JB/T 7024-1993 Technical Specifications for 300～600MW Steam Turbine Cylinder Castings
Some standard content:
Mechanical Industry Standard of the People's Republic of China
300～600MW Steam Turbine
Technical Conditions for Cylinder Steel Castings
Subject Content and Scope of Application
JB/T7024—93
This standard specifies the technical requirements, inspection rules, test methods, certificates and marks for 300～600MW steam turbine cylinder steel castings.
This standard applies to the ordering, manufacturing and inspection of 300～600MW steam turbine cylinder steel castings (hereinafter referred to as parts). 2 Reference standards
GB3323
GB4338
GB4792
GB6395
Methods for sampling samples for chemical analysis of steel and allowable deviations of chemical composition of finished productsChemical analysis methods for iron and alloys
Metal tensile test method
Metal Charpy (U-notch) impact test methodMetal Brinell hardness test method
Radiography and quality classification of steel fusion welded butt jointsMethods for tensile test of metals at high temperature
Basic standards for radiation health protection
Metal high temperature tensile endurance test method
GB/T11351
JB4058
Tolerance of casting weight
Steam turbine cleanliness standard
ZBK54004
ZBK54007
ZBK54010
ZBK54038
ZBK54039
3 Ordering requirements
Magnetic particle testing and quality grading method for steam turbine steel castings Technical conditions for welding of steam turbine main steam pipes, cylinders, steam chambers, inlet and outlet steam pipes and valve casings Ultrasonic testing and quality grading method for steam turbine steel castings Technical conditions for steam turbine steel castings
Technical conditions for repair welding of steam turbine steel castings
3.1 When placing an order, the purchaser shall provide rough processing and flaw detection drawings, and shall specify additional technical requirements other than this standard in the order contract or technical agreement signed by both parties. Castings shall be delivered after heat treatment and rough machining and welding according to the drawings (if required by the drawings). 3.2 The first batch of castings and the first batch of castings produced after major changes in the manufacturing process shall be subject to additional assessment tests. The content and requirements of the test tests are shown in Appendix A (Supplement). In addition, the purchaser may conduct random inspections on all or part of the items of the assessment tests if necessary, and the results of the random inspections shall comply with the provisions of the assessment tests. 4 Technical requirements
4.1 Manufacturing process
4.1.1 Metallurgy
Approved by the Ministry of Machinery Industry of the People's Republic of China on September 21, 1993 196
Implementation on July 1, 1994
JB/T7024—93
Castings shall be made of electric furnace steel, and open-hearth steel may also be used. If the user requires the use of refined steel, the supplier and the purchaser shall agree on this. 4.1.2 Casting
It is not allowed to use core support and internal cooling iron. If it is necessary to use them in some parts, the written consent of the purchaser shall be obtained. 4.1.3 Heat treatment
4.1.3.1 The heat treatment specifications shall be implemented in accordance with the provisions of the order technical agreement. 4.1.3.2 In addition to the performance heat treatment, the castings shall be subjected to stress relief treatment after rough machining, welding repair and welding. The upper limit temperature of stress relief treatment shall be at least 15°C lower than the actual tempering temperature of the performance heat treatment (the average temperature of the specification), and the lower limit temperature shall not be lower than 55°C below the tempering temperature.
4. 1. 3. 3
In special circumstances, it is allowed to slightly adjust the heat treatment temperature. At this time, the supplier shall indicate the actual heat treatment process parameters used in the certificate of conformity.
4.1.4 Welding repair
4. 1.4. 1
Record.
Defects that are not allowed to exist in castings should be recorded and repaired in accordance with the provisions of ZBK54039 standard after thorough removal. In principle, repair welding is not allowed after the final stress relief treatment. If there are a few defects, repair welding is necessary. After welding, local annealing should be carried out and the steel grade and chemical composition should be prepared.
