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ボイラーチューブ故障防止・管理

Bolier Tube Failure Prevention and Management

発行 ETD Consulting 商品コード 312604
出版日 ページ情報 英文
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ボイラーチューブ故障防止・管理 Bolier Tube Failure Prevention and Management
出版日: 2013年01月31日 ページ情報: 英文
概要

当レポートでは、強制停止の減少に役立つことから、チューブ修理/交換に関連した収益損失・コストを最小化するボイラーチューブ故障管理について調査し、プラントの可用性・信頼性の維持によるプラント性能の改善、検査・メンテナンス活動の優先順位付けに役立つリスクベース管理のBTFプログラムへの統合、およびプラント寿命管理・拡張をサポートするBTFプログラムの適正な実施などについて分析しており、プラントエクスペリエンス調査のレビュー、ベストプラクティスなどをまとめ、お届けいたします。

エグゼクティブサマリー

第1章 イントロダクション・背景

第2章 ボイラーチューブ故障(BTF)防止プログラム・プラントエクスペリエンス調査のレビュー

  • BTF防止プログラムのレビュー
  • プラントエクスペリエンス調査

第3章 ボイラー性能に関連したBFT防止プログラム/評価の有効性のレビュー

  • 強制停止要因
  • 計画停止要因
  • 可用性
  • 信頼性
  • チューブ故障頻度

第4章 リスクベース検査(RBI)手法

  • BTF防止におけるリスクベース手法の利用・価値のレビューと評価
  • 故障・リスクベース管理の可能性
  • BTF防止プログラムの「RISKFIT」への統合
  • 参照文献

第5章 BTF防止・管理プログラムのためのベストプラクティスガイドライン

  • BTF防止プログラムのサマリー
  • BTF防止プログラムの実施

第6章 サマリー

付録A:BTF防止関連の重要因子・問題

付録B:損傷のメカニズム・チューブ故障

図表リスト

目次
Product Code: 1180-tp-175

Boiler Tube Failures (BTF) have resulted in increasing numbers of leaks due to thermal fatigue, overheating, corrosion/erosion and original weld defects. Although tube failures may not necessarily lead to catastrophic consequences, they do cause loss of availability of the plant, and this can be quite costly. Implementation of a boiler tube failure prevention program has been proven to save the plant operators millions of dollars by just maintaining the availability and reliability of the plant. This project was involved in preparing easy to follow best practice guidelines for BTF prevention and management. Usually plants have their own program/ procedure / or some sort of formal or informal documents to follow to prevent or minimize BTF. Boiler performance is greatly influenced by the successful execution of a BTF program; hence, it is important to understand issues or factors that may influence the effectiveness of the BTF program.

As a part of the project a survey was carried out to study the actual plant operator experience of BTF prevention. A number of utilities worldwide operating conventional (coal, oil & gas fired) and CCGT plants participated. The survey involved collecting data on plant operator experience on BTF prevention covering all key aspects related to BTF prevention program, boiler maintenance and technical issues. A number of BTF prevention programs from the project participants and/or those available from international reputable organizations have been reviewed. Quantitative analysis of various plants' boiler performance was performed in order to gain deeper understanding of the execution of their BTF programs and their success, degree of success or lack of it. Various performance metrics such as plants' forced outage factor (FOF), planned outage factor (POF), loss of availability, reliability etc. were analyzed and benchmarking of plants BTF prevention programs was performed. The plant data in conjunction with the boiler performance analysis was used to identify the more or less successful BTF prevention programs which were then used for the preparation of best practice guidelines.

The success of the BTF prevention programs has been found to vary from utility to utility in terms of boiler performance. Most of the units showed better performance with respect to the percentage (%) rate of Availability than that of the percentage (%) rate of Reliability performance. The reliability performance is directly related to the forced outage factor (i.e., forced outage hours), which means that the units with low reliability performance are experiencing higher number of forced outages due to BTF. Whereas, the availability performance is related to both forced outage factor and planned outage factor, therefore, a good control of both the forced and planned outages is required to reduce the loss of availability.

