Material selection method for thick-wall part of ultra-supercritical coal-fired power generation boiler

Abstract

According to the ultra-supercritical coal-fired power generation boiler thick-wall component material selection method, the physical performance characteristics of a high-temperature alloy material and the thermal fatigue risk brought by the high-temperature alloy material are fully considered, the current situation of deep peak regulation of a coal-fired unit is fully considered, and firstly, applicable materials are preliminarily screened out through thermal stress; according to the method, the subsequent screening workload can be greatly reduced, various performance indexes of the material are evaluated through a weighted evaluation method according to different requirements of different parts on the material performance, the performance score of unit cost is calculated, the cost performance is fully considered, and reasonable allowance is reserved for the material performance while the operation requirements are met, so that the material performance is improved. The risk after the unit is put into operation is reduced, and a material selection scheme given according to the method is safer and good in economical efficiency.

Description

Technical Field

[0001] This invention belongs to the field of coal-fired power generation technology, and specifically relates to a method for selecting materials for thick-walled components of ultra-supercritical coal-fired power boilers. Background Technology

[0002] The primary energy structure determines the status of coal power as the "pillar" and "ballast". High-parameter coal-fired power generation technology at the 650℃~700℃ level can significantly reduce coal consumption and pollutant (CO2, NO3, SO3, etc.) emissions. Research and development of related technologies are very important.

[0003] The service temperature of high-temperature components in boilers (650℃~700℃) exceeds the upper limit of heat-resistant steel, necessitating the use of austenitic nickel-based (including iron-nickel-based) high-temperature alloys. The physical and mechanical properties, variation patterns, and failure modes of these materials differ significantly from those of commonly used ferritic heat-resistant steels. For example, their thermal conductivity is significantly lower than that of heat-resistant steel, while their coefficient of thermal expansion is significantly higher, thus significantly increasing the risk of thermal fatigue. Furthermore, the cost of high-temperature alloy materials is far greater than that of heat-resistant steel, making the selection of cost-effective materials even more crucial.

[0004] Currently, the key performance considerations for material selection in coal-fired power generation unit components are primarily the material's creep strength, machinability, steam oxidation resistance, flue gas corrosion resistance, and intergranular corrosion tendency. However, in recent years, with the advancement of new energy technologies, coal-fired units have undertaken increasingly heavy peak-shaving tasks. Coupled with the low thermal conductivity and high thermal expansion coefficient of high-temperature alloy materials, the risk of thermal fatigue in thick-walled components has significantly increased. Furthermore, some materials exhibit high creep strength but extremely low creep ductility, which also poses risks. Welding is essential in the manufacturing and installation of boiler components, but some new candidate materials require post-weld heat treatment temperatures exceeding 900℃, making on-site welding difficult. These materials also exhibit significant differences in their weld crack tendencies, which can impact the unit's later operational safety. Therefore, the current lack of a comprehensive material selection method for thick-walled components in high-parameter ultra-supercritical coal-fired power boilers makes it difficult to ensure the rationality and economy of material selection schemes, becoming a pressing technical problem that engineers need to solve. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a material selection method for thick-walled components of ultra-supercritical coal-fired power generation boilers, which fully considers service conditions and the performance characteristics of candidate materials, making the material selection scheme reasonable and economical.

[0006] This invention is achieved through the following technical solution: A method for selecting materials for thick-walled components in an ultra-supercritical coal-fired power boiler includes the following steps: (1) Determine the component design parameters, component service conditions and failure modes; the component design parameters include the reasonable range of the component's design wall thickness and the component's design inner diameter; the component service conditions include the design steam temperature T and the design steam pressure p; (2) Calculate the allowable stress range of the candidate material at the design steam temperature T based on the design steam pressure p, the reasonable range of the design wall thickness of the component, and the design inner diameter of the component; (3) Several candidate materials were selected based on the allowable stress range; (4) Calculate the required wall thickness of each candidate material based on the design steam pressure, the design inner diameter of the component, and the allowable stress of each candidate material; (5) Calculate the thermal stress of each candidate material under start-up, shutdown and deep peak shaving conditions based on the required wall thickness and physical property data of each candidate material; (6) Perform total stress verification based on the thermal stress, and determine whether the primary stress and secondary stress of each candidate material meet the preset requirements, so as to obtain the candidate materials that meet the preset requirements; (7) Calculate the cost of candidate materials that meet the preset requirements; score the performance of each candidate material that meets the preset requirements other than creep durability and fatigue performance, and obtain the performance evaluation score of each candidate material that meets the preset requirements through a weighted evaluation method. (8) Calculate the unit cost performance score based on the cost and performance evaluation scores of the candidate materials that meet the preset requirements; (9) The candidate material with the highest unit cost performance score among the candidate materials that meet the preset requirements is selected as the material selection result.

