ASME VS GB150
ASME VS GB150
In China's pressure vessel standard system, GB150 "Steel Pressure Vessel" is the most basic and widely used standard. It is developed on the basis of continuous experience, scientific research and advanced foreign experience. Quite, but there are also many differences. It comes down to the following aspects:
1. Correspondence between major pressure vessel standards
China's standard classification of pressure vessels is relatively thin, basically according to the type of pressure vessel and the main material of the container to develop corresponding standards, such as steel pressure vessels, aluminum pressure vessels, horizontal vessels, tower vessels, spherical tanks, etc. .
The ASME specification does not specify the corresponding standards according to the type of container, but only refers to different load specifications in the design. For example, the design of the pressure is less than 20MPa, the first volume of the ASME specification, Volume VIII, and the design pressure of less than 70MPa, the ASME specification, VIII. The second volume of the volume, the design pressure is greater than 70MPa, the third volume of the ASME specification, Volume VIII.
2 Standard revision
China's national standards for pressure vessels are prepared and revised by the National Pressure Vessel Standardization Technical Committee and issued after approval by the State Bureau of Quality and Technical Supervision. Relevant industry standards are prepared and revised by various industry standardization committees, and are approved and issued by various departments of the State Economic and Trade Commission. After the implementation of the standards, the local safety supervision departments shall control and supervise the design, manufacture and inspection of pressure vessels in accordance with the Regulations on Pressure Vessel Safety Technical Supervision issued by the State Bureau of Quality and Technical Supervision and relevant standards to ensure product quality and safety. use. The standardization committees use the opinions and suggestions based on the standards of understanding and collection, and are responsible for organizing the revision of the standards, and are issued and implemented after being approved by the original examination and approval department.
The ASME Boiler and Pressure Vessel Committee (BPVC) meets regularly to study the revision of the ASME Code. The revised recommendations approved by the BPVC will be submitted to the American National Standards Institute (ANSl) and published in the US Mechanical Engineering for public consultation. All comments of persons concerned with this issue are revised in the ASME Code Supplement published on December 31 of each year after the expiration of the required public consultation and final approval by ASME. After the specification amendments have been approved by ASME, they can be used from the publication date indicated in the Supplement. Except for the revision of the material standards in the two volumes A and B, the July 1 of the following year becomes mandatory. Except for contracts signed before this date. Revisions to material standards are conducted by the American Society for Testing and Materials (ASTM) and other recognized national or international agencies, and ASME generally adopts these amendments. However, pressure vessel manufacturers need to be aware that when using the revised provisions that are relaxed relative to the original requirements, it must be ensured that the jurisdictions where the pressure vessels are installed are approved by them, otherwise they should not be used.
3. The scope of application of the standard is different
The main differences between China and ASME standards are the pressure limits and materials for containers. The pressure limits of the Chinese standard are clearly defined, the materials used are only steel; ASME gives general provisions, can break the pressure limit after meeting specific requirements, and also specifies non-ferrous metals, nickel-based alloys in addition to steel. The application range of cast steel and other materials allows for stress and manufacturing inspection requirements. Table 1 gives the pressure limits for the two countries' standards.
Comparison of pressure limits in the pressure vessel standards of China and the United States,
| China Pressure Vessel Standard | ASME standard | ||
| Standard | Pressure limit | Standard | Pressure limit |
| GB150 | <=35 | ASMEVIII-1 | <=20. t- |
| JB4732 | <100 | ASMEVIII-2 | <=70 |
| / | / | ASMEVIII-3 | >703 |
4. Design ideas and safety factors
The basic design idea of a pressure vessel is that the primary film stress or maximum direct stress must not exceed the allowable stress. The theory for calculating stress is the theory of maximum stress. This design idea is applied in the pressure vessel standards of various countries. The allowable stress meter published in the standard has a safety factor, which is lower than the measured performance value.
