複循環火力發電廠高溫高壓主蒸氣管線在頻繁起停運轉下的劣化機制與結構優化研究——以 3D 冷作彎管與應力集中控制為核心 (Research on Degradation Mechanisms and Structural Optimization of High-Temperature and High-Pressure Main Steam Piping in Combined Cycle Power Plants Under Frequent Start-Stop Operations—Focusing on 3D Cold Bends and Stress Concentration Control)

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摘要 / Abstract

隨著全球能源結構的快速轉型與再生能源滲透率的急遽攀升，複循環火力發電廠（Combined Cycle Power Plant, CCPP）的運轉模式已由傳統的穩態基載（Base Load）全面轉向為應對電網波動的頻繁起停（Start-Stop/Two-Shifting）調度模式。此種極端的熱力循環，使得連接熱回收爐（HRSG）與汽輪機之間的高溫高壓主蒸氣管線，面臨前所未有的熱梯度（dT/dt）變動與動態機械負載，進而大幅加劇了潛變與熱疲勞（Creep-Fatigue Interaction）的複合劣化效應。  With the rapid transformation of the global energy structure and the sharp increase in renewable energy penetration, the operation mode of Combined Cycle Power Plants (CCPP) has comprehensively shifted from traditional steady base load to frequent start-stop (two-shifting) dispatch modes to cope with grid fluctuations.This extreme thermal cycling subjects the high-temperature and high-pressure main steam piping connecting the Heat Recovery Steam Generator (HRSG) and the steam turbine to unprecedented thermal gradient (dT/dt) variations and dynamic mechanical loads, thereby significantly exacerbating the combined degradation effects of creep-fatigue interaction.

本研究旨在深入探討以 ASTM A335 P91 及 P92 潛變強度強化肥粒鐵鋼（CSEF）為主之管線系統，在上述嚴苛條件下的微觀與巨觀失效機制，特別聚焦於銲接熱影響區（HAZ）的第四型破裂（Type IV Cracking）。為系統性解決此問題，本研究從 EPC 統包商的設計理念出發，提出以 3D/5D 大彎徑冷作彎管取代傳統 1.5D 銲接彎頭、利用 Sweepolet 取代傳統 Weldolet 的結構優化策略。 This study aims to deeply investigate the microscopic and macroscopic failure mechanisms of piping systems primarily made of ASTM A335 P91 and P92 Creep Strength Enhanced Ferritic Steels (CSEF) under the aforementioned severe conditions, with a special focus on Type IV cracking in the heat-affected zone (HAZ).To systematically address this issue, starting from the design philosophy of EPC contractors, this study proposes a structural optimization strategy that replaces traditional 1.5D welded elbows with 3D/5D large-radius cold bends and substitutes traditional Weldolets with Sweepolets.

在分析端，強制導入 ASME B31J 標準的精確應力強度因子（SIF）演算法，並藉由 CAESAR II 對管線進行柔性與疲勞壽命評估；在實務執行端，則探討了導入潁璋工程「三合一工法」（冷作彎管＋感應加熱彎後熱處理＋數位化模組管理）的實質效益，確保材料微觀組織的復原與施工品質的合規性。最終，本研究將宏觀應力熱點與微觀金相特徵深度整合，建構出基於風險基礎檢驗（RBI）的完整性管理框架，為現代高能管線（HEP）的安全營運提供具備高度學術價值與工程指導意義之綜合論述。  On the analytical side, it mandates the introduction of the precise Stress Intensification Factor (SIF) decoupling algorithm from the ASME B31J standard and uses CAESAR II for piping flexibility and fatigue life assessment; on the practical execution side, it explores the substantial benefits of introducing Ying Zhang Engineering’s “Three-in-One Method” (cold bending + induction heating post-bend heat treatment + digital module management) to ensure the restoration of material microstructure and the compliance of construction quality.Ultimately, this study deeply integrates macroscopic stress hotspots with microscopic metallographic features to construct a closed-loop Risk-Based Inspection (RBI) integrity management framework, providing a comprehensive discourse with high academic value and engineering guidance significance for the safe operation of modern High Energy Piping (HEP).

一、 研究背景 / 1. Research Background

1.1 能源轉型下的複循環機組運轉模式轉變 / 1.1 Transition of Combined Cycle Unit Operation Modes Under Energy Transition

現代複循環火力發電廠因具備極高的熱效率與極快的升降載反應能力，在當今以風力與太陽能等間歇性再生能源為主導的現代電網中，扮演著提供穩定電壓、頻率調節以及尖峰備轉容量的關鍵角色1。然而，這類系統及其高能管線在最初的工程設計階段，多半是基於長時間的穩態運行（通常預期壽命為十萬至二十五萬小時）所規劃的2。 Modern combined cycle power plants, possessing extremely high thermal efficiency and rapid ramp-up/down response capabilities, play a critical role in providing stable voltage, frequency regulation, and peak spinning reserve in today’s modern grid dominated by intermittent renewable energy sources such as wind and solar1.However, during the initial engineering design phase, such systems and their high energy piping are mostly planned based on long-term steady-state operation (typically with an expected life of 100,000 to 250,000 hours)2.