The chemical composition of the steel grade and smelting analysis should comply with the provisions of Table 1. Table 1
ZG20CrMo
ZG15CrJMa
ZG15Cr2Mo1
ZG20CrMoV
0.15~0.250.50~0.800.20~0.60
0.50~0.80
0.40~0.70
0. 18~0. 250.40~0. 700. 20~0. 600. 12~0. 200. 40~0. 700. 20~0. 60ZG15Cr1Mo1V
Chemical composition
0.50~0. 800. 40~0. 60
1.00~1.500.45~0.55
2, 00~2. 750. 90~1. 20
0. 90~1. 200. 50~0. 700. 200. 3f1.20~1.700.90~1.200.350.46
Note: ① The molten steel can be deoxidized by general methods. If aluminum is used for deoxidation, the total amount of residual aluminum shall not exceed 0.025%. ② The residual amount of dart in ZG15Cr1Mo steel shall not exceed 0.5%; the residual amount of steel shall not exceed 0.25%; the residual amount of steel shall not exceed 0.03%; the residual amount of titanium shall not exceed 0.035%.
③ The residual amount of other pins and copper shall not exceed 0.30%. Unless otherwise specified in the technical documents or contracts, they are generally not subject to assessment. Allowable deviation of chemical composition
The deviation of the finished casting analysis shall comply with the provisions of Table 2 in GB222. 4.3 Mechanical properties
After heat treatment, the mechanical properties of the casting shall comply with the provisions of Table 2. Table 2 Mechanical properties
ZG20CrMo
ZG15Cr1Mo
ZG15Cr2Mo1
ZG20CrMoV
ZG15Cr1Mo1V
≥275
Note; 1) Hardness is not used as the basis for acceptance.
Casting quality
≥460
485~660
135~180
140~201
4.4.1 General requirements
JB/T7024-93
The quality of castings should be strictly controlled throughout the production process, and the record system should be conscientiously implemented. 4.4.2 Surface quality
4.4.2.1 The surface of the casting is not allowed to have cracks, sand sticking, shrinkage holes, cold shuts and other defects that affect the quality. If the above defects are present, they should be completely removed. If the wall thickness exceeds the tolerance after the defects are removed, repair welding should be performed. 4.4.2.2 The allowable residual height of the gate, riser, process subsidy and cast rib on the non-machined surface after cutting shall comply with the provisions of Table 3. All the remaining and cutting pits of the gate, riser, process subsidy, cast rib and other existing parts shall be finished with arc gouging or grinding wheel to make the surface smoothly transition with the casting body and shall not affect the surface quality. Table 3
Maximum size of gate, back gate, subsidy,
Control| ... 3
The roughness Ra of the machined surface of the casting should reach 6.3μm to ensure that ultrasonic flaw detection can be carried out smoothly. The roughness Ra of the non-machined surface of the casting should reach 25μm, or be evaluated with ACI No. 4 sample block. The ultrasonic flawed parts should be polished with a grinding wheel. After polishing, the surface roughness Ra should reach 12.5pμm, or be evaluated with ACI No. 3 sample block. 4.4.2.5
Surface cleanliness, the inner finishing of the inner cylinder of the high and medium pressure cylinder should meet the requirements of JB4058 medium cleanliness-2, and the outer wall of the inner cylinder and the inner and outer walls of the outer cylinder should meet the requirements of JB4058 medium cleanliness-3. If there is no provision at the time of ordering, generally no assessment is made. 4.4.2.6
The surface after rough machining is not allowed to have casting defects that exceed the standard. 4.4.2.7 Defects allowed on non-machined surfaces 4.4.2.7.1 If the area of a single defect is less than 0.5cm, the distance between two defects is not less than 6 times the maximum length of the defect, and the depth of the defect is less than the tolerance of the wall thickness, then 2 of the above defects are allowed on each 100cm (10cm×10cm) unit surface, but the total unit area with defects on the entire surface shall not exceed 1% of the total inspection area. 4.4.2.7.2 If the diameter of the pinhole defect is less than 1.5mm, the number of defects on each 100cm unit surface is not more than 4, and the total unit area with defects does not exceed 10% of the total inspection area, such pinhole defects are allowed to exist. 4.4.3 Shape and size tolerances
4.4.3.1 The geometric shape of the casting shall comply with the provisions of the drawing. 4. 4.3. 2
The size tolerance of the casting shall comply with the provisions of ZBK54038. 4.4.3.3
: The wall thickness and rib thickness tolerances of castings shall comply with the provisions of ZBK54038, and the upper deviation shall be 0.6 times the tolerance value, and the lower deviation shall be 0.4 times the tolerance value.
