臺灣博碩士論文加值系統

壓力容器的設計規範，如CNS 9788、ASME BPVC等，均假設容器為均質及沒有缺陷；然而長期使用後，容器殼體會發生裂痕或局部減薄缺陷(LTA)，導致原有的設計公式無法適用於評估設備的堪用性。
API的RP 579適用性評估(FFS)就是因應這個狀況所發展的，它將分析程序標準化，可讓第一線人員於發現缺陷時，能立即做初步判定。然而，對於幾何結構及負載複雜的情況下，仍須回到結構應力的評定。從ASME VIII和FFS的定位發現兩者雖是分別是針對新設備設計與舊設備缺陷的評估，但其實背後共同的理論基礎，都使用到設備的極限負載，並以剩餘強度係數(RSF)評定設備的壽命。
因此，本研究將採用RSF值的概念於ANSYS有限元分析平台上發展結構評估方法，將結構的應力計算分割為二階段，首先處理不含缺陷的主模型，再以子模型(Sub-modeling)的作法精算缺陷區域的應力分佈。在計算設備的極限負載時必須在主、子模型間不斷地加載，切換模型，過程極為複雜。
為了驗證方法的正確性，建立了多個比較案例，包含極限負載大小、缺陷輪廓處理、材料特性(彈－全塑、彈－塑)、缺陷大小等，除確認方法的可行性外，也同時檢視本方法對多個影響因子的穩健性。
結果顯示，本方法不僅可有效評估出結構的極限負載，同時符合API 579 Level 3的精神，對小區域缺陷的RSF值估計精確。由於本方法的運算速率及記憶體需求遠較建立全模型低，頗具實用價值。
關鍵詞：局部減薄缺陷、有限元素法、極限負載、剩餘強度係數、適用性評估

Nowadays, the design and construction of pressure vessels often require that some sort of engineering standards or codes, such as CNS 9788 or ASME BPVC be followed. However, in these design codes, one of the key assumptions is that its thickness is uniformly distributed over the entire structure, which implies that defects due to long term effects of corrosion are not considered. In other words, the same formula that was used in the design stage is no longer applicable for assessing the fitness of equipment.
API RP 579 Fitness-for-service (FFS) is published by American Petroleum Institute (API), aiming for a standardize defects analysis procedures for process equipment.
Although, ASME VIII and FFS were developed for different purposes, one for new equipment while the other for aging equipment with defects. However, there exists a common theoretical background, in which they both utilize the limit load of equipment and determine the remaining life of equipment based upon the residual strength factor (RSF). In this study a finite element-based structural assessment methodology was developed on ANSYS, which is designed specifically for handling localized defects on the surface of pressure equipment. In order to compute the limit load of equipment with defects, the solution process must switch back and forth between two finite element models, one designated as the primary model and the defect zone as a sub-model. Solving for the limit load requires the load to be added incrementally until the convergence can no longer be achieved.
The method developed here happens to comply with API 579 and can be treated as a Level 3 method. In order to verify the correctness of results as well as the validity of our method, two defect types were considered and a series of comparisons were made. Issues involved include handling of the profiles of defects, effects of the material property on the limit load, and the size effect of a defect.
Overall speaking, the method developed in this study has been found to successfully evaluate the limit load of structures of several distinct geometries. With this method, a full finite model of the entire equipment can be analyzed, while focus can be placed on the defect zone for better resolution and accuracy. Most importantly, the higher accuracy of results can be achieved in much shorter time and requires less computer memory.
Keywords: local thin area, finite element method, limit load, RSF, FFS

目錄
摘要 I
ABSTRACT II
誌謝 IV
目錄 V
表目錄 VIII
圖目錄 IX
第一章 緒論 1
1.1. 研究背景 1
1.2. 研究目的 6
第二章 文獻回顧 8
2.1. 壓力容器設計概念回顧 8
2.1.1. ASME VIII-1 與 ASME VIII-2 第四篇-按規則設計 11
2.1.2. ASME VIII-2 第五篇-按應力分析設計 12
2.1.2.1 彈性應力分析 13
2.1.2.2 極限負載分析 16
2.1.2.3 彈塑性分析 18
2.2. API 579-1/ASME FFS-1 20
2.2.1. 剩餘強度係數(Remaining Strength Factor, RSF) 21
2.2.2. 缺陷幾何的定義和量測厚度的處理 23
2.3. FEM 30
2.3.1. ANSYS進行有限元素分析 31
2.3.2. 利用有限元素法評估結構之RSF 32
第三章 研究方法 36
3.1. 應用API 579對缺陷的處理於有限元素模型缺陷建立 37
3.2. API 579評估準則RSF值與有限元素分析之應用 39
3.3. 研究流程 43
第四章 方法應用與討論 46
4.1. 局部減薄案例一探討－大區域缺陷 47
4.1.1. 前言 47
4.1.2. 評估設備簡介 49
4.1.3. 設備基本資料與缺陷處置 51
4.1.4. 有限元素模型建置 54
4.1.5. 有限元素分析結果 57
4.1.6. API 579 63
4.1.7. 結果討論 69
4.2. 局部減薄案例二探討－小區域缺陷 71
4.2.1. 前言 71
4.2.2. 設備基本資料與缺陷幾何處置 72
4.2.3. 有限元素模型建置 74
4.2.4. 有限元素分析結果 77
4.2.5. API 579 81
4.2.6. 結果討論 87
4.2.7. 案例一與案例二分析結果討論 89
第五章 結論與建議 91
5.1. 結論 93
5.1.1. 大尺寸缺陷於FEM與API 579的比較－缺陷輪廓處理 93
5.1.2. 大尺寸缺陷於FEM與API 579的比較－材料性質處理 93
5.1.3. 小尺寸缺陷於有限元素法分析與API 579的比較 94
5.2. 建議與限制 95
參考文獻 97

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