當運轉模式轉變為每日頻繁起停甚至快速負載追隨（Load Following）時，系統必須在極短時間內完成燃氣渦輪機的點火與加速，隨後 HRSG 開始產生大量高溫蒸汽，導致主蒸氣管線內部承受劇烈的溫度梯度（dT/dt）與壓力突波4。這種頻繁的熱機交替過程，使得原本僅需抵抗高溫潛變的管線材料，必須同時面臨嚴苛的低週次熱機械疲勞，從而加速了材料內部微觀組織的退化與巨觀結構的損傷。  When the operation mode shifts to frequent daily start-stops or even rapid load following, the system must complete the ignition and acceleration of the gas turbine in a very short time. Subsequently, the HRSG begins to generate large amounts of high-temperature steam, causing the internal main steam piping to withstand severe thermal gradients (dT/dt) and pressure surges4.This frequent thermo-mechanical alternation forces the piping materials, which originally only needed to resist high-temperature creep, to simultaneously face severe low-cycle thermo-mechanical fatigue, thereby accelerating the degradation of the internal microstructure and the damage of the macroscopic structure.

1.2 高能管線材料之極限與第四型破裂挑戰 / 1.2 Limits of High Energy Piping Materials and the Challenge of Type IV Cracking

為因應現代超臨界與複循環機組對蒸汽溫度（約 600°C）與壓力的提升需求，主蒸氣管線普遍採用 Grade 91 (P91) 或 Grade 92 (P92) 這類含 9-12% 鉻的潛變強度強化肥粒鐵鋼6。這類材料在製造初期具有優異的回火麻田散鐵組織與極高的差排密度，能提供極佳的高溫潛變抗力9。To meet the elevated steam temperature (around 600°C) and pressure demands of modern supercritical and combined cycle units, main steam piping widely utilizes Creep Strength Enhanced Ferritic Steels containing 9-12% chromium, such as Grade 91 (P91) or Grade 92 (P92)6.In the initial manufacturing stage, these materials possess an excellent tempered martensite structure and an extremely high dislocation density, providing outstanding high-temperature creep resistance9.

然而，大量工程實務與失效案例顯示，在頻繁起停的熱循環條件下，這類高合金不銹鋼與高鉻鋼材的銲接接頭極易發生過早失效，其中最具毀滅性的便是發生於銲接熱影響區細晶區的第四型破裂11。由於銲接幾何不連續處本就存在嚴重的應力集中，加上熱應力與內壓的疊加，使得傳統的 1.5D 銲接彎頭與分支管成為整個系統中最脆弱的破口14。 However, extensive engineering practices and failure cases indicate that under the thermal cycling conditions of frequent start-stops, the welded joints of such high-alloy stainless steels and high-chromium steels are highly susceptible to premature failure. The most devastating of these is Type IV cracking, which occurs in the fine-grained heat-affected zone11.Due to the inherent severe stress concentration at geometric discontinuities in welds, combined with the superposition of thermal and internal pressure stresses, traditional 1.5D welded elbows and branch pipes become the most vulnerable weak points in the entire system14.

1.3 應力分析規範的範式轉移：從 B31.1 到 B31J / 1.3 Paradigm Shift in Stress Analysis Codes: From B31.1 to B31J

面對頻繁失效的工程挑戰，業界逐漸意識到過去依賴的 ASME B31.1 或 B31.3 附錄 D 中關於應力強度因子（SIF）的經驗公式已顯得過時。這些公式源自 1950 年代基於較小管徑的疲勞試驗，將其外推至現代大管徑或厚壁的高壓管件時，往往會產生過度保守或危險的評估偏差16。Facing the engineering challenge of frequent failures, the industry has gradually realized that the empirical formulas for Stress Intensification Factors (SIF) relied upon in the past, found in ASME B31.1 or B31.3 Appendix D, have become obsolete.These formulas originated from fatigue tests on smaller pipe diameters in the 1950s. Extrapolating them to modern large-diameter or thick-walled high-pressure fittings often results in overly conservative or dangerously inaccurate assessments16.

為此，ASME 在 2020 年版及後續版本的 B31.1 動力管線規範中，強制導入了 ASME B31J 標準18。B31J 將組件的面內、面外與扭轉應力強度因子進行了徹底的解耦，並重新定義了持續應力指標（SSI），這為重新審視管線結構優化與疲勞壽命預測提供了全新的工程視野17。此一規範的演進，也迫使工程界必須回頭檢視材料的微觀劣化本質，進而尋求更具前瞻性的設計解方。 Therefore, in the 2020 edition and subsequent versions of the B31.1 Power Piping Code, ASME mandated the adoption of the ASME B31J standard18.B31J completely decouples the in-plane, out-of-plane, and torsional stress intensification factors of components and redefines the Sustained Stress Index (SSI). This provides a brand-new engineering perspective for re-evaluating piping structural optimization and fatigue life prediction17.The evolution of this code also compels the engineering community to retrospectively examine the fundamental nature of microscopic material degradation, thereby seeking more forward-looking design solutions.

二、 文獻回顧 / 2. Literature Review

2.1 CSEF 鋼之微觀組織退化與潛變疲勞機制 / 2.1 Microstructural Degradation and Creep-Fatigue Mechanisms of CSEF Steels

在建立宏觀的規範認知後，必須進一步深究材料在微觀層面的劣化機制。ASTM A335 P91 及 P92 鋼的卓越高溫強度，主要源自於其複雜的階層性微觀結構，內部均勻散布著富鉻的 M23C6碳化物與極細小的 MX 型碳氮化物，這些奈米級的析出物能有效釘扎晶界並阻礙差排的攀移與滑移9。然而，在長期高溫暴露與循環應變的驅動下，材料內部會發生不可逆的熱力學相變。 After establishing a macroscopic understanding of the codes, it is necessary to delve further into the degradation mechanisms of materials at the microscopic level.The exceptional high-temperature strength of ASTM A335 P91 and P92 steels primarily stems from their complex hierarchical microstructure, internally and uniformly dispersed with chromium-rich M23C6 carbides and extremely fine MX-type carbonitrides. These nanoscale precipitates can effectively pin grain boundaries and hinder dislocation climb and slip9.However, driven by long-term high-temperature exposure and cyclic strain, irreversible thermodynamic phase transformations occur within the material.

