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P92のレビュー:冶金・製造・溶接・欠陥・用途・インテグリティおよび残存耐用年数評価問題のレビュー

The P92 Review- A Review of Metallurgy, Fabrication, Welding, Failure, Application, Integrity and Remaining Life Assessment Issues

発行 ETD Consulting 商品コード 312603
出版日 ページ情報 英文
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P92のレビュー:冶金・製造・溶接・欠陥・用途・インテグリティおよび残存耐用年数評価問題のレビュー The P92 Review- A Review of Metallurgy, Fabrication, Welding, Failure, Application, Integrity and Remaining Life Assessment Issues
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、現在の高強度鋼P92の状況と利用について、冶金、製造、溶接、不具合、および残存耐用年数評価などの面からレビューしています。

第1章 イントロダクション

第2章 開発

  • 耐熱鋼の種類
  • 合金設計のコンセプト

第3章 冶金

  • 化学成分
  • 相変態・一次沈殿物
  • 熱処理
  • 機械的性質
  • クリープ破壊特性
  • 酸化

第4章 製造

  • 熱間曲げ
  • 冷間曲げ
  • 溶接

第5章 用途

  • 米国の発電所におけるマルテンサイト系鋼グレードP92を用いた最近の経験
  • 欧州・世界の発電所におけるP92・E911の利用

第6章 長期的不具合のメカニズム

  • クリープ破壊
  • クリープ疲労/熱疲労の問題

第7章 残存耐用年数評価

  • 微細構造に基づいたインテグリティ評価
  • 9Cr溶接におけるクリープ破損進行の近年の研究
  • 先進超音波検査技術
  • モニタリング/測定技術としての電位降下
  • インテグリティ評価ツールとしての硬度モニタリング

参考資料

付録A:データシート

図表リスト

目次
Product Code: 1201-gsp-180

This review deals with the status and use of the modern high strength steel P92. This is the first review conducted by ETD solely on P92 although three previous reviews in martensitic steels that included P92 were conducted in the years 2000, 2006 and 2011. These reviews were sponsored by international industry from Europe, USA, Canada, Middle East and Asia. The first review had looked at the use of mainly 9Cr martensitic steels, the findings from research and limited plant experience available at that time. The second review, in addition to the above, covered other high strength steels for high temperature application and some of the new developments in the important aspect of integrity and life assessment of these steels. The third review covered the welding, weld consumables, weld repair, cracking and failures, component integrity and life assessment and, in addition, the developments in NDE techniques for the early stage creep cavitation and damage detection in components made from P91 type steel. This fourth review focuses on P92 as its use in the last 10 years has dramatically increased.

One of the most frequent causes for problems with P91 was a general lack of knowledge and experience of the basic metallurgy of this high-alloy steel which requires much greater understanding than the low alloy steels (such as T22) for successful use. Therefore this review gives an overview of the metallurgy of P92 in the belief that an improved understanding of the metallurgy among manufacturers and users will lead to more successful use.

With increased use of P92, and following on from some of the difficulties experienced with its predecessor P91, interest in integrity/life assessment and monitoring of these components is acute. This is especially so because the traditional NDE methods of replication and early stage damage detection in these steels have been found to be less than satisfactory and therefore there has been a need to develop, study and establish new methodologies and techniques for life assessment of these steels. A number of new developments in this area (including those recently explored and developed by ETD led teams) have been reviewed and more promising techniques highlighted. The study has brought together research and plant experience in the area of integrity and life assessment from Japan, Europe and North America to throw light on potentially successful techniques that should be adopted.

The welding and heat treatment of the 9Cr martensitic steels, including P92, is critical in that small deviations from ideal practices can result in devastating consequences. In this era of competition, manufacturers and service providers are keen to save costs and therefore may look for lower cost sub-contractors for component fabrication and welding. However, some of these sub-contractors may not always be aware of the criticality of welding and heat treatment of these steels and incidents are known where this has resulted in problems with plant even before their full fledged operation. Similarly choosing a welding process and welding consumables also requires the knowledge of what is available and the effect of these on the performance of P92 steel components. This issue has therefore been dealt with in detail in this report and guidance provided.

