GB/T 4157-1984 Constant load tensile test method for metal resistance to sulfide stress corrosion cracking
Some standard content:
National Standard of the People's Republic of China
Sustained load tensile test method of metals forresistanceto sulfide stress corrosion crackingUDC 669:620
.186.6
GB 4157—B4
The test method specified in this standard is to test the anti-cracking performance of metals under tensile stress in an acidic aqueous solution containing hydrogen sulfide in a laboratory.
1 Principle
1.1 Sulfide stress corrosion cracking is a delayed brittle fracture phenomenon caused by the combined action of corrosion and tensile stress (even far below the yield stress) of metals in a sulfide environment. 1.2 It is generally believed that sulfide stress corrosion cracking is caused by hydrogen embrittlement. When hydrogen atoms are released cathodeally on the metal surface (for example, due to corrosion or cathode hydrogenation), due to the presence of hydrogen sulfide (or a small amount of other compounds containing cyanide and phosphorus, arsenic, etc.), hydrogen atoms diffuse to high triaxial tensile stress areas or certain microstructure areas, and are trapped in these areas, thereby increasing the brittleness of the metal. 1.3 This test method is to immerse the specimen under tensile stress in an acidified sodium chloride aqueous solution saturated with hydrogen sulfide at room temperature and pressure. In order to obtain sulfide stress corrosion cracking data, the applied stress is added to a series of percentages of the yield strength, and the fracture time of the specimen is measured until the maximum stress at which the specimen does not fracture after 720 hours. 2 Specimens
2.1 Sample requirements: longitudinal for pipes; transverse for plates; sampling locations are carried out in accordance with relevant standards and agreements, but should be noted. 2.2 Stress corrosion tensile specimens
2.2.1 See Figure 1 for stress corrosion tensile specimens. G
Figure 1 Tensile specimen size
Standard specimen size is diameter D = 6.4 ± 0.1mm, gauge length G = 25 ± 0.5mm, transition arc radius R = 7.0mm. Non-standard specimen size is diameter D-2.5 ± 0.05mm, gauge length G = 25 ± 0.5mm, transition arc radius R = 7.0mm. Note: Non-standard specimens can be used when the test material does not meet the standard specimen size, but must be clearly stated. 2.2.2 The eccentricity between the specimen head and the specimen section shall not exceed 0.03mm. 2.2.3 In order to adapt to the connection with the loading fixture and the sealing of the container, the ends of the specimen must be long enough. 2.2.4 During machining, the specimen must be free from overheating and cold working hardening. The cutting amount of the last two passes must be less than 0.05 mm. 2.2.5 The surface finish of the specimen must not be less than FV8. 2.3 Cleaning of the specimen
Issued by the National Bureau of Standards on February 24, 1984
Implemented on January 1, 1985
GE 4157-84
2.8.1 Use tetrachloroethylene or similar solvents to remove oil stains from the specimens, rinse with acetone, and place in a desiccator until it is used. 2.3.2 Clean tweezers or gloves must be used to pick up cleaned specimens. Never touch the clean specimens directly with your hands. 2.4 Mechanical properties of specimen materials
2.4.I Conduct tensile tests in accordance with GB228-76 "Metal Tensile Test Methods" to determine the yield strength, tensile strength, elongation and cross-sectional shrinkage of the material. Tensile specimens and stress corrosion specimens should be taken from adjacent parts of the material. 2.4.2 In addition to the data specified in 2.4.1, the chemical All relevant data on composition, heat treatment system, original material dimensions, sampling location and machining process (such as cold deformation or prestrain) should be noted in the report. 2.4.3 Materials with the same chemical composition but different heat treatment systems and different microstructures should be treated as different materials. 9 Test equipment
3.1 Tensile tests should be carried out with constant load equipment or sustained load equipment. 3.1.1 Static gravity testing machines or hydraulic devices that can maintain constant pressure in the hydraulic chamber can be used for constant load tests. 3.1.2 Sustained load tests can be carried out with spring-type devices and test pieces, requiring that the load reduction caused by relaxation of the fixture or specimen be reduced to a minimum.