首先，M23C6 碳化物會逐漸粗化，基體內析出的 Laves 相顆粒在晶界處快速成長，大量消耗固溶強化元素，並成為微孔洞成核的高應力集中點9。更致命的是，長時間服役後熱力學上更穩定的 Z 相（Cr(V,Nb)N）會開始成核並生長28。Z 相的形成直接消耗了原本提供強大釘扎作用的 MX 碳氮化物，引發局部的非均勻回復，導致麻田散鐵板條變寬、差排密度急遽下降，最終引發長時潛變強度的非預期陡降9。First, M23C6 carbides gradually coarsen, and Laves phase particles precipitating in the matrix grow rapidly at grain boundaries, consuming a massive amount of solid-solution strengthening elements and acting as high stress concentration points for micro-cavity nucleation9.More critically, after prolonged service, the thermodynamically more stable Z-phase (Cr(V,Nb)N) begins to nucleate and grow28.The formation of the Z-phase directly consumes the MX carbonitrides that originally provided a strong pinning effect, triggering localized heterogeneous recovery. This leads to the widening of martensitic laths and a sharp drop in dislocation density, ultimately causing an unexpected breakdown in long-term creep strength9.

2.2 熱影響區細晶區的第四型破裂（Type IV Cracking） / 2.2 Type IV Cracking in the Fine-Grained Heat-Affected Zone

承接上述微觀退化機制，在 P91/P92 鋼的環向銲接處，第四型破裂便成為最常見的失效模式。該破裂專門發生於熱影響區的細晶區（FGHAZ）或相間臨界區（ICHAZ）7。在銲接熱循環中，該區域僅發生部分沃斯田鐵化13。在隨後的冷卻與銲後熱處理過程中，無法重新形成完整的麻田散鐵結構，導致晶界缺乏足夠的析出物進行釘扎12。Following the aforementioned microstructural degradation mechanisms, Type IV cracking becomes the most common failure mode at the circumferential welds of P91/P92 steels.This cracking occurs exclusively in the fine-grained heat-affected zone (FGHAZ) or the intercritical heat-affected zone (ICHAZ)7.During the welding thermal cycle, this region only undergoes partial austenitization13.During the subsequent cooling and post-weld heat treatment processes, it fails to re-form a complete martensitic structure, resulting in a lack of sufficient precipitates at the grain boundaries for pinning12.

在管線系統巨觀彎矩所引發的軸向應力與靜水壓應力作用下，孔洞優先在粗化的 Laves 相周圍成核，並沿著垂直於最大主應力的晶界迅速成長聚合，形成鋸齒狀微裂紋，最終導致巨觀的沿晶斷裂12。為彌補此缺陷，ASME B31.1 引入銲接強度折減因子（WSRF），嚴重制約了高能管線的設計空間與運行彈性20。Under the influence of axial stress and hydrostatic stress induced by the macroscopic bending moments of the piping system, cavities preferentially nucleate around coarsened Laves phases and rapidly grow and coalesce along grain boundaries perpendicular to the maximum principal stress. This forms zigzag microcracks and ultimately leads to macroscopic intergranular fracture12.To compensate for this defect, ASME B31.1 introduced the Weld Strength Reduction Factor (WSRF), which severely constrains the design space and operational flexibility of high energy piping20.

2.3 潛變與熱疲勞的交互作用分析模型 / 2.3 Creep-Fatigue Interaction Analysis Models

在頻繁起停的運轉下，管線承受低週次熱疲勞與應力鬆弛潛變，兩者產生的潛變疲勞交互作用會加速材料破壞。目前學界主要採用兩大分析路徑：時間分率法與延展性耗竭模型34。ASME Section III Division 5 主要採用基於線性損傷累積法則的時間分率法34，透過雙線性損傷包絡線進行保守判定38。然而，歐洲規範則傾向使用延展性耗竭模型35，許多研究表明該模型在預測真實破裂壽命上往往具備更高的準確度40。Under frequent start-stop operations, the piping sustains low-cycle thermal fatigue and stress relaxation creep. The resulting creep-fatigue interaction accelerates material destruction.Currently, the academic community primarily adopts two major analytical approaches: the Time Fraction Approach and the Ductility Exhaustion Model34.ASME Section III Division 5 primarily employs the Time Fraction Approach based on a linear damage accumulation rule34, performing conservative evaluations via a bilinear damage envelope38.However, European codes tend to use the Ductility Exhaustion Model35. Many studies have shown that this model often possesses higher accuracy in predicting true rupture life40.

近年來，為克服 P91 鋼在循環軟化下的應力重分配難題，ASME 更引入了 Code Case N-862，採用彈性-完全塑性（EPP）分析方法43，利用偽屈服應力的等時應力-應變曲線來評估潛變疲勞損傷，成功規避了複雜的應力分類並提供了創新評估工具44。In recent years, to overcome the challenge of stress redistribution under cyclic softening in P91 steel, ASME introduced Code Case N-862. This utilizes an Elastic-Perfectly Plastic (EPP) analysis method43, employing isochronous stress-strain curves with a pseudo-yield stress to evaluate creep-fatigue damage. It successfully bypasses complex stress classifications and provides an innovative assessment tool44.