Dissimilar metal welds are always a problem area in high temperature plant due to, amongst others, different heat treatment requirements for the two adjoining metals. In the case of the high Cr martensitic steels this situation becomes even more demanding and this has been discussed in this report.

As the service life of the predecessor P91 reaches the mid-life stage and the material shows signs of cracking and failure, it is important to learn lessons from the issues involved with weld repairs and explore how these can be applied to P92. This aspect has been researched particularly in Europe and is discussed in this review. The issue of steam-side oxidation has proved to be problematic for T91, and this would also be expected for T92. The consequences of this in terms of tube life, damage to turbine blades etc. have been discussed in this report together with the alternatives available. This has been preceded by the science of various types of oxides that form on these steels and their behaviour and effect on the rise in metal temperature.

It is important to understand the process of creep strengthening in the new high strength steels and how their strength is affected by actual material chemical composition within the standards' specification, fabrication and exposure at high temperatures and pressures. Therefore, this review discusses the microstructural details of these steels and their behaviour and integrity under creep and creep-fatigue (particularly for cycling plant) conditions. The current evaluations indicate that steel P92 is approximately 25-30% stronger than steel P91 at temperatures higher than 575°C.

Much research has been going on P92 steel for the past ten years or so and much has been published, so it is important to synthesise this in to a useful and user-friendly document which can be easily followed by plant engineers without getting lost in the details of the research itself. It was also important to bring together research findings and plant experience so that a comprehensive and comprehensible document can be provided which relates to plant experience and works as a guide for plant manufacturers, service providers and plant operators.

Table of Contents

Contents

Foreword

Figures List

Tables List

1 Introduction

  • 1.1 Study Methodology
  • 1.2 International Standards and Codes for P92

2 Development

  • 2.1 Types of Heat Resistant Steels
  • 2.2 The Alloy Design Concept

3 Metallurgy

  • 3.1 Chemical Composition
    • 3.1.1 Role of Alloying Elements
    • 3.1.2 The N:Al ratio
  • 3.2 Phase Transformations and Initial Precipitation
    • 3.2.1 Characteristics of Precipitates
    • 3.2.2 Mechanisms of transformation
    • 3.2.3 The α - γ Transformation in 9-12%Cr Steels
  • 3.3 Heat Treatments
  • 3.4 Mechanical Properties
    • 3.4.1 Elevated temperature yield / proof strength
  • 3.5 Creep Rupture Properties
  • 3.6 Oxidation
    • 3.6.1 Types of oxide scales and their effects
    • 3.6.2 Loss of tube wall thickness
    • 3.6.3 Increase in Metal Temperature
    • 3.6.4 Oxide spallation
    • 3.6.5 Discussion on T92 Oxidation, Metal Loss and Failure
    • 3.6.6 Concluding remarks on steam-side oxidation

4 Fabrication

  • 4.1 Hot Bending
  • 4.2 Cold Bending
    • 4.2.1 Effects of cold work on creep rupture strength and hardness
  • 4.3 Welding
    • 4.3.1 Welding Consumables
    • 4.3.2 Welding Procedure
    • 4.3.3 Properties of P92 Welds
    • 4.3.4 Weldment properties
    • 4.3.5 Dissimilar Metal Welds

5 Applications

  • 5.1 Recent Experience with Martensitic Steel Grade P92 in US Power Plant
  • 5.2 Use of P92 and E911 in European and Worldwide Power Stations