The limit deviation of the rough-machined surface size of castings shall be implemented in accordance with the provisions of the drawings. If there is no clear provision in the drawings, it shall comply with the provisions of Table 4. Table 4
>125~600
Note: The sum of the cumulative dimensional tolerances shall not exceed the total dimensional tolerance limit deviation
4.4.3.5 The misalignment value of the casting shall not exceed the dimensional tolerance of the wall thickness, and the misalignment shall be rounded (flat) and smoothly transitioned after finishing. 4.4.4 Weight tolerance
JB/T 7024---93
The weight tolerance of castings shall comply with the provisions of MT15 in GB/T11351. 4.4.5 Nondestructive testing
4.4.5.1 Castings shall be subjected to magnetic particle and ultrasonic testing in accordance with the provisions of the flaw detection drawings. Castings that need to be welded with pipes by the supplier shall be subjected to radiographic testing in accordance with the provisions of the drawings or agreements. 4.4.5.2 Defects that are not allowed to exist in castings shall be recorded. 4.4.5.3 The weld repairs of castings shall still be subjected to nondestructive testing in accordance with the quality requirements specified for the main body. 5 Inspection rules and test methods
5.1 Chemical analysis
5.1.1 The molten steel for castings shall be sampled from each furnace for smelting analysis according to the smelting furnace number. The test blocks shall be sampled during the pouring process. The smelting analysis results shall comply with the provisions of Table 1.
5.1.2 The sampling method for chemical analysis samples shall be implemented in accordance with the provisions of GB222. 5.1.3 The chemical composition analysis method shall be carried out in accordance with the provisions of (B223. 5.1.4 The purchaser may perform chemical composition analysis on the attached test block provided by the supplier or on the part 6 mm below the surface of the casting.
5.2 Mechanical properties test
5.2.1 The casting shall be cast with an attached test block. Each half cylinder delivered by the supplier shall be accompanied by an attached test block for acceptance testing by the purchaser. The size of the attached test block shall be provided by the purchaser, and the porcelain injection position shall be agreed upon by the supplier and the purchaser. 5.2.2 Appropriate gaps shall be cut out of the attached test block before heat treatment so that it can be easily removed after heat treatment. The specimens for mechanical properties test shall be taken from the attached test block.
5.2.3 Each ZG20CrMo, ZG20CrMoV and ZG15Cr1Mo1 Take 1 tensile specimen and 3 impact specimens from V casting. The results of the tensile test shall comply with the provisions of Table 2; the average value of the 3 impact test results shall comply with the provisions of Table 2, and one of the test results is allowed to be lower than the specified value, but shall not be lower than 1/3 of the specified value. Take 2 tensile specimens ($12.5mm) from each ZG15Cr1Mo and ZG15Cr2Mo1 casting. The test results shall comply with the provisions of Table 2.
The tensile test shall be carried out in accordance with the provisions of GB228, and the impact test shall be carried out in accordance with the provisions of GB229. 5.2.5
The Brinell hardness of the casting shall be determined according to the method specified in GB231. 5.2.6 The test results shall be invalid in the event of any of the following situations, and the specimen shall be re-prepared for testing: a.
The specimen is not clamped properly during the test. When or the test is abnormal; defects are caused by improper specimen processing;
tensile specimen breaks outside the gauge length;
specimen has casting defects.
5.2.7 Retest is allowed when the mechanical properties test results are unqualified. 5.2.7.1 The tensile test retest should be sampled from a test block that can represent the same casting, and double specimens should be prepared for retest. If the test results all meet the requirements of Table 2, they can be judged as qualified. If one of the test results is unqualified, the part it represents and the test block should be re-heat treated.
2 The impact test retest should be sampled from a test block that can represent the same casting, and 3 specimens should be prepared for testing. If the 3 test results 5.2.7.2
are all qualified, the 6 data of the initial test and the retest are added together to calculate Calculate the average value. If the average value meets the requirements of Table 2, it can be judged as qualified. If one of the test results in the retest is unqualified or the recalculated average value does not meet the requirements, the casting represented by it and the test block shall be reheat treated.
5.2.8 Without the consent of the purchaser, the number of heat treatments of castings and test blocks shall not exceed 3 times (tempering times are not included). If the test results are still unqualified, the batch of castings shall be scrapped.