2.4 流體動力學誘發之複合破壞：水錘、FAC 與 AIV / 2.4 Fluid Dynamics-Induced Complex Failures: Water Hammer, FAC, and AIV

高壓主蒸氣管線除了承受熱機械負荷外，還必須抵禦極端流體動力學所引發的複合破壞機制：In addition to thermo-mechanical loads, high-pressure main steam piping must also withstand complex failure mechanisms induced by extreme fluid dynamics:

  1. 水錘效應：在起停階段，高速蒸汽推動水團引發強烈凝結水衝擊，產生極高的瞬態壓力突波，使銲縫處瞬間承受超過材料降伏極限的衝擊應力46。
  2. Water Hammer Effect: During the start-stop phases, high-speed steam propels slugs of water, triggering intense condensate impacts and generating extremely high transient pressure surges. This causes the welds to instantaneously endure impact stresses exceeding the material’s yield limit46.
  3. 流動加速腐蝕（FAC）：好發於高流速、高紊流區域（如彎管外弧側、三通分岔處）。強烈剪應力會持續剝離管壁表面的保護膜，導致管壁減薄，進而放大局部環向應力，加速潛變孔洞擴展48。
  4. Flow-Accelerated Corrosion (FAC): This frequently occurs in high-velocity, high-turbulence regions (such as the extrados of bends and tee junctions). Intense shear stress continuously strips away the protective oxide film on the pipe wall, leading to wall thinning. This in turn amplifies local hoop stresses and accelerates the expansion of creep cavities48.
  5. 聲致振動（AIV）：在高壓旁路系統或安全閥作動時，巨大的壓降產生強烈高頻聲波。當聲功率級（SWL）超過 155 dB 時，會激發管壁的呼吸模態振動51。這種高頻振動極易在非對稱幾何結構之銲趾處，引發難以預防的高週次疲勞破裂53。
  6. Acoustically Induced Vibration (AIV): When the high-pressure bypass system or safety valves operate, massive pressure drops generate intense high-frequency acoustic waves. When the Sound Power Level (SWL) exceeds 155 dB, it excites the “breathing mode” vibration of the pipe wall51. This high-frequency vibration is highly prone to triggering unpredictable high-cycle fatigue cracking at the weld toes of asymmetric geometric structures53.

為有效防範上述由微觀晶界至巨觀流體動力學所交織成的複合破壞，單憑後端的檢測已不足以確保安全，必須從工程設計源頭進行徹底的理念翻轉與結構優化。 To effectively prevent the aforementioned complex failures intertwined from microscopic grain boundaries to macroscopic fluid dynamics, relying solely on backend inspections is insufficient to ensure safety. A thorough paradigm shift in design philosophy and structural optimization must be initiated from the engineering design source.

三、 分析方法與設計策略 / 3. Analytical Methods and Design Strategies

3.1 EPC 統包商設計單位之管線幾何決策理念：1.5D 與 3D/5D 彎徑之權衡 / 3.1 Piping Geometry Decision Philosophy of EPC Contractors: Trade-offs Between 1.5D and 3D/5D Bends

在 CCPP 建廠初期，EPC 統包商面臨著資本支出（CAPEX）與營運支出（OPEX）的拉鋸戰。過去在穩態基載機組的設計思維下，設計單位傾向於大量採用標準的 1.5D 銲接彎頭。其核心設計理念在於 1.5D 彎頭具備極小的轉彎半徑，能大幅縮減管線佈局所需的空間，進而降低鋼構廠房的體積與建造成本（降低 CAPEX）；且標準管件取得容易，不需委託專業加工廠進行特殊的彎管工法55。During the initial construction phase of a CCPP, EPC contractors face a tug-of-war between Capital Expenditure (CAPEX) and Operational Expenditure (OPEX).In the past, under the design mindset of steady-state base load units, design units tended to heavily utilize standard 1.5D welded elbows.The core design philosophy was that 1.5D elbows possess a minimal turning radius, which drastically reduces the space required for piping layouts, thereby lowering the volume and construction costs of structural steel buildings (reducing CAPEX). Additionally, standard fittings are easy to procure and do not require commissioning specialized fabrication shops for special bending methods55.

然而，隨著機組轉向頻繁起停運轉，高應變的 P91/P92 管線若持續採用 1.5D 銲接彎頭，其幾何上的高應力集中與熱影響區的第四型破裂極易導致管線提早失效。從全生命週期評估（LCA）的角度來看，這會引發驚人的 OPEX——包括巨額的非計畫性停機損失、高昂的修復成本，以及為符合法規所需投入的頻繁檢驗費用55。However, as units shift toward frequent start-stop operations, if high-strain P91/P92 piping continues to use 1.5D welded elbows, their geometric high stress concentrations and the Type IV cracking in the heat-affected zone make the piping highly susceptible to premature failure.From a Life Cycle Assessment (LCA) perspective, this triggers staggering OPEX—including massive losses from unplanned downtime, exorbitant repair costs, and frequent inspection expenses required for regulatory compliance55.

因此，現代先進 EPC 統包商的設計理念已逐漸轉向「以彎代銲」，即在空間佈局許可的前提下，優先導入 3D 甚至 5D 的大彎徑冷作彎管。3D/5D 彎管的設計理念不僅在於緩解流體衝擊，更在於透過幾何展延，徹底消除處於系統最高彎矩點的環向銲縫。儘管大彎徑管線在 3D 建模佈線時需要更寬闊的轉角空間，且前期製造與熱處理成本略高，但其帶來的低壓降、低流動干擾以及大幅延長的熱疲勞壽命，實質上為電廠業主創造了難以估量的長期綠色價值與營運可靠度。Therefore, the design philosophy of modern advanced EPC contractors has gradually shifted towards “replacing welding with bending,” meaning prioritizing the introduction of 3D or even 5D large-radius cold bends, provided spatial layouts permit.The design philosophy behind 3D/5D bends lies not only in mitigating fluid impacts but also in completely eliminating circumferential welds located at the points of highest bending moments in the system through geometric extension.Although large-radius piping requires wider cornering space during 3D modeling and routing, and incurs slightly higher upfront manufacturing and heat treatment costs, the resulting low pressure drop, minimal flow disturbance, and vastly extended thermal fatigue life practically create incalculable long-term green value and operational reliability for power plant owners.