Frequency of tube failure was also determined for all the conventional and CCGT plants studied. Thus highest percentage of annual waterwall tube failure frequency was determined for two conventional plants (identified as plants F and G in the report). But these plants experienced fewer failures for other tubes such as superheater, reheater, economizer etc. and showed good availability and reliability performance. This showed that these plants were controlling their forced outages by following appropriate BTF program. Another plant studied (identified in the report as plant N) also showed a low FOF value and good reliability but low availability performance. Low FOF value (i.e. low forced outage hours) and good reliability performance reflect a good control and management in preventing and reducing the undesired forced outages. However, the plant experienced higher planned outages thus affecting its availability. To achieve overall good performance a plant must show both good availability and reliability.

The survey revealed that the plants studied incorporated all major important steps/ measures in their BTF programs to prevent/ reduce tube failures. In spite of this some plants still experienced higher frequency of tube failures. The main problem for these utilities can be the proper implementation of the BTF program. The state of-the-art understanding of BTF mechanisms, root causes, maintenance, NDE and cycle chemistry are not by themselves sufficient to reduce the unavailability due to BTF. Thus without an overall corporate approach, management support and philosophy document, the goals will not be reached, and unavailability will continue to increase.

A best practice guideline has been developed after reviewing a number of BTF programs and analyzing their performances. The best practice guideline may be enhanced by integrating a risk based method. ETD's risk based methodology 'Riskfit' has been described in this report. It has been shown that the integration of the BTF program into risk-based management will allow the plant operator to manage risks associated with boiler tube failures through understanding of the probability or likelihood of failures and their consequences (i.e. related to run/repair/replace decisions). Such an integrated program will therefore be beneficial for power plant operators in outage planning, for example, in that it will help them to plan outage intervals and prioritize inspection and maintenance activities. It also offers long-term benefits by reducing the number of forced outages and improving plant safety/integrity and reliability.

In summary, managing boiler tube failures can help reduce forced outages, thus minimizing revenue losses and costs associated with tube repair/replacement. Implementation of a BTF prevention program has proved to improve plant performance by maintaining the availability and reliability of the plant. The integration of risk based management with the BTF program can help to prioritize inspection and maintenance activities. In addition, a properly implemented BTF program can support plant life management and extension. For example, sudden shutdown stresses due to forced outages would have a negative impact on the life of many other (in particular thick section) components and the implementation of a successful BTF program will help to reduce such additional risks and help with overall plant integrity and life extension.

Table of Contents

EXECUTIVE SUMMARY

1.0 INTRODUCTION AND BACKGROUND

  • 1.1 References

2.0 REVIEW OF BTF PREVENTION PROGRAMS AND SURVEY OF PLANT EXPERIENCE

  • 2.1 Review of BTF Prevention Programs
  • 2.2 Plant Experience Survey

3.0 REVIEW OF THE EFFECTIVENESS OF BTF PREVENTION PROGRAMS/ MEASURES IN RELATION TO BOILER PERFORMANCE

  • 3.1 Forced Outage Factor
  • 3.2 Planned Outage Factor
  • 3.3 Availability
  • 3.4 Reliability
  • 3.5 Tube Failure Frequency

4.0 RISK BASED INSPECTION (RBI) METHODOLOGY

  • 4.1 Review and Assessment of the Use and Value of Risk Based Methodology in BTF Prevention
    • 4.1.1 API 580 and 581 RBI Procedures
    • 4.1.2 ASME PCC-3-2007 RBI Procedure
    • 4.1.3 RIMAP RBI Procedure
    • 4.1.4 ETD's RBI Procedure - 'RISKFIT'
  • 4.2 Probability of Failure and Risk Based Management
  • 4.3 BTF Prevention Program Integration into 'RISKFIT'
  • 4.4 References