5.2.9 If there are insufficient test blocks, it is allowed to take samples from the castings, but the sampling location shall be agreed by the purchaser. 199
3 Surface quality inspection
JB/T7024-93
The surface quality of castings shall be inspected by visual inspection, comparison samples and conventional measuring tools in accordance with the provisions of Article 4.4.2. 5.4 Dimension and weight inspection
5.4.1 The supplier shall check whether the shape and size of the castings meet the requirements according to the drawings provided by the purchaser and the provisions of Article 4.4.3. 5.4.2 The weight tolerance of the castings is guaranteed by the dimensional tolerance and is generally not inspected. If the order contract stipulates that inspection is required, the inspection result shall comply with the provisions of Article 4.4.4.
5.5 Nondestructive testing
5.5.1 Magnetic particle inspection
5.5.1.1 Magnetic particle inspection is carried out after the final heat treatment. 5.5.1.2
2 The magnetic particle inspection of castings shall be carried out according to the requirements of the inspection drawings, agreed by the supplier and the purchaser, and in accordance with the provisions of Nailu B (supplement) or ZBK54004.
2 Ultrasonic inspection
Ultrasonic inspection is carried out after preliminary finishing or rough machining. Ultrasonic flaw detection of castings shall be carried out according to the requirements of the flaw detection drawings, by agreement between the supplier and the buyer, in accordance with the provisions of Appendix C (supplement) or ZBK545.5.2.2
010.
5.5.3 Radiographic flaw detection
When the cylinder head or pipe of the cylinder body is welded by the supplier, it shall be welded in accordance with the provisions of ZBK54007. After welding, the supplier and the buyer shall agree to carry out radiographic flaw detection on the welded joint in accordance with the provisions of Appendix D (supplement) or GB3323. 5.5.4 After welding repair and finishing, the quality shall be inspected by the non-destructive testing method originally specified. 6 Acceptance
The supplier shall have formal quality control and inspection records at all stages of the production process, including certificates of material quality inspection results and certificates of regular calibration of test equipment. The representative of the buyer may review the above information and make inquiries at any time. 6.2 The buyer has the right to conduct acceptance tests on the qualified castings provided by the supplier according to the contents and items specified in the drawings, technical documents and order contracts.
3 If defects are found in castings that were not found during acceptance, or if water leakage occurs in pumps after fine machining, or if the results of re-inspection do not meet the requirements of this standard, the supplier shall still be responsible for the quality of the castings. 7
Certificate of Qualification
The certificate of qualification of castings shall include the following contents:7.1
Order contract number;
Part drawing number and name;
Pot number;
Standard number;
Smelting furnace number;
Dimensional inspection record;
Measured results of chemical composition;
Measured results of mechanical properties;
Magnetic particle inspection and ultrasonic inspection report; Welding seam radiographic inspection report;
Heat treatment state, actual operation process parameters of heat treatment and furnace batch number: copy of defect welding repair record;
Special project inspection results specified in the order contract:n
Supplier's factory name or its identification mark.
JB/T702493
7.2The certificate of qualification shall be signed and sealed by the person in charge of the supplier's inspection department. 8 Marking and Packaging
After the castings are inspected and qualified, the following contents shall be marked in the designated position with a steel stamp: a.
Order contract number;
Parts drawing number;
Smelting furnace number:
Supplier or inspector code or mark of both parties; Supplier's factory name or its identification mark.
Castings that need to be painted should be indicated in the order contract, and the paint brand shall be specified by the buyer. The supplier shall pack according to the requirements for the transportation of castings. 201
A1 General
JB/T7024-93
Appendix A
Contents and requirements of casting assessment test
(Supplement)
The first batch of castings produced by the supplier shall be assessed in accordance with the contents and requirements specified in this appendix. The first batch of castings refers to the first round furnace castings produced at the beginning of production. This appendix applies to ZG15Cr1Mo and ZG15Cr2Mo1 castings. If the castings produced by the supplier have been subjected to the qualification test, but the manufacturing process has been significantly changed, or the product structure is very different, the qualification test should be repeated.