3.2 結構與幾何優化實務：3D 冷作彎管與 Sweepolet 應用 / 3.2 Structural and Geometric Optimization Practices: Application of 3D Cold Bends and Sweepolets

承接上述 EPC 「以彎代銲」的設計決策理念，本研究在實務配置上全面採用 3D 冷作彎管（彎曲半徑 R=3*NPS）進行結構升級。這項升級將不可避免的環向銲接點推移至遠離應力頂點的直管段57。值得注意的是，由於 P-No. 15E（P91/P92）材質在冷作變形後會產生嚴重的冷作硬化，本研究強調必須執行嚴格的彎後熱處理（PBHT），以確保材料恢復均勻的麻田散鐵基體，此一實務操作的細節與合規效益將於後續 4.5 節深入探討8。Following the aforementioned EPC design decision philosophy of “replacing welding with bending,” this study comprehensively adopts 3D cold bends (bend radius R=3*NPS) for structural upgrades in practical configurations.This upgrade displaces unavoidable circumferential welds to straight pipe sections far away from stress apexes57.It is worth noting that because P-No. 15E (P91/P92) materials experience severe work hardening after cold deformation, this study emphasizes the strict necessity of Post-Bend Heat Treatment (PBHT). This ensures the material restores a uniform martensitic matrix. The details and compliance benefits of this practical operation will be discussed in depth in Section 4.58.

在分支連接優化上，針對高壓降且易受 AIV 與 FAC 影響的節點，本研究以曲率平滑的 Sweepolet 取代傳統的 Weldolet53。Sweepolet 採用一體化鍛造與大曲率漸變設計，與主幹管的連接為全滲透對接銲縫，有效降低了應力集中與強烈的渦流脫落，且無損檢測的施作也更為單純，符合高能管線降低維護複雜度的核心需求61。 For branch connection optimization, specifically targeting nodes with high pressure drops that are vulnerable to AIV and FAC, this study substitutes traditional Weldolets with Sweepolets, which feature a smooth curvature53.Sweepolets utilize an integrally forged, large-curvature transitional design, connecting to the main header via a full-penetration butt weld. This effectively reduces stress concentrations and intense vortex shedding, while also simplifying the execution of Non-Destructive Examination (NDE), thereby meeting the core requirement of minimizing maintenance complexity for high energy piping61.

3.3 ASME B31J 標準的應力強度因子解耦算法 / 3.3 Decoupling Algorithm of Stress Intensification Factors in ASME B31J Standard

為精準量化上述幾何優化帶來的力學效益，本研究全面導入 ASME B31J-2023 標準。B31J 的核心進步在於建立了一套具備方向性與高解析度的 SIF 矩陣，並將動態應力與靜態應力進行了解耦34。對於彎管組件，其柔性特徵（h）與面內、面外 SIF（ii,io）之計算不僅考量了彎曲半徑，更真實反映了截面橢圓化所產生的變形能力62：  To precisely quantify the mechanical benefits brought by the geometric optimizations described above, this study comprehensively adopts the ASME B31J-2023 standard.The core advancement of B31J lies in establishing a highly resolved, directional SIF matrix and decoupling dynamic stresses from static stresses34.For bend components, the calculation of the flexibility characteristic (h) and the in-plane/out-of-plane SIFs (ii,io) not only considers the bend radius but also authentically reflects the deformability generated by cross-sectional ovalization62:

h=T⋅R1/r22

ii=0.9/h2/3

io=0.75/h2/3

對於三通或分支管件，B31J 強制規定柔性係數k=1.0（視為剛性交會），並首次引入扭轉 SIF（it）的考量，取代了以往一律假設為 1.0 的盲點17。更為關鍵的是，B31J 將持續應力指標（SSI）解耦為0.75*i （且≧1.0），確認靜態持續負載的破壞極限遠高於預期，大幅釋放了高溫設計的安全餘裕17。 For tee or branch connections, B31J mandates a flexibility factor of k=1.0 (treating it as a rigid intersection) and introduces the consideration of torsional SIF (it) for the first time, replacing the previous blind spot of universally assuming a value of 1.017.More critically, B31J decouples the Sustained Stress Index (SSI) to 0.75*i (with a minimum of 1.0), confirming that the failure limits for static sustained loads are far higher than expected, thereby significantly releasing safety margins in high-temperature design17.

3.4 CAESAR II 應力分析建模與非線性動態負載邊界 / 3.4 CAESAR II Stress Analysis Modeling and Non-linear Dynamic Load Boundaries

透過上述幾何與理論準則的確立，本研究進一步利用 CAESAR II 建立 CCPP 高壓主蒸氣管線的三維有限元素模型，並於系統總體設定中強制啟用 “Use B31J” 選項，確保軟體自動套用解耦算法18。模型分析工況涵蓋了持續負載（結合 B31.1 規定之 WSRF 參數折減容許應力20）、極端溫差下的熱膨脹負載，以及偶發與動態負載。特別針對水錘衝擊與閥門作動，導入瞬態反作用力並套用動態負載因子，確保非線性分析引擎能貼近真實物理動態，精確驗證設計變更後的力學反應47。  Having established the geometric and theoretical criteria above, this study further utilizes CAESAR II to build a three-dimensional finite element model for the CCPP high-pressure main steam piping. The “Use B31J” option is mandatorily enabled in the system’s global settings to ensure the software automatically applies the decoupling algorithm18.The modeled load cases encompass sustained loads (combining the WSRF parameters stipulated by B31.1 to reduce allowable stress20), thermal expansion loads under extreme temperature differentials, and occasional and dynamic loads.Specifically addressing water hammer impacts and valve actuation, transient reaction forces are introduced and Dynamic Load Factors (DLF) are applied. This ensures the non-linear analysis engine closely approximates true physical dynamics, precisely verifying the mechanical responses following design modifications47.