6 Long-term failure mechanisms

  • 6.1 Creep Rupture
    • 6.1.1 The Type IV zone in 9%Cr martensitic steel weldments
    • 6.1.2 Strength Reduction Factors Predicted for P92 Welds
    • 6.1.3 Base Metal Rupture Strength
    • 6.1.4 Creep Ductility Issues and Implications for Defect Tolerance
    • 6.1.5 Components and welds with abnormal microstructural conditions
  • 6.2 Creep-Fatigue / Thermal Fatigue Issues
    • 6.2.1 Creep and Thermal Fatigue Cracking
    • 6.2.2 Creep-Fatigue Capabilities of High Temperature Alloys

7 Remaining Life Assessment

  • 7.1 Microstructure Based Integrity Assessment
    • 7.1.1 Optical and Scanning Electron Microscopy for Cavitation Measurement
    • 7.1.2 Transmission Electron Microscopy
    • 7.1.3 Use of Microstructural Parameters for Component Life Assessment
    • 7.1.4 Area Fraction of Creep Voids
    • 7.1.5 The Difference in Creep Void and Strength of the 9 and 12%Cr Steels
  • 7.2 Recent Studies of Creep Damage Development in 9Cr Welds
    • 7.2.1 Scanning Force Microscopy for On-Site Cavitation Damage Assessment
  • 7.3 Advanced Ultrasonic Testing Techniques
    • 7.3.1 Detection of Creep Damage by Intelligent Phased Array Ultrasonic Inspection
    • 7.3.2 Ultrasonic Noise Method
    • 7.3.3 Detection of Creep Damage by Ultrasonic Attenuation & Velocity Change Methods
    • 7.3.4 Ultrasonic Backscatter Technique
  • 7.4 Potential Drop As A Monitoring / Measurement Technique
  • 7.5 Hardness Monitoring As An Integrity Assessment Tool

