Comparative Analysis of Creep Cavitation Damage in 0.5Cr-0.5Mo-0.3V Steel after Long-Term Creep Exposure by Metallography and Replica Testing

2017 ◽  
Vol 891 ◽  
pp. 335-340
Author(s):  
Zdeněk Kuboň ◽  
Lenka Pekařová ◽  
Jana Kosňovská ◽  
Pavel Poštulka
Keyword(s):  
Outer Surface ◽  
Creep Damage ◽  
Metallographic Analysis ◽  
Pipe Surface ◽  
Cavitation Damage ◽  
Pipe Elbow ◽  
Creep Cavitation ◽  
Term Creep ◽  
Parallel Evaluation

Complex metallographic analysis was performed on the steam pipe elbow made of 0.5Cr-0.5Mo-0.3V steel after long-term (more than 240 000 hours) of operation at elevated temperature that revealed the extensive creep damage on the outer surface of the pipe elbow. Metallographic analysis confirmed pronounced creep damage at the outer surface but, at the same time, the non-uniform nature of the cavitation. The density of cavities continuously decreased from outer to inner pipe surface in the most damaged area and rapidly waned along the circumference as well as the length of the elbow. Parallel evaluation of actual extent of the cavitation damage made by metallography and replica methods in various parts of the pipe elbow confirmed that replica method is capable to describe and quantify the cavitation damage of this steel in the same way as metallography, including evaluation of creep damage according to Nordtest NT TR 302.

Material Degradation of Steam Pipe Elbow after Long-Term Exposure

2015 ◽  
Vol 647 ◽  
pp. 162-169
Author(s):  
Lenla Pekařová ◽  
Zdeněk Kuboň
Keyword(s):  
Residual Life ◽  
Creep Damage ◽  
Life Extension ◽  
Metallographic Analysis ◽  
Material Degradation ◽  
Pipe Surface ◽  
Pipe Elbow ◽  
Toughness Testing ◽  
Steam Pipe ◽  
Stable Growth

Routine non-destructive examination of the steam pipe elbow after more than 240 000 hours of operation at elevated temperature revealed the extensive creep damage on the outer surface of the pipe elbow. Complex metallographic analysis made in this area confirmed creep damage as well as the non-uniform nature of the cavitation. The density of cavities continuously decreased from the outer pipe surface towards the inner surface, but also its density rapidly waned beyond the damaged area in both directions, along the circumference as well as the length of the elbow. The actual extent of the material degradation was then evaluated by testing of mechanical properties, Charpy-V and fracture toughness testing and the results were used in calculation of the residual life of the pipe elbow. It was shown that although the creep damage was perhaps one of the worst detected in Czech Republic, the cracks in the pipe elbow would spread by the stable growth until the half of the pipe wall thickness. This result thus confirms the possibility of creep life extension far beyond the limit criteria used so far.

Preliminary Review of the Influence of Cavitation Behavior in Creep Damage Constitutive Equations

2014 ◽  
Vol 940 ◽  
pp. 46-51 ◽  
Author(s):  
Xin Yang ◽  
Qiang Xu ◽  
Zhong Yu Lu ◽  
Simon Barrans
Keyword(s):  
Reference Value ◽  
Creep Damage ◽  
Preliminary Review ◽  
Current Application ◽  
Cavitation Damage ◽  
X Ray ◽  
Creep Cavitation ◽  
Cr Steels ◽  
Cavitation Behavior ◽  
Damage Equation

This review paper mainly consists of from two aspects: (a) the evolution of the cavitation damage equation from Dyson to current application in high Cr steels by traditional techniques; (b) quantitation analyses of cavitation behavior in brass, copper, dual phase steel from X-ray microtomtograph. Though there is a lack of experimental data for high Cr steels by X-ray microtomography currently, but (b) has provided reference value for studying creep cavitation behavior in high Cr steels. This paper will be the fundamental of development new creep damage constitutive equation through quantitation analyses of X-ray tomography.

Prediction of long-term creep behaviour of Grade 91 steel at 873 K in the framework of microstructure-based creep damage mechanics approach

2018 ◽  
Vol 28 (6) ◽  
pp. 877-895 ◽  
Author(s):  
J Christopher ◽  
BK Choudhary
Keyword(s):  
Damage Mechanics ◽  
Creep Behaviour ◽  
Creep Damage ◽  
Time Data ◽  
Grade 91 ◽  
Term Creep ◽  
Kinetic Creep ◽  
Grade 91 Steel

A detailed analysis has been performed for the prediction of long-term creep behaviour of tempered martensitic Grade 91 steel at 873 K using the microstructure-based creep damage mechanics approach. Necessary modifications have been made into the original kinetic creep law proposed by Dyson and McLean in order to account for the influence of microstructural damages arising from the coarsening of M23C6 and conversion of useful MX precipitates into deleterious Z-phase on creep behaviour of the steel. An exponential rate relationship has been introduced for the evolution of number density of MX precipitates with time. It has been shown that the developed model adequately predicts the experimental long-term creep strain–time as well as creep rate-time data. The role of Z-phase on long-term creep behaviour of Grade 91 steel has also been discussed.

