Evaluation of the Creep Strength of 9Cr-1Mo-V and 1Cr-1Mo-1/4V Castings and Weldments Using Accelerated Creep Testing

2020 ◽  
Author(s):  
Scot Laney
Keyword(s):  
Creep Testing ◽  
Stress Relaxation Test ◽  
Creep Data ◽  
Test Program ◽  
Creep Properties ◽  
Type Iv ◽  
Accelerated Creep ◽  
Identical Test ◽  
Type Iv Cracking

Abstract The traditional method to generate creep data requires several long term tests; in some cases upwards of 100,000 hours. These tests are often time and cost prohibitive to perform. Creep data in literature is limited to commonly available materials in set processing conditions. This speaks very little to the properties for new materials, alternate processing of existing materials, as well as properties for weldments and heat affected zones (HAZ) that occur in the fabrication of large equipment. Due to this, several methods have been developed for accelerated creep testing. One such method, namely, the Stress Relaxation Test (SRT), is discussed as the means to evaluate two different materials and their weldments used in the manufacturing of steam turbine casings. Cast 9Cr-1Mo-V material from two different foundries as well as their weldments and Heat Affected Zones (HAZ) were tested at temperatures between 550oC and 700oC. The SRT generated data closely matches that given in literature. In a nearly identical test program, cast 1Cr1Mo¼V steel showed anomalies in the weld and HAZ behavior. Further investigation showed that the incorrect weld metal was used and a second attempt, poor welding practice lead to failure due to Type IV cracking. These two case studies illustrate the ability of the SRT method to accurately predict creep properties and its sensitivity to detect variations in properties, which can make it useful for rapid verification of casting suppliers and welding procedures for high temperature applications.

Evaluation of the Creep Strength of 9Cr-1Mo-V and 1Cr-1Mo-1/4V Castings and Weldments Using Accelerated Creep Testing

2020 ◽  
Author(s):  
Scot J. Laney
Keyword(s):  
Stress Relaxation ◽  
Weld Metal ◽  
Filler Metal ◽  
Creep Testing ◽  
Relaxation Test ◽  
Stress Relaxation Test ◽  
Creep Data ◽  
Creep Properties ◽  
First Case ◽  
Accelerated Creep

Abstract Knowledge of creep properties is vital in determining the allowable stresses for rotating equipment design at high temperatures. Unfortunately, the traditional method to generate creep data requires several long term tests; in some cases, upwards of 100,000 hours are needed. These tests are often time and cost prohibitive to perform. Some data is available from sources such as the ASME Boiler and Pressure Vessel Code, but these are limited to commonly available materials in set processing conditions. They speak very little to the properties for new materials, alternate processing of existing materials, and properties for weldments and heat affected zones (HAZ) that occur in the fabrication of large equipment. Due to this, several methods have been developed for accelerated creep testing. One such method is the Stress Relaxation Test (SRT) developed by Woodford. This high precision stress relaxation test can generate five decades of creep data in a single, one-day test. This paper discusses the use of the SRT method to evaluate two different materials and their weldments used in the manufacturing of steam turbine casings. The first material is cast 9Cr-1Mo-V (SA-217, Grade C12A). In this first case, material from two different foundries was tested at temperatures between 550°C and 700°C. Specimens consisting entirely of matching weld metal and those that that include the HAZ centered between weld metal and the base casting were also tested as a means to verify fabrication and casting upgrade procedures. In this case, the data generated for all three sample types very closely match those given in literature. In a nearly identical test program, testing was performed on cast 1Cr-1Mo-¼V steel (ASTM A356, Grade 9). In this second case, the base casting closely matched literature data, while the weldments did not. In one instance, through a significant reduction in properties of the weld metal specimen, the SRT method was able to detect that an under matching filler metal was used. In another instance, the HAZ specimen, from a weldment using matching filler metal, failed during the test. It was found that the welding procedure resulted in overheating the sample. These two case studies illustrate the ability of the SRT method to accurately predict creep properties and its sensitivity to detect variations in properties, which can make it useful for rapid verification of welding procedures for high temperature applications.

