Correlation Between Intercritical Heat-Affected Zone and Type IV Creep Damage Zone in 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.

Download Full-text

Creep damage in long-term grade 91 steel component tests

Materials at High Temperatures ◽

10.1080/09603409.2020.1813963 ◽

2020 ◽

Vol 37 (6) ◽

pp. 425-433

Author(s):

Jonathan Parker ◽

John Siefert

Keyword(s):

Creep Damage ◽

Steel Component ◽

Grade 91 ◽

Grade 91 Steel

Download Full-text

Transition from Type IV to Type I cracking in heat-treated grade 91 steel weldments

Materials Science and Engineering A ◽

10.1016/j.msea.2017.12.088 ◽

2018 ◽

Vol 714 ◽

pp. 1-13 ◽

Cited By ~ 15

Author(s):

Yiyu Wang ◽

Leijun Li ◽

Rangasayee Kannan

Keyword(s):

Type I ◽

Type Iv ◽

Heat Treated ◽

Grade 91 ◽

Grade 91 Steel

Download Full-text

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

Volume 6A: Materials and Fabrication ◽

10.1115/pvp2017-65849 ◽

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.

Download Full-text

Continuum damage mechanics predictions of creep damage initiation and growth in ferritic steel weldments in a medium bore branched pipe under constant pressure at 590 °C using a five-material weld model

Proceedings of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rspa.2005.1488 ◽

2005 ◽

Vol 461 (2060) ◽

pp. 2303-2326 ◽

Cited By ~ 22

Author(s):

D.R Hayhurst ◽

R.J Hayhurst ◽

F Vakili-Tahami

Keyword(s):

Heat Affected Zone ◽

Ferritic Steel ◽

Damage Mechanics ◽

Constant Pressure ◽

Creep Damage ◽

Continuum Damage Mechanics ◽

Coarse Grained ◽

Continuum Damage ◽

Damage Initiation ◽

Type Iv

The paper reports three-dimensional creep continuum damage mechanics (CDM) analyses of creep failure in a medium bore Cr–Mo–V low alloy ferritic steel welded branched-pressure vessel that has been tested under a constant pressure of 4 MPa, at a uniform temperature of 590 °C. The use of the CDM computer software Damage XXX to analyse the initiation and growth of creep damage and subsequent failure in the branch weld is reported for a five-material model that includes: parent, Type IV, refined heat affected zone (R-HAZ), coarse grained heat affected zone (CG-HAZ) and weld materials. The results of the analyses are presented for two cases: the first without the CG-HAZ; and, the second with the CG-HAZ included. For both cases, lifetimes are conservatively, yet accurately predicted. It is shown that it is necessary to use a Type IV thickness of 0.7 mm to accurately predict the failure location and mode. The results of metallographic examinations of a tested vessel and the predicted damage fields are in close accord. Failure is predicted to take place, by steam leakage, from the interior of the vessel, through the Type IV zone adjacent to the main pipe, connecting through the R-HAZ to the CG-HAZ, where leakage takes place at the weld toe in the crotch plane.

Download Full-text

Creep Rupture Life Prediction of Grade 91 Circumferential Welded Tube Under Combined Internal Pressure With Axial Load

Volume 6A: Materials and Fabrication ◽

10.1115/pvp2016-63010 ◽

2016 ◽

Author(s):

Takashi Ogata ◽

Toshiki Mitsueda ◽

Hiroshi Sakai

Keyword(s):

Internal Pressure ◽

Axial Load ◽

Axial Stress ◽

Creep Damage ◽

Load Level ◽

Rupture Time ◽

Type Iv ◽

Welded Tube ◽

Grade 91 ◽

Type Iv Cracking

Grade 91 steels are widely used for high temperature pipes in ultra-super-critical thermal power plants. It was recently reported that the creep damage was detected in the fine grain region within the heat affected zone (HAZ) in the welded pipes, so called “Type IV” damage. So far, studies on creep damage and life assessment methods for welded joints of the Grade 91 steel were concentrated on longitudinal welded pipes. Circumferential welded joints are also susceptible to Type IV damage due to the increase of axial thermal stress superimposed with pipe weight. In this study, the effect of additional axial stress to the axial stress produced by the internal pressure on damage and rupture property is discussed based on internal pressure creep tests adding different levels of the axial loads using the Grade 91 circumferential welded tubes. Rupture time of the circumferential welded tube decreases with increasing additional axial load level. Longitudinal cracking in the weld metal was observed in the specimens tested under lower additional load level, and Type IV cracking was observed in the specimens under higher additional load level. The stress analysis results indicate that the longitudinal stress in the HAZ increases with the axial load. Type IV cracking occurs at a certain value of a ratio of the total longitudinal stress to the circumferential stress. Under the test condition where Type IV cracking occurs, the rupture time is significantly shorter than the predicted rupture time based on the creep rupture data of the longitudinal welded tubes. The limited creep strain concept is introduced to predict the rupture time of the circumferential welded tubes by considering the effect of stress multiaxiality. Eventually, the rupture times caused by Type IV cracking of both the longitudinal and the circumferential welded tubes were accurately predicted by the limited creep strain concept.

Download Full-text

Retention of Delta Ferrite in the Heat-Affected Zone of Grade 91 Steel Dissimilar Metal Welds

Metallurgical and Materials Transactions A ◽

10.1007/s11661-019-05182-4 ◽

2019 ◽

Vol 50 (6) ◽

pp. 2732-2747 ◽

Cited By ~ 3

Author(s):

Michael W. Kuper ◽

Boian T. Alexandrov

Keyword(s):

Heat Affected Zone ◽

Delta Ferrite ◽

Dissimilar Metal ◽

Grade 91 ◽

Grade 91 Steel

Download Full-text

A Quantitative Assessment of Microstructural Evolution for Grade 91

Volume 6A: Materials and Fabrication ◽

10.1115/pvp2018-84273 ◽

2018 ◽

Author(s):

Chang Che ◽

Gong Qian ◽

Xisheng Yang

Keyword(s):

High Temperature ◽

Microstructural Evolution ◽

Quantitative Assessment ◽

Creep Damage ◽

Precipitated Phase ◽

High Temperature Components ◽

Grade 91 ◽

Term Creep ◽

Grade 91 Steel

China has the most supercritical boilers in the world. Grade 91 steels are widely used for high temperature components of supercritical boiler. During high temperature service, microstructural evolution of Grade 91 steel may affect the mechanical properties, including creep strength. However, there are very few studies on quantitative assessment of microstructural evolution for Grade 91 steel, especially on precipitates content. In this article, microstructural evolution of Grade 91 was studied. A quantitative assessment of microstructure evolution was given during long-term creep, focusing on the precipitated phase content in Grade 91 steel. The results show, the precipitates content of Grade 91 steel has a corresponding relationship with creep damage.

Download Full-text