Creep damage characteristics and evolution of HR3C austenitic steel during long term creep

2021 ◽  
pp. 142432
Author(s):  
Jie Zhang ◽  
Zhengfei Hu ◽  
Guoli Zhai ◽  
Zhen Zhang ◽  
Ziyi Gao
Keyword(s):  
Austenitic Steel ◽  
Creep Damage ◽  
Damage Characteristics ◽  
Term Creep

Unified Viscoplastic Model Coupled With Damage for Evaluation of Creep-Fatigue of Grade 91 Steel

2017 ◽  
Author(s):  
Nazrul Islam ◽  
David J. Dewees ◽  
Tasnim Hassan
Keyword(s):  
Damage Mechanics ◽  
Creep Damage ◽  
Continuum Damage Mechanics ◽  
Creep Model ◽  
Damage Evaluation ◽  
Creep Fatigue ◽  
Grade 91 ◽  
Term Creep ◽  
Grade 91 Steel

A continuum damage mechanics (CDM) coupled unified viscoplasticity model has been developed to predict the creep-fatigue life of modified Grade 91 steel. A tertiary creep model termed MPC-Omega codified in Part 10 of API (and also implemented in the ASME BP&V Code for Grade 22V and more recently Grade 91 Steel) is also employed for creep damage evaluation. As MPC-Omega has a direct relationship with Larson-Miller parameter (LMP) coefficients, creep damage coefficients in the unified constitutive model (UCM) are tied with MPC-Omega coefficients in order to utilize WRC and API 579-1 Grade 91 creep rupture database. The model is validated against long-term creep, LCF, creep-fatigue and TMF experimental responses at T = 20–600°C.

Creep Damage Evaluation by Hardness in Advanced High Cr Ferritic Steels

2007 ◽  
Vol 561-565 ◽  
pp. 2217-2220 ◽  
Author(s):  
Hassan Ghassemi Armaki ◽  
Kyosuke Yoshimi ◽  
Kouichi Maruyama ◽  
Mitsuru Yoshizawa ◽  
Masaaki Igarashi
Keyword(s):  
Activation Energy ◽  
Rupture Life ◽  
Creep Damage ◽  
Ferritic Steels ◽  
Tempered Martensite ◽  
Short Term ◽  
Term Creep ◽  
Martensitic Lath ◽  
Short Term Creep

The apparent activation energy for rupture life sometimes changes from a high value of short term creep to a low value of long term creep. This change results in overestimation of rupture life recognized recently in advanced high Cr ferritic steels. The present study examined how to detect the decrease of activation energy in 9-12 %Cr steels with tempered martensitic lath microstructure. During aging without stress hardness of the tempered martensite microstructures remains almost constant in short term, whereas it decreases with increasing time after long term exposure. The onset of hardness drop can be a good measure of the decrease of activation energy. Causes of the hardness drop and the decrease of activation energy are discussed.

Creep Damage, Ductility and Expected Life for Materials With Defects

2008 ◽  
Author(s):  
Pertti Auerkari ◽  
Stefan Holmstro¨m ◽  
Juhani Rantala ◽  
Jorma Salonen
Keyword(s):  
Structural Integrity ◽  
Creep Damage ◽  
Life Assessment ◽  
Intergranular Cracking ◽  
Short Term ◽  
Assessment Techniques ◽  
Term Creep ◽  
Free Material ◽  
Creep Loading

Defects can pre-exist and grow by creep in structures subjected to loading at high temperatures. As structural integrity is not necessarily conveniently predicted and managed by applying design and life assessment techniques intended for nominally defect-free material, it is important that methods are available for quantified and safe assessment of defects. In addition to the assessment methods, also materials behaviour will affect the likely outcome. In particular, ductility of the materials is important, and unfortunately ductility tends to decrease when shifting from short-term testing to long term creep conditions. In this paper, two examples are shown of materials with such ductility effects when combined with defects. The first example involves 316H stainless steel subjected to creep loading with an extensive crack-like defect, resulting in a transformation from microscopically ductile to brittle intergranular cracking within a relatively modest time span. The second example will demonstrate a corresponding shift in OFP copper that shows a radical ductility and life reduction in creep when including so small weld defects that they would be undetectable in conventional NDT.

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