基於 ASME 最新規範之主蒸汽管線支管線(4″含以下)防護策略與冷作彎管工法對提升全壽命週期可靠度之應用研究(Research on Protection Strategies for Small-Bore Main Steam Branch Piping (NPS 4 and Below) Based on the Latest ASME Codes and the Application of Cold Bending Processes to Enhance Life Cycle Reliability)

/ Uncategorized / 作者:

一、緒論 / I. Introduction

在現代化火力發電廠、複循環發電廠（CCPP）以及超臨界水壓發電系統的演進過程中，系統運轉溫度與壓力不斷攀升，主蒸汽管線與高溫再熱管線等高能管線（High-Energy Piping）的結構完整性，已成為維持電廠高可用率之關鍵。然而，全球電力產業的歷史失效數據與美國電力研究院（EPRI）的研究報告均指出，導致電廠發生非計畫性停機（Unplanned Outage）的最頻繁肇因，往往並非大管徑主幹管的破裂，而是公稱管徑（NPS）4 吋含以下之小管徑支管線（Small Bore Piping, SBP）的疲勞失效1。這類小管徑管線廣泛應用於儀表接管、排放管（Drains）、排氣管（Vents）及取樣系統中，其內部承載著與主蒸汽幹管完全相同的高溫高壓流體，但在幾何配置上通常呈現懸臂結構，極易成為應力集中的脆弱節點3。During the evolution of modern thermal power plants, Combined Cycle Power Plants (CCPP), and supercritical water-pressure power systems, operating temperatures and pressures have continuously escalated. The structural integrity of high-energy piping, such as main steam lines and high-temperature reheat lines, has become the key to maintaining high plant availability. However, historical failure data from the global power industry and research reports by the Electric Power Research Institute (EPRI) both indicate that the most frequent cause of unplanned plant outages is often not the rupture of large-diameter main pipes, but rather the fatigue failure of small-bore piping (SBP) with a nominal pipe size (NPS) of 4 inches and below1. These small-bore pipes are widely used in instrument connections, drains, vents, and sampling systems. They carry the exact same high-temperature and high-pressure fluids as the main steam pipes, but their geometric configurations typically present as cantilever structures, making them highly vulnerable nodes for stress concentration3.

長期以來，工程界在小管徑管線的設計與組裝上，高度依賴傳統的承插銲（Socket Weld）以及 1.5D 短半徑銲接彎頭。然而，此類傳統幾何結構在應對高頻機械振動與熱疲勞時顯得力有未逮。隨著美國機械工程師學會（ASME）B31.1《動力管線規範》的持續更新，特別是 ASME B31J 規範在應力強化係數（Stress Intensification Factor, SIF）計算上的強制導入，傳統管件的設計裕度已被嚴格限縮6。同時，潛變強度強化鐵素體鋼（Creep-Strength Enhanced Ferritic Steels, CSEF，如 Grade 91）的廣泛應用，使得管線在製造與成形階段的冶金控制條件達到前所未有的嚴苛程度8。For a long time, the engineering field has heavily relied on traditional socket welds and 1.5D short-radius welded elbows for the design and assembly of small-bore piping. However, such traditional geometric structures prove inadequate when dealing with high-frequency mechanical vibration and thermal fatigue. With the continuous updates to the American Society of Mechanical Engineers (ASME) B31.1 “Power Piping Code,” particularly the mandatory implementation of the ASME B31J standard for calculating Stress Intensification Factors (SIF), the design margins of traditional fittings have been strictly constrained6. Simultaneously, the widespread application of Creep-Strength Enhanced Ferritic Steels (CSEF, such as Grade 91) has elevated the metallurgical control conditions during the manufacturing and forming stages of piping to unprecedented levels of stringency8.

有鑑於此，本研究旨在深入探討基於 ASME 最新規範框架下，主蒸汽系統中小管徑支管線的防護與設計策略。研究核心將剖析導入 3D 或 5D 大半徑冷作彎管（Cold Bending）工法，在力學設計、流體動力學、複雜冶金熱處理以及非破壞檢測（NDT）等層面，如何徹底消除傳統銲接管件的先天缺陷。同時，結合 ASME PCC-3 的風險基準檢驗（RBI）架構，論證此工法在提升電廠系統可靠度與優化全壽命週期管理（Life Cycle Management）上的具體應用效益。In light of this, this study aims to delve deeply into the protection and design strategies for small-bore branch piping in main steam systems under the framework of the latest ASME codes. The core of the research will analyze how the introduction of 3D or 5D large-radius cold bending processes can thoroughly eliminate the inherent defects of traditional welded fittings across the dimensions of mechanical design, fluid dynamics, complex metallurgical heat treatment, and Non-Destructive Examination (NDE). Furthermore, by integrating the Risk-Based Inspection (RBI) framework of ASME PCC-3, it will demonstrate the specific application benefits of this process in enhancing plant system reliability and optimizing Life Cycle Management.

二、小管徑支管線之幾何弱點與疲勞失效機制解析 / II. Analysis of Geometric Vulnerabilities and Fatigue Failure Mechanisms in Small-Bore Branch Piping

小管徑支管線的失效特徵，主要表現為銲道區域的高周波疲勞（High Cycle Fatigue, HCF）開裂。EPRI 的 TR-104534 等早期報告已明確指出，高達 80% 的小管徑連接處失效肇因於承插銲的振動疲勞1。這種疲勞現象源於機械振動、熱應力與流體動力學負載的複雜耦合效應。The failure characteristics of small-bore branch piping are primarily manifested as High Cycle Fatigue (HCF) cracking in the weld areas. Early reports, such as EPRI’s TR-104534, have clearly indicated that up to 80% of failures in small-bore connections are caused by the vibration fatigue of socket welds1. This fatigue phenomenon stems from the complex coupling effects of mechanical vibration, thermal stress, and fluid dynamic loads.

2.1 承插銲接頭之應力集中與安裝公差侷限 / 2.1 Stress Concentration and Installation Tolerance Limitations of Socket Weld Joints

在小管徑管線的組裝實務中，承插銲接頭與 ASME B16.11 鍛造配件因免除了端面開坡口（Beveling）的繁瑣工序而被大量採用。然而，其幾何構造卻隱含著嚴重的應力集中風險。根據 ASME B31.1 規範的製造要求，承插銲的填角銲（Fillet Weld）最小腿長（Leg Length）必須大於或等於公稱管壁厚度（tn）的 1.09 倍1。除了銲道尺寸的限制外，規範更強力要求在將管子插入承插口後，必須將其退出約 1.6 mm（1/16 吋），以保留銲接冷卻與系統升溫時的膨脹間隙（Expansion Gap）1。In the assembly practices of small-bore piping, socket weld joints and ASME B16.11 forged fittings are widely adopted because they eliminate the tedious process of end beveling. However, their geometric construction harbors severe stress concentration risks. According to the manufacturing requirements of the ASME B31.1 code, the minimum leg length of a socket weld’s fillet weld must be greater than or equal to 1.09 times the nominal pipe wall thickness (tn)4. Beyond weld dimension limits, the code strictly mandates that after inserting the pipe into the socket, it must be withdrawn by approximately 1.6 mm (1/16 inch) to provide an expansion gap for cooling after welding and thermal expansion during system heat-up1.

在實際工程現場中，這個 1.6 mm 的退讓間隙往往因為管夾固定不當或人為疏忽而消失。當管端直接頂死於承插口底部時，系統在啟動升溫的過程中，軸向熱膨脹受到物理阻擋，巨大的壓應力將直接傳導至填角銲道上；而在系統降溫時，此應力又反轉為張應力15。長期的熱應力循環（Thermal Cycling），疊加上銲趾（Weld Toe）與銲根（Weld Root）本就存在的幾何不連續性，極易導致熱疲勞裂紋的萌生。In actual engineering sites, this 1.6 mm withdrawal gap often disappears due to improper clamping or human error. When the pipe end bottoms out directly against the socket base, axial thermal expansion is physically blocked during system heat-up, and tremendous compressive stress is directly transferred to the fillet weld; during system cooldown, this stress reverses into tensile stress15. Long-term thermal cycling, superimposed on the pre-existing geometric discontinuities at the weld toe and weld root, easily leads to the initiation of thermal fatigue cracks.

EPRI 針對承插銲的改良曾進行多項疲勞測試。例如，嘗試將銲道外型從標準的 1:1 比例改良為 2:1 的不對稱輪廓，藉此降低疲勞強度折減係數1。然而，測試數據亦表明，若盲目對小管徑承插銲實施銲後熱處理（PWHT）以期改善疲勞壽命，反而可能適得其反。PWHT 會中和原本存在於銲趾處有益的殘餘壓應力，導致疲勞失效位置從典型的銲根轉移至管側的銲趾處，加速裂紋的形成4。此現象充分顯示出傳統銲接接頭在設計極限值上的先天脆弱性。EPRI has conducted multiple fatigue tests aimed at improving socket welds. For instance, attempts were made to modify the weld profile from a standard 1:1 ratio to an asymmetric 2:1 contour, thereby reducing the fatigue strength reduction factor1. However, test data also indicated that blindly applying Post-Weld Heat Treatment (PWHT) to small-bore socket welds in hopes of improving fatigue life might be counterproductive. PWHT neutralizes the beneficial residual compressive stresses originally present at the weld toe, shifting the fatigue failure location from the typical weld root to the pipe-side weld toe, and accelerating crack formation4. This phenomenon fully demonstrates the inherent vulnerability of traditional welded joints at their design limits.

2.2 流體誘發振動 (FIV) 與動量通量評估 / 2.2 Flow-Induced Vibration (FIV) and Momentum Flux Assessment

除了熱應力之外，流體在管網中高速流動所激發的機械振動是導致支管線失效的另一主因。流體誘發振動（Flow-Induced Vibration, FIV）主要發生於高質量流率的液體或兩相流系統中。其振動源來自於管線內部的紊流（Turbulence）、流經障礙物時的渦流脫落（Vortex Shedding）或控制閥後方的空穴現象（Cavitation）17。In addition to thermal stress, mechanical vibration excited by fluids flowing at high speeds in the pipe network is another major cause of branch piping failures. Flow-Induced Vibration (FIV) primarily occurs in liquid or two-phase flow systems with high mass flow rates. The vibration sources originate from internal turbulence, vortex shedding when flowing past obstacles, or cavitation downstream of control valves17.

FIV 的特徵為低頻振動（通常低於 100 Hz），但其伴隨的動態力極大，會引發管線在縱向與橫向上的大幅度位移18。在工程評估上，動量通量（Momentum Flux）是篩選 FIV 風險的重要指標，其計算公式為：FIV is characterized by low-frequency vibration (usually below 100 Hz), but the accompanying dynamic forces are immense, causing significant longitudinal and transverse displacements of the piping18. In engineering assessments, momentum flux is a critical indicator for screening FIV risks, and its calculation formula is:

Momentum Flux=ρv2

其中 ρ 為流體密度（kg/m3），v為流速（m/s）17。當動量通量超過 10,000 kg/ms2  時，流體的動能足以激發懸臂式小管徑支管線的結構共振，進而導致剛性不足的管線支架損壞或銲道撕裂。對於附著於主幹管上的儀表引壓管或排放管，若未能透過適當的支撐設計（如兩向或三向防震拉撐）來提高其自然頻率，FIV 將在極短的運轉週期內造成疲勞斷裂。Where ρ is the fluid density (kg/m3), and v is the flow velocity (m/s) 17. When the momentum flux exceeds 10,000 kg/ms2  , the kinetic energy of the fluid is sufficient to excite structural resonance in cantilevered small-bore branch piping, leading to damage to insufficiently rigid pipe supports or tearing of welds. For instrument impulse lines or drain lines attached to the main pipe, if their natural frequencies are not elevated through appropriate support designs (such as two-way or three-way vibration damping braces), FIV will cause fatigue fracture within an extremely short operating cycle.

