Method for determining heating band width of local heat treatment of large pressure-bearing equipment

Abstract

The application belongs to the technical field of pressure-bearing equipment manufacturing and safe service, and particularly discloses a method for determining the heating band width of local heat treatment of large pressure-bearing equipment. The method effectively solves the problems of poor stress relief effect and high difficulty in field implementation in the prior art. The method comprises the following steps: (1) determining a local heat treatment distributed deformation expression of the coupling heating band width, the heating band edge temperature and the heat treatment temperature; (2) determining the axial and ring residual stresses of the inner surface and the weld center after the local heat treatment cooling; and (3) drawing the evolution law of the axial and ring stresses of the inner surface and the weld center of the pressure-bearing equipment under different heating band widths by using drawing software, obtaining a general relationship formula of the heating band width meeting the residual stress elimination rate of more than 70%, and obtaining a relationship equation of the expected residual stress elimination rate and the heating band width. According to the actual production needs, the heating band width meeting the expected stress elimination rate can be determined by the application, and the local heat treatment cost can be reduced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of pressure-bearing equipment manufacturing and safe service, and particularly relates to a method for determining the heating band width of local heat treatment of large pressure-bearing equipment. BACKGROUND

[0002] As the core infrastructure of the modern industrial system, the safety and reliability of pressure-bearing equipment are directly related to national energy security, ecological protection and social public safety. Welding, as a key technology in the manufacturing of pressure-bearing equipment, determines the overall performance and service life of the equipment. However, welding process is prone to problems such as residual stress, deformation and microstructure changes, which seriously affect the structural integrity and safe service of the equipment. Post-weld heat treatment is a key technical link for eliminating welding residual stress and improving material performance, which is crucial for ensuring that pressure-bearing equipment moves from "manufacturing qualified" to "service reliable".

[0003] The formulation of GB / T 30583-2014 "Post-weld Heat Treatment Procedure for Pressure-bearing Equipment" has solved the problem of whether there is a standard for pressure-bearing equipment heat treatment in China and has made a great contribution to the pressure-bearing equipment industry. However, the 2014 version only specifies the heating band width criteria for local heat treatment of wall thickness less than 50mm, and does not make explicit provisions for wall thickness greater than 50mm. However, after the large-scale of petrochemical plants such as ten-million-ton refinery, million-ton ethylene and million-ton aromatic hydrocarbon, the pressure-bearing equipment will inevitably be large-scale, and the equipment wall thickness is generally greater than 50mm, so the 14 version cannot guide the implementation. At the same time, with the development of pressure-bearing equipment towards super-thick wall, super-large diameter and super-severe working conditions, the traditional heat treatment technology faces multi-dimensional bottlenecks: the heat conduction lag of thick-walled vessels makes it difficult to meet the requirements of temperature uniformity; the necking deformation caused by local heat treatment can induce secondary stress on the inner surface of the vessel, which aggravates the risk of stress corrosion cracking. In the existing technology, the heating band width is a key parameter that determines the effect of local heat treatment, but there are significant limitations in domestic and foreign standards and related technologies, and there is a problem of too wide heating band for local heat treatment of large pressure-bearing equipment, which cannot be implemented on site. This leads to difficulty in eliminating residual stress.

[0004] Therefore, there is an urgent need for a method for determining the heating band width of local heat treatment of large pressure-bearing equipment to solve the key problems of poor stress relief effect and high difficulty in on-site implementation in the prior art. SUMMARY

[0005] The purpose of the present application is to provide a method for determining the heating band width of local heat treatment of large pressure-bearing equipment, which effectively solves the problems of poor stress relief effect and high difficulty in on-site implementation in the prior art.

[0006] To solve the above technical problems, the technical solution adopted by the present application is:

[0007] A method for determining the heating band width of local heat treatment of large pressure equipment, comprising the following steps: S1, determining the local heat treatment distributed deformation expression coupled with the heating band width, the heating band edge temperature and the heat treatment temperature:

[0008]

[0009] In the formula, R is the radius, w is the deflection, β is the size parameter, T max is the heat treatment peak temperature at the center of the weld, x is the distance from the center of the weld in the axial direction, λ is the axial temperature gradient parameter, HB is the heating band width, T b is the heating band edge temperature, and t represents the wall thickness.