Microstructures of Grade 91 Steels Under Long-Term Creep Conditions

2018 ◽  
Author(s):  
Kenji Kako ◽  
Susumu Yamada ◽  
Masatsugu Yaguchi ◽  
Yusuke Minami
Keyword(s):  
Remaining Life ◽  
Martensitic Steels ◽  
Creep Data ◽  
Creep Life ◽  
Creep Tests ◽  
Microstructural Observation ◽  
Type Iv ◽  
Grade 91 ◽  
Term Creep

Type IV damage has been found at several ultra-supercritical (USC) plants that used high-chromium martensitic steels in Japan, and the assessment of the remaining life of the steels is important for electric power companies. The assessment of the remaining life needs long-term creep data for over 10 years, but such data are limited. We have attempted to assess the remaining life by creep tests and by microstructural observation of Grade 91 steels welded pipes which were used in USC plants for over 10 years. Following the results of microstructural observation of USC plant pipes, we find that microstructures, especially distribution of MX precipitates, have large effect on the creep life of Grade 91 steels.

scholarly journals Stepwise loading-unloading creep testing of fly ash concrete and its constitutive model

2019 ◽  
Vol 23 (3 Part A) ◽  
pp. 1539-1545
Author(s):  
Bing Li ◽  
Lian-Ying Zhang ◽  
Yan Li ◽  
Hui-Guang Yin ◽  
Rui-Xue Liu
Keyword(s):  
Fly Ash ◽  
Time Course ◽  
Constitutive Relations ◽  
Creep Testing ◽  
Model Parameters ◽  
Creep Properties ◽  
Fly Ash Concrete ◽  
Accelerated Creep ◽  
Linear Viscoelastic ◽  
Stepwise Loading

Stepwise loading-unloading creep testing of concrete with fly ash content of 35%, and 50% was conducted. The time course curve of stepwise creep in fly ash concrete was obtained. Analyses have revealed that it had decelerated creep, constant velocity, and accelerated creep properties. Based on rheological theory, a non-linear viscoelastic-plastic rheological model (MSSB-NVPB) was constructed, and its constitutive relations and creep equations were obtained. Combined with experimental data, the model parameters were determined. The results showed that this model can characterize the creep properties of the fly ash concrete fairly well.

Creep Properties of Hastelloy-X Alloy for the High Temperature Gas-Cooled Reactor

2006 ◽  
Vol 326-328 ◽  
pp. 1105-1108 ◽  
Author(s):  
Woo Gon Kim ◽  
Sang Nan Yin ◽  
Woo Seog Ryu ◽  
Jong Hwa Chang
Keyword(s):  
High Temperature ◽  
Creep Data ◽  
Creep Life ◽  
Statistical Process ◽  
Hastelloy X ◽  
Creep Properties ◽  
Rupture Data ◽  
Term Creep ◽  
High Temperature Gas

The creep properties for the Hastelloy-X alloy which is one of candidate alloys for a high temperature gas-cooled reactor are presented. The creep data was obtained with different stresses at 950oC, and a number of the creep data was collected through literature surveys. All of the creep data were combined together to obtain the creep constants and to predict a long-term creep life. In the Norton’s creep law and the Monkman-Grant relationship, the creep constants, A, n, m, and m’ were obtained. Creep master curves based on the Larson-Miller parameter were presented for the standard deviations of 1σ, 2σ and 3σ. Creep life at each temperature was predicted for a longer-time rupture above 105 hours. Failure probability was also estimated by a statistical process of all the creep rupture data.

scholarly journals Accelerated Creep Test (ACT) Qualification of Creep-Resistance Using the WCS Constitutive Model and Stepped Isostress Method (SSM)

2021 ◽  
Author(s):  
Jaime A. Cano ◽  
Calvin M. Stewart
Keyword(s):  
Constitutive Model ◽  
Strain Rate ◽  
Creep Strain ◽  
Creep Deformation ◽  
Inconel 718 ◽  
Creep Resistance ◽  
Stress Rupture ◽  
Creep Testing ◽  
Accelerated Creep