(1) The complexity of the stress assessment method;
(2) a certain degree of stress concentration and its type;
(3) a certain degree of non-uniformity of the material;
(4) geometric factors;
(5) Defects in the welded joint. The safety factors specified in national standards are different, mainly based on experience, experimental evidence and theoretical evaluation, and are compatible with the specified material standards, calculation methods, manufacturing requirements and inspection requirements.
5. Welded joint coefficient
The weld joint coefficient in the ASME specification depends only on the weld joint type and the degree of non-destructive testing, regardless of the degree of non-destructive testing of any other joint, ie different joints of one vessel can use different weld joint coefficients for A, B, The C and D four types of welded joints all specify the welded joint coefficient, and at the same time allow the reduction of the welded joint coefficient to eliminate the non-destructive testing requirements. In China's GB 150, the welded joint coefficient refers to the A and B welded joints. It is not allowed to reduce the welded joint coefficient and avoid the non-destructive testing requirements. After the product is manufactured, the A and B joints must be tested by ray or ultrasonic.
6. Strength calculation
In the design of pressure vessels, two failure theories are mainly considered: one is excessive elastic deformation, including elastic instability based on elastic theory; the other is due to excessive elastic deformation and plastic instability, ie incremental collapse, design It is usually assumed that the elastic failure. Elastic failure is a failure that occurs when the material has reached the elastic limit beyond which excessive deformation or fracture failure will occur. For metallic materials, the elastic limit is determined by three factors: tensile strength, yield strength, and breaking strength. The three general theories for determining elastic failure are the maximum principal stress theory, the maximum shear stress theory, and the deformation energy theory. The pressure theory of the above countries applies the above strength theory to the design of pressure vessels, but there are differences in the specific calculation formulas.
7. Setting of external pressure cylinder reinforcement ring
The reinforcing ring may be disposed inside or outside the container, and should be circled around the circumference of the cylinder. The components inside the container, such as trays, may also be used for reinforcement when designed to strengthen. Continuous or indirect welding may be used between the reinforcing ring and the cylinder. When the reinforcing ring is disposed outside the container, the total length of the intermittent welding of each side of the reinforcing ring shall be not less than 1/2 of the outer circumference of the cylinder, when disposed at When inside the container, it should be no less than 1/3 of the circumference of the cylinder. For the above-mentioned reinforcement circle setting guidelines, China's pressure vessel standards are consistent with the ASME specifications.
The ASME code stipulates that the length of each fillet weld should be not less than 51mm, and the maximum clearance between adjacent sections is: outer reinforcement ring 8t, inner reinforcement ring 12t, t is the wall thickness of the outer ring of the reinforcement ring. In accordance with the relevant conditions of the ASME standard, the fillet weld on one side of the reinforcement ring is allowed to be continuous welding, and the other side is welded by intermittent welding. The length of the welded section is not less than 51 mm, and the maximum net between adjacent weld segments The distance should be 24t. In China's pressure vessel standard, the length of each fillet weld is not specified, and it is not recommended to use one side continuous welding, and the other side is intermittent welding.
8. Opening and opening dimensions
China GBl50 stipulates that the opening on the shell should be round, elliptical or oblong. When opening an elliptical or oblong hole in the shell, the ratio of the long diameter to the short diameter of the hole should be no more than 2.0. The first volume of the ASME Code Volume VIII allows the ratio of the long diameter to the short diameter of the hole to be greater than 2.0, but the reinforcement in the short diameter direction should be enhanced to avoid excessive deformation caused by the torsional moment, and the shape is not limited to a circular shape or an elliptical shape. And oblong, but all corners should have an appropriate radius. At the same time, there are differences in the limits of the opening size.
9. Welder examination and management
Welders who weld pressure vessels must pass the welding skill assessment or examination to obtain the welder's certificate before they can perform the welding work within the scope of the qualified project within the validity period. The newly published "Boiler and Pressure Vessel Pressure Pipe Welder Examination and Management Rules" is consistent with the requirements of the ASME Code Volume IX in many respects, but there are also some differences.
