Creep Failure Behavior of Creep-Strength Enhanced Ferritic Steels

2004 ◽  
Author(s):  
F. Masuyama ◽  
N. Komai
Keyword(s):  
Creep Strength ◽  
Power Plants ◽  
Void Formation ◽  
Thick Wall ◽  
Failure Behavior ◽  
Ferritic Steels ◽  
Physical Damage ◽  
Creep Failure ◽  
Type Iv ◽  
Microstructural Morphology

Creep-strength enhanced ferritic steels such as Gr.92, Gr.122, Gr.23 and Gr.91 have recently been introduced for power plant applications, and some of these have experienced creep failure in boiler tubes and thick wall components after several years of operation. In order to use these steels safely in power plants, understanding of creep failure behavior is essential. In this study the creep failure of Gr.91 and Gr.92 boiler tube base metal and Type IV cracking of Gr.92, Gr.122, Gr.23 and Gr.91 welds were reproduced in test piece of actual components size. Creep failure mode was investigated, as was microstructural morphology during creep, particularly in the weldment, with discussion based on evidence of void formation and changes in the physical damage in terms of creep life.

Water Hammer Analysis/Prevention/Mitigation in Fire Protection Systems at Power Plants

2003 ◽  
Author(s):  
Asif H. Arastu ◽  
Eugene Tom
Keyword(s):  
Fire Protection ◽  
Nuclear Power ◽  
Power Plants ◽  
Void Formation ◽  
Water Hammer ◽  
Mitigation Strategies ◽  
Physical Damage ◽  
Protection Systems ◽  
Piping Networks ◽  
In Fire

Fire Protection water systems are typically piping networks where water is pumped from a low elevation reservoir at atmospheric pressure to higher elevations in the buildings served by the system. Because of this nature of their design, they are prone to water hammers due to water column separation & rejoining. A loss of pressure can lead to void formation at high elevations whose collapse can result in severe water hammer. A damaging water hammer event that occurred at a nuclear power plant (Arastu, et al, 1999) causing a catastrophic valve failure pointed to the need to prevent and mitigate such potential events at other plants. One important aspect of that event is that prior to it, several events of similar magnitude had occurred that did not apparently cause physical damage but degraded the system sufficiently to make it susceptible to damage. This paper discusses the causes of water hammer in Fire Protection Systems at power plants and identifies analysis, prevention, and mitigation strategies. Using a Method Of Characteristics based program, computer simulation results of the application of the mitigative measures are given for three large plant systems to demonstrate the effectiveness of the measures proposed at these plants.

scholarly journals Effect of Postweld Heat Treatments on Type IV Creep Failure in the Intercritical Heat-Affected Zone of 10% Cr Martensitic Steel Welded with Haynes 282 Filler

Metals ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 726
Author(s):  
Namkyu Kim ◽  
Yongjoon Kang ◽  
Jinhyeok Bang ◽  
Sangwoo Song ◽  
Seong-Moon Seo ◽  
...  
Keyword(s):  
Heat Affected Zone ◽  
Welded Joints ◽  
Martensitic Steel ◽  
Laves Phase ◽  
Lower Amount ◽  
Failure Behavior ◽  
Creep Life ◽  
Creep Failure ◽  
Type Iv ◽  
Postweld Heat

This study investigated the effect of postweld heat treatment (PWHT) conditions on Type IV failure behavior of 10% Cr martensitic steel welds using Haynes 282 filler. The welded joints were subjected to PWHT at temperatures of 688, 738, and 788 °C for 4 and 8 h. Creep tests were carried out at 600 °C under a stress of 200 MPa. The as-welded joint without PWHT showed Type IV cracking due to growth of voids around Laves phase by localized creep deformation in the intercritical heat-affected zone (ICHAZ). The creep properties of the PWHTed joints at 688 °C were similar to those of the as-welded joints without PWHT. On the other hand, the PWHTed joints at 738 °C exhibited a significantly longer creep life by a lower amount of Laves phase in the ICHAZ than those at 688 °C; this could be a result of the homogenization of ICHAZ microstructure during PWHT at 738 °C. However, the PWHT at 688 and 738 °C showed the same Type IV creep failure mode. Meanwhile, the PWHTed joints at 788 °C exhibited the shortest creep life in this study. The failure location was shifted to the base metal away from the HAZ, and severe plastic deformation occurred due to the softened matrix by excessive tempering.

Study on Type-IV Damage Prevention in High-Temperature Welded Structures of Next-Generation Reactor Plants: Part II — Effect of Boron on Creep Properties and Microstructures of HAZ for High Cr Steels

2006 ◽  
Author(s):  
Masaaki Tabuchi ◽  
Hiromichi Hongo ◽  
Yukio Takahashi
Keyword(s):  
Creep Strength ◽  
Ferritic Steels ◽  
Strengthening Effect ◽  
Creep Properties ◽  
Fine Grained ◽  
9Cr Steel ◽  
Type Iv ◽  
Weld Thermal Cycle ◽  
Nitrogen Contents

Creep strength of welded joints for high Cr ferritic steels is decreased for long-term services at high temperatures due to Type IV creep damages that occur in heat affected zone (HAZ). Aiming at improving the creep strength of HAZ, we have investigated the effect of boron and nitrogen content on the microstructures and creep strength of HAZ for the 9Cr and 12Cr steels produced based on the P91 and P122 steel. It was found that the effect of boron appeared remarkably for the 12Cr steel. By increasing boron and decreasing nitrogen, the formation of fine-grained HAZ structure during weld thermal cycle could be suppressed and the creep strength of HAZ was considerably improved. For the 9Cr steel, while the formation of fine-grained HAZ structure could be inevitable independent of boron and nitrogen contents, the creep strength of fine-grained HAZ was improved by grain boundary strengthening effect of boron.