四、 結果與討論 / 4. Results and Discussion

4.1 3D 冷作彎管對 SIF 下降與柔性矩陣之綜合效益 / 4.1 Comprehensive Benefits of 3D Cold Bends on SIF Reduction and Flexibility Matrix

依據 CAESAR II 輸出之 B31J 分析結果，將傳統 1.5D 銲接彎頭升級為 3D 冷作彎管，印證了 EPC 設計理念中所預期的正面變革，其數據對比如表 1 所示。 Based on the B31J analysis results outputted by CAESAR II, upgrading traditional 1.5D welded elbows to 3D cold bends confirms the positive transformations anticipated in the EPC design philosophy. The data comparison is shown in Table 1.

評估參數 (Evaluation Parameter) 1.5D 銲接彎頭 (1.5D Welded Elbow) 3D 冷作彎管 (3D Cold Bend) 物理機制與系統影響分析 (Physical Mechanisms and System Impact Analysis)
彎曲半徑 (Bend Radius,R1) 1.5 倍公稱管徑 (1.5x Nominal Pipe Size) 3.0 倍公稱管徑 (3.0x Nominal Pipe Size) 曲率變緩，流體衝擊力減弱，直接降低 FAC 與水錘侵蝕機率49。 (Gentler curvature weakens fluid impact forces, directly lowering the probability of FAC and water hammer erosion49.)
柔性特徵 (Flexibility Characteristic, h) 較低（基準值） (Lower – baseline value) 約為基準值的 2 倍 (Approx. 2x the baseline value) 由於 h 正比於R1 ，3D 彎管的 h 值顯著提升62。 (Since h is proportional to R1 , the h value for 3D bends increases significantly62.)
疲勞 SIF (Fatigue SIF,ii,io) 面內外因子偏高 (High in-plane/out-of-plane factors) 降幅約 30-40% (Reduction of approx. 30-40%) SIF 呈h-2/3 遞減，極大提升熱機械循環壽命。 (SIF decreases proportionally to h-2/3, immensely improving thermo-mechanical cyclic life.)
持續應力指標 (SSI) 受高 SIF 影響偏高 (High due to high SIF influence) 降低至貼近 1.0 底限 (Reduced close to the 1.0 floor) SSI 下降直接減少了持續應力，釋放高溫設計餘裕。 (The drop in SSI directly reduces sustained stress, releasing high-temperature design margins.)
微觀 HAZ 分佈 (Microscopic HAZ Distribution) 處於幾何頂點 (Located at the geometric apex) 無中段環向銲縫 (No mid-section circumferential weld) 消除應力極值區的 HAZ，切斷 Z 相與彎矩耦合的 Type IV 破裂鏈12。 (Eliminates the HAZ in the extreme stress zone, severing the Type IV cracking chain coupled with Z-phase and bending moments12.)

此一空間上的錯位，不僅在巨觀上緩解了流體應力，更在微觀上完美規避了 P91/P92 鋼因 Z 相析出消耗 MX 碳氮化物所造成的延展性耗竭區間，實質阻斷了潛變與熱疲勞的破壞共振效應14。 This spatial displacement not only alleviates fluid stress on a macroscopic level but also perfectly evades the ductility exhaustion regime caused by the consumption of MX carbonitrides during Z-phase precipitation in P91/P92 steels at a microscopic level. It substantially severs the destructive resonance effects of creep and thermal fatigue14.

4.2 Sweepolet 應用於抗 AIV 與分支結構優化 / 4.2 Application of Sweepolets for Anti-AIV and Branch Structural Optimization

在高壓降旁路系統的分析中，傳統 Weldolet 的陡峭角銲縫在 B31J 規範下呈現極高的io 與 it。替換為 Sweepolet 模型後，計算顯示其分支 SIF 與 SSI 顯著下降。結合 Energy Institute 的 AIV 評估指南51，Sweepolet 因長半徑平滑漸變設計，不僅減弱了聲波能量的反射與駐波效應，更消除了底部銲縫的尖銳缺口。在面對管壁超過 155 dB 極限值的呼吸模態振動時，能成功將局部應力振幅壓制在材料的高週疲勞耐久極限之下，化解快速撕裂風險53。  In the analysis of high-pressure drop bypass systems, the steep fillet welds of traditional Weldolets exhibit extremely high io and it values under the B31J code. After replacing them with the Sweepolet model, calculations indicate a significant drop in both branch SIF and SSI.Coupled with the AIV evaluation guidelines from the Energy Institute51, Sweepolets—thanks to their long-radius, smoothly contoured designs—not only dampen the reflection and standing wave effects of acoustic energy but also eliminate sharp notches at the root welds.When facing the “breathing mode” vibrations of pipe walls exceeding the 155 dB limit, they can successfully suppress local stress amplitudes below the material’s high-cycle fatigue endurance limit, thereby neutralizing the risk of rapid tearing53.