[0010] S2, determining the axial and circumferential residual stress distribution equations of the inner surface after local heat treatment cooling:

[0011]

[0012] γ=λ / β;

[0013] In the formula, E is the elastic modulus of the material, σ x is the axial residual stress, σ θ is the circumferential residual stress, and α is the thermal expansion coefficient.

[0014] S3, according to the axial and circumferential residual stress distribution equations of the inner surface, solving the axial and circumferential residual stresses generated at the center of the weld respectively:

[0015]

[0016] S4, according to the calculation equations of the axial and circumferential residual stresses generated at the center of the weld, using drawing software to draw the evolution law of the axial and circumferential stresses of the inner surface at the center of the weld of the pressure equipment under different heating band widths, wherein the abscissa of the curve is normalized.

[0017] S5, according to the law curve fitted in step S4, obtaining the general relationship between the heating band width and the heating band edge temperature reaching the overall heat treatment stress relief effect, and the relationship equation between the expected residual stress relief rate and the heating band width.

[0018] The general relationship between the heating band width and the heating band edge temperature is:

[0019]

[0020] In the formula, R represents the radius of the container, and t represents the wall thickness.

[0021] The relationship equation between the expected residual stress relief rate and the heating band width is:​

[0022]

[0023] wherein η is stress relief rate, A1, A2, κ, τ are parameters related to heating mode, when using ceramic sheet local heat treatment, local heat treatment heating method of cartridge furnace, A1, A2, κ, τ are -0.357, 1.00, 1.445, 1.95 respectively; when using induction heating mode, A1, A2, κ, τ are -0.434, 1.00, 0.935, 1.915 respectively.

[0024] Further, in step S1, according to the highest temperature of heat treatment, the edge temperature of heating band, the axial temperature distribution equation T(x) of the holding stage of local heat treatment is established:

[0025] T(x) = T max e -λx (cos λx + sin λx).

[0026] Further, the deflection differential equation of the cooling stage of local heat treatment is established:

[0027]

[0028] wherein w is deflection, R is radius.

[0029] Further, in step S1, according to the boundary condition that the position of weld center, i.e. x = 0 is zero slope and zero shear force, thus the first derivative and the third derivative of w are 0, and then the distributed deformation expression of local heat treatment is obtained.

[0030] Further, in step S2, according to the geometric relationship between strain and displacement and the physical relationship between stress and strain, the axial and circumferential residual stress on the inner surface after local heat treatment cooling is solved from the deflection differential equation.

[0031] Further, according to actual production, the edge temperature of heating band of large pressure-bearing equipment is at least 60% higher than the peak temperature of heat treatment, if considering that the local heat treatment heater is an ideal heat source, i.e. the edge temperature of heating band is equal to the center temperature of heating band, under the above different boundary conditions, the heating band width solved according to the general relationship between the heating band width and the edge temperature of heating band needs to meet the criterion:

[0032]

[0033] Further, if the production demand does not need to meet the stress relief rate of 70% or requires a higher stress relief rate, the heating band width value meeting the expected stress relief rate is solved through the relationship equation between the expected stress relief rate and the heating band width:

[0034]

[0035] Further, according to the criterion required to be met by the heating band width solved by the general formula, when local heat treatment is performed on certain pressure equipment, first, the heat treatment temperature, holding time and holding rate are determined according to the heat treatment object and in combination with the heat treatment technical document and standard specification.

[0036] In combination with the general formula of the heating band width and the heating band edge temperature, and according to the characteristics of the local heat treatment heater, the local heat treatment heating band width meeting the stress relief effect required by production is selected.

[0037] According to the local heat treatment heating band width, when the heating band edge temperature is less than the calculated temperature value, the heating rate should be reduced or the holding cotton thickness or length should be increased, so as to ensure that the heating band edge temperature during the heat treatment holding stage is greater than or equal to the value required by the general formula of the heating band width and the heating band edge temperature.

[0038] Further, when ceramic sheets or cartridge furnaces are used for heating, the ratio of the heating band edge temperature to the heating band center temperature is determined as 0.7; when an induction heating mode is used, the ratio of the heating band edge temperature to the heating band center temperature is selected as 0.8; or the ratio of the heating band edge temperature to the heating band center temperature of different heaters is determined through pre-experiment.