If the castings submitted by the supplier to the buyer are the first batch, but similar products have been provided to third parties and have been subjected to the qualification test, the supplier shall submit the results of the qualification test to the buyer for review. With the agreement of both parties, the qualification test may not be repeated. If the buyer deems it necessary, the normally supplied castings may be sampled according to all or part of the qualification test items. The supplier shall ensure that the test results of all sampled items meet the requirements of the qualification test. A2
Test content and requirements
The qualification test items include chemical composition, short-term tensile properties at room temperature and high temperature, high temperature endurance strength, metallographic structure and inclusion rating. A2.1 Sampling
For the test, two test specimens (except hydrogen determination specimens) for each test are selected from the first four furnaces and cut from the test specimens. See Figure A1 for the sampling position. The samples for chemical composition analysis are drilled 6mm below the casting surface, and the samples for hydrogen determination are taken from the ladle. 102
Specimen number
1.2, 3 Warm tensile test;
For 15Cr1Mo steel: 510C, 240MPa Endurance strength test: For 15Cr2Mo1 steel: 566C, 160MPa Endurance strength test: 538C, 195MPa Endurance strength acid test;
Evaluation of metallographic structure and inclusions (central part);8
Evaluation of metallographic structure and inclusions (surface part);10 Chemical analysis:
11,12 High overflow short time tensile test
Figure A1 Test block and sample position
A2.2 Chemical composition
JB/T7024--93
In addition to the elements listed in Table 1 of this standard, the residual alloying elements, harmful impurities and gas content in the steel should be additionally determined. The specified values in Table A1 can be used as a reference, but not as a basis for acceptance. Take samples from the center of the largest riser connection surface of the cylinder casting to analyze the carbon and sulfur content and indicate the riser size.
A2.3 Mechanical properties
≤0.0025
Table A2 lists the room temperature and high temperature short-time mechanical properties of ZG15Cr1Mo and ZG15Cr2Mo1. The values listed in the table are representative, but not used as assessment indicators.
Room temperature tensile test is carried out in accordance with the provisions of GB228, and high temperature short-time tensile test is carried out in accordance with the provisions of GB4338. Table A2
ZG15Cr1Mo
ZG15Cr2Mo1
A2.4 High temperature endurance strength test
Specimen number
Test temperature
Two groups of endurance strength specimens are cut from the parts shown in Figure A1, processed into smooth and notched combination specimens according to Figure A2, and endurance strength tests are carried out according to the provisions of Table A3.
The test is carried out in accordance with the provisions of GB6395 until the specimen breaks. ! If the fracture occurs on the notched section, the middle section is machined into threads and the test is repeated under the same intensity and stress until the specimen breaks. The ratio of the fracture time at the notch to the fracture time at the smooth section should be greater than 1. If the specimen breaks at the notch, this should be noted in the test report. If one set of tests is qualified, the other set may not be tested. Table A3
ZG15Cr1Mo
ZG15Cr2Mo1wwW.bzxz.Net
Testing temperature
A2.5 Metallographic and inclusion inspection
Photographs of the center and near the surface of Figure A1.
Fracture time
Elongation
Sectional reduction
Side sampling to observe the metallographic structure and inclusion collection, take 100 times and 500203
Applicable scope
JB/T7024--93
44.45±0.50
0.07±0.025
Polish with emery cloth
19. 05±0. 20,19.05±0.20
60*±1*
Root of the defect
RO.25±0.025
+9. 07 ± 0. 025
Test specimens with a combination of smoothness and notch
Appendix B
Magnetic particle inspection of 300-600MW steam turbine cylinder castings (supplement)
This appendix applies to magnetic particle inspection of 300-600MW steam turbine cylinder castings. B2
Testing time
Final magnetic particle inspection is carried out after the final heat treatment. B3
Testing surface state
The casting should be sandblasted after sand removal to make the surface smooth and its roughness Ra is 12.5um. Grease, paint, sand attachment, oxide scale, etc. should be removed from the surface. The surface roughness Ra of the machined surface should reach 6.3μm. B4
Testing device
Magnetic device with sufficient magnetic force and continuous operation that can detect surface and surface defects of steel castings. It is recommended to use 8000A (CRV-8) three-way full-wave DC magnetization power supply equipment (3000A half-wave rectifier flaw detector is only suitable for local magnetization inspection by contact method). Other equipment that meets the magnetization conditions and flaw detection sensitivity can also be used. B5
Magnetic powder and magnetic suspension
For the selection of magnetic powder and its liquid, please refer to Table B1. When preparing water magnetic powder, it is necessary to add an adjusting agent (to prevent rust, suspend and moisturize). 204
Flaw detection method
Main points of flaw detection
Type of magnetic powder
Red or brown magnetic powder
Fluorescent magnetic powder
JB/T7024-93
Suspension liquid
Kerosene and others
Dry magnetic powder
B6.1 Magnetization method and magnetization current
B6.1.1 Contact method
Concentration +g/L
Preferred recommendation
Applicable contact method
The magnetization current should be HWDC400A/100mm, and the contact spacing should not exceed 250mm. For the processed surface, avoid direct contact of the contact with the flange surface, and energize it on the side (about 10mm away from the end face). B6.1.2 Combined magnetization
The entire workpiece is combined with current magnetization in three directions (current is supplied in the first and second directions, and winding is conducted in the third direction). The magnetization current is determined by the A-30/100 standard test piece.