10. Product test board
In order to test the mechanical properties and bending properties of welded joints and other pressure-bearing components, China's "Conditions" clearly stipulates that the longitudinal welds of pressure vessels should be made of welded test panels, and the specimens are taken for stretching, cold bending and necessary impact. Test, for each pressure vessel in one of the following cases, the product welding test plate shall be made:
(1) Mobile pressure vessels (except for mass production);
(2) Designing a pressure vessel with a pressure greater than 10 MPa;
(3) Spherical storage tanks welded on site;
(4) Medium and high pressure vessels made of non-ferrous metals or pressure vessels made of high-strength steel with σb of 540 MPa or more;
(5) Pressure vessels welded by dissimilar steel (different groups);
(6) The pressure vessel on the design drawing or the user's request to make the product welding test plate according to the table;
(7) The pressure vessel specified in GB 150 shall be welded to each test piece.
The first volume of the ASME Code Volume VIII does not require the product welding test plate to pass the normal welding process qualification, and the following conditions require the production of the product welding test plate according to the specifications:
(1) For welded joints with a coefficient of not more than 0.8, any joints prepared by the ASME code (except for resistance welding) shall be welded to the joints of such joints on the container or parts. The sample may be taken from the casing itself or from the extension of the longitudinal weld. When the container has no longitudinal weld, the test piece of the same material, the same thickness and welded by the same process may be taken, and a small section is drawn. The test specimen and the two side bend specimens were tested.
(2) If the welding procedure qualification is required to be used in the weld and heat affected zone impact test, the container impact test plate shall be prepared from one of the steel plates used in the single or multiple containers, for the type A joint. The test panel shall, when possible, be an extension of the end of the product joint so that the test panel weld is as close as possible to the quality and form of the welded joint of the container. For Class B joints with different welding processes and Class A joints, the test panels shall be welded under the same welding conditions for the manufacture of the containers, using the same type of equipment, the same position, the same welding process, and the welding shall be carried out simultaneously with the welding of the products. Or when the welding product is about to start.
11. Non-destructive testing:
The non-destructive testing method detects, locates, measures, evaluates and evaluates defects without damaging their usefulness and usability. In the manufacture of pressure vessels, it is mainly used to detect materials, welds and the surface and interior of manufactured parts and components. Any discontinuity or defect in the physical structure or shape. China's GB 150 and ASME Code Volume VIII, the first volume has some differences in the qualifications of non-destructive testing personnel, the proportion of weld penetration, and assessment requirements.
12. Welding repair:
China's GBl50 regulations for welding rework must be carried out by the certified welder according to the qualified process, the number of repairs of the same part of the weld should not exceed two times, such as more than two times, before the repair should be approved by the technical owner of the pressure vessel manufacturer, repair The number, location and repair status should be recorded in the quality certificate of the container. The ASME Code does not specify the number of repairs for the same part, but the method of repair should be approved by an Authorized Inspector (AI) before each weld is returned for repair.
13. Pressure test;
The pressure vessel manufactured shall be subjected to a pressure test (hydraulic test or air pressure test) as required by the drawings. The pressure test shall use two pressure gauges of the same range and verified. The range of the pressure gauge should generally be about 2 times the test pressure, but should not be less than 1.5 times and more than 4 times the test pressure.
sum up
Under normal circumstances, it is designed to be ASME VIII-1, easy to use, mature, and reliable. It has been the mainstream specification for pressure vessel construction that does not include fatigue analysis requirements for many years, as it continuously introduces new theories and complements new structures. This trend will continue.
In addition, the use of finite element method for stress analysis design is also a means worthy of attention at home and abroad. However, there are differences between China's pressure vessel standard system and ASME standard system. The content of the standard is also quite different. In the actual use, the comparison and analysis of the relevant standards of the two standard systems will help to understand and implement the ASME specification. It also helps to understand the development of pressure vessel standards in China.
