Type IV Creep Damage Analysis for Full Size Component Test on Welded P91 Boiler Hot Reheat Piping

2004 ◽  
Author(s):  
Fumio Takemasa ◽  
Isamu Nonaka ◽  
Takuya Ito ◽  
Kensuke Saitou ◽  
Yoshikazu Miyachi ◽  
...  
Keyword(s):  
Welded Joints ◽  
Power Plants ◽  
Creep Damage ◽  
Assessment Method ◽  
Life Assessment ◽  
Creep Tests ◽  
Full Size ◽  
Type Iv ◽  
Component Test ◽  
Creep Life Assessment

In order to establish the creep life assessment method for modified 9Cr-1Mo steel welded joints on hot reheat piping of generating power plants, internal pressure creep tests conducted with full size components are analysed using the finite element method (FEM). As a result, it is shown that the creep damage distribution in weld heat affected zone (HAZ) can be predicted by stress distribution in HAZ, and that average stress in HAZ can be a representative value for creep strength of welded joints.

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

2009 ◽  
Vol 131 (2) ◽  
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.

Full Size Internal Pressure Creep Test for Welded P91 Hot Reheat Piping

2004 ◽  
Author(s):  
Isamu Nonaka ◽  
Takuya Ito ◽  
Fumio Takemasa ◽  
Kensuke Saito ◽  
Yoshikazu Miyachi ◽  
...  
Keyword(s):  
Internal Pressure ◽  
Damage Detection ◽  
Creep Test ◽  
Life Prediction ◽  
Prediction Method ◽  
Creep Damage ◽  
Assessment Method ◽  
Life Assessment ◽  
Full Size ◽  
Test Component

In order to establish the life assessment method for the welded modified 9Cr-1Mo steel hot reheat piping, an internal pressure creep test is conducted with a full size test component. As a result, the fracture mode of the component is clarified and the life prediction method is established. Furthermore, the creep damage detection procedures are proposed.

Power Plant Life/Risk Assessment Techniques

2002 ◽  
Author(s):  
M. A. Clark ◽  
R. Browne ◽  
M. Flaman ◽  
E. M. LeHockey ◽  
I. Thompson
Keyword(s):  
Power Plant ◽  
Asset Management ◽  
Power Plants ◽  
Orientation Imaging Microscopy ◽  
Creep Damage ◽  
High Energy ◽  
Life Assessment ◽  
Original Design ◽  
Type Iv ◽  
Plant Operations

Many fossil power plants in N. America are now required to operate in excess of 20 years beyond their original design life. To ensure safe reliable operation, life assessment of key high-risk components is required. Life assessment of older power plant requires the application of many diverse techniques and the integration of several engineering disciplines with plant operations experience. Traditional approaches to life assessment of high temperature components will be described and illustrated with examples taken from experience on large coal fired plants from the old Ontario Hydro system. These results will include a number of high energy piping welds with approximately 160,000 hours of service that contain intercritical region heat affected zone (HAZ) creep damage (Type IV). These welds have been monitored through in-situ metallography techniques for over 20,000 hours since damage was first detected. New techniques are also being developed or employed: miniature sample testing for evaluating creep and fracture properties along with miniature EDM sample removal techniques. The use of innovative mechanical scratch gauges for the purpose on-line strain monitoring of mechanical or civil structures. The use of orientation imaging microscopy (OIM) for simultaneous comprehensive characterization of the interaction between residual plastic strains, texture, grains size distribution and other crystallographic features as applied to root cause failure analysis. Finally risk based asset management software RBMS for the purpose of detailed component assessments. Examples/results of these techniques will also be presented in the paper.

Full Size Internal Pressure Creep Test for Welded P91 Hot Reheat Elbow

2004 ◽  
Author(s):  
Isamu Nonaka ◽  
Takuya Ito ◽  
Fumio Takemasa ◽  
Kensuke Saitou ◽  
Yoshikazu Miyachi ◽  
...  
Keyword(s):  
Internal Pressure ◽  
Damage Detection ◽  
Creep Test ◽  
Life Prediction ◽  
Prediction Method ◽  
Creep Damage ◽  
Assessment Method ◽  
Life Assessment ◽  
Full Size ◽  
Test Component

In order to establish the life assessment method for the welded modified 9Cr-1Mo steel hot reheat elbow, an internal pressure creep test is conducted with a full size test component. As a result, the fracture mode of the component is clarified and the life prediction method is established. Furthermore, the creep damage detection procedures are proposed.

Creep Damage Evaluation of Fine-Grained HAZ in Mod. 9Cr Ferritic Heat-Resistant Steel Weldments

2007 ◽  
Author(s):  
N. Yoneyama ◽  
K. Kubushiro ◽  
H. Yoshizawa
Keyword(s):  
Creep Damage ◽  
Life Time ◽  
Creep Life ◽  
Creep Tests ◽  
Boundary Density ◽  
Fine Grained ◽  
Type Iv ◽  
Fine Grain ◽  
Type Iv Cracking ◽  
Rupture Mechanism

9Cr steel weldments are concerned with evaluation of creep life time and creep rupture mechanism. In fine grain HAZ (FG-HAZ) of weldments, TYPE IV cracking and creep voids occurred at lower stress than rupture stress level of base metal. In the crept specimen, FG-HAZ sometime has large coarsening grains near creep voids. These recovery phenomena are localized in FG-HAZ, and recovered microstructures are dependent on heat input of welding. In this study, creep tests are examined in two types of weldments, and relations between creep life time and coarsened sub-grains or grains have been studied by microstructural changing with EBSP analysis. In crept specimens, boundaries are moved and boundary density is decreasing in the fine-grained HAZ. Maximum grain size and creep life time have linear function, and EBSP can evaluate creep life time of 9Cr weldments. These microstructural changing are considered by morphology of precipitates in the several crept specimens.