2.3 聲學誘發振動 (AIV) 與殼模態激發 / 2.3 Acoustic-Induced Vibration (AIV) and Shell-Mode Excitation

在主蒸汽系統或高壓氣體排放管線中，聲學誘發振動（Acoustic-Induced Vibration, AIV）造成的破壞往往比 FIV 更為迅猛且難以察覺。AIV 的成因在於高壓氣體流經減壓閥（PRV）、安全閥或限流孔板時，急遽的壓力降會產生強烈的高頻聲學能量17。In main steam systems or high-pressure gas venting lines, the damage caused by Acoustic-Induced Vibration (AIV) is often more rapid and difficult to detect than FIV. The root cause of AIV is that when high-pressure gas flows through pressure-reducing valves (PRV), safety valves, or restriction orifices, the abrupt pressure drop generates intense high-frequency acoustic energy17.

這種聲波在管內傳遞時，其頻率通常落在 500 Hz 至 2000 Hz 的寬頻範圍內。當聲波能量足夠大時，會直接激發管壁的殼模態振動（Shell-mode Vibration），使管壁產生高頻的徑向彎曲變形。在 AIV 作用下，小管徑支管線的連接處（特別是與主幹管的非等徑三通或銲接分支處）會承受數百甚至數千赫茲的交變應力。由於累積疲勞循環數的速度極快，此類失效往往在電廠試運轉或起槽後的數小時至數天內便會發生20。As these sound waves travel through the pipe, their frequencies typically fall within a broadband range of 500 Hz to 2000 Hz. When the acoustic energy is sufficiently high, it directly excites the shell-mode vibration of the pipe wall, causing high-frequency radial bending deformation. Under the action of AIV, connections of small-bore branch lines (especially reducing tees or welded branches attached to the main pipe) will endure alternating stresses of hundreds or even thousands of Hertz. Due to the extremely fast accumulation of fatigue cycles, such failures often occur within hours to days after plant commissioning or start-up20.

評估 AIV 風險的核心參數為聲功率級（Sound Power Level, Lw或 PWL），其計算基於 Energy Institute (EI) 的準則：The core parameter for assessing AIV risks is the Sound Power Level (Lw or PWL), which is calculated based on the Energy Institute (EI) guidelines:

Lw=10 log[M2×((P1-P2)/P1 )3.6×(T/W)1.2 ]+126.1+K

其中 M 為質量流率，P1 與 P2 為上下游絕對壓力，T 為流體溫度，W 為分子量，K 為音速流動的修正係數。利用 Lw 值結合管線的管徑與壁厚比（D/T Ratio），可計算出失效可能性（Likelihood of Failure, LOF）。當 LOF ≧ 1.0 時，代表該節點處於極高風險，必須強制進行結構重設計或採用聲學阻尼對策；即使 LOF 介於 0.3 至 0.5 之間，也必須對小管徑連接進行嚴格的完整性評估18。Where M is the mass flow rate, P1 and P2 are the upstream and downstream absolute pressures, T is the fluid temperature, W is the molecular weight, and K is the correction factor for sonic flow. By utilizing the Lw value in combination with the pipe’s diameter-to-thickness ratio (D/T Ratio), the Likelihood of Failure (LOF) can be calculated. An LOF ≧ 1.0  indicates that the node is at extremely high risk, mandating structural redesign or the adoption of acoustic damping countermeasures; even if the LOF is between 0.3 and 0.5, a strict integrity assessment must be conducted for the small-bore connections18.

三、ASME 規範演進與應力強化係數 (SIF) 之重構 / III. Evolution of ASME Codes and Restructuring of Stress Intensification Factors (SIF)

要從根本解決小管徑管線的疲勞問題，必須回歸到管件應力分析的規範層面。ASME B31.1《動力管線規範》是確保發電廠高溫高壓管線安全設計的最高準則5。近年來，該規範在管網位移應力分析與管件應力評估上，發生了歷史性的典範轉移。To fundamentally resolve the fatigue issues of small-bore piping, one must return to the regulatory level of piping component stress analysis. The ASME B31.1 “Power Piping Code” serves as the highest standard ensuring the safe design of high-temperature and high-pressure piping in power plants5. In recent years, this code has undergone a historic paradigm shift in piping network displacement stress analysis and component stress evaluation.

3.1 從 A.R.C. Markl 的經驗公式到 Appendix D / 3.1 From A.R.C. Markl’s Empirical Formulas to Appendix D

應力強化係數（SIF, 代號 i）的概念，最早可追溯至 1940 年代末至 1950 年代初 A.R.C. Markl 及其團隊的開創性研究22。Markl 透過大量的彎管與三通疲勞測試發現，彎頭在承受彎矩時會發生橢圓化變形（Ovalization），使得管壁外層纖維更靠近中性軸，這雖然增加了管件的柔性（Flexibility），但也導致了局部截面模數的降低與應力的急遽增加25。The concept of the Stress Intensification Factor (SIF, denoted as i) dates back to the pioneering research of A.R.C. Markl and his team in the late 1940s and early 1950s1. Through extensive fatigue testing of bends and tees, Markl discovered that elbows undergo ovalization when subjected to bending moments, bringing the outer fibers of the pipe wall closer to the neutral axis. While this increases the component’s flexibility, it also leads to a reduction in the local section modulus and a sharp increase in stress25.

基於這些觀察，Markl 提出了柔性特徵值（Flexibility Characteristic, h）的概念。對於對接銲接彎頭，其 SIF 被定義為i=0.9/h2/3，其中h=tn*R/r2（tn 為公稱壁厚，R 為彎曲半徑，r 為平均截面半徑）22。這些基於單一力矩推導出的經驗公式，隨後被納入 ASME B31 規範的 Mandatory Appendix D 中，統治了管線應力分析長達半個多世紀6。Based on these observations, Markl proposed the concept of the Flexibility Characteristic (h). For butt-welded elbows, the SIF was defined as i=0.9/h2/3, where h=tn*R/r2 (tn being nominal wall thickness, R the bend radius, and r the mean cross-sectional radius) 22. These empirical formulas derived from a single moment were subsequently incorporated into Mandatory Appendix D of the ASME B31 codes, dominating piping stress analysis for over half a century6.

然而，舊版 Appendix D 的侷限性在於其採用的「綜合 SIF」概念。它無法準確區分空間中不同方向力矩對管件造成的真實應力集中差異。此外，對於非等徑分支（Reduced Branch Connections），早期的外推法被證明是偏向非保守（Non-conservative）的，實際的應力強化效應可能比公式預測高出兩倍。However, the limitation of the older Appendix D lay in its adoption of a “comprehensive SIF” concept. It failed to accurately differentiate the true stress concentration differences caused by moments in different spatial directions. Furthermore, for reduced branch connections, the early extrapolation method was proven to be non-conservative; the actual stress intensification effect could be up to twice as high as the formula predicted.

3.2 ASME B31J 的全面導入與三維應力邊界修正 / 3.2 Comprehensive Implementation of ASME B31J and 3D Stress Boundary Corrections

隨著現代有限元素分析（FEA）技術的成熟與更精確疲勞測試數據的累積，ASME 意識到單一 SIF 公式的不足。從 2016 年版 ASME B31.1 開始，規範逐步引入 ASME B31J《Standard for Determining Stress Intensification Factors (i-Factors) for Metallic Piping Components》的資料6。經歷了 2018 年的替代選項與 2020 年的條文重寫，最終在 2024 年版的 B31.1 中，徹底廢除了舊有的 Appendix D，強制規定位移應力範圍（Displacement Stress Range）的計算必須全面採用 B31J 的數值6。With the maturation of modern Finite Element Analysis (FEA) technologies and the accumulation of more precise fatigue test data, ASME recognized the inadequacies of a single SIF formula. Starting with the 2016 edition of ASME B31.1, the code gradually introduced data from ASME B31J “Standard for Determining Stress Intensification Factors (i-Factors) for Metallic Piping Components”6. After going through alternative options in 2018 and a rewrite of provisions in 2020, the 2024 edition of B31.1 finally abolished the old Appendix D entirely, mandating that the calculation of the Displacement Stress Range must comprehensively adopt B31J values6.

B31J 的核心在於將 SIF 與柔性係數（k-factor）進行了三維空間的精確拆解7。在最新規範框架下，彎管或分支連接的等效彈性應力（SE）計算必須分別代入面內（In-plane）、面外（Out-of-plane）與扭轉（Torsional）三個獨立的 SIF 值：The core of B31J lies in the precise tri-dimensional spatial decomposition of the SIF and the flexibility factor (k-factor) 7. Under the latest code framework, the calculation of equivalent elastic stress (SE) for bends or branch connections must individually incorporate three independent SIF values: In-plane, Out-of-plane, and Torsional:

SE=√[(iiMi)2+(ioMo)2+(itMt)2]/Z

在傳統分析中，扭轉力矩對 SIF 的影響通常被忽略（即設定為 1.0）。但 B31J 首次強制針對多種管件導入了it≠1.0 的條件7。在空間配置緊湊的小管徑管網中，熱膨脹極易轉化為管線末端的扭轉位移。若繼續依賴傳統短半徑管件，其面內外 SIF（ii,io）往往高達 3.0 至 5.0，而新加入的扭轉 SIF（it）更會進一步推升綜合應力7。這種理論精確度的提升，實質上大幅壓縮了傳統管件的設計裕度，迫使工程設計必須尋求應力集中度更低的管件替代方案。In traditional analysis, the impact of torsional moments on the SIF was typically ignored (i.e., set to 1.0). However, B31J mandates, for the first time, conditions where it≠1.0 for various fittings7. In compactly arranged small-bore pipe networks, thermal expansion easily translates into torsional displacement at the pipe ends. If relying continuously on traditional short-radius fittings, their in-plane and out-of-plane SIFs (ii,io) are often as high as 3.0 to 5.0, and the newly added torsional SIF (it) will further drive up the comprehensive stress7. This enhancement in theoretical precision essentially drastically compresses the design margins of traditional fittings, compelling engineering designs to seek alternative components with lower stress concentrations.

四、3D/5D 冷作彎管工法之優勢與系統性能提升 / IV. Advantages of 3D/5D Cold Bending Processes and System Performance Enhancement

在嚴格的 B31J 規範標準下，傳統 1.5D 鍛造銲接彎頭往往面臨應力超標的困境，這導致設計師不得不增加昂貴的恆力彈簧吊架（Constant Spring Hangers）或大幅修改管線走向（Routing）以吸收熱應力26。為突破此瓶頸，導入以高精度 CNC 機床製作的 3D 或 5D 大半徑冷作彎管（Cold Bending），成為高能管線設計的顯學。Under the stringent B31J code standards, traditional 1.5D forged welded elbows frequently face the predicament of exceeding stress limits, which forces designers to add expensive Constant Spring Hangers or significantly alter the routing to absorb thermal stress26. To break through this bottleneck, adopting 3D or 5D large-radius Cold Bending manufactured by high-precision CNC machines has become a prominent trend in high-energy piping design.