References

APPENDIX A - Data Sheets -159

Figures List

  • Fig. 2-1 A comparison of required wall thickness for various steels for the same design conditions
  • Fig. 2-2 Stress rupture strengths of the traditional and the newly developed power station steels
  • Fig. 2-3 Compositions of heat resistant steels in Fe-Cr-Ni ternary phase diagram at 800°C
  • Fig. 2-4 General concept of alloy design for heat resistant steels
  • Fig. 3-1 The development of ferritic steels for power plants
  • Fig. 3-2 N:Al ratio of grade 91 material in different product forms
  • Fig. 3-3 Illustration of martensitic 9Cr steel after tempering: (a) subgrain structure; (b) distribution of M23C6 and MX
  • Fig. 3-4 Z-Phase in P92 in (a) bright field TEM image and (b) precipitate map where red = M23C6, blue = MX, green = Laves phase and purple = Z-Phase
  • Fig. 3-5 Main mechanisms of transformation: parent crystal contains two kinds of atoms; figures on right represent partially transformed samples with parent and product unit cells outlined in bold; transformations are unconstrained in this illustration
  • Fig. 3-6 Summary of essential characteristics of solid state transformations in steels
  • Fig. 3-7 Nature of reconstructive transformations (left) and displacive transformations (right) from austenite on cooling: for bainite and martensite s = 0.22-0.26 and δ = 0.02-0.03
  • Fig. 3-8 Dilatometric diagram of A508 class 3 reactor pressure vessel steel heated at 30 K s-1 and cooled at 2 K s-1
  • Fig. 3-9 Diagram of the heating dilatometric response of α→γ transformation and the carbide dissolution process of martensitic 9-12%Cr steels
  • Fig. 3-10 Cooling dilatometric curve of a carbon-manganese steel (Fe- 0.20C-1.1Mn-0.34Si) obtained at a cooling rate of 1 K s-1
  • Fig. 3-11 (a) Cooling dilatometric curve and (b) microstructure of a low carbon manganese steel (Fe - 0.07C-1.56Mn-0.41Si) after cooling at a rate of 234 K s-1
  • Fig. 3-12 Effect of individual element variation from their base levels to the P92 specification limits on the Ae1 temperature. Dark shading within the bars indicates the element at its maximum allowable composition whilst the light shading within the bar indicates an element at its minimum composition. Blue bars are ferrite stabilizers, red bars are austenite stabilizers.
  • Fig. 3-13 Heat treatment conditions used by Masuyama (31). P92 was first normalized at 1070°C and then tempered at temperatures ranging from -60 to +5°C relative to the Ac1
  • Fig. 3-14 Results of simulated P92 tempering treatments at temperatures above and below Ac1. The results show that transformation is taking place at temperatures 30°C lower then Ac1.
  • Fig. 3-15 Continuous cooling transformation (CCT) diagram for P92 steel
  • Fig. 3-16 Effect of austenitising temperature on rupture life of P91 material; rupture lives are shown at 570°C and 600°C
  • Fig. 3-17 Stress rupture strength of two P92 steel casts tempered at 775 and 835°C (1427 and 1535°F) (Both austenitised at 1070°C/1958°F)
  • Fig. 3-18 Comparison of yield strength at elevated temperatures for P91, P92 and P911, using data from EN 10216-2
  • Fig. 3-19 Creep rupture strength values for P92 using data from different standards/codes (ASME and Japanese values based on maximum allowable stress values in ASME and METI codes, respectively)
  • Fig. 3-20 100,000h creep rupture strength values from EN 10216-2 for P91, P92 and P911
  • Fig. 3-21 200,000h creep rupture strength values from EN 10216-2 for P91, P92 and P911
  • Fig. 3-22 100,000h creep rupture strength values for P91, P92 and P911 based on maximum allowable stress values in ASME code
  • Fig. 3-23 Microstructure of the oxide scale formed on 9Cr steel in steam (Nickel coating protects the oxide during sample preparation)
  • Fig. 3-24 Comparison of oxidation rates in steam of various power plant steels
  • Fig. 3-25 Metal loss due to oxidation in different plant environments
  • Fig. 3-26 Extrapolated metal losses on boiler tubes (NF616 is the non-standard version of P92)
  • Fig. 3-27 Calculated effect of oxidation/corrosion on the stress rupture life of T92 tubes of different wall thickness
  • Fig. 3-28 Effect of oxidation on superheater tube temperature and life
  • Fig. 3-29 Cracking and exfoliation of steam-side oxide on 9Cr reheater tube
  • Fig. 4-1 Stress corrosion cracks in T91 reheater tube bends
  • Fig. 4-2 The effect of oxygen on toughness of weld metal at room temperature
  • Fig. 4-3 Influence of nitrogen on toughness
  • Fig. 4-4 Effect of boron on toughness at room temperature
  • Fig. 4-5 Effect of boron on creep resistance in iso-stress tests at 85MPa
  • Fig. 4-6 Weld thermal cycle for P92
  • Fig. 4-7 Compositional dependence of Ac1 of P92 weld metals
  • Fig. 4-8 Effect of PWHT time on hardness of P92 SMAW weld metal (Böhler Welding Thermanit Chromo 9V)
  • Fig. 4-9 Impact of PWHT on toughness of all weld metal
  • Fig. 4-10 Hardness profile of P92 welded joint creep specimen
  • Fig. 4-11 Creep rupture test results for P92 weld metals - compared with ECCC (2005) base material scatterband
  • Fig. 4-12 Cross-weld creep rupture test results for P92 weldments - compared with weld-metal test results and base material scatterband
  • Fig. 4-13 Interface cracking in dissimilar metal weld
  • Fig. 4-14 Schematic of relative coefficient of thermal expansion