3.2 The specimen must be electrically insulated from any other metal in contact with the test solution. 3.3 The seal around the specimen must be electrically insulating and airtight, but the friction generated by the seal when the specimen is displaced must be small enough to be ignored.
3.4 If the entire test apparatus needs to be immersed in the test solution, the specimen must be electrically insulated from the loading fixture and other metal parts, and the fixture must be made of materials that are not sensitive to sulfide stress cracking. Fixtures that are sensitive to cracking must be thoroughly coated with a non-conductive and impermeable coating.
3.5 Test container
3.5.1 The size and shape of the test container depends on the actual The force-adding device of the testing machine. 3.5.2 Before the test begins, oxygen in the container should be removed, and during the test, air should not enter the container. A small outlet trap should be installed on the flow line of hydrogen sulfide, and positive pressure should be maintained in the test container to prevent oxygen from diffusing into the container through small leaks or from the exhaust line.
3.5.3 During the test process 4, due to the consumption of acetic acid, the pH value increases with time. In order to make the pH value increase rate relatively stable, the volume of the test container should be able to maintain 20~100ml of solution per square centimeter of sample area. 3.5.4 The container and the central tool materials should be basically inert. 4 Test conditions and test steps
4.1 Reagents
4.1.1 Purity of reagents
4.1.1.1 Hydrogen sulfide, sodium chloride, and acetic acid should all be chemically pure chemicals. 4.1.1.2 Distilled water or deionized water should be used. 4.1.2 Solution preparation
4.1.2.1 Dissolve 50g sodium chloride and 5g glacial acetic acid in 945g water. The initial acidity should be close to pH 3. The pH may increase during the test, but not more than 4.5.
4.2 The temperature of the test solution should be maintained at 24±3℃. 4.3 Test steps
4.3.1 Sample loading and test start
4.3.1.1 Test sequence
: Place the cleaned sample into the test container and connect the necessary sealing device, then purge the test container with inert gas. b. After the test container is purged, load it carefully and do not exceed half of the set loading water. c. Immediately inject the deaerated solution into the test container, and then pass hydrogen sulfide at a flow rate of 100~200ml/min for about 10~15min, GB4157-84
to saturate the solution with hydrogen sulfide, and record the start time of the test. d. During the test, hydrogen sulfide must continue to flow through the test container and the outlet trap at a rate of several bubbles per minute, so that the hydrogen sulfide concentration is maintained and a small positive pressure is maintained, thereby preventing air from entering the test container through the leak. e. When testing certain high-alloy corrosion-resistant materials, in order to prevent the re-formation of the protective film, it is necessary to change the loading sequence to a, c, b. (If the test is carried out in this order, it should be noted in the report). 4.3.2 Detection of Destruction
4.3.2.1 Record the fracture time with an electric timer and a microswitch. 4.3.2.2 The tensile specimen can be loaded to a series of percentage increments of the yield strength. 4.3.2.3 In order to strictly determine the stress of failure and non-destruction, additional specimens should be tested. 5 Report of Test Results
5.1 At each stress level, the fracture time and non-destruction data obtained must be reported. 5.2 The chemical composition, heat treatment system, original material size, sampling location, mechanical properties and other data obtained for all steel materials should be reported.
5.3 The test results shall be reported in Table 1, Table 2 or in figures. Table 1 Composition and properties of test specimens
Chemical composition, distance
Applied stress
kg/mm2
Breaking time
Heat treatment system
kg/mm2
Machine properties
Table 2 Test results
kkgf/mm2
Material: bzxZ.net
Chemical composition:
Mechanical properties,
Others:
GB 4157-84
Breaking time, h
Breaking time, b
A.1 Toxicity
GE 4157--84
Appendix A
Safety precautions when handling hydrogen sulfide
(Supplement)
Hydrogen sulfide may cause more industrial poisoning accidents than any other single chemical. Therefore, hydrogen sulfide should be handled with caution. All experiments using hydrogen sulfide should be carefully arranged. According to the emission standards for hazardous substances in industrial enterprises, the maximum allowable concentration of hazardous substances in the atmosphere of residential areas is 0.01 mg/m\, and the maximum allowable concentration for air in places where work is carried out for more than 8 hours is 20 mg/m. The latter concentration has greatly exceeded the level that the membrane can detect, but the membrane nerves will become dull in such an atmosphere. Therefore, the membrane sense is not a completely reliable alarm system.