4.1 消除局部銲縫與降低應力強化係數 / 4.1 Eliminating Local Welds and Reducing Stress Intensification Factors

冷作彎管工法是在室溫或次臨界溫度下，直接將無縫鋼管成形為特定半徑與角度的彎管，徹底消除了傳統彎頭與直管連接處的對接或承插銲縫。從結構力學的觀點來看，銲縫本質上就是冶金不連續與應力集中的區域。The cold bending process forms seamless steel pipes directly into bends of a specific radius and angle at room or subcritical temperatures, completely eliminating the butt or socket welds where traditional elbows connect to straight pipes. From a structural mechanics perspective, welds are inherently regions of metallurgical discontinuity and stress concentration.

將冷彎管代入 B31J 的方程式中，由於其彎曲半徑（R1）為管外徑的 3 倍至 5 倍，大幅提高了柔性特徵值（h）。這使得 3D/5D 冷彎管的面內外 SIF 值（ii,io）降至 1.0 至 1.2 左右，幾乎等同於完美直管的應力狀態；且扭轉 SIF（it）完美維持在 1.0，沒有任何幾何放大效應。這意味著在相同的熱膨脹與設備動態位移下，冷作彎管能以極低的局部應力平順地傳導載荷，有效化解了高周波疲勞的破壞風險。Substituting cold bends into the B31J equations reveals that since their bend radius (R1) is 3 to 5 times the outer diameter of the pipe, the flexibility characteristic (h) is significantly increased. This lowers the in-plane and out-of-plane SIF values (ii,io) of 3D/5D cold bends to roughly 1.0 to 1.2, which is nearly equivalent to the stress state of a perfect straight pipe; moreover, the torsional SIF (it) remains perfectly at 1.0, with no geometric amplification effect whatsoever. This means that under the same thermal expansion and dynamic equipment displacement, cold bends can smoothly transmit loads with extremely low local stress, effectively neutralizing the risk of high-cycle fatigue failure.

4.2 幾何成形控制：應變率、減薄率與橢圓度 / 4.2 Geometric Forming Control: Strain Rate, Wall Thinning, and Ovality

冷作彎管的品質取決於對材料塑性變形的精密控制。彎曲過程中，外弧側受拉伸導致管壁減薄（Wall Thinning），內弧側受擠壓導致管壁增厚，而整體管截面會產生橢圓化變形（Ovality）。The quality of cold bends depends on the precise control of the material’s plastic deformation. During the bending process, the outer arc (extrados) is stretched, causing wall thinning, while the inner arc (intrados) is compressed, causing wall thickening, and the overall cross-section undergoes ovality deformation.

依據 ASME B31.1 的容許標準，動力管線彎管的最大橢圓度通常限制在 8% 以內，最大管壁減薄率則限制在 12%。現代化帶有內部芯棒（Mandrel）支撐的旋轉拉彎（Rotary Draw Bending）技術，能將 5D 彎管的減薄率嚴格控制在 8% 以內，使其無需依賴採購特製的超厚母管即可滿足內壓計算（tm=P⋅Do/2(S⋅E⋅W+P⋅y) +A）的設計要求11。According to the tolerance standards of ASME B31.1, the maximum ovality of power piping bends is typically limited to 8%, and the maximum wall thinning is limited to 12%. Modern Rotary Draw Bending technology, equipped with internal mandrel support, can strictly control the thinning rate of 5D bends to within 8%, allowing them to meet the internal pressure calculation design requirements (tm=P⋅Do/2(S⋅E⋅W+P⋅y) +A) without relying on the procurement of expensive, custom extra-heavy parent pipes11.

成形塑性應變率（ϵ）是另一個決定後續熱處理需求的關鍵指標，其幾何估算公式為：The forming plastic strain rate (ϵ) is another critical indicator that determines the need for subsequent heat treatment, with its geometric estimation formula being:

ϵ=Do/2R1×100%

計算顯示，3D 彎管的成形應變率約為 16.7%，而 5D 彎管的應變率更低，約為 10.0%。這種較低的應變率對於後續處理高等級合金鋼具有決定性的冶金優勢。Calculations show that the forming strain rate for a 3D bend is approximately 16.7%, while that of a 5D bend is even lower at about 10.0%. This lower strain rate provides a decisive metallurgical advantage for the subsequent processing of high-grade alloy steels.

4.3 根絕流體加速腐蝕 (FAC) 與冷凝水誘發水錘 (CIWH) / 4.3 Eradicating Flow-Accelerated Corrosion (FAC) and Condensate-Induced Water Hammer (CIWH)

從流體力學的層面檢視，傳統 1.5D 短半徑彎頭因急遽改變流向，內部會產生強烈的邊界層分離與二次渦流，這是引發流體加速腐蝕（Flow-Accelerated Corrosion, FAC）的溫床。改用 5D 冷彎管後，平緩的曲率使得流體的流線（Streamlines）能緊貼管壁，不僅大幅抑制了渦流生成，降低了管線系統 20% 至 30% 的壓力降，更從物理根源上拔除了 FAC 賴以生成的紊流剪切力。Examined from a fluid mechanics perspective, traditional 1.5D short-radius elbows, due to abrupt changes in flow direction, generate severe boundary layer separation and secondary vortices internally, serving as breeding grounds for Flow-Accelerated Corrosion (FAC). By switching to 5D cold bends, the gentle curvature ensures that fluid streamlines remain closely attached to the wall. This not only significantly suppresses vortex generation and reduces system pressure drop by 20% to 30% but also uproots the turbulent shear stress that FAC relies on from its physical source.

此外，在主蒸汽支管線（如排放管）中，若疏水坡度設計不良，積存的冷凝水在遭遇高速蒸汽時，極易引發熱力學狀態崩潰，產生極具破壞力的冷凝水誘發水錘（Condensate Induced Water Hammer, CIWH）。CIWH 瞬間釋放的動能可輕易摧毀管線支撐系統並撕裂銲道。CNC 數控冷作彎管能在成形過程中，精準刻劃出 1° 至 3° 的微洩水坡度，確保冷凝水在重力作用下徹底排出，從系統端根除了 CIWH 的潛在危機。Additionally, in main steam branch lines (such as drain lines), if the drainage slope is poorly designed, accumulated condensate encountering high-velocity steam can easily trigger a thermodynamic state collapse, producing highly destructive Condensate-Induced Water Hammer (CIWH). The kinetic energy released instantaneously by CIWH can easily destroy pipe support systems and tear welds. CNC cold bending processes can precisely machine micro-drainage slopes of 1° to 3° during forming, ensuring that condensate is completely drained under gravity, thereby eliminating the potential crisis of CIWH at a systemic level.

五、潛變強度強化鐵素體鋼 (CSEF) 之冶金挑戰與熱處理對策 / V. Metallurgical Challenges and Heat Treatment Countermeasures for Creep-Strength Enhanced Ferritic Steels (CSEF)

在先進火力發電系統中，主蒸汽與高溫再熱管線廣泛採用潛變強度強化鐵素體鋼（CSEF），其中以 ASME P-No. 15E（即 Grade 91 / P91）最為典型。P91 的卓越高溫潛變抗力，並非單純依靠固溶強化，而是源自極其精密的微觀組織控制8。In advanced thermal power generation systems, main steam and high-temperature reheat lines widely employ Creep-Strength Enhanced Ferritic Steels (CSEF), with ASME P-No. 15E (i.e., Grade 91 / P91) being the most typical. The outstanding high-temperature creep resistance of P91 does not rely solely on solid solution strengthening, but rather originates from extremely precise microstructural control8.

5.1 P91 鋼之微觀組織與潛變強化機制 / 5.1 Microstructure and Creep Strengthening Mechanisms of P91 Steel

P91 鋼的標準製造程序包含高溫的正規化（Normalizing，通常在 1040–1080°C）與隨後的回火（Tempering，通常在 730–800°C）27。此熱處理程序能確保材料形成 100% 的回火馬氏體（Tempered Martensite）基質，並在原奧氏體晶界與馬氏體板條（Lath）邊界上析出富含鉻的 M23C6 碳化物，以及在基質內部散佈奈米級的釩、鈮碳氮化物（MX）8。這些穩定的析出物能有效釘扎（Pinning）錯位，阻礙其在高溫服役下的滑移與攀移，從而賦予 P91 優異的潛變強度9。The standard manufacturing process for P91 steel involves high-temperature Normalizing (typically at 1040–1080°C) followed by Tempering (typically at 730–800°C) 27. This heat treatment procedure ensures the material forms a 100% Tempered Martensite matrix, precipitating chromium-rich M23C6 carbides on prior austenite grain boundaries and martensite lath boundaries, while dispersing nano-scale vanadium/niobium carbonitrides (MX) inside the matrix8. These stable precipitates effectively pin dislocations, hindering their slip and climb during high-temperature service, thereby endowing P91 with excellent creep strength9.

為了確保不產生有害的 δ-鐵素體（Delta-ferrite），P91 的合金成分必須受到嚴格控制，通常透過鉻鎳當量平衡（CNB）公式來檢驗：To ensure the prevention of detrimental delta-ferrite, the alloy composition of P91 must be strictly controlled, which is typically verified using the Chromium-Nickel Balance (CNB) formula:

CNB=Cr+6Si+4Mo+1.5W+11V+5Nb+9Ti+12Al-40C-30N-4Ni-2Mn-1Cu

當 CNB 值小於 10 時，方能確保材料不含 δ-鐵素體，維持組織的均一性。Only when the CNB value is less than 10 can it be assured that the material contains no delta-ferrite, maintaining microstructural uniformity.

5.2 冷作應變對微觀結構的破壞與 ASME 熱處理規範 / 5.2 Destruction of Microstructure by Cold Strain and ASME Heat Treatment Codes

儘管 P91 在高溫下表現優異，但其對冷作變形極度敏感11。冷彎成形過程會在管壁內部引入極高的位錯密度與應變能。如果直接將冷加工狀態的 P91 投入高溫服役環境，這些儲存的應變能將作為熱力學驅動力，誘發材料發生應變誘導回復（Strain-induced Recovery）與靜態再結晶（Static Recrystallization）。這會導致釘扎錯位的析出物粗化、馬氏體板條結構瓦解，進而使基質急遽軟化，其潛變壽命可能驟減一至兩個數量級8。Despite its superb performance at high temperatures, P91 is extremely sensitive to cold deformation11. The cold bending process introduces a very high dislocation density and strain energy into the pipe wall. If P91 in its cold-worked state is directly placed into a high-temperature service environment, this stored strain energy acts as a thermodynamic driving force, inducing Strain-induced Recovery and Static Recrystallization in the material. This causes the coarsening of precipitates that pin dislocations and the breakdown of the martensite lath structure, leading to rapid softening of the matrix. Consequently, its creep life may plummet by one to two orders of magnitude8.

為防範此一冶金災難，ASME B31.1 第 129.3 節明確規範了 P-No. 15E 材料的彎管後熱處理（PBHT）要求，且不適用任何基於管徑或壁厚的熱處理豁免條款（No exemptions from PWHT）28。To prevent this metallurgical catastrophe, ASME B31.1 Section 129.3 explicitly stipulates Post-Bend Heat Treatment (PBHT) requirements for P-No. 15E materials, explicitly stating that no heat treatment exemptions based on pipe diameter or wall thickness are applicable (No exemptions from PWHT) 28.

