Creep Damage Analysis of Welded Joints Including HAZ Softening Region.

Grade 91 is widely used for steam pipes and tubes in high temperature boilers of ultra-super critical power plants in Japan. It was reported that creep damage may initiate at the fine grain region within the heat affected zone (HAZ) in welded joints prior to the base metal, so called “Type IV” damage, which causes steam leakage in existing power plants. Therefore, development of creep damage assessment methods is not only an important but also an urgent subject to maintain operation reliability. In order to evaluate creep damage of welded joints based on finite element analyses, creep deformation properties of a base metal, a weld metal and a HAZ have to be obtained from creep tests. However, it is difficult to cut a standard size creep specimen from the HAZ region. Only a miniature size specimen is available from the narrow HAZ region. Therefore, development of creep testing and evaluation technique for miniature size specimens is highly expected. In this study, a miniature tensile type solid bar specimen with 1mm diameter was machined from a base metal, a weld metal and a HAZ of a new and a used Grade 91 welded joints, and creep tests of these miniature specimens were conducted by using a special developed creep testing machine. It was found that creep deformation property is almost identical between the base metal and weld metal, and creep strain rate of the HAZ is much faster than that of these metals in the new welded joint. Relationships between stress and creep strain rates of the base metal and the HAZ in the used welded joint are within scatter bands of those in the new material. On the other hand, creep strain rate of the weld metal in the used welded joint became much faster than that in the new one. Then both the standard size and the miniature size cross weld specimens were machined from the new and the used welded joints and were tested under the same temperature and stress conditions. Rupture time of the miniature cross weld specimen is much shorter than that of the standard size cross weld specimen. The finite element creep analysis of the specimens indicates that higher triaxiality stress yields within the HAZ of the standard size specimen than that of the miniature specimen causing faster creep strain rate in the HAZ of the miniature cross weld specimen.

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A Damage Evaluation Model of Turbine Blade for Gas Turbine

Volume 6: Ceramics; Controls, Diagnostics and Instrumentation; Education; Manufacturing Materials and Metallurgy ◽

10.1115/gt2016-56817 ◽

2016 ◽

Author(s):

Dengji Zhou ◽

Meishan Chen ◽

Huisheng Zhang ◽

Shilie Weng

Keyword(s):

High Temperature ◽

Real Time ◽

Gas Turbine ◽

Evaluation Model ◽

Creep Damage ◽

Operating Conditions ◽

Damage Analysis ◽

Damage Evaluation ◽

Analysis Model ◽

Estimation Model

Current maintenance, having a great impact on the safety, reliability and economics of gas turbine, becomes the major obstacle of the application of gas turbine in energy field. An effective solution is to process Condition based Maintenance (CBM) thoroughly for gas turbine. Maintenance of high temperature blade, accounting for most of the maintenance cost and time, is the crucial section of gas turbine maintenance. The suggested life of high temperature blade by Original Equipment Manufacturer (OEM) is based on several certain operating conditions, which is used for Time based Maintenance (TBM). Thus, for the requirement of gas turbine CBM, a damage evaluation model is demanded to estimate the life consumption in real time. A physics-based model is built, consisting of thermodynamic performance simulation model, mechanical stress estimation model, thermal estimation model, creep damage analysis model and fatigue damage analysis model. Unmeasured parameters are simulated by the thermodynamic performance simulation model, as the input of the mechanical stress estimation model and the thermal estimation model. Then the stress and temperature distribution of blades will be got as the input of the creep damage analysis model and the fatigue damage analysis model. The real-time damage of blades will be evaluated based on the creep and fatigue analysis results. To validate this physics-based model, it is used to calculate the lifes of high temperature blade under several certain operating conditions. And the results are compared to the suggestion value of OEM. An application case is designed to evaluate the application effect of this model. The result shows that the relative error of this model is less than 10.4% in selected cases. And it can cut overhaul costs and increase the availability of gas turbine significantly. Therefore, the physical-based damage evaluation model proposed in this paper, is found to be a useful tool to tracing the real-time life consumption of high temperature blade, to support the implementation of CBM for gas turbine, and to guarantee the reliability of gas turbine with lowest maintenance costs.

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Creep-Damage Analysis: Comparison Between Coupled and Uncoupled Models

Journal of Pressure Vessel Technology ◽

10.1115/1.1310364 ◽

2000 ◽

Vol 122 (4) ◽

pp. 408-412 ◽

Cited By ~ 4

Author(s):

S. Bhandari ◽

X. Feral ◽

J.-M. Bergheau ◽

G. Mottet ◽

P. Dupas ◽

...