[0007] Preferably, in step (2), the allowable stress range obtained is [σ]. min ~[σ] max ; in, , p is the design steam pressure, D i For the design inner diameter of the component, The minimum value within the reasonable range of wall thickness for the component. The maximum value of the reasonable range of wall thickness for the component design, where ψ is the reduction coefficient.

[0008] Preferably, the wall thickness in step (4) is calculated using the following formula: +C, where p is the design steam pressure, D i For the design inner diameter of the component, ψ is the allowable stress of the candidate material, ψ is the reduction coefficient, and C is the corrosion allowance.

[0009] Preferably, step (5) specifically involves: calculating using the finite element method or using empirical formulas. The estimation is given by: ΔT = (temperature difference between the inner and outer walls of the component), ΔT / Δτ = (heating / cooling rate), α = (coefficient of thermal expansion), E = (elastic modulus of the metal), δ = (required wall thickness of the candidate material), and λ = (thermal conductivity). It is Poisson's ratio.

[0010] Preferably, in step (7), the cost of candidate materials that meet the preset requirements... C i Calculate using the following formula: C i = M i × D i ,in M i This represents the required weight of the candidate material. D i This represents the unit price of the candidate material.

[0011] Preferably, in step (7), the properties of each candidate material that meet the preset requirements, other than creep durability and fatigue performance, include at least one of the following: microstructure stability, steam oxidation resistance, processing performance, ductile-brittle transition temperature, welding crack tendency, intergranular corrosion sensitivity, stress corrosion sensitivity, durable plasticity, and fracture toughness.

[0012] Furthermore, the processing performance includes at least one of post-weld heat treatment performance, bending performance, and flattening performance.

[0013] Furthermore, the weld cracking tendency includes at least one of hot cracking, reheat cracking, and strain aging cracking.

[0014] Preferably, in step (7), various properties of candidate materials that meet the preset requirements, other than creep durability and fatigue performance, are scored, and then multiplied by the corresponding performance evaluation weight coefficient to calculate the performance evaluation score of the candidate materials.

[0015] Preferably, step (8) specifically involves dividing the performance evaluation score of the candidate material by the cost to obtain the unit cost performance score of the candidate material.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention fully considers the physical properties of high-temperature alloy materials and the associated thermal fatigue risks, as well as the current status of deep peak shaving in coal-fired power units. It first uses thermal stress to preliminarily screen suitable materials, significantly reducing subsequent screening workload. Then, based on the different performance requirements of various components, it evaluates the various performance indicators of the materials using a weighted evaluation method and calculates the performance score per unit cost, fully considering cost-effectiveness. While meeting operational requirements, it leaves a reasonable margin for material performance, reducing risks after the unit is put into operation. The material selection scheme provided by this invention is safer and more economical. Attached Figure Description

[0017] Figure 1 This is a flowchart illustrating a specific embodiment of the present invention. Detailed Implementation

[0018] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0019] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0020] The present invention will now be described in further detail with reference to the accompanying drawings: like Figure 1 As shown, the material selection method for thick-walled components of ultra-supercritical coal-fired power boilers of the present invention includes the following steps: (1) Determine the component design parameters (including the reasonable range of design wall thickness and the design inner diameter of the component), the component service conditions (including design steam temperature T, design steam pressure p, start-up / stop / peak shaving frequency) and possible failure modes (including plastic failure caused by primary stress (such as internal pressure overload), fatigue failure caused by secondary stress (such as thermal expansion constraint), creep-fatigue interactive damage (high temperature long-term service) and corrosion / oxidation failure).

[0021] (2) Calculate the allowable stress range of the candidate material based on the design steam temperature T, design steam pressure p, reasonable range of design wall thickness of the component, and design inner diameter; the calculated allowable stress range at the design steam temperature T is [σ]. min ~[σ] max ; in, , p is the design steam pressure, D i For the design inner diameter of the component, The minimum value within the reasonable range of wall thickness for the component. The maximum value of the reasonable range of wall thickness for the component design, where ψ is the reduction coefficient.

[0022] (3) Consult material handbooks or relevant standards to select the allowable stress at the design steam temperature T within [σ]. min ~[σ] max Several candidate materials between them.

[0023] (4) Calculate the required wall thickness for each candidate material based on the design steam pressure, the design inner diameter of the component, and the allowable stress of the candidate materials; the wall thickness is calculated using the following formula: +C Where p is the design steam pressure, and D i For the design inner diameter of the component, ψ is the allowable stress of the candidate material, ψ is the reduction coefficient, and C is the corrosion allowance.