依據 ASME BPVC 第 I 卷（PG-20）與 B31.1 規範，冷作成形的應變率直接決定了熱處理的層級：

According to ASME BPVC Section I (PG-20) and the B31.1 code, the cold forming strain rate directly dictates the level of heat treatment required:

  1. 高應變率（> 20%）： 若彎管的成形應變率超過 20%（如5D 或部分 2D 短半徑彎管），原有的析出物分佈已遭嚴重破壞，必須重新將整支管件進行完全的正規化與回火（Full Normalizing and Tempering, N&T）熱處理，以重建微觀組織16。High Strain Rate (> 20%): If the forming strain rate of the bend exceeds 20% (such as in 1.5D or some 2D short-radius bends), the original precipitate distribution is severely destroyed. The entire component must undergo a Full Normalizing and Tempering (N&T) heat treatment to reconstruct the microstructure16.
  2. 低應變率（< 20%）： 若採用 5D 大半徑冷作彎管，其成形應變率僅約 10%，未觸及 20% 的臨界門檻。因此，規範允許僅執行次臨界回火熱處理（Subcritical Tempering PBHT），即可有效釋放殘餘應力並穩定微觀組織，避免了重新高溫奧氏體化所帶來的高昂成本與管件變形風險26。Low Strain Rate (< 20%): If 5D large-radius cold bends are utilized, their forming strain rate is only about 10%, not reaching the 20% critical threshold. Therefore, the code permits the execution of only a Subcritical Tempering PBHT, which effectively relieves residual stresses and stabilizes the microstructure. This avoids the exorbitant costs and pipe deformation risks associated with re-austenitizing at high temperatures26.

5.3 次臨界 PBHT 之溫度控制極限與微量元素干擾 / 5.3 Temperature Control Limits of Subcritical PBHT and Trace Element Interference

執行次臨界 PBHT 的最大挑戰，在於熱處理溫度絕對不可跨越材料的下臨界相變溫度（AC1）。一旦加熱溫度超過 AC1，基質會開始發生部分的奧氏體逆轉變。在隨後的冷卻過程中，這些奧氏體會轉變為未經回火的脆硬新鮮馬氏體（Fresh Martensite），形成軟硬相間的「雙相」結構9。這種結構極度不穩定，尤其在銲接熱影響區（HAZ）的細晶區（Fine-grained HAZ），是引發致命 Type IV 潛變開裂（Type IV Cracking）的元兇9。The greatest challenge in executing Subcritical PBHT lies in ensuring that the heat treatment temperature absolutely never crosses the material’s lower critical transformation temperature (AC1). Once the heating temperature exceeds AC1, the matrix begins a partial reverse transformation to austenite. During subsequent cooling, this austenite transforms into untempered, brittle “Fresh Martensite,” forming a dual-phase structure of alternating soft and hard zones9. This structure is highly unstable, particularly in the fine-grained Heat-Affected Zone (HAZ) of welds, serving as the prime culprit for initiating fatal Type IV creep cracking9.

實務上，P91 鋼中的微量合金元素會對 AC1 溫度產生劇烈影響。特別是鎳（Ni）與錳（Mn）等奧氏體穩定元素，會顯著壓低 AC1 的溫度極限值。根據 ASME B31.1 Table 132.1.1-1 與相關研究，當鋼材中的 Ni+Mn 含量 ≦ 1.0% 時，最高熱處理溫度可設定為 790°C（實際 AC1 約在 800°C – 825°C 之間）。但若鋼廠為了提升材料韌性而將 Ni+Mn 含量提高至 > 1.2%，則該批次材料的 AC1 溫度會大幅降低。此時，必須透過膨脹儀或熱分析實驗獨立量測實測的 AC1 溫度，且 PBHT 的最高溫度必須嚴格控制在低於實測 AC1 至少 10°C 以上之安全區間內。In practice, trace alloying elements in P91 steel have a dramatic impact on the AC1 temperature. Specifically, austenite stabilizers like Nickel (Ni) and Manganese (Mn) significantly depress the AC1 temperature limits. According to ASME B31.1 Table 132.1.1-1 and related studies, when the Ni+Mn content in the steel is ≦ 1.0%, the maximum heat treatment temperature can be set to 790°C (actual AC1 is approximately 800°C – 825°C). However, if the steel mill increases the Ni+Mn content to > 1.2% to enhance material toughness, the AC1 temperature of that batch will drop substantially. In this case, the actual AC1 temperature must be independently measured using dilatometry or thermal analysis experiments, and the maximum temperature for PBHT must be strictly controlled within a safe margin of at least 10°C below the measured AC1.

為確保絕對安全，業界通常將 P91 的 PBHT 目標溫度區間設定在 730°C 至 770°C 之間30。此外，熱處理設備必須採用具備閉迴路數位溫控的感應加熱（Induction Heating）系統，嚴密監控升降溫速率（通常限制為 Max 400°F/hr ÷ 壁厚），並確保保溫時間充足（通常為每英吋壁厚 1 小時，最低 30 分鐘）。To ensure absolute safety, the industry typically sets the target PBHT temperature range for P91 between 730°C and 770°C30. Moreover, the heat treatment equipment must utilize an Induction Heating system equipped with closed-loop digital temperature control, closely monitoring heating and cooling rates (usually limited to Max 400°F/hr ÷ wall thickness), and ensuring adequate holding time (typically 1 hour per inch of wall thickness, with a minimum of 30 minutes).

5.4 防止氫致開裂之全程熱工序管理 / 5.4 Comprehensive Thermal Process Management to Prevent Hydrogen-Induced Cold Cracking

除了防範高溫潛變退化外，P91 這類高硬化能鋼種在常溫下對氫致延遲開裂（Hydrogen-Induced Cold Cracking, HICC）亦非常敏感。因此，無論是進行銲接或熱加工，都必須實施嚴格的全程溫度路徑控制：In addition to preventing high-temperature creep degradation, high-hardenability steels like P91 are also extremely sensitive to Hydrogen-Induced Cold Cracking (HICC) at room temperature. Therefore, whether performing welding or hot working, a strict comprehensive temperature path control must be implemented:

  1. 預熱（Preheat）： 在進行任何銲接或成形之前，必須將工作區域均勻預熱至至少 200°C ~ 204°C（400°F）。預熱能降低液態金屬與熱影響區的冷卻速率，避免產生脆性極高的馬氏體組織，並提供足夠的時間讓擴散氫（Diffusible Hydrogen）從晶格中逸出7。Preheat: Before any welding or forming, the work area must be uniformly preheated to at least 200°C ~ 204°C (400°F). Preheating lowers the cooling rate of the liquid metal and the Heat-Affected Zone (HAZ), preventing the formation of highly brittle martensitic structures and allowing sufficient time for Diffusible Hydrogen to escape from the crystal lattice.
  2. 除氫烘烤（Hydrogen Bake-out/Post-heating）： 在銲接或加工完成後，絕不能讓工件直接冷卻至室溫。必須立即將溫度提升至 300°C ~ 350°C，並持溫 2 至 3 小時進行除氫烘烤。此一步驟旨在將殘留的氫原子徹底驅離材料內部，切斷 HICC 的發生條件。Hydrogen Bake-out/Post-heating: After welding or processing is complete, the workpiece must never be allowed to cool directly to room temperature. The temperature must immediately be raised to 300°C ~ 350°C and held for 2 to 3 hours for a hydrogen bake-out. This step aims to thoroughly drive residual hydrogen atoms out of the material, cutting off the conditions for HICC to occur.
  3. 馬氏體轉變冷卻（Martensite Transformation Cooling）： 這是最容易被忽略卻至關重要的環節。在執行最終的 PBHT 之前，必須讓材料緩慢冷卻至馬氏體轉變終了溫度（Mf，約 96°C）以下。實務上，規範建議降溫至 90°C 以下。此步驟確保高溫生成的奧氏體能夠 100% 轉變為馬氏體。若未降至此溫度即開始升溫回火，殘留的奧氏體會在熱處理冷卻後才轉變為新鮮馬氏體，導致二次體積膨脹，引發微觀應力裂紋。Martensite Transformation Cooling: This is the most easily overlooked yet crucial step. Before executing the final PBHT, the material must be allowed to cool slowly below the martensite finish temperature (Mf, approx. 96°C). In practice, codes recommend cooling below 90°C. This ensures that the high-temperature-generated austenite can 100% transform into martensite. If reheating for tempering begins before dropping to this temperature, the retained austenite will only transform into fresh martensite after the heat treatment cools down, causing secondary volumetric expansion and initiating microscopic stress cracks.

最後，為確認 PBHT 的成效，硬度測試是不可或缺的品質驗證手段。ASME 規範通常要求 P91 銲道與熱影響區在熱處理後的最高硬度不得超過 250 HB（或 265 HV / 25 HRC），部分嚴格的業主規範更將上限緊縮至 248 HB，以確保材料具備足夠的韌性與良好的微觀組織平衡。Finally, to confirm the effectiveness of PBHT, hardness testing is an indispensable quality verification tool. ASME codes generally require that the maximum hardness of the P91 weld and HAZ after heat treatment must not exceed 250 HB (or 265 HV / 25 HRC). Some stringent owner specifications further tighten this limit to 248 HB, ensuring the material possesses adequate toughness and a well-balanced microstructure.

六、小管徑管線之檢驗標準與非破壞檢測 (NDE) 技術進展 / VI. Inspection Standards and Nondestructive Examination (NDE) Technological Advancements for Small-Bore Piping

要將冷作彎管的高可靠度轉化為電廠的實際運轉資產，嚴謹的品質檢驗是最後一哩路。ASME B31.1 第六章對動力管線的檢查、檢驗與測試制定了強制性標準。To translate the high reliability of cold bends into tangible operating assets for a power plant, rigorous quality inspection represents the final mile. Chapter VI of ASME B31.1 establishes mandatory standards for the inspection, examination, and testing of power piping.

6.1 視覺檢驗 (VT) 之嚴格允收標準 / 6.1 Strict Acceptance Criteria for Visual Examination (VT)

依據 ASME B31.1 Table 136.4 規定，視覺檢驗（Visual Examination, VT）是所有銲道最基本且強制的第一道防線31。視覺檢驗的執行細節必須遵循 ASME BPVC 第 V 卷 Article 9 的準則。According to the provisions of ASME B31.1 Table 136.4, Visual Examination (VT) is the most basic and mandatory first line of defense for all welds31. The execution details for visual examination must comply with the guidelines in ASME BPVC Section V, Article 9.

對於銲道表面的缺陷，B31.1 第 136.4.2 節設定了明確的剔除標準：For surface defects on welds, Section 136.4.2 of B31.1 sets explicit rejection criteria:

  • 咬边（Undercut）： 圓周對接銲道表面的咬边深度最大不得超過8 mm（1/32 吋），且深度不得侵犯管線設計所需的最小壁厚斷面31。Undercut: The maximum depth of undercut on the surface of circumferential butt welds must not exceed 0.8 mm (1/32 in.), and the depth must not encroach upon the minimum wall thickness required for the piping design31.
  • 表面氣孔（Surface Porosity）： 任何單一圓形指示（Rounded Indication）其尺寸超過 5 mm（3/16 吋），或者四個以上的圓形指示形成群聚且彼此邊緣間距小於或等於5 mm（1/16 吋）時，該銲道即判定為不合格6。Surface Porosity: If any single rounded indication exceeds 5 mm (3/16 in.) in dimension, or if a cluster of four or more rounded indications is separated by 1.5 mm (1/16 in.) or less edge-to-edge, the weld is judged as unacceptable6.
  • 銲道加強層（Weld Reinforcement）： 外部加強層的厚度必須符合規範圖表的限制，過高的加強層會導致應力集中，尤其在承受 AIV/FIV 負載時極易引發銲趾疲勞。Weld Reinforcement: The thickness of external reinforcement must comply with code table limits; excessive reinforcement leads to stress concentration, making it highly susceptible to weld toe fatigue, especially when bearing AIV/FIV loads.