Keyword(s):

Numerical Simulation ◽

Internal Pressure ◽

Validation Study ◽

Pressure Vessel ◽

Creep Damage ◽

Damage Analysis ◽

Hypothetical Accident ◽

Computer Codes ◽

Damage Theory ◽

Reactor Pressure

Numerical simulation of creep rupture of a reactor pressure vessel in a severe hypothetical accident needs to perfectly take account of interactions between creep phenomena and damage. The continuous damage theory enables to formulate models strongly coupling elasto-visco-plasticity and damage. Such models have been implemented in various computer codes and, in particular, in ASTER at Electricite´ de France, CASTEM 2000 at Commissariat a` l’Energie Atomique and SYSTUS+® at SYSTUS International. The objective of this paper is to present briefly a validation study of the three different numerical implementations and to compare the coupled approach to an uncoupled one on an example of a cylinder of the program “RUPTHER,” under internal pressure and heated to a temperature of 700°C. [S0094-9930(00)01004-0]

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Evaluating Creep Damage of Aged Modified 9Cr-1Mo Steel Welded Joints through Indentation Creep Test Methodology

INTERNATIONAL JOURNAL OF EMERGING TRENDS IN SCIENCE AND TECHNOLOGY ◽

10.18535/ijetst/v3i02.20 ◽

2016 ◽

Author(s):

Ravindra D. Grampurohit ◽

Keyword(s):

Creep Test ◽

Welded Joints ◽

Creep Damage ◽

Indentation Creep ◽

Test Methodology

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Development of Creep Damage in Similar Weld Joints of P92 Steel Pipe

Solid State Phenomena ◽

10.4028/www.scientific.net/ssp.270.162 ◽

2017 ◽

Vol 270 ◽

pp. 162-167

Author(s):

Petr Král ◽

Vaclav Sklenička ◽

Květa Kuchařová ◽

Marie Svobodová ◽

Marie Kvapilová ◽

...

Keyword(s):

Welded Joints ◽

Creep Behaviour ◽

Creep Damage ◽

Electron Back Scatter Diffraction ◽

Steel Pipe ◽

Tensile Creep ◽

Creep Tests ◽

P92 Steel ◽

Welding Technology ◽

Fracture Ductility

The microstructure and creep behaviour of the welded joints of P92 steel pipe were investigated in order to determine the influence of orbital heat welding technology on the creep resistance. Creep specimens were machined from the welded joints. Tensile creep tests of welded joints were performed at 873 K using different stresses. The microstructure of tested specimens was investigated by scanning electron microscope Tescan equipped with an electron-back scatter diffraction. The creep results showed that the creep fracture strain of the welded joints decreases with decreasing value of applied stress. Microstructure investigation showed that fracture behaviour of welded joints is influenced by an enhanced cavity formation at grain boundaries in the heat-affected zone causing lower fracture ductility.

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Literature Review on the Development of Computational Software System for Creep Damage Analysis for Weldment

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.510.490 ◽

2012 ◽

Vol 510 ◽

pp. 490-494 ◽

Cited By ~ 1

Author(s):

Feng Tan ◽

Qiang Xu ◽

Zhong Yu Lu ◽

Dong Lai Xu

Keyword(s):

Constitutive Equation ◽

Literature Review ◽

Creep Damage ◽

Computational Approach ◽

Software System ◽

Damage Analysis ◽

Computational System

This paper reports a literature review on the development of computational software system for creep damage analysis for weldment. It starts with a brief review on the creep damage problem in weldment and the computational approach; identifies the need for computational approach and the un-availability of such computational system; further details on the preliminary development progress of a transfer programme and constitutive equation subroutines. This paper contributes to knowledge to the development of computational system for creep damage analysis.

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Findings on Creep-Fatigue Damage in Pressure Parts of Long-Term Service-Exposed Thermal Power Plants

Journal of Pressure Vessel Technology ◽

10.1115/1.3264447 ◽

1985 ◽

Vol 107 (3) ◽

pp. 260-270 ◽

Cited By ~ 4

Author(s):

F. Masuyama ◽

K. Setoguchi ◽

H. Haneda ◽

F. Nanjo

Keyword(s):