[0024] (5) Calculate the thermal stress of each candidate material under start-up, shutdown, and deep peak-shaving conditions; use the finite element method for precise calculation or empirical formulas. The estimation is given, where ΔT is the temperature difference between the inner and outer walls of the pipe, ΔT / Δτ is the heating / cooling rate, α is the coefficient of thermal expansion, E is the elastic modulus of the metal, δ is the wall thickness, and λ is the thermal conductivity. It is Poisson's ratio.

[0025] (6) Perform total stress verification based on the thermal stress to check whether the primary stress and secondary stress of each candidate material meet the preset requirements, and obtain candidate materials that meet the preset requirements.

[0026] (7) Calculate the cost of candidate materials that meet the preset requirements. Ci The following formula is used for calculation: C i = M i × D i ,in M i This represents the required weight of the candidate material. D i This is the unit price.

[0027] (8) Scoring the properties of various candidate materials that meet the preset requirements, other than creep durability and fatigue performance, to obtain the following results. X ij Multiply by the corresponding performance evaluation weighting coefficient Y ij The performance evaluation scores of different candidate materials were calculated. E i = .

[0028] Other properties include the candidate material's microstructure stability, resistance to flue gas corrosion, resistance to steam oxidation, processing performance, ductile-brittle transition temperature, weld cracking tendency (hot cracking, reheat cracking, strain-aging cracking), intergranular corrosion sensitivity, stress corrosion sensitivity, creep ductility, and fracture toughness. Processing performance includes post-weld heat treatment performance, bending performance, and flattening performance. The performance evaluation weighting coefficients vary depending on the component's service conditions and material performance indicators.

[0029] (9) Calculate the unit cost performance score of different candidate materials that meet the preset requirements. A i = E i / C i .

[0030] (10) Evaluate the unit cost performance of different candidate materials that meet the preset requirements. A i The candidate materials are sorted from highest to lowest score, and the highest-scoring candidate materials are the most cost-effective materials. This will be used as the final selection result.

[0031] Example 1 Material Selection for Main Steam Pipelines of a 660MW Ultra-Supercritical Boiler Component parameters: Design parameters: Design steam temperature T = 620℃, design steam pressure p = 28MPa, design inner diameter D of main steam pipeline. i =380mm, design wall thickness range δ min=60mm, δmax=80mm, corrosion allowance C=1mm, ψ=1; Service conditions: 30 start-ups and shutdowns per year, deep peak shaving (load 30%~100%), medium is supercritical steam.

[0032] Material selection implementation steps: (1) Failure modes: creep-fatigue interaction damage, steam oxidation, and welded joint failure.

[0033] (2) Calculate the allowable stress range: [σ] min = ((28×380) / 80+28) / (2×1) = 80.5MPa;[σ] max =((28×380) / 60+28) / (2×1)=102MPa (3) Screening of candidate materials: According to Appendix A of DL 5366-2014, the materials with allowable stress range at 620℃ are T / P92[σ]=100MPa and T / P122[σ]=95MPa.

[0034] (4) Calculate the wall thickness: T / P92: δ = 28×380 / (2× 1.0× 100-28) + 1 = 61.8 + 1 = 62.8mm; T / P122: δ = 28× 380 / (2× 1.0× 95-28) + 1 = 65.70 + 1 = 66.7mm.

[0035] (5) Thermal stress calculation:

[0036] Steady-state temperature difference between inner and outer walls ΔT = 50℃, thermal stress σ = T / P92 th =120MPa, thermal stress σ of T / P122 th =115MPa.

[0037] (6) Total stress check: T / P92: Primary stress S1 = 85MPa (internal pressure + self-weight) ≤ 100MPa (allowable stress), secondary stress S2 = 120MPa (thermal stress) ≤ 3 × 100 = 300MPa; S1 + S2 = 205MPa ≤ 320MPa (compliant with DL 5366-2014); T / P122 also meets the requirements.

[0038] (7) Cost calculation (length L=10m): T / P92: Density 7.85 g / cm³, weight M = 6.85 t, unit price 80,000 yuan / t, C i =6.85×8=548,000 yuan; T / P122: Weight 7.34t, unit price 100,000 yuan / t, C i =7.34×10=734,000 yuan.

[0039] (8) Performance score X ij and E i : structural stability, resistance to steam oxidation, processing performance, ductile-brittle transition temperature, tendency to weld cracking (hot cracking, reheat cracking, strain aging cracking), intergranular corrosion sensitivity, stress corrosion sensitivity, endurance plasticity, and fracture toughness.

[0040]

[0041] (9) A i T / P92 is 814 / 54.8 = 14.85, and T / P122 is 769 / 73.4 = 10.48.