  • Fig. 6-1 Type IV cracking in the ICHAZ of a low alloy CrMoV steel weld
  • Fig. 6-2 Type IV cracking and creep cavitation damage in the FGHAZ (and ICHAZ) of E911 martensitic steel cross-weld creep rupture test specimen
  • Fig. 6-3 Microstructure of simulated FGHAZ of P92 steel, after heating to a peak temperature of 950°C (just above Ac3) (
  • Fig. 6-4 SEM image of the FGHAZ microstructure after creep exposure, showing coarsened precipitates (left); EBSD image showing recovered, non-martensitic grain structure (right)
  • Fig. 6-5 Changes in martensitic lath structure of the base metal (top) and equiaxed subgrain structure of the FGHAZ (bottom) during creep exposure
  • Fig. 6-6 Stress vs Rupture Time of E911 cross-weld specimens showing Type IV cracking compared with the base metal rupture strength for E911
  • Fig. 6-7 Weld strength reduction factors for P91 welds as a function of rupture time
  • Fig. 6-8 WSRF values from ASME B31.1 and ASME Section I codes for Cr-Mo steels and CSEF steels
  • Fig. 6-9 UKHTPPF testing at 600°C
  • Fig. 6-10 Creep rupture strength values for P92 using data from different standards/codes (ASME and Japanese values based on maximum allowable stress values in ASME and METI codes, respectively)
  • Fig. 6-11 Reduction in area of P92 for specimens ruptured at 550°C, 600°C and 650°C
  • Fig. 6-12 Creep rupture strength of soft band material compared with strength of adjacent normal hardness material and grade 91 scatterband (119)
  • Fig. 6-13 Creep-fatigue crack growth curve for P91 compared with P22 and Type 316L(N)
  • Fig. 7-1 Surface micrographs of 9Cr test tube crept (655°C, ~8000 hours)
  • Fig. 7-2 Number density of cavities vs. life consumption rate (LCR) of T91 tube base metal [Ref
  • Fig. 7-3 Evolution of microstructural parameters versus creep loading time (P91, 600°C) (125)
  • Fig. 7-4 (a) Area fraction of voids vs. applied stress; (b) Area fraction of voids vs. applied temperature
  • Fig. 7-5 Area fraction of voids vs. (a) rupture strain and (b) rupture time when test temperature and stress change
  • Fig. 7-6 Results of P92 creep rupture of base metal, weld metal and weldment including HAZ at 600°C, 215.8MPa (area fraction of voids on fracture surface at each position)
  • Fig. 7-7 Results of creep crack growth testing of base metal and weldment containing HAZ at 600°C, 23.5MPa√m in P92 steel and cavities at the crack tip (×400)
  • Fig. 7-8 Example of in-service creep cavitation damage in an X20 steam line, observed from a surface replica of a branch weld
  • Fig. 7-9 Observed creep cavitation and crack initiation in a notched specimen of steel E911 (HAZ) after creep testing (9500h / 625°C)
  • Fig. 7-10 Creep damage development in cross-weld test specimens as a function of creep life fraction
  • Fig. 7-11 Number fraction and area fraction of creep cavities through the material thickness as a function of creep life
  • Fig. 7-12 Creep cavitation damage and cracking at the Type IV position on either side of a longitudinal seam weld in T91 tube sample
  • Fig. 7-13 Number fraction and area fraction of creep cavities at mid-thickness position and outer surface as a function of creep life
  • Fig. 7-14 Portable SFM being used on a creep damaged P91 welded pipe
  • Fig. 7-15 Comparison of SEM images of 9Cr steel with SFM images
  • Fig. 7-16 Surface topography profile from the SFM revealing the depth of cavities in a 9Cr steel
  • Fig. 7-17 Relationship between area fraction of void and peak amplitude
  • Fig. 7-18 UT noise value at the intrados of the elbow component
  • Fig. 7-19 Tube specimens (A), (B) and (C)
  • Fig. 7-20 Attenuation and propagation speed measurements for tube specimens A, B, and C. The middle and inner/outer blue lines show the respective mean values and standard deviations of the measurements along the lengths of the tubes. The regions of visible damage due to exposure to high temperature are indicated in red.
  • Fig. 7-21 9Cr weld specimen and UT phased array hardware
  • Fig. 7-22 Locations of the array imagery for the weld specimen (Left) Pipe outside (central darker shaded area shows the weld) (Right) Pipe bore (central darker shaded area shows the weld)
  • Fig. 7-23 Backscatter images obtained from the pipe outside surface
  • Fig. 7-24 Images obtained from the pipe bore
  • Fig. 7-25 Principle of on-line PD crack monitoring
  • Fig. 7-26 Schematic of creep damage detection by PD method
  • Fig. 7-27 Potential drop ratio vs. creep life fraction relationship
  • Fig. 7-28 ACPD analysis of the P91 tube samples (0.3 kHz)
  • Fig. 7-29 ACPD analysis of the P91 tube samples (1kHz)
  • Fig. 7-30 ACPD analysis of the P91 tube samples (30 kHz)
  • Fig. 7-31 DCPD analysis of the 9Cr tube samples
  • Fig. 7-32 Hardness measurements on weldment and base metal creep testpieces
  • Fig. 7-33 Hardness profile across the weldment as a function of time (life fraction)
  • Fig. 7-34 Hardness of weldment and base metal as a function of Larson-Miller parameter
  • Fig. 7-35 Relationship between creep life fraction and hardness for the base metal and the weldment HAZ
  • Fig. 7-36 Relationship between hardness ratio and creep life fraction for the base metal and the weldment HAZ
  • Fig. 7-37 Relationship between hardness drop and Larson-Miller parameter for high stress creep, low stress creep and thermal aging