6.2 先進非破壞檢測：克服小管徑的幾何限制 / 6.2 Advanced NDE: Overcoming Geometric Limitations of Small-Bore Piping

儘管目視檢驗能過濾表面缺陷，但對於內部隱藏的銲根未熔合（Lack of Penetration）、夾渣或微裂紋，必須依賴體積型非破壞檢測（Volumetric NDE）。然而，對於 NPS 4 吋以下的小管徑厚壁管，傳統的射線檢測（RT）常受限於雙壁透影的解析度，而傳統超音波檢測（UT）則難以在極小的曲面上貼合探頭並進行精確掃描2。Although visual examination can filter out surface defects, detecting internally hidden Lack of Penetration at the weld root, slag inclusions, or micro-cracks requires reliance on Volumetric Non-Destructive Examination (NDE). However, for thick-walled small-bore piping of NPS 4 and below, traditional Radiographic Testing (RT) is often limited by the resolution of double-wall radiography, while conventional Ultrasonic Testing (UT) struggles to seat probes flatly on tiny curved surfaces for precise scanning2.

為突破此限制，現代電廠檢測大量導入了先進的 NDT 技術：To break through this limitation, modern power plant inspections have massively adopted advanced NDT technologies:

  1. 相位陣列超音波檢測 (Phased Array Ultrasonic Testing, PAUT)： 對於必須保留的終端對接銲道或小管徑分支銲道（Branch Connections），PAUT 展現了無與倫比的優勢。PAUT 探頭內部包含數十個獨立壓電晶片，透過電腦精密控制各晶片激發的微小時間差，產生多角度的偏轉射束，形成高解析度的扇形掃描（S-scan）影像2。這種電子掃描能力不僅克服了探頭無法在小管徑曲面上順暢移動的困難，更能多維度重構銲道內部的 3D 缺陷圖像，極大地提升了檢出率與定性精度。Phased Array Ultrasonic Testing (PAUT): For terminal butt welds that must be retained or small-bore Branch Connections, PAUT demonstrates unparalleled advantages. The PAUT probe contains dozens of independent piezoelectric elements; by precisely controlling the minute time delays in exciting each element via computer, it generates multi-angle deflected beams to form high-resolution Sectorial Scan (S-scan) images2. This electronic scanning capability not only overcomes the difficulty of moving probes smoothly on small-bore curved surfaces but also multi-dimensionally reconstructs 3D defect images inside the weld, vastly improving detection rates and qualitative accuracy.
  2. 電磁聲學換能器 (Electromagnetic Acoustic Transducer, EMAT)： 對於 5D 冷作彎管在長期服役期間的管壁減薄（Thinning）與流體加速腐蝕（FAC）追蹤，EMAT 技術帶來了革命性的改變35。傳統 UT 需要使用液體耦合劑（Couplant），且表面必須打磨光滑，這在運轉中的高溫管線或帶有氧化皮的表面幾乎無法執行35。EMAT 的原理是利用強磁場與交流線圈，直接在金屬內部透過洛倫茲力（Lorentz Force）與磁致伸縮效應激發出超音波35。因為聲波是在金屬表面之下生成，EMAT 不需要任何液體耦合劑，且超音波訊號能夠輕易穿透外層的氧化皮（Oxide Scale）或輕微鏽蝕，直達真實的金屬底壁反射。 透過配備週期性永久磁鐵（PPM）或高溫專用探頭，EMAT 系統能夠在管線不降溫、不停機的狀態下，於彎管外弧側進行多點連續的線上壁厚監測（Online Thickness Monitoring）。這項技術為捕捉局部的 FAC 減薄或隱蔽的應力腐蝕開裂（SCC），提供了即時且高度可靠的量化數據支撐35。Electromagnetic Acoustic Transducer (EMAT): For tracking wall thinning and Flow-Accelerated Corrosion (FAC) in 5D cold bends over long-term service, EMAT technology has brought revolutionary changes35. Traditional UT requires the use of liquid couplants and smoothed surfaces, which is nearly impossible to execute on operating high-temperature piping or surfaces with oxide scale35. The principle of EMAT involves using strong magnetic fields and alternating current coils to directly excite ultrasonic waves inside the metal via Lorentz Force and magnetostrictive effects35. Because the sound waves are generated beneath the metal surface, EMAT requires no liquid couplant, and the ultrasonic signals can easily penetrate outer Oxide Scale or slight rust to reach the true metal back-wall reflection. Equipped with Periodic Permanent Magnets (PPM) or high-temperature probes, EMAT systems can perform multi-point, continuous Online Thickness Monitoring on the extrados of bends without shutting down or cooling the pipe. This technology provides real-time, highly reliable quantitative data support for capturing localized FAC thinning or hidden Stress Corrosion Cracking (SCC) 35.
NDE 技術 / NDE Technology 原理與優勢 / Principles and Advantages 在小管徑/冷彎管系統之應用場景 / Application Scenarios in Small-Bore/Cold Bend Systems 參考依據 / References
視覺檢驗 (VT) / Visual Examination (VT) 檢視表面幾何不連續性 / Inspecting surface geometric discontinuities 捕捉銲趾咬边、加強層超標與表面氣孔 / Capturing weld toe undercut, excessive reinforcement, and surface porosity ASME B31.1 Table 136.46
相位陣列超音波 (PAUT) / Phased Array Ultrasonic Testing (PAUT) 電子射束偏轉形成 S-scan 影像 / Electronic beam deflection forming S-scan images 小管徑銲道內部未熔合、微裂紋之精確定位 / Precise localization of internal lack of fusion and micro-cracks in small-bore welds 高解析度體積掃描 / High-resolution volumetric scanning
電磁聲學換能器 (EMAT) / Electromagnetic Acoustic Transducer (EMAT) 洛倫茲力激發，無液體耦合劑需求 / Lorentz force excitation, no liquid couplant required 高溫運轉中之冷作彎管壁厚減薄與 FAC 監測 / Online monitoring of cold bend wall thinning and FAC during high-temp operation 線上檢測，穿透氧化皮 / Online inspection, penetrates oxide scale

七、全壽命週期管理：RBI 與完整性操作窗口 (IOW) 之整合 / VII. Life Cycle Management: Integration of RBI and Integrity Operating Windows (IOW)

硬體設計的優化與先進的檢測技術，最終必須收斂於系統化的資產管理框架中。將 5D 冷作彎管應用於小管徑主蒸汽支管線，不僅是為了符合當下 ASME B31.1 的建廠標準，更是為了降低電廠在未來數十年的維運成本，實現真正的全壽命週期管理。The optimization of hardware design and advanced inspection technologies must ultimately converge within a systematic asset management framework. Applying 5D cold bends to small-bore main steam branch lines is not only to comply with current ASME B31.1 construction standards but also to reduce O&M costs for the power plant over the coming decades, achieving genuine Life Cycle Management.

7.1 ASME PCC-3 與 API 581 風險基準檢驗 (RBI) / 7.1 ASME PCC-3 and API 581 Risk-Based Inspection (RBI)

傳統的管線檢測計畫通常採取基於時間（Time-based）或法規強制規定的固定週期抽測，這往往導致資源錯置—過度檢驗低風險區域，卻漏檢高風險節點。引入 ASME PCC-3《Inspection Planning Using Risk-Based Methods》與 API RP 581 的風險基準檢驗（Risk-Based Inspection, RBI）架構，能有效解決此一痛點39。Traditional piping inspection plans usually adopt Time-based or legally mandated fixed-interval sampling, which often leads to resource misallocation—over-inspecting low-risk areas while missing high-risk nodes. Introducing the Risk-Based Inspection (RBI) framework from ASME PCC-3 “Inspection Planning Using Risk-Based Methods” and API RP 581 can effectively resolve this pain point39.

RBI 的核心精神在於將檢驗資源優先投注於「風險（Risk）」最高的區域。風險值定義為失效機率（Probability of Failure, POF）與失效後果（Consequence of Failure, COF）的乘積。The core spirit of RBI is to prioritize inspection resources on areas with the highest “Risk.” The risk value is defined as the product of the Probability of Failure (POF) and the Consequence of Failure (COF).

  • 失效機率 (POF) 的降低： 在傳統設計中，承插銲與1.5D 短半徑彎頭因應力強化係數極高，且對 FIV/AIV 敏感，屬於 POF 極高的高風險節點。當系統導入 5D 冷作彎管後，由於徹底消除了局部銲縫的應力集中，且流場變得平順（降低 FAC 與 AIV 誘發機率），其 POF 得以呈指數級下降20。Reduction of POF: In traditional designs, socket welds and 1.5D short-radius elbows, due to their extremely high stress intensification factors and sensitivity to FIV/AIV, are high-risk nodes with extremely high POF. Once the system adopts 5D cold bends, completely eliminating stress concentration at local welds and smoothing the flow field (lowering the probability of inducing FAC and AIV), the POF drops exponentially20.
  • 檢測策略的轉移： 依據 PCC-3 的指導原則，當該區域的 POF 大幅降低後，系統的整體風險評級亦隨之下降。電廠便可合理、合法地將檢驗間隔（Inspection Intervals）拉長，或是將檢驗重點從繁瑣的銲道疲勞裂紋探傷，轉向長週期的冷彎管外壁減薄量測（透過 EMAT 技術）35。這不僅大幅減少了歲修期間搭設施工架（Scaffolding）與拆除保溫層的龐大費用，更降低了人員暴露於惡劣環境的安全風險43。Shift in Inspection Strategy: According to the guiding principles of PCC-3, when the POF of a specific area decreases significantly, the overall risk rating of the system also drops. The plant can then reasonably and legally extend the Inspection Intervals or shift the inspection focus from tedious fatigue crack flaw detection on welds to long-cycle wall thinning measurements on cold bend extrados (via EMAT technology) 35. This not only significantly reduces the massive costs of erecting scaffolding and removing insulation during outages but also lowers the safety risks of personnel exposure to harsh environments43.

7.2 完整性操作窗口 (IOW) 的落實 / 7.2 Implementation of Integrity Operating Windows (IOW)

為了確保 POF 始終維持在低水平，RBI 系統必須與 API RP 584 提出的完整性操作窗口（Integrity Operating Windows, IOW）緊密結合40。IOW 定義了設備安全運轉的關鍵參數（如溫度、壓力、流速、水化學指標等）的上下限。若偏離這些界限，將導致新的損傷機制出現或加速既有損傷（如 P91 材質因超溫運轉導致潛變速率急升）。To ensure that POF remains consistently at a low level, the RBI system must be tightly integrated with the Integrity Operating Windows (IOW) proposed by API RP 58440. IOW defines the upper and lower limits of key parameters for the safe operation of equipment (such as temperature, pressure, flow rate, and water chemistry indicators). Deviating from these boundaries will lead to the emergence of new damage mechanisms or accelerate existing ones (e.g., P91 material experiencing a rapid rise in creep rate due to over-temperature operation).

透過整合 5D 冷彎管的力學分析模型、EMAT 蒐集的即時壁厚數據，以及分散式控制系統（DCS）監控的操作參數，電廠管理團隊能夠動態更新 IOW 的邊界值。當偵測到特定支管線區域的操作參數逼近 IOW 極限時，系統可提前觸發預警，使工程師在發生疲勞斷裂或潛變破裂前，主動採取介入措施（如調整降壓閥開度以減緩 AIV，或修正水化學控制以減緩腐蝕），從而確保高能管線在長達 30 至 40 年的全壽命週期內，始終維持最高的結構完整性與運轉可靠度。By integrating the mechanical analysis models of 5D cold bends, real-time wall thickness data gathered by EMAT, and operating parameters monitored by the Distributed Control System (DCS), the plant management team can dynamically update the boundary values of the IOW. When it detects that operating parameters in a specific branch line area are approaching IOW limits, the system can trigger early warnings, allowing engineers to take proactive intervention measures (such as adjusting pressure-reducing valve openings to mitigate AIV or correcting water chemistry control to slow corrosion) before fatigue fracture or creep rupture occurs. This ensures that high-energy piping consistently maintains the highest structural integrity and operational reliability throughout a lifecycle spanning 30 to 40 years.