[0039] Further, during the local heat treatment, the heating band is symmetrically arranged with the weld as the center, and the welding of the thermocouple, the installation of the heating sheet and the holding cotton are performed, and it is noted that the holding cotton should be arranged on the inner and outer walls; wherein, in addition to meeting the standard requirements, the thermocouple should be arranged to measure the temperature of the heating band edge to monitor the temperature change of the heating band edge.

[0040] Compared with the prior art, the beneficial technical effects of the present application are:

[0041] The present application considers the influence of shrinkage deformation generated during the cooling stage of local heat treatment, and proposes a local heat treatment distributed deformation calculation formula and a distributed stress calculation formula coupling the heating band width, the heating band edge temperature and the heat treatment temperature. On the basis of the distributed theory, the local heat treatment process is optimized, and a local heat treatment process criterion considering the residual stress relief effect is proposed, effectively solving the problems of poor stress relief effect and high on-site implementation difficulty in the prior art. On the one hand, it is beneficial to make the residual stress relief effect reach the overall heat treatment, that is, the residual stress relief rate is more than 70%, and at the same time, the heating band width meeting the expected residual stress relief rate can be determined according to the actual production needs. On the other hand, it is beneficial to greatly reduce the cost of local heat treatment, shorten the manufacturing cycle and improve the safety and reliability of the pressure equipment. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1is the evolution law of the axial residual stress at the center of the weld of example 1 with the heating zone width.

[0043] Figure 2 is the evolution law of the hoop residual stress at the center of the weld of example 1 with the heating zone width.

[0044] Figure 3 is the axial residual stress test value of example 1 after local heat treatment using the heating zone width determination method of the application.

[0045] Figure 4 is the hoop residual stress test value of example 1 after local heat treatment using the heating zone width determination method of the application.

[0046] Figure 5 is the axial and hoop residual stress test value of example 2 after local heat treatment using the heating zone width determination method of the application. DETAILED DESCRIPTION

[0047] The application considers the influence of shrinkage deformation generated in the cooling stage of local heat treatment, which will generate new secondary axial and hoop stresses on the inner surface of the container, and proposes a distributed deformation calculation formula and a distributed stress calculation formula of local heat treatment coupled with heating zone width-heating zone edge temperature-heat treatment temperature. On the basis of the distributed theory, the local heat treatment process is optimized, and a local heat treatment process criterion considering the residual stress elimination effect is proposed. The residual stress elimination effect can reach the overall heat treatment, that is, the residual stress elimination rate is more than 70%, and the heating zone width meeting the expected residual stress elimination rate can be determined according to the actual production needs. The cost of local heat treatment can be greatly reduced, the manufacturing cycle can be shortened, and the safety and reliability of pressure equipment can be improved.

[0048] The application provides a heating zone width determination method for local heat treatment of large pressure equipment, and the large pressure equipment refers to a kind of equipment that cannot adopt overall heat treatment for total assembly and closing weld and must adopt local heat treatment. The method comprises the following steps: S1, determining a distributed deformation expression of local heat treatment coupled with heating zone width, heating zone edge temperature and heat treatment temperature.

[0049] The expansion deformation generated in the holding stage of local heat treatment will increase the radius of the container, but the expansion deformation generated by the large pressure equipment is much smaller than the radius of the container, so the change of the radius can be ignored when solving the stress. The differential equation of the moment theory of the axisymmetric problem of cylindrical shell is:

[0050]

[0051] In the formula, R is the radius, t is the wall thickness, w is the deflection, E is the elastic modulus of the material, x is the distance from the center of the weld in the axial direction, D and p respectively represent the bending stiffness and temperature load. z respectively.

[0052]

[0053] where, α is the thermal expansion coefficient; μ is the Poisson's ratio, 0.3; T x is the temperature of each point in the axial direction in the holding stage; T i is the room temperature.

[0054] Since T i is much smaller than T x , (T i -T x ) can be directly expressed by the axial temperature distribution equation-T x , that is:

[0055]

[0056] Based on the above, the deflection differential equation in the cooling stage of the local heat treatment is established as follows:

[0057]

[0058] Further, the axial temperature distribution equation T(x) in the holding stage of the local heat treatment is established according to the highest temperature of the heat treatment and the edge temperature of the heating band as follows:

[0059] T(x) = T max e -λx (cos λx + sin λx).