4.3 應用 Code Case N-862 與 Larson-Miller 壽命預測 / 4.3 Life Prediction Using Code Case N-862 and Larson-Miller Parameter

為精確量化壽命貢獻，本研究導入 ASME Code Case N-862 的 EPP 模型。P91 鋼在承受 TMF 時具備循環軟化特徵43，EPP 模型生成的等時應力-應變曲線配合 CAESAR II 下降的 SSI 與熱應力幅，使得總損傷座標點從危險邊緣成功回縮至 ASME D-Diagram 的安全內側象限39。 在穩態潛變時間推演上，依據 Larson-Miller 參數（LMP）模型：To accurately quantify life contributions, this study adopts the EPP model from ASME Code Case N-862.P91 steel exhibits cyclic softening characteristics when subjected to TMF43. Isochronous stress-strain curves generated by the EPP model, paired with the reduced SSI and thermal stress amplitudes from CAESAR II, successfully retract the total damage coordinate points from the hazardous edge to the safe inner quadrant of the ASME D-Diagram39.In projecting steady-state creep time, based on the Larson-Miller Parameter (LMP) model:

LMP=T(C+logtr)

對於高鉻鋼，常數 C 取值約 30 至 338。CAESAR II 輸出的持續應力下降，使得代入 LMP 主曲線求得的容許破裂時間呈指數增長，在數學上證明了解耦算法與彎管優化對於 OPEX 樽節的長遠效益2。 For high-chromium steels, the constant C takes a value of approximately 30 to 33 8.The reduction in sustained stress outputted by CAESAR II leads to an exponential increase in the allowable rupture time when substituted into the LMP master curve. This mathematically proves the long-term benefits of the decoupling algorithm and bend optimization for OPEX savings2.

4.4 構建風險基礎檢驗（RBI）的閉環框架 / 4.4 Construction of a Closed-Loop Risk-Based Inspection (RBI) Framework

基於 CAESAR II 應力分析熱點與 P91 鋼微觀退化的高度關聯，本研究建構了「應力引導式」的進階 RBI 檢驗框架。透過標定 B31J 綜合應力超過容許值 80% 的熱點50，運用相控陣超音波（PAUT）與飛時測距（TOFD）技術偵測 HAZ 的初期微孔洞74；並輔以金相覆膜監控 Laves 相與 Z 相的粗化情形8。Based on the high correlation between CAESAR II stress analysis hotspots and the microscopic degradation of P91 steel, this study constructs a “stress-guided” advanced RBI framework.By mapping hotspots where the B31J combined stress exceeds 80% of the allowable limit50, Phased Array Ultrasonic Testing (PAUT) and Time of Flight Diffraction (TOFD) techniques are deployed to detect early-stage micro-cavities in the HAZ74. This is supplemented by metallographic replicas to monitor the coarsening of the Laves and Z phases8.

測得之 FAC 減薄率與金相損傷資料隨後會回饋至 LMP 與 CAESAR II 模型中動態修正剩餘壽命49，形成具備自我修正能力的閉環資產完整性管理系統。 The measured FAC thinning rates and metallographic damage data are subsequently fed back into the LMP and CAESAR II models to dynamically adjust the remaining life49, forming a closed-loop asset integrity management system with self-correcting capabilities.

4.5 潁璋工程「三合一工法」於 3D 彎管之實務應用與合規效益 / 4.5 Practical Application and Compliance Benefits of Ying Zhang Engineering’s “Three-in-One Method” in 3D Bends

縱然數值模擬與設計理念已充分證實 3D/5D 冷作彎管的優越性，但在製造實務上，如何確保 P91/P92 管材在冷作變形後的微觀組織得以完全恢復，一直是工程界的一大難題。為解決此一實務瓶頸，本研究特別納入潁璋工程興業有限公司所倡導的「冷作彎管＋感應加熱彎後熱處理（IH-PBHT）＋數位化模組管理」三合一整合工法，並以通霄電廠 M501JAC 機組為實證案例進行效益梳理76。Even though numerical simulations and design philosophies have fully validated the superiority of 3D/5D cold bends, in manufacturing practice, ensuring the complete restoration of the microstructure in P91/P92 piping after cold deformation remains a major challenge in the engineering community.To overcome this practical bottleneck, this study specifically incorporates the “Three-in-One” integrated method championed by Ying Zhang Engineering Co., Ltd.—comprising cold bending, induction heating post-bend heat treatment (IH-PBHT), and digital module management—and analyzes its benefits using the M501JAC unit at the Tongxiao Power Plant as an empirical case study76.

此三合一工法在實務操作上帶來顯著的綜合效益：This three-in-one method yields remarkable comprehensive benefits in practical operations:

首先，在常溫下透過 CNC 數控彎管機床進行 3D 彎曲時，能精確將成型應變率控制於安全區間內，並嚴密監控管壁減薄率與外徑橢圓度，確保物理幾何不失穩77； First, when performing 3D bending at ambient temperatures using CNC bending machines, the forming strain rate can be precisely controlled within a safe range, while wall thinning rates and outer diameter ovality are strictly monitored to ensure physical geometric stability77.

其次，有別於傳統爐內熱處理的侷限，IH-PBHT 技術能提供極精準的局部升溫與溫控，確保材料達到完全正常化與高溫回火，徹底消除冷作硬化並恢復麻田散鐵基體，從而量化並降低 HAZ 的潛在風險63； Second, unlike the limitations of traditional furnace heat treatments, IH-PBHT technology provides extremely precise localized heating and temperature control, ensuring the material achieves full normalization and high-temperature tempering. This completely eliminates cold work hardening and restores the martensitic matrix, thereby quantifying and reducing potential HAZ risks63.