八、CCPP工廠 1.5D 電銲彎頭工序與 4吋含以下 3D/5D 大半徑冷作彎管工法差異化分析 / VIII. Differential Analysis of 1.5D Welded Elbow Procedures and 3D/5D Large-Radius Cold Bending Processes for NPS 4 and Below in CCPP Plants

針對現代大型燃氣複循環發電廠（CCPP）的高能管線系統，1.5D 短半徑電銲彎頭與 3D/5D 大半徑冷作彎管在設計、施工與維運上存在顯著差異。以下將從產業鏈中不同關鍵利害關係人之實務視角進行深度剖析。For high-energy piping systems in modern large Combined Cycle Power Plants (CCPP), 1.5D short-radius welded elbows and 3D/5D large-radius cold bends exhibit significant differences in design, construction, and O&M. The following provides an in-depth analysis from the practical perspectives of various key stakeholders in the industrial chain.

8.1 業主對於高能蒸汽管線銲道與冷作彎管維護管理及營運決策 / 8.1 Owner’s Maintenance Management and Operational Decision-Making Regarding Welds vs. Cold Bends in High-Energy Steam Piping

對 CCPP 業主而言，高能管線的非計畫性停機（Unplanned Outage）往往帶來鉅額營運損失。統計指出，小管徑承插銲或電銲彎頭因熱疲勞或振動破裂所引發的停機事件，單次損失常高達十四萬美元以上。在營運與維護決策上，採用冷作彎管徹底消除了路徑轉折處的銲縫，免除了每次歲修期間必須額外編列的射線檢測（RT）與超音波檢測（UT）等非破壞檢測（NDT）之龐大費用44。在 RBI 管理架構下，冷作彎管能顯著降低系統失效機率（POF），賦予業主合理延長歲修與檢測週期的法規依據，從而實現全壽命週期成本（LCC）的最佳化控制。For CCPP owners, unplanned outages caused by high-energy piping often result in massive operational losses. Statistics indicate that outage events triggered by thermal fatigue or vibration cracking in small-bore socket welds or welded elbows often cost upwards of $140,000 per incident. Regarding O&M decision-making, utilizing cold bends thoroughly eliminates welds at path turns, bypassing the enormous costs that must be additionally budgeted for NDT—like Radiographic Testing (RT) and Ultrasonic Testing (UT)—during every turnaround44. Under the RBI management framework, cold bends can significantly reduce the system’s Probability of Failure (POF), giving owners the regulatory basis to reasonably extend turnaround and inspection intervals, thereby achieving optimized control over Life Cycle Costs (LCC).

8.2 EPC承包商設計單位對於空間佈置與實務考量 / 8.2 Spatial Layout and Practical Considerations for EPC Contractor Design Units

EPC 統包商在進行廠區高密度管網佈置時，深受 ASME B31J 強制導入之應力評估標準約束。傳統 1.5D 彎頭極小的柔性特徵值，導致其面內、面外及扭轉應力強化係數（SIF）高達 3.0 至 5.0，迫使設計單位必須配置複雜的膨脹環（Expansion Loops）或昂貴的恆力彈簧吊架以吸收熱應力。若改採 5D 大半徑冷彎管，其 SIF 值趨近於 1.0，大幅提升了空間佈置的彈性並減少管架數量。此外，依據規範，3D 彎管需預留高達 25% 的壁厚補償（1.25tm），常導致必須採購昂貴的客製化超厚母管；相較之下，5D 冷彎管的外弧減薄率極低，僅需預留 8% 的壁厚餘裕（1.08tm），大幅優化了 EPC 端的材料採購成本與施工期程。When mapping out high-density pipe networks in the plant, EPC contractors are deeply constrained by the stress evaluation standards mandatorily introduced by ASME B31J. The extremely small flexibility characteristic of traditional 1.5D elbows results in in-plane, out-of-plane, and torsional Stress Intensification Factors (SIF) as high as 3.0 to 5.0, forcing design units to configure complex Expansion Loops or expensive constant spring hangers to absorb thermal stress. If 5D large-radius cold bends are adopted instead, their SIF values approach 1.0, substantially increasing the flexibility of spatial layout and reducing the number of pipe supports. Moreover, according to code, 3D bends require reserving up to 25% wall thickness compensation (1.25tm), which often forces the procurement of expensive, customized extra-heavy parent pipes; in contrast, 5D cold bends have an extremely low extrados thinning rate, requiring only an 8% wall thickness allowance (1.08tm), significantly optimizing material procurement costs and construction schedules on the EPC end.

8.3 廠務管理者角度看待管線要求 / 8.3 Plant Manager’s Perspective on Piping Requirements

對廠務管理者而言，確保系統無洩漏且抗干擾能力強是最高指導原則。高能蒸汽系統中的流體誘發振動（FIV）與聲學誘發振動（AIV）是導致傳統小管徑銲道疲勞斷裂的主因17。傳統銲接彎頭不僅是應力集中點，其突兀的流向改變更容易引發渦流與流體加速腐蝕（FAC）。改採 3D/5D 冷作彎管後，平滑的流線型內壁有效降低了系統 20% 至 30% 的壓力降，並徹底根絕了因積水引發的冷凝水誘發水錘（CIWH）風險。這使得廠務維修團隊得以免除頻繁搭設高空施工架及拆除保溫層進行銲趾探傷的繁瑣工作，極大化提升了現場工安與維護效率。For plant managers, ensuring a leak-free system with strong interference-resistance is the highest guiding principle. Flow-Induced Vibration (FIV) and Acoustic-Induced Vibration (AIV) in high-energy steam systems are the main culprits leading to fatigue fractures in traditional small-bore welds17. Traditional welded elbows are not only stress concentration points, but their abrupt change in flow direction makes it easier to trigger vortices and Flow-Accelerated Corrosion (FAC). By switching to 3D/5D cold bends, the smooth, streamlined inner walls effectively reduce system pressure drops by 20% to 30%, and completely eradicate the CIWH risks caused by pooled water. This relieves the plant maintenance team from the tedious tasks of frequently erecting high-altitude scaffolding and removing insulation to perform flaw detection on weld toes, maximizing on-site safety and maintenance efficiency.

8.4 冷作彎管施作協力廠商角度及因應策略 / 8.4 Perspectives and Response Strategies of Cold Bending Subcontractors

身為專業冷作彎管協力廠商，其技術核心在於克服嚴苛的成形極限值與冶金控制。在實務作業中，必須運用高精度 CNC 數控彎管機搭配內部芯棒（Mandrel）支撐技術，精準控制彎管的最大橢圓度於 8% 以內，且最大管壁減薄率不得超過 12%。針對極易產生氫致延遲開裂（HICC）的 P91 等厚壁高強度合金，協力廠商必須嚴格執行至少 204°C 的預熱，並在成形後立即實施 300°C 至 350°C 的除氫烘烤，隨後緩慢冷卻至馬氏體轉變終了溫度（約 90°C）以下，確保奧氏體 100% 轉變後，方能進行後續的安全熱處理26。As professional cold bending subcontractors, their technical core lies in overcoming stringent forming limits and metallurgical controls. In practical operations, they must utilize high-precision CNC tube bending machines paired with internal mandrel support technology to precisely control the maximum ovality of the bend to within 8%, and the maximum wall thinning to no more than 12%. For thick-walled, high-strength alloys like P91 that are highly susceptible to Hydrogen-Induced Cold Cracking (HICC), subcontractors must strictly execute a preheat of at least 204°C. Immediately after forming, they must apply a hydrogen bake-out at 300°C to 350°C, followed by slow cooling to below the martensite finish temperature (approx. 90°C) to ensure 100% transformation of austenite, before proceeding to subsequent safe heat treatments26.

8.5 導入潁璋工程「能彎不銲」之三合一工法管理核心價值優化與合規性落實 / 8.5 Optimization of Management Core Value and Compliance Implementation by Adopting Ying-Zhang Engineering’s “Bend Rather Than Weld” Three-in-One Process

導入潁璋工程（Ying-Zhang Engineering）所提倡的「三合一工法」（3D/5D CNC 大半徑冷作彎管 + IH-PBHT 單管感應亞臨界彎後熱處理 + QR Code 雲端數位履歷），乃是發揮大半徑優勢之最佳實務解方45。此工法管理的核心價值在於徹底落實「能彎不銲」的設計理念，從源頭將易受流體沖刷與疲勞破壞的銲縫，轉化為連續平滑的母材彎曲段7。針對 P9x 高能管線，此工法的執行不僅是製造手段的升級，更是嚴格對接 ASME B31.1 與 B31J 規範的合規性展現7。Adopting the “Three-in-One Process” (3D/5D CNC Large-Radius Cold Bending + IH-PBHT Single-Tube Induction Subcritical Post-Bend Heat Treatment + QR Code Cloud Digital Traceability) advocated by Ying-Zhang Engineering is the best practical solution for leveraging the advantages of large radii45. The core management value of this process lies in thoroughly implementing the “bend rather than weld” design philosophy, transforming the welds—which are susceptible to fluid erosion and fatigue destruction—into continuous, smooth parent material bend segments right from the source7. For P9x high-energy piping, the execution of this process is not merely an upgrade in manufacturing means, but also a demonstration of strict compliance alignment with ASME B31.1 and B31J codes7.

在極度深入的實務分析中，此三合一工法的核心效益可拆解為以下三大維度：In a highly in-depth practical analysis, the core benefits of this three-in-one process can be decomposed into the following three dimensions:

