GB/T 15970.5-1998 Corrosion of metals and alloys - Stress corrosion testing - Part 5: Preparation and application of C-ring specimens
Some standard content:
GB/T15970.5—1998
This standard adopts the international standard ISO 7539-5:1989 "Stress corrosion testing of metals and alloys - Part 5: Preparation and application of C-ring specimens".
GB/T15970 includes the following parts under the general title of "Corrosion stress corrosion test for metals and alloys": Part 1: (GB/T15970.1-1995) General principles of test methods Part 2: Preparation and application of bent beam specimens Part 3: (GB/T15970.3-1995) Preparation and application of U-shaped bending specimens Part 4: Preparation and application of uniaxially loaded tensile specimens Part 5: (GB/T15970.5-1998) Preparation and application of C-shaped ring specimens Part 6: (GB/T15970.6-1998) Preparation and application of pre-crack specimens Part 7: Slow strain rate test
Part 8: Preparation and application of welded specimens Parts 2, 4.7 and 4.8 will be formulated in succession. Appendix A of this standard It is the appendix of the standard. This standard was proposed by the former Ministry of Metallurgical Industry.
This standard is under the jurisdiction of the former Information Standards Institute of the Ministry of Metallurgy. The drafting units of this standard are the former Iron and Steel Research Institute of the Ministry of Metallurgy, the Upstream Nuclear Engineering Research and Design Institute, and the former Information Standards Institute of the Ministry of Metallurgy. The main drafters of this standard: He Mingshan, Zhou Mingyao, Ji Xiaochun, Liu Ze, GB/T15970.5—1998
ISO Foreword
ISO (International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member groups). The formulation of international standards is formally carried out through ISO technical committees. For a certain topic Each member body interested has the right to participate in the technical committee established for the subject. International organizations, governmental and non-governmental organizations collaborating with ISO may also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IFEC) on all matters of electrotechnical standardization.
Draft international standards adopted by technical committees are adopted as international standards by ISO committees after they have been circulated and approved by the member bodies. According to ISO procedures, a draft requires at least 75% of the member bodies to vote in favor for it to be adopted. International Standard ISO7539-5 was developed by ISO/TC15G* Technical Committee "Corrosion of metals and alloys". ISO 7539 is under the general title of "Corrosion stress corrosion testing of metals and alloys" and includes the following parts: Part 1: General test methods
Part 2: Preparation and application of bent beam specimens Part 3, Preparation and application of U-shaped bend specimens Part 4: Preparation and application of uniaxially loaded tensile specimens Part 5: Preparation and application of C-ring specimens Part 6: Preparation and application of pre-cracked specimens Part 7: Slow strain rate test
Part 8: Preparation and application of welded specimens Annex A constitutes an integral part of ISO7539-5. GB/T15970.5—1998 ||tt ||This standard is one of the GB/T15970 series of standards, which provides test procedures for designing, preparing and applying different types of test specimens to evaluate the performance of metals against stress corrosion. When using any standard in this series of standards, the relevant provisions of GB/T15970.1 must be read. This helps to select appropriate test procedures for specific environments and also helps to provide guidance on the importance of evaluating test results. 1 Scope
National Standard of the People's Republic of China
Corrosion of metals and alloys Stress corrosion testing Part 5: Preparation and application of C-ring test specimens of metals and alloy---Stress corrosion testingPart 5.Preparation and use of C-ring specimensGB/T 15970.5—1998
idt Iso 7539-5:1989
1.1 This standard covers the design, preparation, loading, exposure and inspection of C-ring specimens used to test the stress corrosion sensitivity of metals and alloys. It provides analysis of the stress state and distribution of C-ring specimens. The word "metal" in this standard also includes alloys. 1. 2C Type bad, Kun - a widely used and economical specimen for determining the sensitivity of various metals to stress corrosion cracking. It is suitable for a variety of product forms including weldments. It is particularly suitable for testing pipes, samples and plates (see Figure 1). It can also be used with a test group with a notch (see 5.3.8) 1.3 The type ring specimen can be loaded to the preset value using a simple load or constant strain device. 2 Reference standards
The provisions contained in the following standards constitute the provisions of this standard through reference in this standard. At the time of publication of this standard, the versions shown are valid. All standards will be revised, and parties using this standard should explore the possibility of using the latest versions of the following standards. GB/T15970, 1-1995 Corrosion and stress corrosion testing of metals and alloys Part 1: General test methods (B/I 15970.61998
Corrosion and stress corrosion testing of metals and alloys Part 6: Preparation and application of pre-cracked specimens 3 Definitions
GB/T The definitions given in 15970.1 apply to this standard. A. Principle
4.1 The test consists of subjecting the specimen to a constant load or constant strain. The purpose is to determine the stress corrosion susceptibility of the specimen with reference to one or more parameters given in Section 1.