[0060] where, T max is the peak temperature of the heat treatment at the center of the weld, x is the distance from the center of the weld in the axial direction, and λ is the axial temperature gradient parameter. The value of λ is related to the width HB of the heating band, the peak temperature T max of the heat treatment at the center of the weld, and the edge temperature T b of the heating band, and the expression is as follows:

[0061]

[0062] According to the boundary conditions that the position at the center of the weld, i.e., x = 0, is the zero slope and the zero shear force, i.e., the first derivative and the third derivative of w are 0, the distributed deformation expression of the local heat treatment can be obtained as follows:

[0063]

[0064] where, β is a size parameter.

[0065] S2, according to the geometric relationship between the strain and the displacement and the physical relationship between the stress and the strain, the distributed equation of the axial and circumferential residual stresses on the inner surface after the cooling of the local heat treatment is solved from the deflection differential equation as follows:

[0066]

[0067] where E is the modulus of elasticity of the material, σ x is the axial residual stress, σ θ is the hoop residual stress; γ = λ / β, which can be expressed as γ = σ and the relationship between the heating strip width, i.e.

[0068] S3, according to the axial and hoop residual stress distribution equation of the inner surface, the axial residual stress and the hoop residual stress generated at the weld center are respectively:

[0069]

[0070] S4, according to the calculation equation of the axial residual stress and the hoop residual stress generated at the weld center, the evolution law of the axial and hoop stresses of the inner surface weld center of the pressure equipment under different heating strip widths is drawn by using Originpro or other drawing software, wherein the abscissa of the curve is normalized, that is, the specific value of the abscissa represents the multiple relationship between the heating strip width and the size parameter , and the ordinate is the residual stress value.

[0071] Each edge temperature and heat treatment peak temperature (i.e. heating strip center temperature) can be drawn into a curve. Further, based on the overall heat treatment residual stress elimination effect, i.e. the residual stress elimination rate is 70%, the heating strip width value that meets the above requirements under different heating strip edge temperatures can be obtained.

[0072] S5, according to the law curve fitted in step S4, the general relationship between the heating strip width and the heating strip edge temperature to achieve the overall heat treatment stress elimination effect (residual stress elimination rate above 70%) is obtained, and the expected residual stress elimination rate and the relationship equation of the heating strip width.

[0073] (1) The general relationship between the heating strip width and the heating strip edge temperature is:

[0074]

[0075] According to the actual production, the heating strip edge temperature of the large pressure equipment is greater than 60% of the heat treatment peak temperature, and if the local heat treatment heater is considered as an ideal heat source, i.e. the heating strip edge temperature is equal to the heating strip center temperature, then according to the general relationship between the heating strip width and the heating strip edge temperature to meet the residual stress elimination rate above 70%, the heating strip width needs to meet the criterion:

[0076]

[0077] When the edge temperature is 60%, take the larger value on the right side of the inequality; when it is an ideal heat source, the edge temperature is equal to the center temperature, take the smaller value on the left side of the inequality.

[0078] According to the above criteria, when a certain pressure equipment is subjected to local heat treatment, first of all, according to the heat treatment object, combined with the heat treatment technical file, standard specification to determine the heat treatment temperature rising and falling rate, holding temperature and holding time;

[0079] Combined with the general relationship between the heating band width and the edge temperature of the heating band, and according to the characteristics of the local heat treatment heater, the local heat treatment heating band width that meets the stress relief effect required by production is selected. The specific selection method is as follows: when ceramic sheet or cartridge furnace heating is used, the ratio of the edge temperature of the heating band to the center temperature of the heating band can be determined as 0.7; when induction heating is used, the ratio of the edge temperature of the heating band to the center temperature of the heating band can be selected as 0.8; or the ratio of the edge temperature of the heating band to the center temperature of the heating band of different heaters is determined through pre-experiment.

[0080] Further, according to the heating band width selected by the general relationship between the heating band width and the edge temperature of the heating band, when the edge temperature of the heating band is less than the calculated temperature value, the heating rate should be reduced or the thickness or length of the holding cotton should be increased to ensure that the edge temperature of the heating band during the heat treatment holding stage is greater than or equal to the value required by the general relationship between the heating band width and the edge temperature of the heating band.