  1. 物理力學與流場之絕對優化（CNC 大半徑冷作彎管）： 透過高精度 CNC 設備將直管直接成形為 5D 彎管，去除了傳統幾何轉折處的銲接熱應力與銲道本身所引起的流體阻抗效應。在 ASME B31J 規範框架下，此舉不僅使應力強化係數降至最低，更結合波登效應（Bourdon effect）與計算流體力學（CFD）之流場特徵，大幅降低高頻交變負載環境下的管線疲勞風險。Absolute Optimization of Physical Mechanics and Flow Fields (CNC Large-Radius Cold Bending): Forming straight pipes directly into 5D bends via high-precision CNC equipment eliminates welding thermal stresses at traditional geometric turns and the fluid impedance effects caused by the welds themselves. Under the ASME B31J code framework, this act not only reduces SIFs to a minimum but also, combined with the Bourdon effect and Computational Fluid Dynamics (CFD) flow characteristics, vastly lowers piping fatigue risks under high-frequency alternating load environments.
  2. 嚴苛冶金極限之精準跨越（IH-PBHT 單管感應亞臨界彎後熱處理）： 面對 P91 等對熱輸入極度敏感的材料，傳統整體爐溫控制往往因熱延遲而導致局部超溫。三合一工法採用獨立的單管中頻感應加熱（IH-PBHT），確保升降溫速率與恆溫區間嚴格控制在下臨界溫度（AC1）之下，完美修復 5% 至 20% 冷作應變所產生的晶格畸變，同時避免第四型（Type IV）潛變破裂的萌生，完全符合 ASME B31.1 之法定放寬要求7。Precise Traversing of Stringent Metallurgical Limits (IH-PBHT Single-Tube Induction Subcritical Post-Bend Heat Treatment): When dealing with materials extremely sensitive to heat input like P91, traditional bulk furnace temperature controls often lead to localized overheating due to thermal lag. The three-in-one process utilizes independent single-tube medium-frequency induction heating (IH-PBHT), ensuring that heating/cooling rates and soaking ranges are strictly controlled below the lower critical temperature (AC1). This perfectly repairs lattice distortions generated by 5% to 20% cold strain while preventing the initiation of Type IV creep cracking, fully complying with the statutory relaxation requirements of ASME B31.17.
  3. 全壽命週期管理與數位孿生（QR Code 雲端數位履歷）： 在現場施工端，免除銲道意味著直接省去龐大的射線檢測（RT）與超音波檢測（UT）等非破壞檢測費用，更大幅減少了對高階電銲工的依賴，有效化解現場缺工危機並降低工時成本。在管理端，每一支冷作彎管皆綁定專屬的 QR Code 雲端數位履歷，將製造參數、壁厚減薄率測試、硬度檢驗與熱處理曲線全面透明化。這不僅將 ASME B31.1 附錄 R 所要求的數位履歷節點呈指數級壓縮，更為電廠日後的風險基準檢驗（RBI）提供了具備高度學術嚴謹性與可操作性的數據基礎。Life Cycle Management and Digital Twins (QR Code Cloud Digital Traceability): On the site construction end, eliminating welds means directly saving on massive NDE costs like Radiographic Testing (RT) and Ultrasonic Testing (UT), and drastically reducing reliance on high-level welders, effectively resolving on-site labor shortage crises and lowering labor hour costs. On the management end, every cold bend is bound to an exclusive QR Code cloud digital record, making manufacturing parameters, wall thinning tests, hardness inspections, and heat treatment curves fully transparent. This not only compresses the digital trace nodes required by ASME B31.1 Appendix R exponentially but also provides a data foundation with high academic rigor and operability for the plant’s future Risk-Based Inspections (RBI).

8.6 複循環燃氣機組頻繁起停之物理瞬態與熱力學循環破壞機制及應變率放寬解析 / 8.6 Analysis of Physical Transients, Thermodynamic Cyclic Destruction Mechanisms, and Strain Rate Relaxation for Frequently Started and Stopped CCPP Units

現代 CCPP 複循環燃氣機組為配合再生能源之電網調峰，頻繁的起停（Start-stop）操作使高能管網承受劇烈的熱力學瞬態變化。此極端操作環境極易誘發致命的潛變-疲勞交互作用（Creep-Fatigue Interaction, CFI）。依據疲勞延性公式 Δϵp/2=ϵf‘(2Nf )c 分析，傳統 1.5D 彎頭的高 SIF 值會將局部塑性應變幅（Δϵp）急遽放大，在負指數特徵影響下，導致疲勞壽命以三次方的速率崩跌。Modern CCPP units, to accommodate power grid peak shaving for renewable energy, endure frequent start-stop operations, subjecting high-energy pipe networks to violent thermodynamic transients. This extreme operational environment is highly prone to inducing fatal Creep-Fatigue Interaction (CFI). Analyzing based on the fatigue ductility formula Δϵp/2=ϵf‘(2Nf )c, the high SIF value of traditional 1.5D elbows drastically amplifies the local plastic strain amplitude (Δϵp). Influenced by the negative exponent characteristic, this causes the fatigue life to plummet at a cubic rate.

然而，導入 5D 冷作彎管工法迎來了法規層面的重大突破。依據冷作應變率計算，5D 彎管的成形應變率約為 10%，精準落入最新 ASME B31.1 規範針對 P91 等潛變強度強化材料所定義的「5% 至 20%」應變率放寬極限值區間內7。這項法規放寬具有決定性的實務意義：它允許 5D 冷彎管豁免執行極高風險與高成本的完全正規化與回火（N&T）重工，僅需實施次臨界的 IH-PBHT，即可有效修復晶格畸變與差排堆積，完美保留 P91 鋼卓越的潛變抗力，為 CCPP 高能系統帶來了最可靠的結構防護解方7。However, introducing the 5D cold bending process brings a major breakthrough at the regulatory level. Based on cold strain rate calculations, the forming strain rate of a 5D bend is approximately 10%, falling precisely into the “5% to 20%” strain rate relaxation limit range defined by the latest ASME B31.1 code for creep-strength enhanced materials like P917. This regulatory relaxation holds decisive practical significance: it exempts 5D cold bends from executing the extremely high-risk and high-cost Full Normalizing and Tempering (N&T) rework, requiring only subcritical IH-PBHT to effectively repair lattice distortions and dislocation pile-ups. This perfectly preserves the superb creep resistance of P91 steel, providing the most reliable structural protection solution for CCPP high-energy systems7.

九、結論 / IX. Conclusion

主蒸汽系統中公稱管徑 4 吋及以下之小管徑支管線，因其獨特的幾何配置與剛性不足，長期以來承受著熱應力、流體誘發振動（FIV）與聲學誘發振動（AIV）的嚴苛考驗。傳統廣泛使用的承插銲接頭與 1.5D 短半徑彎頭，由於先天內建了極高的應力集中源，成為電廠系統中最脆弱的疲勞斷裂節點。Small-bore branch lines of NPS 4 and below in main steam systems, due to their unique geometric configurations and lack of rigidity, have long endured the severe trials of thermal stress, Flow-Induced Vibration (FIV), and Acoustic-Induced Vibration (AIV). Traditionally widely used socket weld joints and 1.5D short-radius elbows, having inherently built-in extreme stress concentration sources, act as the most vulnerable fatigue fracture nodes in power plant systems.

隨著 ASME B31.1《動力管線規範》強制導入 B31J 的應力評估標準，工程界對於管件局部應力的解析從單一經驗公式邁入了三維精密分解的時代。在面內、面外以及扭轉應力強化係數（ii,io,it）的嚴格檢視下，傳統 1.5D 彎頭與承插銲的設計裕度被大幅壓縮，迫使產業界尋求更安全的結構替代方案。With the ASME B31.1 “Power Piping Code” mandatorily introducing B31J stress evaluation standards, the engineering community’s resolution of local component stress has moved from single empirical formulas into an era of precise 3D decomposition. Under the strict scrutiny of in-plane, out-of-plane, and torsional stress intensification factors (ii,io,it), the design margins of traditional 1.5D elbows and socket welds have been substantially compressed, forcing the industry to seek safer structural alternatives.

本研究證實，導入 3D 或 5D 大半徑冷作彎管（Cold Bending）工法，是突破此一工程困境的最佳防護策略。冷作彎管徹底消除了高壓組件間的局部銲縫，其柔順的幾何特徵使得應力強化係數降至接近直管的水準，並透過平緩的流線分佈，從物理流場的根源拔除了引發流體加速腐蝕（FAC）與冷凝水誘發水錘（CIWH）的條件。This study confirms that adopting the 3D or 5D large-radius Cold Bending process is the best protection strategy to break through this engineering dilemma. Cold bends completely eliminate local welds between high-pressure components; their smooth geometric features reduce SIFs to levels approaching straight pipes, and through gentle streamline distribution, they uproot the conditions that trigger Flow-Accelerated Corrosion (FAC) and Condensate-Induced Water Hammer (CIWH) from the physical flow field source.

在冶金防護方面，針對對冷作應變極度敏感的 P-No. 15E（Grade 91）潛變強度強化鐵素體鋼，5D 冷彎工法因成形應變率控制在 10% 左右，使得熱處理工序免於高昂的完全正規化與回火（N&T）重工。只需嚴密監控次臨界彎管後熱處理（PBHT）的最高溫度低於材料的 AC1 臨界值，並配合嚴格的預熱、除氫烘烤與馬氏體轉變冷卻程序，即可完美保留 P91 鋼卓越的高溫潛變抗力與韌性。In terms of metallurgical protection, addressing the extreme sensitivity to cold strain in P-No. 15E (Grade 91) creep-strength enhanced ferritic steel, the 5D cold bending process controls the forming strain rate around 10%, sparing the heat treatment procedure from exorbitant Full Normalizing and Tempering (N&T) rework. By simply strictly monitoring that the maximum temperature of subcritical Post-Bend Heat Treatment (PBHT) remains below the material’s AC1 critical limit, paired with strict preheating, hydrogen bake-out, and martensite transformation cooling procedures, the excellent high-temperature creep resistance and toughness of P91 steel can be perfectly preserved.

最後，在全壽命週期管理的維度上，冷作彎管降低失效機率（POF）的物理特性，完美契合了 ASME PCC-3 的風險基準檢驗（RBI）精神。搭配無需耦合劑的高溫電磁聲學換能器（EMAT）技術與相位陣列超音波檢測（PAUT），電廠得以實現非侵入式的線上狀態監測，使維護策略從事後被動搶修躍升為主動預測與防範。此一整合力學設計、精密冶金控制與現代風險管理框架的綜合防護策略，不僅符合最新版 ASME 規範的嚴格標準，更為提升現代發電廠高能系統的整體可靠度與經濟效益，提供了極具學理依據與實務價值的最佳解方。Finally, in the dimension of Life Cycle Management, the physical characteristic of cold bends lowering the Probability of Failure (POF) perfectly aligns with the spirit of Risk-Based Inspection (RBI) in ASME PCC-3. Paired with couplant-free high-temperature Electromagnetic Acoustic Transducer (EMAT) technology and Phased Array Ultrasonic Testing (PAUT), power plants can achieve non-invasive online condition monitoring, elevating maintenance strategies from passive post-event emergency repairs to proactive prediction and prevention. This comprehensive protection strategy—integrating mechanical design, precise metallurgical control, and modern risk management frameworks—not only complies with the strict standards of the latest ASME codes but also provides the most academically sound and practically valuable solution for enhancing the overall reliability and economic efficiency of high-energy systems in modern power plants.