Fatigue Damage ◽

Power Plants ◽

Thermal Power ◽

Field Experiences ◽

Creep Damage ◽

Thermal Power Plants ◽

Damage Analysis ◽

Creep Fatigue ◽

Fatigue Damage Analysis

The increase of long-term service exposure to thermal power plants, the tendency toward intermediate and cyclic operation to meet the change in electric power demand and supply situation, and the requirement to develop higher-temperature and higher-pressure plants have led to increasing attention towards the reliability improvement. This paper presents findings from field experiences of cracking or failure and two types of damage analyses—(1) creep-fatigue damage analysis based on the life fraction rule and (2) metallurgical damage analysis—of boiler pressure parts that have been exposed to long-term elevated temperature service. The field experiences are (1) cracking or failure of thick-walled Type 316 stainless steel pressure parts in the main steam line of an ultra-supercritical thermal power plant and (2) dissimilar metal weld joints for boiler tubing. The creep-fatigue damage analysis of these pressure parts showed a reasonable correspondence with the field experience. According to the creep-fatigue damage analysis and the metallurgical damage analysis, most of damage was restrained creep mode phenomenon without deformation. The creep damage was composed of metallurgical damage and mechanical damage such as microvoids and structural defects. One method of simulating field experienced creep damage was proposed and performed. As a result, the process of creep voids being generated and growing into cracks without deformation was successfully observed. Also a review of the current status of nondestructive detecting methods of creep damage suggests that detecting the creep voids metallurgically is more practical at the present time than doing so analyzing the changes in physical properties of the material. It is also suggested that, in the metallurgical approach, detecting the creep voids and cracks by replica method and anlayzing precipitates for evaluation of material deterioration by precipitate extraction method will make it possible to successfully address the problem of plant equipment creep damage evaluation and life prediction.

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Notch Behavior of Components Under the Stress-Controlled Creep–Fatigue Condition: Weakening or Strengthening?

Journal of Pressure Vessel Technology ◽

10.1115/1.4033731 ◽

2016 ◽

Vol 139 (1) ◽

Cited By ~ 8

Author(s):

Jian-Guo Gong ◽

Fu-Zhen Xuan

Keyword(s):

Stress Ratio ◽

Maximum Stress ◽

Strain Range ◽

Creep Damage ◽

Equivalent Strain ◽

Holding Time ◽

Damage Analysis ◽

Strengthening Effect ◽

Creep Fatigue ◽

The Difference

Notch-related weakening and strengthening behavior under creep–fatigue conditions was studied in terms of the elastic–viscoplasticity finite-element method (FEM). A coupled damage analysis, i.e., the skeletal point method for creep damage evaluation coupled with the equivalent strain range method for fatigue damage, was employed in the notch effect evaluation. The results revealed that, under the short holding time condition, a weakening behavior was observed for the notch, while a strengthening effect was detected with the increase of holding time. The difference could be ascribed to the creep damage contribution in the holding stage. The influence of stress concentration factor (SCF), stress ratio, and the maximum stress was strongly dependent on the competition of creep and fatigue mechanism.

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Evaluation of Microstructures and Creep Damages in the HAZ of P91 Steel Weldment

Journal of Pressure Vessel Technology ◽

10.1115/1.3028021 ◽

2009 ◽

Vol 131 (2) ◽

Cited By ~ 17

Author(s):

Masaaki Tabuchi ◽

Hiromichi Hongo ◽

Yongkui Li ◽

Takashi Watanabe ◽

Yukio Takahashi

Keyword(s):

Welded Joints ◽

Damage Mechanics ◽

Early Stage ◽

Axial Stress ◽

Creep Damage ◽

Specimen Thickness ◽

Creep Tests ◽

Fine Grained ◽

Type Iv

The creep strength of welded joints in high Cr steels decreases due to the formation of Type IV creep damage in heat-affected zones (HAZs) during long-term use at high temperatures. This paper aims to elucidate the processes and mechanisms of Type IV creep damage using Mod.9Cr–1Mo (ASME Grade 91) steel weldments. Long-term creep tests for base metal, simulated fine-grained HAZ, and welded joints were conducted at 550°C, 600°C, and 650°C. Furthermore, creep tests of thick welded joint specimens were interrupted at 0.1, 0.2, 0.5, 0.7, 0.8, and 0.9 of rupture life and damage distributions were measured quantitatively. It was found that creep voids were initiated at an early stage of life inside the specimen thickness and coalesced to form cracks at a later stage of life. Creep damage was observed mostly at 25% below the surface of the plate. Experimental creep damage distributions were compared with computed versions using finite element method and damage mechanics analysis. Both multi-axial stress state and strain concentration in fine-grained HAZ appear to influence the formation and distribution of creep voids.

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