[0081] (2) If the production requirement does not require to meet the stress relief rate of 70% or requires a higher stress relief rate, the heating band width value that meets the expected stress relief rate is solved through the relationship equation between the expected stress relief rate and the heating band width.

[0082] The relationship equation between the expected residual stress relief rate and the heating band width is:

[0083]

[0084] In the formula, η is the stress relief rate, A1, A2, κ, τ are parameters related to the heating method, when ceramic sheet local heat treatment, cartridge furnace local heat treatment heating method is used, A1, A2, κ, τ are-0.357, 1.00, 1.445, 1.95 respectively; when induction heating is used, A1, A2, κ, τ are-0.434, 1.00, 0.935, 1.915 respectively.

[0085] During local heat treatment, the heating band is symmetrically arranged with the weld as the center, and the installation of thermocouple welding, heating sheet and holding cotton is carried out, and it is noted that holding cotton should be arranged on the inner and outer walls. In addition to meeting the standard requirements, the thermocouple should be arranged at the edge of the heating band to monitor the temperature change of the edge of the heating band.

[0086] Example 1: Taking the local heat treatment of a certain tower as the research object, the material is Q345R, and the geometric size is Φ4400mm*66mm*56910mm. The local heat treatment heating method adopted is the heating of ceramic resistance heating sheet. First, Figure 1 and Figure 2 respectively represent the calculation equations of the axial residual stress and the circumferential residual stress generated at the weld center provided by the present application, and the evolution law of the axial residual stress and the circumferential residual stress at the weld center of the device under different heating band widths is drawn.

[0087] Through testing, the edge temperature of the ceramic heating sheet used in the field is 76.0% of the heat treatment peak temperature. Then, according to the formula provided by the present application: The calculated heating band width HB that satisfies the stress relief effect is Specifically, 1040mm, the holding width is 2HB, and the highest holding temperature is 600℃. Through residual stress testing, after local heat treatment, as shown in Figure 3 , the axial residual stress of the inner wall decreases by 71%; as shown in Figure 4 , the circumferential residual stress decreases by 81%. The overall heat treatment effect is achieved.

[0088] Example 2: Taking the closing ring seam of a certain container as the verification object, the diameter is 3048mm, the wall thickness is 16mm, and the total length is 142100mm. The residual stress before and after heat treatment is tested by using the indentation energy method. Through testing, the edge temperature of the ceramic heating used in the field is 70% of the heat treatment peak temperature. According to the heating band width determination method provided by the present application, the calculated heating band width HB is Specifically, 487.2mm. The inner and outer walls are held, the holding band width is 2HB, and the holding temperature is 600℃. Figure 5 The test results of the axial and circumferential residual stresses of the inner surface before and after heat treatment are given. The maximum axial as-welded stress is 200.3MPa, after heat treatment, the axial residual stress is significantly reduced and homogenized, and the maximum stress is reduced to 47.1MPa, with a decrease of 73.5%. The maximum circumferential as-welded stress is 229.3MPa, which is reduced to 49.1MPa after heat treatment, with a decrease of 78.4%, which verifies that the heating band width criterion proposed by the present application is reasonable.

[0089] Of course, the above description is not a limitation on the present application, and the present application is not limited to the above examples. Changes, modifications, additions or substitutions made by those skilled in the art within the essential scope of the present application should also be within the protection scope of the present application.