Tables List

  • Table 1-1 Some of the key International Standards and Codes for P92 14
  • Table 3-1 Chemical compositions of 9-12%Cr steels*
  • Table 3-2 ASTM composition of P92 and reported compositions of P92 from the literature
  • Table 3-3 Influence of heat treatment on microstructural parameters of P92 steel
  • Table 3-4 Typical transformation temperature ranges for P92 (9)
  • Table 3-5 Minimum and maximum compositions of each element as seen in weld metals with increased limits for Mn, Ni and the addition of Co and Cu.
  • Table 3-6 Composition of P92 used to investigate transformations below Ac1 by Masuyama (31)
  • Table 3-7 Tensile strength and hardness ranges*
  • Table 4-1 Heat treatment after cold bending according to different European Codes or Standards
  • Table 4-2 Post-bend heat treatment of cold-formed tube bends according to EN 12952-5
  • Table 4-3 Hardness of T91 tube bend (50% cold strain) (82)
  • Table 4-4 Typical composition ranges for P92 and P91 weld consumables
  • Table 4-5 Transformation temperatures (°C) for P92 and P91 (88)
  • Table 4-6 Common consumables for welding P92
  • Table 4-7 Typical all weld metal compositions for Metrode consumables (89)
  • Table 4-8 Impact energy for P92 all weld metal tests and pipe welds (83)
  • Table 4-9 Properties of P92 all weld metal (94)
  • Table 5-1 Steam parameters of P92 in John W Turk power plant
  • Table 5-2 Selected applications of new W-bearing steels in European power stations
  • Table 5-3 European Plants under construction or recently commissioned using V&M P92 Steel
  • Table 6-1 ASME B31.1a-2008, Table 102.4.7, Weld Strength Reduction Factors for Longitudinal Seam Welds in CSEF Steels and Cr-Mo Steels
  • Table 6-2 Weld strength reduction factors for P91 steel (100,000 hours) (112)
  • Table 6-3 ASME Section I, PG-26, Weld Strength Reduction Factors for Seam Welds in CSEF Steels and Cr-Mo Steels
  • Table 7-1 Typical phases in 9-12% Cr-steels (125)
  • Table 7-2 Methods for identification and quantitative description of microstructural parameters (125)
  • Table 7-3 Comparison of ACPD and DCPD techniques (133)
  • Table 7-4 Nominal P91 tube specimen dimensions
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