4.2 The corrosive environment may cause the material to deteriorate more when stressed than when unstressed in the same environment. The degree of this degradation may be expressed in several different ways to assess the stress corrosion susceptibility. 4.3 The most common form of damage caused by stress corrosion involves the initiation and propagation of cracks. When the test is conducted for an appropriate period of time, one or more cracks may eventually lead to the failure of the specimen. 4.4 Even with nominally identical specimens, the test results for a given environment may vary greatly, so repeated tests are often necessary. The differences may be even greater if the specimens are of different size, orientation, or loading method. 4.5 The time required for cracks to appear after exposure of the stressed specimen to the test environment or the critical stress below which no cracks will appear may be used to assess the material's resistance to stress fanning at the stress levels actually used in the test environment. Approved by the State Administration of Quality and Technical Supervision on December 7, 1998 and implemented on July 1, 1999
Long section
GB/T 15970.51998
Rods and bars
Short section
Sampling methods for various products
5 Test specimens
5.1 Test specimen design
GB/T15970.5-1998
5.1.1 The size of C-rings varies within a wide range, but C-rings with an outer diameter less than 15 mm are not recommended, otherwise it will increase the difficulty of machining and reduce the accuracy of loading. The size of the ring affects the stress state, which is discussed in Section 5.2. Figure 2 is a T diagram of a C-ring showing typical sizes.
5.1. 2 When testing thick sections of material with only a fixed grain structure, it is important to make the principal stress of the C-ring perpendicular to the plane with the lowest stress corrosion cracking resistance. Otherwise, cracks may occur somewhere outside the center of the ring, where the stress is unknown and lower than the calculated value (see 5.3.3). The processing personnel should provide appropriate processing. C-ring specimens can also be made into notched or prefabricated fatigue cracked specimens, and their stress states are considered in 5.3.8 and GB/T15970.6 respectively. 19 millimeters small!
5.2 Stress analysis
Example of C-ring specimen
Net system is still ±n,05
5.2.The main stress on the C-ring specimen is the circumferential stress. This stress is an uneven stress that changes gradiently along the thickness direction, that is, from the tensile stress on a certain surface to the maximum compressive stress on the opposite surface. The stress also changes around the circumference of the C-ring - from zero at each hole to the maximum value across the width of the body at the center of the arc opposite the loaded screw. If the strain should be the maximum value of the ratio of width to thickness, the stress value calculated by A (Annex of the Standard) only represents the strain value measured on the tensile stress surface of the C-ring in the arc. The change along the width of the body is determined by the change in the degree of the trial determination of the ring. When loaded in the manner shown in Figure 3b), the tensile stress on the outer surface is smaller near the edge than in the center. The stress is the transverse and circumferential stress. The transverse stress has the same sign as the circumferential stress from the center of the width. Generally speaking, transverse stress decreases with increasing width and thickness. In the case of C-rings, there is axial stress near the root of the notch. Here, the circumferential stress at the root of the notch will be greater than the calculated stress. When machining C-rings with materials that have obvious residual stresses, or heat treating (including economic) the C-rings that have been machined, these internal stresses can lead to errors in the calculated stresses. In order to calculate the residual stress in the pipe, there may be internal stresses in the pipe. When measuring the pipe diameter before and after the axial cutting section, the diameter of the pipe must be measured. 5.2.5 It should be considered that the specimen is exposed ( The potential for stress relaxation during the test is particularly high temperature. If the auxiliary variables of the ring and the bolt can be obtained, this stress relaxation can be estimated: Note: If the ring and bolt have different thermal expansion coefficients during the test, the applied stress may change significantly. Similarly, if plastic insulators are used to avoid electrochemical corrosion, the possibility of stress relaxation should also be predicted. 5.3 Loading method 5.3.1 C-ring specimens are usually loaded with constant displacement, that is, the bolts are tightened in the direction of the ring diameter, and tensile stress is generated on the outer surface of the ring (see Figure 3a). 2 C-rings can also be loaded in the opposite direction by opening the ring to generate tensile stress on the inner surface (see Figure 3c), or preferably by using a wedge-shaped tensioning technique, so that the two arms of the C-ring are displaced outwards as shown in Figure 4. The required displacement is achieved by inserting a precision machined strain gauge, which should be made of the same material as the C-type strain gauge to avoid galvanic effects. Figure 4 shows a suitable type loading fixture: 5.3.3 The type ring test can be modified to use a properly calibrated spring placed on the loading screw to make it a test under approximately constant load conditions (see Figure 3b)).