scholarly journals Estimating the Influences of Prior Residual Stress on the Creep Rupture Mechanism for P92 Steel

Metals ◽  
2019 ◽  
Vol 9 (6) ◽  
pp. 639 ◽  
Author(s):  
Dezheng Liu ◽  
Yan Li ◽  
Xiangdong Xie ◽  
Guijie Liang ◽  
Jing Zhao
Keyword(s):  
Residual Stress ◽  
Flow Stress ◽  
Power Plants ◽  
Creep Damage ◽  
Creep Rupture ◽  
Transgranular Fracture ◽  
Creep Tests ◽  
Energy Principle ◽  
P92 Steel ◽  
Rupture Mechanism

Creep damage is one of the main failure mechanisms of high Cr heat-resistant steel in power plants. Due to the complex changes of stress, strain, and damage at the tip of a creep crack with time, it is difficult to accurately evaluate the effects of residual stress on the creep rupture mechanism. In this study, two levels of residual stress were introduced in P92 high Cr alloy specimens using the local out-of-plane compression approach. The specimens were then subjected to thermal exposure at the temperature of 650 °C for accelerated creep tests. The chemical composition of P92 specimens was obtained using an FLS980-stm Edinburgh fluorescence spectrometer. Then, the constitutive coupling relation between the temperature and material intrinsic flow stress was established based on the Gibbs free energy principle. The effects of prior residual stress on the creep rupture mechanism were investigated by the finite element method (FEM) and experimental method. A comparison of the experimental and simulated results demonstrates that the effect of prior residual stress on the propagation of micro-cracks and the creep rupture time is significant. In sum, the transgranular fracture and the intergranular fracture can be observed in micrographs when the value of prior residual stress exceeds and is less than the material intrinsic flow stress, respectively.

Creep Behavior of a Large Full-Size Welded Austenitic Steel Plate

1998 ◽  
Vol 120 (3) ◽  
pp. 262-269
Author(s):  
V. Koundy ◽  
L. Allais ◽  
M. Delhaye
Keyword(s):  
Creep Behavior ◽  
Welded Joints ◽  
Numerical Study ◽  
High Stress ◽  
Creep Tests ◽  
Time Duration ◽  
Theoretical Formulation ◽  
Full Size ◽  
Significant Difference ◽  
Reduction Factors

The high-temperature design codes are presently considering the use of stress reduction factors for designing welded structures submitted to creep. These reduction factors are derived from creep tests which are generally made on small specimens and are not necessarily representative of large-size geometries. These codes are very likely overconservative, consequently uneconomical and need to be improved; an investigation to assess and quantify the supposed size effect is required. This paper presents an experimental and numerical study on creep behavior at 600°C of full-size welded joints taking into account real full-thickness of weldings. The material investigated is the austenitic stainless steel 316L(N) with manual metal arc welds using the 19 Cr 12 Ni 2 Mo electrode grade. The creep laws used in calculations are those obtained from tests using small specimens, but some coefficients of their theoretical formulation have been modified to obtain a better coherence with fullsize specimen data. Between small and large full-size specimens, experimental results show no significant difference in time to rupture, and the same location of fracture, at the center of the weldment, is observed. Finite element simulations performed for full-size welded joints provide rupture times that are consistent with measured values. The calculated percentage of the damaged volume in the weld metal as a function of load levels and of creep-time duration is studied; it shows that the creep-rupture times for high stress loading are determined with higher accuracy than for low stress loading.

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

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.

THE LIFE ASSESSMENT OF STEAM TURBINE ROTORS FOR FOSSIL POWER PLANTS

2006 ◽  
Vol 20 (25n27) ◽  
pp. 4371-4376
Author(s):  
SUNGHO CHANG ◽  
GEEWOOK SONG ◽  
BUMSHIN KIM ◽  
JUNGSEB HYUN ◽  
JEONGSOO HA
Keyword(s):  
Power Plant ◽  
Steam Turbine ◽  
Rotational Speed ◽  
Power Plants ◽  
Thermal Power ◽  
Creep Damage ◽  
Life Assessment ◽  
Life Extension ◽  
Start Up ◽  
Operational Life

The operational mode of thermal power plants has been changed from base load to duty cycle. From the changeover, fossil power plants cannot avoid frequent thermal transient states, for example, start up and stop, which results in thermal fatigue damage at the heavy section components. The rotor is the highest capital cost component in a steam turbine and requires long outage for replacing with a new one. For an optimized power plant operational life, inspection management of the rotor is necessary. It is known in general that the start-up and shutdown operations greatly affect the steam turbine life. The start-up operational condition is especially severe because of the rapid temperature and rotational speed increase, which causes damage and reduction of life of the main components life of the steam turbine. The start-up stress of a rotor which is directly related to life is composed of thermal and rotational stresses. The thermal stress is due to the variation of steam flow temperature and rotational stress is due to the rotational speed of the turbine. In this paper, the analysis method for the start-up stress of a rotor is proposed, which considers simultaneously temperature and rotational speed transition, and includes a case study regarding a 500MW fossil power plant steam turbine rotor. Also, the method of quantitative damage estimation for fatigue-creep damage to operational conditions, is described. The method can be applied to find weak points for fatigue-creep damage. Using the method, total life consumption can be obtained, and can be also be used for determining future operational modes and life extension of old fossil power units.

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