scholarly journals The use of a solution of the inverse heat conduction problem to monitor thermal stresses

2019 ◽  
Vol 108 ◽  
pp. 01003
Author(s):  
Jan Taler ◽  
Piotr Dzierwa ◽  
Magdalena Jaremkiewicz ◽  
Dawid Taler ◽  
Karol Kaczmarski ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Power Plants ◽  
Thermal Stresses ◽  
Thermal Power ◽  
Temperature Fields ◽  
Thick Wall ◽  
Fluid Temperature ◽  
Unsteady Temperature

Thick-wall components of the thermal power unit limit maximum heating and cooling rates during start-up or shut-down of the unit. A method of monitoring the thermal stresses in thick-walled components of thermal power plants is presented. The time variations of the local heat transfer coefficient on the inner surface of the pressure component are determined based on the measurement of the wall temperature at one or six points respectively for one- and three-dimensional unsteady temperature fields in the component. The temperature sensors are located close to the internal surface of the component. A technique for measuring the fastchanging fluid temperature was developed. Thermal stresses in pressure components with complicated shapes can be computed using FEM (Finite Element Method) based on experimentally estimated fluid temperature and heat transfer coefficient

Prediction of Type IV creep failure of a seam-welded mod. 9Cr-1Mo elbow based on microscopic damage simulation

2017 ◽  
Vol 34 (3) ◽  
pp. 194-207 ◽  
Author(s):  
Takuya Fukahori ◽  
Takumi Tokiyoshi ◽  
Toshihide Igari ◽  
Yasuharu Chuman ◽  
Nobuyoshi Komai
Keyword(s):  
Creep Failure ◽  
Type Iv ◽  
Microscopic Damage ◽  
Damage Simulation

Numerical Simulation to Study the Effect of Arc Travelling Speed and Welding Sequences on Residual Stresses in Welded Sections of New Ferritic P92 Pipes

2016 ◽  
Vol 35 (2) ◽  
pp. 121-128 ◽  
Author(s):  
Xiaowei Wang ◽  
Jianming Gong ◽  
Yanping Zhao ◽  
Yanfei Wang ◽  
Zhiqiang Ge
Keyword(s):  
Residual Stresses ◽  
Power Plants ◽  
Small Diameter ◽  
Good Combination ◽  
Thick Wall ◽  
P92 Steel ◽  
Welding Technology ◽  
Symmetrical Distribution ◽  
Mechanical And Physical Properties ◽  
Welding Sequences

AbstractNew ferritic P92 steel is widely used in modern power plants due to its good combination of mechanical and physical properties. However, cracks are often formed in the welded sections during the fabrication or service. In order to ensure the structure integrity, the effects of residual stresses need to be considered. The objective of this paper is to investigate the influence of arc travelling speed and welding sequences on the residual stresses distribution in the welded sections of P92 pipes by finite element method (FEM). Results show that arc travelling speed and welding sequences have great effects on residual stresses distribution. With the arc travelling speed increasing, the residual stresses increase. Meanwhile, welding sequences of case B present smaller residual stresses and more symmetrical distribution of residual stresses at the weld centre line. Therefore, using slower arc travelling speed and case B welding sequences can be useful to decrease the residual stresses, which provides a reference for optimizing the welding technology and improving the fabrication process of new ferritic P92 welded pipes with small diameter and thick wall.

scholarly journals Development of Welding P92 Pipes Using the Reduced Pressure Electron Beam Welding Process for a Study of Creep Performance

2014 ◽  
Author(s):  
Nick Bagshaw ◽  
Chris Punshon ◽  
John Rothwell
Keyword(s):  
Electron Beam ◽  
Heat Input ◽  
Power Plants ◽  
Electron Beam Welding ◽  
Welding Process ◽  
Welding Parameters ◽  
Pipe Material ◽  
Reduced Pressure ◽  
Type Iv ◽  
Type Iv Cracking

Boiler and steam piping components in power plants are fabricated using creep strength enhanced ferritic (CSEF) steels, which often operate at temperatures above 550°C. Modification of alloy content within these steels has produced better creep performance and higher operating temperatures, which increases the process efficiency of power plants. The improved materials, however, are susceptible to type IV cracking at the welded regions. A better understanding of type IV cracking in these materials is required and is the basis of the Technology Strategy Board (TSB) UK funded VALID (Verified Approaches to Life Management & Improved Design of High Temperature Steels for Advanced Steam Plants) project. In order to study the relationship between creep performance and heat input during welding, several welds with varying amounts of heat input and resultant HAZ widths were produced using the electron beam welding process. The welding parameters were developed with the aid of weld process modeling using the finite element (FE) method, in which the welding parameters were optimized to produce low, medium and high heat input welds. In this paper, the modeling approach and the development of electron beam welds in ASTM A387 grade P92 pipe material are presented. Creep specimens were extracted from the welded pipes and testing is ongoing. The authors acknowledge the VALID project partners, contributors and funding body: Air Liquide, Metrode, Polysoude, E.ON New Build & Technology Ltd, UKE.ON, Doosan, Centrica Energy, SSE, Tenaris, TU Chemnitz, The University of Nottingham, The Open University and UK TSB. Paper published with permission.

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