5.0 BEST PRACTICE GUIDELINES FOR A BTF PREVENTION AND MANAGEMENT PROGRAM

  • 5.1 Summary of BTF Prevention Program
  • 5.2 Implementation of BTF Prevention Program

6.0 SUMMARY

APPENDIX A.0 IMPORTANT FACTORS AND ISSUES RELATED TO BTF PREVENTION

  • A.1 Materials of Construction for Boiler Tubing
    • A.1.1 A Brief History of the Development of Alloy Steels
    • A.1.2 Materials Used for Conventional Boiler and HRSG Tubing
  • A.2 Damage Mechanisms and Engineering Solutions
    • A.2.1 Damage in Conventional Boiler Tubing
    • A.2.2 Damage in HRSG (CCGT Plant Boiler) Tubing
  • A.3 Boiler Water Chemistry Issues
  • A.4 Decision for Run, Repair or Replacement
    • A.4.1 Methodologies for Complete Failure Investigation
  • A.5 Inspection and Monitoring Techniques
    • A.5.1 Inspection Techniques
    • A.5.2 Monitoring Techniques
  • A.6 References

APPENDIX B.0 DAMAGE MECHANISMS AND TUBE FAILURE

  • B.1 Creep
  • B.2 Fatigue
  • B.3 Creep-Fatigue Interaction
  • B.4 Erosion
  • B.5 Corrosion Damage Mechanisms
    • B.5.1 Water-side Corrosion
    • B.5.2 Gas-side Corrosion
  • B.6 Steam Oxidation
  • B.7 References -124

LIST OF TABLES

  • Table 2-1 List of Power Plant Boilers included in the Study
  • Table 2-2 Boiler Unit Characteristics
  • Table 2-3 Inspection Techniques and Tube Materials.
  • Table 2-4 BTF Prevention Measures of the Participating Plants
  • Table 3-1 Performance metrics for the participating plants
  • Table 3-2 Frequency of Annual Tube Failure (%) for Each Type of Tube Component
  • Table 4-1 Boiler Risk Scoring
  • Table 6-1 Typical low alloy steels used for boiler tubes
  • Table 6-2 Chemical composition of modern heat resistant steels in accordance with ASTM Standard
  • Table 6-3 Standardisation of modern heat resistant steels
  • Table 6-4 Chemical composition and applications of ferritic steels for boiler tubing
  • Table 6-5 Chemical composition and applications of austenitic steels for boiler tubing
  • Table 6-6 Water chemistry specification for feed water and boiler water
  • Table 6-7 Failures due to water treatment

