對於絕大多數的煉油或石化煉製工廠而言，壓力容器及製程管線 (壓力設備) 在操作工廠主要的固定設備中，一直是扮演著重要的角色。因此，基於工廠整體的安全管理，事業主應當建立一套適合工廠特性的客觀評估機制，在檢測及維修資源的最佳化配置下，有效降低操作工廠的風險。 然而，在既有的壓力設備檢測程序中，由於檢測方法及現場環境上的差異，導致在檢測過程中存在一些無法控制的變數，此一變數往往導致檢測數據的誤差，進而影響壓力設備預估腐蝕率的評估結果。此一誤差情況如未能在評估過程中有效的處置，所得到預估腐蝕率的評估結果，往往會產生低估或不合理的評估數據，進而導致工廠潛在風險的產生。且在預估腐蝕率的評估參數之中，如操作壓力、腐蝕程度、材料抗拉強度等，觀察參數表徵往往是常態分配或是非常態分配；在這種情況下，壓力設備的破損機率往往因評估參數分布的影響，導致工廠在操作末期的風險，遠高於以參數公稱值所進行評估的結果。
為使長期操作的壓力設備，得到較為保守、合理且客觀的評估，本文的研究方法將區分為三個部分。首先，以壓力設備均勻腐蝕為例，利用統計的方式計算壓力設備的預估腐蝕率區間；在研究的第二部分則將預估腐蝕率計算結果，以較保守的上限值，利用「一次二階矩」 (First Order Second Moment – FOSM) 之可靠度計算方法，計算壓力設備及其元件的破損機率。為更進一步有效利用既有的檢測及維修資源，進而降低操作工廠的風險，風險基準檢查 (Risk Based Inspection – RBI) 的概念亦運用於計算所得的破損機率，以利工廠整體的安全管理。此外，保護壓力設備的最後一道防線 – 安全閥，亦是壓力系統整體評估及安全管理上的重要環節。因此，本研究亦以半定量之風險基準檢查概念，建立一套客觀的評估模式，並有效且保守地制定其檢測周期。
在本文研究結果中顯示，壓力系統的操作風險，來自少部分高破損機率的壓力元件；有效的將有限的檢測維修資源，挪移到此等高風險的區域，並掌控工廠中高破損機率的壓力元件，即可降低壓力系統的操作風險。此外，在安全閥的監測方面，本文研究的結果亦顯示安全閥的檢測周期，需突破目前法令規定以二年為檢測周期的檢測方式，修正為以監測狀況為基準的檢測方式，方能降低工廠的操作風險。

In overwhelming majority of the petroleum or petrochemical plants, pressure vessels and process piping play important roles among the major elements of static equipments. So, based on the integrity of safety management for the petroleum or petrochemical plants and reduction of the operation risks, some objective schemes of the systematic failure evaluations and assessments should be established in order to optimize the resources of inspection and maintenance. However, performing the inspections based on the conventional methodologies, some uncontrolled factors which caused by the environments and inspection methods may exist and affect the assessment of the estimated corrosion rate. If the influences of the uncontrolled factors were not considered and compensated in the assessment of the estimated corrosion rate, some underestimate or unreasonable results would be obtained which lead potential risks may exist in the plants. Moreover, the measured data of some parameters, for example, operation pressure, corrosion condition, allowable stress, which were used to evaluate the estimated corrosion rate of the pressure components may exhibit a normal or non-normal distribution. Under such circumferences, if one used the nominal values of the measured parameters to assessment the safety conditions of the pressure components, potential risks may exist in the petroleum or petrochemical plants at the final stage of long-term operation.
With an eye to obtain more conservative and objective assess results for pressure equipments in the long-term operation, three subjects will be differentiated between the evaluation of estimated corrosion rate, failure probability of pressure vessels and pressure safety valve (PSVs). First, based on the pressure boundaries suffered from general corrosion, a statistical methodology was proposed to modify the assessment of estimated corrosion rates for the pressure components in conventional methodology. Furthermore, the obtained results of the estimated corrosion rates will be used to assess the failure probability of pressure components based on the upper limited value. By adopting First Order Second Moment (FOSM) method, the failure probability was approached for the pressure components in long term operation. Moreover, for the sake of optimize the inspection and maintenance resources based on the acceptable risk of the plant owners, typical semi-quantitative risk based inspection (RBI) methodology to each pressure vessel are proposed in safety management based on the approached failure probability. Besides, the final protection for the pressure equipments when the pressure systems were upset - pressure safety valves (PSVs), are also play important roles to system evaluation and safety management for pressurized system. So, follow the semi-quantitative RBI methodology, the objective evaluation schemes together with the suggested inspection interval were conservatively established.
Based on the conclusion of the studies, few pressure components with high failure probability will raise the operation risk of the pressurized system. It is an effective way to reduce the operation risk of the pressurized system by shift the limited resource of inspection/maintenance on the pressure components with high risk and obtain further control with effective strategies. Moreover, the conclusion also shows the prospective inspection intervals of PSVs which time-based strategy according to the local regulations (2-year based) should be change to condition-based strategy to reduce the operation risk.