Claims

1. A method for determining the width of a heating zone in localized heat treatment of large pressure-bearing equipment, characterized in that, Includes the following steps: S1. Determine the expression for the local heat treatment distributed deformation based on the width of the coupled heating band, the edge temperature of the heating band, and the heat treatment temperature: ； ； ； In the formula, For radius, For deflection, For dimensional parameters, This is the peak temperature of the heat treatment at the center of the weld. This is the axial distance from the center of the weld. For axial temperature gradient parameters, For the width of the heating band, This refers to the temperature at the edge of the heating zone. Indicates wall thickness; S2. Determine the axial and circumferential residual stress distribution equations on the inner surface after local heat treatment and cooling: ； ； ； In the formula, The elastic modulus of the material, This is the axial residual stress. For circumferential residual stress, The coefficient of thermal expansion; S3. Based on the distributed equations of axial and circumferential residual stresses on the inner surface, solve for the axial and circumferential residual stresses generated at the weld center: ； ； S4. Based on the calculation equations for the axial and circumferential residual stresses generated at the weld center, use drawing software to plot the evolution of axial and circumferential stresses at the weld center on the inner surface of the pressure equipment with varying heating band widths. The horizontal axis of the graph is represented by... / Normalization processing; S5. Based on the regular curve fitted in step S4, obtain the general relationship of the heating band width to achieve the overall heat treatment stress relief effect, and the relationship equation between the expected residual stress relief rate and the heating band width. The general formula for the width of the heating band is: ； Based on actual production, the edge temperature of the heating band in large pressure equipment is at least 60% higher than the peak temperature of the heat treatment. If we consider the local heat treatment heater as an ideal heat source, meaning the edge temperature of the heating band is equal to the center temperature, then under the above different boundary conditions, the heating band width, calculated using the general formula for heating band width, must meet the following criteria: ； The equation relating the expected residual stress relief rate to the width of the heating band is as follows: ； In the formula, For stress relief rate, , , , For parameters related to the heating method, when using localized heat treatment with ceramic discs or localized heat treatment with a portable gasket, , , , The values ​​are -0.357, 1.00, 1.445, and 1.95 respectively; when induction heating is used, , , , The values ​​are -0.434, 1.00, 0.935, and 1.915, respectively.

2. The method for determining the width of the heating band in local heat treatment of large pressure equipment according to claim 1, characterized in that, In step S1, an axial temperature distribution equation for the local heat treatment holding stage is established based on the highest heat treatment temperature and the edge temperature of the heating zone. : 。 3. The method for determining the width of the heating band in local heat treatment of large pressure equipment according to claim 2, characterized in that, Establish the deflection differential equation during the local heat treatment cooling stage: ； In the formula, For deflection, Let be the radius.

4. The method for determining the width of the heating band in local heat treatment of large pressure equipment according to claim 3, characterized in that, In step S1, based on the weld center, i.e. The boundary conditions at that location are zero slope and zero shear force, therefore, The first and third derivatives are 0, thus yielding the expression for the distributed deformation of local heat treatment.

5. The method for determining the width of the heating band in local heat treatment of large pressure equipment according to claim 4, characterized in that, In step S2, the axial and circumferential residual stresses on the inner surface after local heat treatment cooling are solved by the deflection differential equation based on the geometric relationship between strain and displacement and the physical relationship between stress and strain.

6. The method for determining the width of the heating band in local heat treatment of large pressure equipment according to claim 5, characterized in that, Based on the criteria that the width of the heating band must meet, which are solved by general formulas, when local heat treatment is performed on pressure equipment, the heat treatment heating and cooling rate, holding temperature and holding time should be determined first according to the heat treatment object, combined with heat treatment technical documents and standard specifications. Based on the general formula for heating band width and the characteristics of the local heat treatment heater, select the local heat treatment heating band width that meets the stress relief effect required for production. Based on the width of the heating band in the local heat treatment, when the edge temperature of the heating band is less than the calculated temperature value, the heating rate should be reduced or the thickness or length of the insulation cotton should be increased to ensure that the edge temperature of the heating band is greater than or equal to the value required by the general formula for the width of the heating band during the heat treatment insulation stage.

7. The method for determining the width of the heating band in local heat treatment of large pressure equipment according to claim 6, characterized in that, When using ceramic discs or a portable gas stove for heating, the ratio of the edge temperature to the center temperature of the heating band is determined to be 0.7; when using induction heating, the ratio of the edge temperature to the center temperature of the heating band is selected to be 0.8; or the ratio of the edge temperature to the center temperature of the heating band for different heaters can be determined through preliminary experiments.

8. The method for determining the width of the heating band in local heat treatment of large pressure equipment according to claim 7, characterized in that, During localized heat treatment, the heating bands are arranged symmetrically around the weld seam, and the thermocouples are welded, heating elements and insulation cotton are installed. Note that insulation cotton should be placed on both the inner and outer walls. In addition to meeting the standard requirements, temperature measuring thermocouples should be placed at the edge of the heating band to monitor the temperature change at the edge of the heating band.

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