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Life-based design method for fatigue strength of ultrahigh-pressure container

A design method and fatigue strength technology, applied in the field of fatigue strength design of ultra-high pressure vessels based on life, can solve the problems of inability to accurately consider the influence of local structural stress distribution, large safety margin, and failure of ultra-high pressure vessels.

Active Publication Date: 2014-10-29
HEFEI GENERAL MACHINERY RES INST
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  • Summary
  • Abstract
  • Description
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  • Application Information

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Problems solved by technology

However, in the fatigue design, the simplified analytical form is mainly used, and the influence of the local structure on the stress distribution cannot be accurately considered. At present, the failure problem of the ultra-high pressure vessel caused by this still occurs from time to time; in addition, the fracture mechanics analysis is also mainly Considering the simple linear expansion of fatigue cracks without considering the near-threshold expansion that accounts for a large fraction of fatigue life will lead to excessive design safety margin and serious waste, so it is urgent to develop a more reasonable design method

Method used

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  • Life-based design method for fatigue strength of ultrahigh-pressure container
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  • Life-based design method for fatigue strength of ultrahigh-pressure container

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Embodiment 1

[0088] In order to explain the present invention, an ultra-high pressure reaction tube used in the production of low-density polyethylene in the petrochemical industry is taken as an example to introduce the entire design process and give the design life.

[0089] The working pressure of the equipment is 245MPa and the temperature is 90°C. The material is AISI4340 alloy steel pipe, and its yield strength is σ s =1026MPa, the tensile strength is σ b =1091MPa, the measured fatigue performance curve (S-N curve) of stress ratio R=-1 see figure 2 , take a safety factor of 15 for the life, and take a safety factor of 1.5 for the stress amplitude to establish a design curve, and convert the average stress to the design curve through the Goodman formula. The fatigue design curve of R=0 is shown in image 3 .

[0090] 1) Carry out preliminary structural design according to process requirements and material properties

[0091] When only considering the ultra-high pressure reaction ...

Embodiment 2

[0112]Taking the fatigue crack growth of AISI4333M4 alloy steel with excessive defects as an example, it is further illustrated that the method of the present invention is more accurate and reasonable than the linear fatigue life calculation method based on fracture mechanics.

[0113] ①Using AISI4333M4 alloy steel for fatigue crack growth test, the results are shown in Figure 7 , the fatigue crack has experienced 100600 cycles from the threshold value to fracture.

[0114] ②Aiming at the fatigue crack growth rate, the linear relational expression is used for life prediction. Firstly, the correlation coefficient is obtained by fitting in the logarithmic coordinate system, and the following Paris relational expression is established:

[0115] da / dN=1.15×10 -29 (ΔK) 2.93

[0116] The fatigue life obtained by integration is only 19956 cycles, which is far lower than the measured fatigue life.

[0117] 3. Apply the method in the present invention to carry out life prediction ...

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Abstract

The invention relates to a life-based design method for the fatigue strength of an ultrahigh-pressure container. The design method comprises the following steps: firstly carrying out primary structure designing; then carrying out an optimal design of self-enhanced treatment according to the principle of minimum shearing stress; then calculating by utilizing finite element software so as to obtain largest local equivalent stress, and comparing with the designed fatigue strength, if the designed fatigue strength is met, calculating the minimum initial fatigue crack length according to a design pressure and a threshold value of fatigue crack propagation of materials; determining the maximum fatigue crack length by utilizing the fracture toughness of the materials and establishing an accurate description equation on the basis of data of a fatigue crack propagation test; and carrying out iterative calculation on the basis, judging whether the fatigue design life is met, if so, finishing the structure design. The design method has the advantages that multiple risk factors in the process of manufacture and operation of the ultrahigh-pressure container are considered and controlled at a design phase, and the fatigue design life is given according to a modern numerical calculation technology; the designing method is safer compared with a conventional elastic-plastic design method and is more accurate and reasonable compared with the existing fracture-mechanics design method.

Description

technical field [0001] The invention belongs to the field of pressure vessel design and relates to a fatigue strength design method of an ultra-high pressure vessel based on life. Background technique [0002] In the industry, containers with an operating pressure above 100 MPa are usually called ultra-high pressure containers, which have been used in petrochemical, artificial crystal, powder metallurgy, metal forming, food processing and other technical fields. With the expansion of people's cognition of ultra-high pressure technology , and its application prospects will be more extensive. Since ultra-high pressure vessels usually operate under extremely harsh conditions (for example, the pressure of ultra-high pressure polyethylene reactors can be as high as 350MPa, the temperature can be as high as 350°C, etc.), and the interior is flammable and explosive, once it fails, it will often cause fire and environmental damage. Pollution and other catastrophic accidents serious...

Claims

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Application Information

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IPC IPC(8): G01N3/00G01N3/32
Inventor 陈学东聂德福范志超危书涛许明汪睿
Owner HEFEI GENERAL MACHINERY RES INST
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