) Constant strain
b) Constant load
Figure 3 Loading method for C-type ring specimens
) Constant strain
5.3.4 The most accurate loading method is to attach circumferential transverse resistance strain gauges to the tensile stress surface and then tighten the bolts until the strain measurement reaches the required circumferential stress. Circumferential stress {. and transverse stress, as long as they are within the elastic range, can be calculated as follows: E
Where: E-
elastic modulus, Pa;
Poisson's ratio!
Circumferential strain:
Transverse strain.
(e + er)
When using resistance strain gauges on thin rings, corrections will be allowed for the displacement of the strain gauges on the ring surface. All traces of strain gauges and adhesives must be removed from the rings during exposure tests. When calculating stresses above the elastic limit, this can be done on the basis of elastic-plastic analysis. 5.3.5 When loading several C-rings of the same alloy and opposite sizes, in order to avoid the trouble of measuring each ring, a calibration curve of circumferential stress versus ring tension can be determined.
5.3.6 In the C-ring 1, only the degree of compression and elastic strain required to produce elastic strain can be calculated in theory. Therefore, the C-ring can be loaded according to the modified bending beam formula shown in Appendix A, substituting the size of each member, and then loading according to the calculated deflection required to produce the predetermined elastic stress. Experience has shown that the stress calculated by this method is in good agreement with the stress measured by the strain gauge attached to the specimen. GB/T15970.5—1998
5.3.7 In addition, to calculate the stress-strain distribution of the entire C-ring specimen 1 under different applied displacements, the finite element stress analysis method can be used for calculation. This analysis should be performed using a compiled finite element program by personnel who are fully familiar with finite element technology. For specimens with complex geometric shapes and loading methods, simple theoretical analysis cannot be used for calculation, and this finite element stress analysis method is usually used for calculation.
5.3.8 For the "Van notch specimen (see 5.2. 3) The nominal stress is sieved using the outside diameter of the measuring ring at the root of the notch. The maximum stress at the notch is then calculated from the product of the nominal stress and the stress concentration factor Kt for the specific notch. 5.4 Machining and surface treatment
5.4.1 In addition to the requirement to inspect the original surface of the tube or bar, corrosion testing always requires that the specimens have a high-quality machined surface. When using solid blanks to add T-ring specimens, overheating, plastic deformation or residual stress on the metal surface should be prevented during operation. Machining should be carried out in stages, and the root mean square roughness of the main surface after the last cutting operation is equal to or less than 1 mm. Grinding, mechanical polishing and other similar operations that can cause plastic flow of the metal should be avoided. 5.4.2 The surface of the specimen should be treated to remove the seam before exposure. Chemical and electrochemical methods can be used to remove oxide films or thin deformation layers on the metal surface during machining. If these two methods are used, it must be ensured that the treatment conditions do not cause selective phase corrosion of the metal or the deposition of undesirable residues on the surface. For materials that are damaged by polymorphism or hydrogen, treatment methods that can produce oxygen on the surface of the specimen must never be used.