The following briefly explains the physiological response of humans to various concentrations of hydrogen sulfide. In the concentration range of 230-310 mg/m2, long-term stay will cause pulmonary edema. The signs of poisoning in this concentration range are nausea, back pain, hiccups, coughing, headache, dizziness and watery feet. Under this subacute exposure, pulmonary complications such as pneumonia are very likely to occur. Under the condition of 770 mg/m\, unconsciousness usually occurs within 30 minutes, and acute poisoning reactions occur. In the range of 1080-1540 mg/m\, unconsciousness occurs in less than 15 minutes, and death occurs within 30 minutes. When the concentration exceeds 1540 mg/m\, a deep breath will cause instantaneous unconsciousness, followed by rapid death due to complete respiratory failure and cardiac arrest.
A,2 Fire and explosion hazards
Hydrogen sulfide is a flammable gas, and the combustion product is toxic sulfur dioxide. In addition, the explosion limit of hydrogen sulfide in air ranges from 4 to 46%, and appropriate precautions should be taken to prevent these hazards. A,3 Some suggestions for experimental work
All tests should be carried out in a well-ventilated gas cabinet that can exhaust all hydrogen sulfide. The flow rate of hydrogen sulfide should be kept very small to minimize the amount of hydrogen sulfide discharged. In order to further reduce the amount of hydrogen sulfide gas discharged, the outflowing gas can be absorbed by 10% NaOH solution. This solution needs to be renewed regularly. Measures should be taken to prevent the sodium hydroxide solution from flowing back into the test container when hydrogen sulfide is interrupted. Where hydrogen sulfide is used in work, appropriate safety facilities should be prepared. Special attention should be paid to the output pressure on the pressure regulator, because the downstream pressure increases due to blockage by corrosion product fragments, etc., which interferes with the low flow rate regulation. The gas cylinder should be firmly fixed to prevent the cylinder from tipping over and the head from being damaged. The hydrogen sulfide in the cylinder is in liquid state. When the last bit of liquid hydrogen sulfide evaporates, the time it takes for the pressure to drop from 17kgf/cm to atmospheric pressure is relatively short. Therefore, the high pressure gauge should be checked frequently. When the pressure drops to 5-7 kkl/cm2, the control of the regulator may become passive, and the cylinder should be replaced. It is not allowed to stop the gas flow without closing the valve or disconnecting the air inlet pipeline. Otherwise, the solution will continue to absorb hydrogen sulfide and flow back into the pipeline, regulator, and even into the hydrogen sulfide cylinder. A check valve should be installed on the pipeline. Under normal working conditions of the check valve, the above problems can be prevented. In the event of such an accident, the remaining hydrogen sulfide should be discharged as quickly and safely as possible, and the manufacturer should be notified to pay special attention to this cylinder.
B.1 Reasons for requiring electrical insulation of the specimen
GB 4157-84
Appendix B
Explanation of the test method
(Supplement)
Electrical potential is one of the factors that strongly affect stress corrosion cracking of metal sulfides. In laboratory tests or field conditions, due to lack of insulation or poor insulation, dissimilar metals are coupled, causing changes in corrosion potential and changing the mechanism of sulfide stress brain corrosion cracking. B.2 Reasons for excluding and isolating oxygen
In field and laboratory studies, the important influence of oxygen has been noted. Therefore, it is considered very important to obtain an environment with minimal dissolved oxygen pollution and maintain this condition. In salt water containing hydrogen sulfide, oxygen pollution can cause a sharp increase in corrosion rate by two orders of magnitude. In general, oxygen can also reduce the release of hydrogen and reduce the entry of hydrogen into the metal. However, systematic studies on the parameters that affect these phenomena have not been reported in the literature.