List of Tables…..……...……………………………………………....………….…..vi
List of Figures…….…..………………………………………………………….…viii
摘要…………………………………………………..………………………………xi
Abstract………………………………………………………….…...……………xiii
Nomenclature……………………………….………………..……………………...xv

Chapter 1 Introduction………………………….…..……………………………1
1.1 Background……………….……………………………………………………..1
1.2 Literatures Review………………………………………………...……….…..4
1.2.1 Evaluation of corrosion condition in the process piping…………………4
1.2.2 Evaluation of corrosion condition in the pressure vessels of the petroleum process……………………………………………………………………5
1.2.3 Reliability analysis of the pressure vessels for risk based inspection……..6
1.2.4 Strategies for the risk based inspection of the pressure safety valves….….7
1.3 Structures of the Dissertation …………………………..…………………….…9
Chapter 2 Corrosion Rate Evaluations …………………………………………12
2.1 Conventional Methodology…...………..……………………...….………….12
2.2 Statistical Methodology……………………………………………………....17
2.2.1 Evaluation of the possible range of mean value to the measured thickness data………………………………………..………………………….....17
2.2.2 Statistical evaluation for corrosion rate of the pressure component……19
2.3 Histogram of the Deterioration Condition for the Pressure System……………22
2.4 Summary of Conventional and Statistical Methodology………………………22
2.5 Corrosion Rate Evaluation for Process Piping and Pressure Vessel Component……………………………………………………………………..23
Chapter 3 Risk Based Inspection and the Reliability Analysis………………32
3.1 Basic Theory of Risk Based Inspection Methodology....………………………32
3.2 Types of RBI Assessment.………………………………..……….……………34
3.3 Typical RBI Assessment and the Reliability of the Pressure Components ……36
3.3.1 Strength evaluation of pressure component……..………………….……37
3.3.2 Evaluation of the future corrosion allowance………..…..………….……39
3.3.3 Limit state function of the pressure component…………………………40
3.3.4 Calculation of the failure probability……………………………………42
3.4 Typical RBI Assessment and the Analysis Procedure in PSVs Risk Evaluation………………………………………………………………………44
3.4.1 Characteristic of the PSV and the data assessment.….…….…….………44
3.4.2 Analysis of variation (ANOVA)……………………………………….…46
3.4.3 Process dealings with the non-significant influence parameters after ANOVA......................................................................................................47
3.4.4 RBI assessments for the PSVs……………………………………………48
3.4.5 Analysis for the likelihood of failure (LOF)……………………………48
3.4.6 Analysis for the Consequence of failure (COF)…………………………49
Chapter 4 Case Studies and Discussion.…………………………………………54
4.1 Cases Study of the Corrosion Rate Evaluation in the Process Piping …………54
4.1.1 Piping spool examples in a petroleum process…………………………54
4.1.2 Example (1): Estimate result is reasonable by conventional approach..…54
4.1.3 Example (2): Estimate result is unreasonable by conventional approach………………………………………………………………….57
4.1.4 Practical application in the piping system of a lubricant process………58
4.1.5 Results and discussion in the piping system for a lubricant process……60
4.2 Case Study of the Corrosion Rate Evaluation in the Pressure Vessel.…………61
4.2.1 Pressure vessel example in a petroleum process…………………………61
4.2.2 Evaluation steps to the pressure vessel example…………………………61
4.2.3 Results and discussion for the pressure vessel example …………………64
4.2.4 Practical application for the pressurized system of a lubricant process.…65
4.2.5 Results and discussion in the pressurized system of a lubricant process……………………………………………………………………65
4.3 Cases Study of the Risk Based Inspection and the Reliability Analysis.………67
4.3.1 An example of the failure probability calculations for a heat exchange…67
4.3.2 Results and discussion for the sampled heat exchanger…………………69
4.3.3 Practical application in the heat exchangers of a lubricant process……70
4.3.4 System description……………………………………...………………71
4.3.5 Results and discussion for the heat exchangers of a lubricant process…71
4.4 Case Study of the Risk Based Inspection for Pressure Safety Valves…………73
4.4.1 System description…………………………………………………...…73
4.4.2 Analysis of variation (ANOVA)………………………………………..75
4.4.3 Characteristic of the PSV and the data analysis…………………………76
4.4.4 Non-significant influential parameters on the PSV aging conditions……76
4.4.5 Correlations of significant influential parameters on PSV aging conditions………………………………………………………………...77
4.4.6 Influence of the PSV inlet size…………………………………………78
4.4.7 Influence of different process units………………………………………79
4.4.8 RBI assessments……………………………………………………..….80
4.4.9 Likelihood factor assessment of the LOF………………………………80
4.4.10 Generic failure condition factor assessment of the LOF…………………81
4.4.11 Assessment of the COF…………………………………………………82
4.4.12 Risk calculation of PSVs………………………………………..……...82
4.4.13 Inspection interval suggestion……………………………………………83
4.4.14 Results and discussion for risk based inspection assessment of the PSVs……………………………………………………………………85
Chapter 5 Conclusions…………………………………………………………121
5.1 Summary..……………….…………………………………..…...……..…..…121
5.2 Future Prospects.…………………………………………………..………….122
Reference……………………………………………….…......……….…….......…124
VITA……………………………….…………………....…......……….…………130

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