5.4.3 Except for the loading area, which can be degreased at the end, the surface treatment of the remaining parts should be completed before the C-ring is loaded. 5.4. 4 After the final surface treatment, care must be taken to avoid fingerprints or any rough handling that will damage the surface roughness. Slow Village Finishing
C-Ring
Figure 4 Fixture for placing wedge-shaped opening inserts
5.5 Test Marks
5. 5. 1 The specimen number may be engraved near one end of the C-ring cutout. The loading section between the two bolt holes shall not be marked in any way. A non-metallic label may be fixed to the loading bolt using an auxiliary nut. 5.5.2 The wedge-shaped open loading specimen number may be engraved on the outer surface of the wedge near the progressive loading wedge. 1:6 Test steps
6.1 The C-ring specimen can be exposed to almost any kind of corrosive environment due to its small size and simple loading method. When supporting the specimen, it should be ensured that the critical loading part of the specimen does not contact any other object except the corrosive medium. 6.2 Care must be taken to avoid the galvanic effect between the C-ring, the loading bolts, nuts or the loading fan and the exposure frame. This can be protected by an insulating sleeve (Figure 5a) and b) or a coating (Figure 5r:). Crevice corrosion must also be prevented because crevice corrosion will produce corrosion products between the ring body and the loading device, causing changes in the stress value of the C-ring. The coating protection method shown in the figure is also applicable to the prevention of positive crevice corrosion. The selected coating or insulation should neither be contaminated by the corrosive medium nor destroyed by the corrosive medium. 1 Need to be separated from the insulating sleeve
b) Spherical edge abandoned
Figure 5 Methods for preventing crevice corrosion and galvanic corrosion c) Coating
6.3 After loading, the sample should be immediately exposed to the test environment or stored to avoid contamination or damage to the sample before exposure. 7 Evaluation of test results
7.1 The time required for cracks to appear in the loaded specimen after exposure to the test environment or the critical stress below which cracks do not appear (the stress below which cracks do not appear) can be used to evaluate the material's stress corrosion resistance in the test environment and at the service stress level. 7.2 For C-ring specimens made of alloys sensitive to corrosion, the cracks are usually obvious when subjected to high stress. 7.3 For C-ring specimens subjected to low stress or C-ring specimens made of corrosion-resistant alloys, the cracks may be very subtle, especially when the cracks are obscured by corrosion products. 7.4 If the C-ring is not broken, it must be evaluated based on the degree of damage. Cracks are generally inspected with the naked eye or a magnifying glass. 7.5 If cracks are observed using the above inspection methods, but it cannot be clearly determined to be a crack,The researcher should choose one of the following two options to make a judgment:
) Record the time and date of the suspected first crack, continue the exposure test, and observe the further expansion of the crack to confirm whether the time of the suspected first crack as the fracture time is correct; t) Stop the burst test and perform a metallographic examination on the cross section of the suspected crack to determine whether there is a crack. 7.6 Metallographic examination of broken or cracked C-rings can also help determine whether the damage is caused by stress corrosion cracking or other forms of corrosion.
8 Test Report
8.1 Except In addition to reporting the number of specimens that broke and the time of each specimen breaking, the following test contents shall also be reported: a) loading method b) the size of the applied stress c) specimen selection time d) specimen size and surface preparation e) test medium f) test duration 8.2 All materials related to the test metal, including the following, shall also be reported: a) metal grade or technical condition number b) composition of the test material C? Manufacturing process:
d) Heat treatment system:
e) Mechanical properties:
GB/T 15970. 5-1998
Time Record A
(Standard Appendix)
The calculation formula of the stress of the die ring specimenWww.bzxZ.net
The following formula can be used to calculate the expected stress (die ring final outer diameter DD - D + AD
AL) = oRd/E2
The outer diameter of the die ring before loading, mm:
(Outer diameter of the C-ring after loading (the measurement of the outer diameter is perpendicular to the center line passing through the maximum stress point) Mm; Minimum stress (within the proportional limit), MP=; Change in the required stress, mMm;
Average diameter {).mm
Wall thickness, m;
Elongation modulus.MPa:
Correction coefficient of bending beam (see Figure A1).
When multiple tests are conducted on a given C-ring size, in order to avoid repeated calculations, a table like Table A1 can be made. The error in this method mainly comes from the maximum size of the C-ring. If the outer diameter is 19㎡m and the wall thickness is 1.5 mm For a typical C-ring, the measurement accuracy can reach 0.03mm, and the error of the calculated value is no more than 3%. For longer and thicker rings, this error will be smaller. However, the 0.03mm2 error in measuring the outer diameter of the ring before and after loading will have different effects on the actual production response, and the degree of influence varies with the required stress and the size of the outer diameter of the ring. For the above-mentioned dimensions, the percentage error is -3% when a=350 MPa. When a=5 MPa, it is ±30%. A1 is the deflection AL of a type ring with a nominal outer diameter of 1 mm, a wall thickness of 1.5 II, and a tensile modulus of 10000 MPa when loaded with 500 MPa. 15970.5--1998
Table A first)
a specific C-shaped ring, in order to determine the required length to produce the predetermined stress, the corresponding figures of the outer diameter and wall thickness of the ring can be found in the table, and then multiplied by
For alloys with different elastic moduli E, the D value found in the outer table or in the above table can be calculated and divided by E×10-2
Figure A on
bending beam correction coefficient
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