[0042] (10) Conclusion: T / P92 has a higher unit cost performance score and is selected as the best material.

[0043] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for selecting materials for thick-walled components of an ultra-supercritical coal-fired power boiler, characterized in that, Includes the following steps: (1) Determine the component design parameters, component service conditions and failure modes; the component design parameters include the reasonable range of the component's design wall thickness and the component's design inner diameter; the component service conditions include the design steam temperature T and the design steam pressure p; (2) Calculate the allowable stress range of the candidate material at the design steam temperature T based on the design steam pressure p, the reasonable range of the design wall thickness of the component, and the design inner diameter of the component; (3) Several candidate materials were selected based on the allowable stress range; (4) Calculate the required wall thickness of each candidate material based on the design steam pressure, the design inner diameter of the component, and the allowable stress of each candidate material; (5) Calculate the thermal stress of each candidate material under start-up, shutdown and deep peak shaving conditions based on the required wall thickness and physical property data of each candidate material; (6) Perform total stress verification based on the thermal stress, and determine whether the primary stress and secondary stress of each candidate material meet the preset requirements, so as to obtain the candidate materials that meet the preset requirements; (7) Calculate the cost of candidate materials that meet the preset requirements; The properties of each candidate material that meet the preset requirements, other than creep durability and fatigue performance, are scored, and the performance evaluation score of each candidate material that meets the preset requirements is obtained by weighted evaluation method. (8) Calculate the unit cost performance score based on the cost and performance evaluation scores of the candidate materials that meet the preset requirements; (9) The candidate material with the highest unit cost performance score among the candidate materials that meet the preset requirements is selected as the material selection result.

2. The method for selecting materials for thick-walled components of an ultra-supercritical coal-fired power boiler according to claim 1, characterized in that, In step (2), the allowable stress range obtained is [σ]. min ~[σ] max ; in, , p is the design steam pressure, D i For the design inner diameter of the component, The minimum value within the reasonable range of wall thickness for the component. The maximum value of the reasonable range of wall thickness for the component design, where ψ is the reduction coefficient.

3. The method for selecting materials for thick-walled components of an ultra-supercritical coal-fired power boiler according to claim 1, characterized in that, The wall thickness in step (4) is calculated using the following formula: +C, where p is the design steam pressure, D i For the design inner diameter of the component, ψ is the allowable stress of the candidate material, ψ is the reduction coefficient, and C is the corrosion allowance.

4. The method for selecting materials for thick-walled components of an ultra-supercritical coal-fired power boiler according to claim 1, characterized in that, Step (5) specifically involves: calculating using the finite element method or using empirical formulas. The estimation is given by: ΔT = (temperature difference between the inner and outer walls of the component), ΔT / Δτ = (heating / cooling rate), α = (coefficient of thermal expansion), E = (elastic modulus of the metal), δ = (required wall thickness of the candidate material), and λ = (thermal conductivity). It is Poisson's ratio.

5. The method for selecting materials for thick-walled components of an ultra-supercritical coal-fired power boiler according to claim 1, characterized in that, In step (7), the cost of candidate materials that meet the preset requirements is... C i Calculate using the following formula: C i = M i × D i ,in M i This represents the required weight of the candidate material. D i This represents the unit price of the candidate material.

6. The method for selecting materials for thick-walled components of an ultra-supercritical coal-fired power boiler according to claim 1, characterized in that, In step (7), the properties of each candidate material that meet the preset requirements, other than creep durability and fatigue performance, include at least one of the following: microstructure stability, steam oxidation resistance, processing performance, ductile-brittle transition temperature, welding crack tendency, intergranular corrosion sensitivity, stress corrosion sensitivity, durable plasticity, and fracture toughness.

7. The method for selecting materials for thick-walled components of an ultra-supercritical coal-fired power boiler according to claim 6, characterized in that, The processing performance includes at least one of post-weld heat treatment performance, bending performance, and flattening performance.

8. The method for selecting materials for thick-walled components of an ultra-supercritical coal-fired power boiler according to claim 6, characterized in that, The welding cracking tendency includes at least one of hot cracking, reheat cracking, and strain aging cracking.

9. The method for selecting materials for thick-walled components of an ultra-supercritical coal-fired power boiler according to claim 1, characterized in that, In step (7), various properties of candidate materials that meet the preset requirements, other than creep durability and fatigue performance, are scored, and then multiplied by the corresponding performance evaluation weight coefficient to calculate the performance evaluation score of the candidate materials.

10. The method for selecting materials for thick-walled components of an ultra-supercritical coal-fired power boiler according to claim 1, characterized in that, Step (8) specifically involves dividing the performance evaluation score of the candidate material by the cost to obtain the unit cost performance score of the candidate material.

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