranular corrosion. 6 Evaluation of test results
6.1 Corrosion characteristics.
6.2 Average corrosion rate, expressed in mm/a.
6.3 Peripheral corrosion depth, including average depth and maximum depth, expressed in mm. 6.4 Pitting density, expressed in number of points/m2. 6.5 Mechanical property loss, expressed as the percentage of mechanical property loss. 6.6 Intergranular corrosion, observed by metallographic method.
7 Test report
7.1 Test materials, grades, chemical composition, mechanical properties, heat treatment status and sample preparation and processing methods, etc. 7.2 Test location, test conditions, test time and marine environmental factors, etc. 7.3 Corrosion characteristics, average corrosion rate, peripheral corrosion depth, etc. 7.4 Mechanical property loss and other corrosion analysis, etc. 668
Aluminum and aluminum alloys
GB5776—86
Appendix A
Cleaning of sample surface before test
(Supplement)
Remove grease from the sample surface with an organic solvent. Etch in 10% sodium hydroxide solution at 50-60℃ for 1-2 minutes. If there is an aluminum coating, remove twice the thickness of the aluminum coating. Take out and rinse with tap water.
Purify in 30% nitric acid for 2-6 minutes.
Take out and rinse with tap water.
Immerse in 70-90℃ distilled water for cleaning.
Finally blow 1 and store in a desiccator for later use. Copper and stainless steel
Use organic solvent to remove grease from the surface of the sample. Wash with anhydrous alcohol and blow, then store in a desiccator for later use. Steel, cast iron
Use detergent or organic solvent to remove grease from the surface. Rinse with tap water.
Put in anhydrous alcohol and set to bubble for dehydration.
Take out and blow, then store in a desiccator for later use. 669
B.1 Steel, cast iron
GB5776—86
Appendix B
Surface cleaning of sample after test
(Supplement)
Clean the corrosion products in acid, acid ratio: hydrochloric acid (HC1 specific gravity 1.1) 500ml, hexamethylenetetramine 20g, B.1.1
Add water to 1, remove until it is completely removed at 50℃.
B.1.2 Take out and rinse with fresh water.
Put in anhydrous alcohol to soak and dehydrate.
Take out and blow immediately, put in a desiccator for 124h and weigh again. Stainless steel
Nitric acid (HNO specific gravity 1.42) 100ml, add water to 1L. Soak at 60℃ for 20min.
After taking it out, rinse it with tap water, blow it for 1 minute, place it in a desiccator for 124 hours, and weigh it. Aluminum and aluminum alloyswww.bzxz.net
Phosphoric acid (HPO. Specific gravity 1.70) 50ml, chromic anhydride (CrO3) 20g, add water to 1L. Soak at 80-90℃ for 10min.
After taking it out, rinse it with tap water for 1 minute, blow it for 1 minute, place it in a desiccator for 124 hours, and weigh it again. Copper and copper alloys
Sulfuric acid (H2SO4, specific gravity 1.84) 100ml, add water to 1L. Soak at room temperature for 1-3min.
After taking it out, rinse it with tap water, blow it out, put it in a desiccator for 124 hours and weigh it again. Titanium and titanium alloys
Hydrochloric acid (Specific gravity of HC1: 1.19) 50ml, add water to 1L. Soak it at room temperature for a few minutes.
After taking it out, rinse it with tap water, blow it out, put it in a desiccator for 124 hours and weigh it again. C.1
Average corrosion rate
GB5776-86
Appendix C
Corrosion rate calculation and local corrosion depth measurement (supplement)
Average corrosion rate (mm/a) = (K×W)/(A×T×D) Where: K=3.65×103,
W——Corrosion weight loss of sample, g,
T —Test time, day
A-—Specimen area, cm2,
D-Material density, g/cm3.
C.2 Measurement of local corrosion depth
Select the 10 deepest pits from the two sides of each specimen (5 on each side), and pits within 5mm from the edge shall not be selected. C.2.2
Measurement reference surface
For materials with relatively typical local corrosion, such as stainless steel and aluminum alloy, the surface within 5mm around the pit is used as the measurement reference surface.
For the selection of the reference surface for measuring the pit depth of carbon steel and low alloy steel, a standard plate can be used. The standard plate can be made of glass or corrosion-resistant hard alloy. The thickness is uniform, and the tolerance is ±0.01mm. The size is 80×30mm. C.2.3 Semi-uniform Local corrosion depth: average value of the depth of 30 pits measured on three parallel samples. Maximum pit depth: maximum value of 30 pits measured on three parallel samples. C.2.4
Pitting density: use a 200×100mm (plexiglass) gridded cover plate (grid size can be 2-3cm) to count the number of pits on both sides of the sample. Then calculate the number of points/m2. Additional remarks:
This standard was proposed by the Ministry of Metallurgical Industry of the People's Republic of China. This standard was drafted by the Qingdao Marine Corrosion Research Institute of the Iron and Steel Research Institute of the Ministry of Metallurgy. The main drafter of this standard is Wang Xiangrun.
This standard refers to the American Society for Testing and Materials standard ASTMG52-76 "Recommended Implementation Standard for Seawater Exposure Test of Metal and Alloy Surfaces".
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