In the absence of sufficient data to determine and clarify the effects of these phenomena on sulfide stress corrosion cracking, it is considered that all reasonable precautions should be taken to exclude and isolate oxygen. B.3 Reasons for the purity requirements of reagents
There are two main concerns about impurities in water. One is the alkaline and acidic buffer components, which will change the pH of the test solution. The other is organic and inorganic compounds, which will change the nature of the corrosion reaction. Oxidants will convert part of the hydrogen sulfide into soluble products, such as polysulfides and polythionic acids, which will also affect the corrosion process. In order to obtain a lower partial pressure of hydrogen sulfide in the gas, nitrogen (or other inert gases) must be continuously mixed with hydrogen sulfide, so that a lower concentration of hydrogen sulfide can also be obtained in the solution. In this case, the presence of trace impurities of oxygen in nitrogen or other inert gases is extremely critical. The accumulation of oxidation products leads to changes in the corrosion rate and (or) changes in the rate of hydrogen incorporation into the metal. 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 Iron and Steel Research Institute of the Ministry of Metallurgical Industry. The main drafters of this standard are Chen Shujun and Ying Zichun.2. Rationale for exclusion and isolation of oxygen
In field and laboratory studies, the important influence of oxygen has been noted. It is therefore considered very important to obtain and maintain an environment with minimal dissolved oxygen contamination. In brines containing hydrogen sulfide, oxygen contamination can cause a dramatic increase in corrosion rates by up to two orders of magnitude. Oxygen can also reduce hydrogen evolution and reduce hydrogen incorporation into metals. However, a systematic study of the parameters that influence these phenomena has not been reported in the literature.
In the absence of sufficient data to determine and clarify the effects of these phenomena on sulfide stress corrosion cracking, it is considered that all reasonable precautions should be taken to exclude and isolate oxygen. B.3 Rationale for reagent purity requirements
There are two main areas of concern for impurities in water. One is alkaline and acidic buffer components, which change the pH of the test solution. The other is organic and inorganic compounds, which change the nature of the corrosion reaction. Oxidants can convert part of the hydrogen sulfide into soluble products, such as polysulfides and polythionic acids, which also affect the corrosion process. In order to obtain a lower partial pressure of hydrogen sulfide in the gas, nitrogen (or other inert gases) needs to be continuously mixed with hydrogen sulfide, so that a lower concentration of hydrogen sulfide can also be obtained in the solution. In this case, the presence of trace impurities of oxygen in nitrogen or other inert gases is extremely critical. The accumulation of oxidation products leads to changes in corrosion rate and (or) changes in the rate of hydrogen entry into the metal. 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 Iron and Steel Research Institute of the Ministry of Metallurgical Industry. The main drafters of this standard are Chen Shujun and Ying Zichun.2. Rationale for exclusion and isolation of oxygen
In field and laboratory studies, the important influence of oxygen has been noted. It is therefore considered very important to obtain and maintain an environment with minimal dissolved oxygen contamination. In brines containing hydrogen sulfide, oxygen contamination can cause a dramatic increase in corrosion rates by up to two orders of magnitude. Oxygen can also reduce hydrogen evolution and reduce hydrogen incorporation into metals. However, a systematic study of the parameters that influence these phenomena has not been reported in the literature.
In the absence of sufficient data to determine and clarify the effects of these phenomena on sulfide stress corrosion cracking, it is considered that all reasonable precautions should be taken to exclude and isolate oxygen. B.3 Rationale for reagent purity requirements
There are two main areas of concern for impurities in water. One is alkaline and acidic buffer components, which change the pH of the test solution. The other is organic and inorganic compounds, which change the nature of the corrosion reaction. Oxidants can convert part of the hydrogen sulfide into soluble products, such as polysulfides and polythionic acids, which also affect the corrosion process. In order to obtain a lower partial pressure of hydrogen sulfide in the gas, nitrogen (or other inert gases) needs to be continuously mixed with hydrogen sulfide, so that a lower concentration of hydrogen sulfide can also be obtained in the solution. In this case, the presence of trace impurities of oxygen in nitrogen or other inert gases is extremely critical. The accumulation of oxidation products leads to changes in corrosion rate and (or) changes in the rate of hydrogen entry into the metal. 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 Iron and Steel Research Institute of the Ministry of Metallurgical Industry. The main drafters of this standard are Chen Shujun and Ying Zichun.
Tip: This standard content only shows part of the intercepted content of the complete standard. If you need the complete standard, please go to the top to download the complete standard document for free.