參考文獻 / References

  1. Socket Weld Resolution Guideline – EPRI, https://restservice.epri.com/publicdownload/000000000001003542/0/Product
  2. Steam generator small bore piping socket weld inspection using the, https://www.tandfonline.com/doi/full/10.1080/00223131.2014.855151
  3. Reducing Vibration-Induced Stress in Small-bore Piping, https://www.structint.com/reducing-vibration-induced-stress-in-small-bore-piping-using-damped-support-systems/
  4. Pipe and Round Tube Bending – Bend It Inc, https://benditinc.com/pipe-and-round-tube-bending/
  5. ASME B31.1-2024: Power Piping [New] [Changes] – The ANSI Blog, https://blog.ansi.org/ansi/asme-b31-1-2024-power-piping-changes/
  6. ASME B31.1-2024 Stress Intensification Factors (SIFs) — FAQ, https://pipingtoolset.com/faq/b311-stress-intensification-factors/
  7. 基於2026 ASME B31J 規範之CCPP 高能管線銲接彎頭與3D/5D 冷作, https://yz-pipe-bending.com.tw/%E5%9F%BA%E6%96%BC-2026-asme-b31j-%E8%A6%8F%E7%AF%84%E4%B9%8B-ccpp-%E9%AB%98%E8%83%BD%E7%AE%A1%E7%B7%9A%E9%8A%B2%E6%8E%A5%E5%BD%8E%E9%A0%AD%E8%88%87-3d-5d-%E5%86%B7%E4%BD%9C%E5%BD%8E%E7%AE%A1%E7%B5%90/
  8. EPRI – Best Practice Guidelines For Manufacturing and Construction, https://www.scribd.com/document/412726426/EPRI-Best-Practice-Guidelines-for-Manufacturing-and-Construction-of-Grade-91-9Cr-1Mo-Steel-Components
  9. EPRI 3002001465 – Grade 91 Steel Handbook – Scribd, https://www.scribd.com/document/689638950/EPRI-3002001465-Grade-91-Steel-Handbook
  10. 2026 ASME 規範架構下1 & B31.3 成型應變率之深度剖析：5D, https://yz-pipe-bending.com.tw/2026-asme-%E8%A6%8F%E7%AF%84%E6%9E%B6%E6%A7%8B%E4%B8%8B-b31-1-b31-3-%E6%88%90%E5%9E%8B%E6%87%89%E8%AE%8A%E7%8E%87%E4%B9%8B%E6%B7%B1%E5%BA%A6%E5%89%96%E6%9E%90%EF%BC%9A5d-%E5%86%B7%E4%BD%9C%E5%BD%8E/
  11. ASME B31.1 Power Piping Code 2026 — Inspection Requirements, https://atlantisndt.com/blog/asme-b31-1-power-piping-code-explained
  12. 1, POWER PIPING – ASME Digital Collection, https://asmedigitalcollection.asme.org/ebooks/book/chapter-pdf/2793221/802183_ch16.pdf
  13. Stress Intensification Factor for Socket Welds – Eng-Tips, https://www.eng-tips.com/threads/stress-intensification-factor-for-socket-welds.80410/
  14. Stress Indices for Circumferential Fillet Welded and Socket … – EPRI, https://restservice.epri.com/publicdownload/000000000001006867/0/Product
  15. What is Socket Welding? The Ultimate Guide to Socket Weld Pipe, https://epcland.com/socket-weld-pipe-fittings-guide/
  16. 4 B31.1 Bending, Forming, Assembly & Code Records, https://open-exam-prep.com/study-guides/aws-cwi-endorsement-asme-ix/b31-1-pwht-examination/b31-1-bending-forming-assembly-records
  17. FIV and AIV – Flow Induced Vibration – Design and Engineering, https://designandengg.com/fiv-and-aiv/
  18. Piping Vibration: Causes, Risks, and Prevention – JSC Engineers, https://jscengineers.com/piping-vibration-analysis/
  19. Acoustic Induced Vibration (AIV) Solutions | Piping Tech, https://pipingtech.com/services/acoustic-induced-vibration-aiv/
  20. AIV & FIV Screening and Analysis Services – iFluids Engineering, https://ifluids.com/aiv-fiv-screening-and-analysis-services/
  21. ASME B31.1-2016 – Standards Michigan, https://standardsmichigan.com/wp-content/uploads/2018/01/Proposed-Revision-of-B31.X-Power-Piping-Public-Review-Draft-2346.pdf
  22. Background of SIFs and Stress Indices for Moment Loadings … – OSTI, https://www.osti.gov/servlets/purl/841246
  23. Stress Intensification Factors – caepipe, https://www.sstcae.com/technical-articles/stress-intensification-factors
  24. Stress Intensification Factors (SIFs) in Pipe Stress Analysis, https://simumech.com/stress-intensification-factors-sifs-in-pipe-stress-analysis/
  25. 3 Stress Intensification Factors, https://www.littlepeng.com/single-post/2020/03/29/13-stress-intensification-factors
  26. CCPP廠高能廢熱回收管線之冷作彎管與電銲彎頭差異化分析, https://yz-pipe-bending.com.tw/ccpp%E5%BB%A0%E9%AB%98%E8%83%BD%E5%BB%A2%E7%86%B1%E5%9B%9E%E6%94%B6%E7%AE%A1%E7%B7%9A%E4%B9%8B%E5%86%B7%E4%BD%9C%E5%BD%8E%E7%AE%A1%E8%88%87%E9%9B%BB%E9%8A%B2%E5%BD%8E%E9%A0%AD%E5%B7%AE%E7%95%B0/
  27. Coal Power Plant Materials And Life Assessment – Vdoc.pub, https://vdoc.pub/documents/coal-power-plant-materials-and-life-assessment-developments-and-applications-5c5poetuu6n0
  28. 6 Brazing Records 129 BENDING AND FORMING 129.1, https://files.engineering.com/files/d889f527-1e00-4a87-9f5f-6f7abb04b4d7/PWHT_Recommendation.pdf
  29. Asme B31P-2023 | PDF | Heat Treating – Scribd, https://www.scribd.com/document/836254264/ASME-B31P-2023
  30. Post-Weld Heat Treatment (PWHT): ASME Section VIII Compliance, https://zxweldingrobot.com/blog/post-weld-heat-treatment/
  31. Acceptance Standards for Visual Weld Inspection as per B31.1, https://www.weldfabworld.com/visual-examination-b31-1/
  32. ASME B31.1 NDE Requirements Overview | PDF – Scribd, https://www.scribd.com/document/625428262/Visual-examination-B31-1
  33. Why Small Bore Piping Fabrication Problems Happen, https://leadingtopunion.com/blog/why-heavy-steel-fabrication-problems-happen-and-how-buyers-can-prevent-them-20260513-after/
  34. Phased Array Inspection of Socket Welds | PDF | Ultrasound – Scribd, https://www.scribd.com/document/718226823/Steam-generator-small-bore-piping-socket-weld-inspection-using-the-phased-array-ultrasonic-technique
  35. How to Measure Pipe Wall Thickness Without Couplant Using EMAT, https://www.brkndt.com/application/measure-pipe-wall-thickness-without-couplant-emat-gauge.html
  36. EMAT – MVA Inspection, https://mvainspection.com/emat/
  37. Buried Gas Pipeline Inspection with EMAT’s, https://dr.lib.iastate.edu/server/api/core/bitstreams/ecf60877-4100-4e0e-a543-719bdec22b8a/content
  38. PPM EMAT for Defect Detection in 90-Degree Pipe Bend – MDPI, https://www.mdpi.com/1996-1944/15/13/4630
  39. Guidelines for Pressure Boundary Bolted Flange Joint Assembly, https://tecedu.academy/storage/training-content/000369/1/1/2p60Pv4VuHKTFNTwuiP0lQ3XRqLGILipoUIMhYA1.pdf
  40. Integrity Operating Windows, https://eballotprodstorage.blob.core.windows.net/eballotscontainer/API%20RP%20584%20Second%20Edition%204th%20Ballot%20Spring%202021%20Red%20Line.pdf
  41. ASME PD-077: Piping Failure Prevention | PDF | Corrosion – Scribd, https://www.scribd.com/document/838043971/ASME-L-D-PD-077-January-22-26-2024
  42. ASME PCC-2-2022 Repair Standards | PDF | Welding – Scribd, https://www.scribd.com/document/702991837/ASME-PCC-2-2022-HIGHLIGHTED
  43. High-Precision Wall Thickness Monitoring in a Nuclear Power Plant, https://ionixadvancedtechnologies.co.uk/2023/03/16/case-study-high-precision-wall-thickness-monitoring-in-nuclear-power-plant/
  44. 彎管配管當所有路徑轉折點，都沒有經過焊接工序處理… 思考: 1.無, https://www.facebook.com/100057434619150/photos/%E5%BD%8E%E7%AE%A1%E9%85%8D%E7%AE%A1%E7%95%B6%E6%89%80%E6%9C%89%E8%B7%AF%E5%BE%91%E8%BD%89%E6%8A%98%E9%BB%9E%E9%83%BD%E6%B2%92%E6%9C%89%E7%B6%93%E9%81%8E%E7%84%8A%E6%8E%A5%E5%B7%A5%E5%BA%8F%E8%99%95%E7%90%86%E6%80%9D%E8%80%831%E7%84%A1%E7%84%8A%E6%8E%A5%E9%81%8E%E5%BE%8C%E7%9A%84%E7%86%B1%E6%87%89%E5%8A%9B%E5%BD%B1%E9%9F%BF2%E7%84%A1%E9%8A%B2%E9%81%93%E6%89%80%E5%BC%95%E8%B5%B7%E7%9A%84%E9%98%BB%E6%8A%97%E6%95%88%E6%87%893%E7%84%A1%E9%9C%80%E9%A1%8D%E5%A4%96%E6%94%AF%E4%BB%98%E9%8A%B2%E9%81%93x-ray%E9%9D%9E%E7%A0%B4%E5%A3%9E%E6%AA%A2%E6%B8%AC%E8%B2%BB%E7%94%A84%E6%B8%9B%E5%B0%91%E9%85%8D%E7%AE%A1%E5%B7%A5%E4%BA%BA%E6%95%B85%E6%B8%9B/851334765237632/
  45. 潁璋重型彎管工程- 基於最新版ASME B31J 規範（金屬管線元件的, https://www.facebook.com/100057434619150/photos/%E5%9F%BA%E6%96%BC%E6%9C%80%E6%96%B0%E7%89%88-asme-b31j-%E8%A6%8F%E7%AF%84%E9%87%91%E5%B1%AC%E7%AE%A1%E7%B7%9A%E5%85%83%E4%BB%B6%E7%9A%84%E6%87%89%E5%8A%9B%E5%BC%B7%E5%BA%A6%E5%9B%A0%E5%AD%90%E8%88%87%E6%9F%94%E6%80%A7%E5%9B%A0%E5%AD%90%E6%B1%BA%E5%AE%9A%E6%96%B9%E6%B3%95%E9%87%9D%E5%B0%8D-ccpp-%E5%BB%A0%E5%85%A7%E5%BB%A3%E6%B3%9B%E4%BD%BF%E7%94%A8%E7%9A%84%E9%AB%98%E5%BC%B7%E5%BA%A6%E9%A6%AC%E6%B0%8F%E9%AB%94%E8%80%90%E7%86%B1%E9%8B%BC-sa-335-p91%E9%80%B2%E8%A1%8C-np/1489662249624915/
  46. 基於2026 ASME B31.1 與B31J 規範之複循環發電廠動力管線3D/5D, https://yz-pipe-bending.com.tw/%E5%9F%BA%E6%96%BC-2026-asme-b31-1-%E8%88%87-b31j-%E8%A6%8F%E7%AF%84%E4%B9%8B%E8%A4%87%E5%BE%AA%E7%92%B0%E7%99%BC%E9%9B%BB%E5%BB%A0%E5%8B%95%E5%8A%9B%E7%AE%A1%E7%B7%9A-3d-5d-%E5%86%B7%E4%BD%9C/
  47. 基於2026 ASME B31J 規範之大型CCPP 專案管線工法優化, https://yz-pipe-bending.com.tw/%E5%9F%BA%E6%96%BC-2026-asme-b31j-%E8%A6%8F%E7%AF%84%E4%B9%8B%E5%A4%A7%E5%9E%8B-ccpp-%E5%B0%88%E6%A1%88%E7%AE%A1%E7%B7%9A%E5%B7%A5%E6%B3%95%E5%84%AA%E5%8C%96%EF%BC%9Aepc-%E4%BB%8B%E9%9D%A2%E5%8D%94/
  48. P91高合金耐熱鋼二次熱處理之潛變退化機制與CCPP高能管線以彎代, https://yz-pipe-bending.com.tw/p91%E9%AB%98%E5%90%88%E9%87%91%E8%80%90%E7%86%B1%E9%8B%BC%E4%BA%8C%E6%AC%A1%E7%86%B1%E8%99%95%E7%90%86%E4%B9%8B%E6%BD%9B%E8%AE%8A%E9%80%80%E5%8C%96%E6%A9%9F%E5%88%B6%E8%88%87ccpp%E9%AB%98%E8%83%BD/
購物車