LIST OF ILLUSTRATIONS

  • Figure 1-1 General types of tubing in a conventional power boiler
  • Figure 2-1 Failures of straight tubes, bends and tube welds in conventional and HRSG (CCGT boiler) units (% of total number of all failures in this study)
  • Figure 2-2 Tube failures due to different damage mechanisms in conventional and HRSG (CCGT boiler) units (% of total number of all failures in this study)
  • Figure 2-3 Failures due to different damage mechanisms in different types of tubing in conventional boiler units participating in this study
  • Figure 3-1 Forced Outage Factor (FOF) v. Age for Conventional Plants A to S
  • Figure 3-2 Forced Outage Factor (FOF) v. Age for CCGT Plants T and U
  • Figure 3-3 Planned Outage Factor (POF) v. Age for Conventional Plants A to S
  • Figure 3-4 Planned Outage Factor (POF) v. Age for CCGT Plants T and U
  • Figure 3-5 Availability v. Age for Conventional Plants A to S
  • Figure 3-6 Availability v. Age for CCGT Plants T and U
  • Figure 3-7 Loss of Availability due to both Forced & Planned Outages for Conventional Plants A to S
  • Figure 3-8 Loss of Availability due to both Forced & Planned Outages for CCGT Plants T and U
  • Figure 3-9 Loss of Availability due to Forced Outages for Conventional Plants A to S
  • Figure 3-10 Loss of Availability due to Forced Outages for CCGT Plants T and U
  • Figure 3-11 Loss of Availability due to Planned Outages for Conventional Plants A to S
  • Figure 3-12 Loss of Availability due to Planned Outages for CCGT Plants T and U
  • Figure 3-13 Reliability v. Age for Conventional Plants A to S
  • Figure 3-14 Reliability v. Age for CCGT Plants T and U
  • Figure 3-15 Annual Failure Frequency for Superheater tubes for conventional plants A to S
  • Figure 3-16 Annual Failure Frequency for Reheater tubes for conventional plants A to S
  • Figure 3-17 Annual Failure Frequency for Economizer tubes for conventional plants A to S
  • Figure 3-18 Annual Failure Frequency for Waterwall tubes for conventional plants A to S
  • Figure 4-1 Risk Waterfall Model of ETD
  • Figure 4-2 An example of Program attributes assessment output carried out for a boiler system
  • Figure 4-3 An example of the Implementation Risk Score (IRS) calculation (quantitative RBM) for a boiler tubing
  • Figure 4-4 An example of a Generic Tubing Condition Assessment Template
  • Figure 4-5 Flow chart of the 'Riskfit' procedure for Boiler Risk Based Inspection
  • Figure 4-6 BTF prevention program integration into 'Riskfit'
  • Figure A-1 Growth in superheater pressure industry requirements in UK, Europe and Japan - from 1930 to 2005
  • Figure A-2 Material application with respect to the tube operating temperature
  • Figure A-3 Oxygen pitting corrosion damage in carbon steel waterwall tube
  • Figure A-4 Example photographs of an as-received tube sample
  • Figure A-5 Example of wall thickness measurement
  • Figure A-6 Example of metallographic sample sectioning plan
  • Figure A-7 Example of microstructure observed under the optical microscope
  • Figure A-8 Logic tree for root cause failure analysis
  • Figure B-1 Typical creep curve
  • Figure B-2 Intergranular fracture surface (left) and aligned cavities on grain boundaries (right)
  • Figure B-3 Creep deformation process evolution from cavity formation to macro-cracks and creep rupture failure
  • Figure B-4 Overheating creep failures in tubes - (left) short-term, significant overheating, and (right) long-term creep failure due to small overheat
  • Figure B-5 Images of ductile, wedge and brittle cracking
  • Figure B-6 Thermal fatigue cracking at tube to header weld
  • Figure B-7 Creep-fatigue cracking at tube stub
  • Figure B-8 Erosion damage to an economizer tube bend due to channelled gas flow
  • Figure B-9 Typical jetting damage
  • Figure B-10 Sectional view of pitting corrosion
  • Figure B-11 Internal surface of tube with longitudinally oriented crack-like pitting corrosion
  • Figure B-12 Sectional view of crack-like pitting corrosion
  • Figure B-13 Caustic attack occurred in water wall tube
  • Figure B-14 Hydrogen damage in water wall tubes
  • Figure B-15 Typical Corrosion Fatigue
  • Figure B-16 Corrosion-fatigue cracking on inside surface of furnace water wall tube
  • Figure B-17 Austenitic Stainless; Brass/Ammonia; Alloy Steel/Caustic Chloride
  • Figure B-18 Intergranular SCC in LP superheater tube bend caused by sodium hydroxide in water carried over from the drum
  • Figure B-19 Scalloped surface appearance of Flow Assisted Corrosion
  • Figure B-20 Oil ash high-temperature corrosion in superheater tube (TP321H) and reheater tube (TP304H)
  • Figure B-21 Sectional microstructure of oil ash corroded tube (TP321H)
  • Figure B-22 Coal ash corrosion in TP321 and T22 superheater tubes
  • Figure B-23 Acid dew point corrosion
  • Figure B-24 Sectional microstructures of steam oxidation scale on 2.25Cr-1Mo
  • Figure B-25 Sectional microstructures of steam oxidation scale on 9-12%Cr steels
  • Figure B-26 Appearance of steam oxidation scale on TP321H SH tube
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