最後，透過數位孿生技術所導入的數位化模組管理，能自動編譯並生成不可竄改的管線系統最終報告。這不僅能為 EPC 統包商創造商業利基，更能協助業主順利簽署 ASME 合規證明，消弭資料斷層造成的驗收爭議，實現工程品質與規範要求的無縫接軌。 Finally, the digital module management introduced via digital twin technology automatically compiles and generates immutable final piping system reports. This not only creates a commercial niche for EPC contractors but also assists owners in smoothly signing off on ASME compliance certifications. It eliminates acceptance disputes caused by data disconnects, achieving a seamless integration of engineering quality and regulatory requirements.

五、 結論與建議 / 5. Conclusions and Recommendations

本研究針對複循環火力發電廠在面臨高頻率起停運轉時，主蒸氣管線遭遇的熱機械疲勞與潛變耦合劣化進行了深度的學術剖析與工程論證，綜合成果得出以下結論： This study provides a deep academic analysis and engineering demonstration of the thermo-mechanical fatigue and creep-coupled degradation encountered by main steam piping in combined cycle power plants facing high-frequency start-stop operations. The synthesized findings yield the following conclusions:

  1. EPC 設計理念的翻轉與幾何優化 (Reversal of EPC Design Philosophy and Geometric Optimization)：EPC 統包商應摒棄著眼於初期 CAPEX 的1.5D 銲接彎頭設計，轉向重視全生命週期 OPEX 的 3D/5D 冷作彎管。此舉大幅降低了 ASME B31J 定義的 SIF，並將最脆弱的 HAZ 移出幾何頂點，完美阻斷了 P91/P92 鋼因 Z 相析出與 Laves 相粗化所導致的 Type IV 破裂鏈。EPC contractors should abandon 1.5D welded elbow designs focused on initial CAPEX and pivot towards prioritizing full-life cycle OPEX via 3D/5D cold bends. This drastically lowers the SIF defined by ASME B31J and removes the most fragile HAZ from geometric apexes, perfectly severing the Type IV cracking chain caused by Z-phase precipitation and Laves phase coarsening in P91/P92 steels.
  2. 動態流體破壞的防護對策 (Protective Countermeasures Against Dynamic Fluid Failures)：採用 Sweepolet 替換傳統 Weldolet 分支，實質降低了流場剝離效應與聲功率級，有效緩解管壁高頻振動，減少保護膜被剪應力剝離的 FAC 風險。Substituting traditional Weldolets with Sweepolets substantially reduces flow separation effects and sound power levels. This effectively mitigates high-frequency pipe wall vibrations and decreases the FAC risk of protective films being stripped away by shear stress.
  3. 分析規範升級與精確壽命量化 (Analytical Code Upgrades and Precise Life Quantification)：強制導入 ASME B31J 標準並利用 CAESAR II 進行 SIF 與 SSI 解耦，釋放了隱藏的設計餘裕。結合 Code Case N-862 的 EPP 分析與 Larson-Miller 參數（C≒30~33），精確掌握了管線在循環軟化下的真實應力鬆弛狀態。Mandating the ASME B31J standard and utilizing CAESAR II to decouple SIF and SSI liberates hidden design margins. Combining EPP analysis from Code Case N-862 with the Larson-Miller Parameter (C≒30~33) precisely captures the true stress relaxation state of piping under cyclic softening.
  4. 精準導向的 RBI 完整性管理 (Precision-Guided RBI Integrity Management)：整合 CAESAR II 應力熱點圖譜與微觀相變特徵，透過 PAUT、TOFD 與金相覆膜技術，精準捕捉次表面微孔洞的早期劣變，實現動態科學的剩餘壽命管理。Integrating CAESAR II stress hotspot mapping with microscopic phase transformation features—using PAUT, TOFD, and metallographic replicas—accurately detects the early deterioration of subsurface micro-cavities, realizing a dynamic and scientific remaining life management.
  5. 「三合一工法」落實實務合規與商業雙贏 (“Three-in-One Method” Realizes Practical Compliance and Commercial Win-Wins)：透過潁璋工程提倡的冷作彎管、IH-PBHT 與數位化模組管理整合工法，不僅在製造端確保了管材微觀組織的修復，更保證了 ASME 表單的驗收合規性，為 EPC 統包商與業主帶來實質的營運效益。The integrated method advocated by Ying Zhang Engineering (cold bending, IH-PBHT, and digital module management) not only guarantees the restoration of the piping’s microstructure on the manufacturing end but also ensures acceptance compliance for ASME forms, bringing substantial operational benefits to both EPC contractors and owners.

實務建議 (Practical Recommendations)： 強烈建議未來的 CCPP 建廠 EPC 統包商及現有機組的延壽改造工程，應將 ASME B31J 算法列為應力分析的強制規範；在空間佈局許可下，主蒸氣管線應優先指定使用 3D/5D 冷作彎管與 Sweepolet。此外，業主端應積極導入並稽核如「三合一工法」般具備高度數位化與精準熱處理能力的製造流程，確保其麻田散鐵微觀組織的完整性，方能從容應對未來淨零碳排趨勢下日益嚴苛的電網調度挑戰。 It is strongly recommended that EPC contractors for future CCPP builds and life-extension retrofits for existing units mandate the ASME B31J algorithm for stress analysis. Where spatial layouts permit, 3D/5D cold bends and Sweepolets should be specified as priorities for main steam piping. Furthermore, owners should actively adopt and audit manufacturing processes that possess high degrees of digitalization and precise heat treatment capabilities—such as the “Three-in-One Method.” This ensures the integrity of the martensitic microstructure, which is the only way to comfortably meet the increasingly stringent grid dispatch challenges under future net-zero carbon emission trends.

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