B6.2 Observation
When using fluorescent magnetic particles, visually inspect defects with ultraviolet light in a brightly lit place (it is recommended to use a movable darkroom). When using non-fluorescent magnetic particles for flaw detection, defects can be inspected in a brightly lit place. B7
Acceptance criteria
Castings cannot be accepted if linear or nonlinear defects exceed the following provisions. Note: Linear marks are those powder contact marks whose length is at least equal to 3 of their width. Nonlinear marks are those circular or box-circular powder contact marks whose length is less than 3 of their width,
Clear linear magnetic particle accumulation marks greater than or equal to 5 mm. B7.2 Any nonlinear marks whose major axis dimension is greater than 5 mm. B7.3 There are 4 or more chain-shaped nonlinear defects with a long axis less than 5 mm, separated from each other and a distance equal to or less than 2 mm distributed in a straight line.
B7.4 In any 40cm surface, the nonlinear traces are defective areas with a feed size of more than 40mm in the long axis direction and the maximum size of the area is not more than 150mm.
All defects exceeding the above provisions should be removed, and then the magnetic particle inspection should be carried out on the scraped surface to check whether the defects in the area are removed. If the removal depth is greater than the wall thickness tolerance, repair welding should be carried out. And the repair welding area should be inspected again to meet the above acceptance requirements. B9
In the report, the customer
sample number and name of the inspection part;
smelting furnace number or its identification number;
work number,
model of the inspection machine:
magnetization method and specification;
magnetic particle and magnetic suspension reduction specifications;
inspection results;
inspection date;
signature of the inspector.
Scope of application
JB/T 7024-93
Ultrasonic flaw detection of 300~600MW steam turbine cylinder castings (supplement)
This appendix applies to ultrasonic flaw detection of 300~600MW steam turbine cylinder castings. C2 Flaw detectors
Flaw detectors must have a qualification certificate issued by the national competent authority and suitable for their work. C3 Flaw detection system
C3.1 Flaw detector
C3.1.1 A pulse reflection ultrasonic flaw detector is used. The instrument should have a flaw detection frequency of at least 1~5MHz, and a gain adjuster or attenuator (error ±10%) in dB units and a distance gain correction device (DAC loop). C3.1.2 The vertical linear range is at least equal to 38mm, and the vertical linear deviation is ±5%. C3.1.3 Horizontal linear deviation is ±5%.
C3.2 Probe
C3.2.1 The diameter of the single crystal straight probe is $10~$30mm, and the frequency is 15MHz. It is recommended to use a soft protective film probe. C3.2.2 The frequency of the dual crystal straight probe is 2~4MHz. C3.3 Reference test block
C3.3.1 The reference test block shown in Figure C1 is used for ultrasonic flaw detection in the horizontal flange of cast steel parts and for adjusting the flaw detection sensitivity of defects within 19mm in depth.
Distance from detection surface to hole
31.838.144.5#6.4 Flat bottom hole
Reference test block for defect depth within 19mm Note: ① Material ZG15Cr1Mo normalizing and same quenching. ② The roughness Ra of the test block detection surface should reach 6.3m or equivalent to the roughness of the casting test surface. ③ The flat bottom hole with a diameter of 6.4mm must have a bottom surface flatness of 0.05mm. The diameter tolerance must reach 0.12mm, and the verticality between the hole axis and the bottom surface of the test block must be within 0°~0°30°.
① The flat bottom hole must be blocked (after ultrasonic inspection). If other test blocks are to be used, the ordering factory must approve it before use. C3.3.2 The reference test block shown in Figure C2 is used for instrument calibration of ultrasonic defects in other parts of steel castings. When the thickness of the steel casting is less than or equal to 206
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