Abstract In this study, a qualification of accelerated creep-resistance of Inconel 718 is assessed using the novel Wilshire-Cano-Stewart (WCS) model and the stepped isostress method (SSM) and predictions are made to conventional creep data. Conventional creep testing (CCT) is a long-term continuous process, in fact, the ASME B&PV III requires that 10,000+ hours of experiments must be conducted to each heat for materials employed in boilers and/or pressure vessel components. This process is costly and not feasible for rapid development of new materials. As an alternative, accelerated creep testing techniques have been developed to reduce the time needed to characterize the creep resistance of materials. Most techniques are based upon the time-temperature-stress superposition principle (TTSSP) that predicts minimum-creep-strain-rate (MCSR) and stress-rupture behaviors but lack the ability to predict creep deformation and consider deformation mechanisms that occur for experiments of longer duration. The stepped isostress method (SSM) has been developed which enables the prediction of creep deformation response as well as reduce the time needed for qualification of materials. The SSM approach has been successful for polymer, polymeric composites, and recently has been introduced for metals. In this study, the WCS constitutive model, calibrated to SSM test data, qualifies the creep resistance of Inconel 718 at 750°C and predictions are compared to CCT data. The WCS model has proven to make long-term predictions for stress-rupture, minimum-creep-strain-rate (MCSR), creep deformation, and damage in metallic materials. The SSM varies stress levels after time interval adding damage to the material, which can be tracked by the WCS model. The SSM data is calibrated into the model and the WCS model generates realistic predictions of stress-rupture, MSCR, damage, and creep deformation. The calibrated material constants are used to generate predictions of stress-rupture and are post-audit validated using the National Institute of Material Science (NIMS) database. Similarly, the MCSR predictions are compared from previous studies. Finally the creep deformation predictions are compared with real data and is determined that the results are well in between the expected boundaries. Material characterization and mechanical properties can be determined at a faster rate and with a more cost-effective method. This is beneficial for multiple applications such as in additive manufacturing, composites, spacecraft, and Industrial Gas Turbines (IGT).

Effects of a layered structure on the physicomechanical properties and extended creep behavior of bamboo-polypropylene composites (BPCs) determined by the stepped isostress method

Holzforschung ◽  
2018 ◽  
Vol 72 (7) ◽  
pp. 589-597 ◽  
Author(s):  
Chin-Yin Hsu ◽  
Teng-Chun Yang ◽  
Tung-Lin Wu ◽  
Ke-Chang Hung ◽  
Jyh-Horng Wu
Keyword(s):  
Creep Behavior ◽  
Bottom Layer ◽  
Short Term ◽  
Creep Properties ◽  
Polypropylene Composites ◽  
Plastic Composite ◽  
Accelerated Creep ◽  
Term Creep ◽  
Better Than

AbstractA layered bamboo-plastic composite (BPC) consisting of bamboo (Phyllostachys makinoi) particles and polypropylene was investigated. The influence of the layering conditions, including the thickness and bamboo content in various layers, was the focus in terms of the physicomechanical and creep properties of the BPCs. The results showed that a three-layered BPC (BPC3L) with a 1:3:1 thickness ratio and with top/bottom layer containing 40% bamboo exhibited the best specific flexural properties. An accelerated creep test approach was applied, known as the short-term stepped isostress method (SSM), to predict the long-term creep behavior of BPC3L. The results indicated that the creep master curves, which are constructed from different SSM testing parameters, agree well with the long-term experimental creep data and that the creep resistance of homogeneous single-layered BPC was better than that of BPC3L.

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 Effect of straw reinforcement on the shearing and creep behaviours of Quaternary loess

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Zhong-Fei Xue ◽  
Wen-Chieh Cheng ◽  
Lin Wang
Keyword(s):  
Shear Strength ◽  
Shear Plane ◽  
Interparticle Contact ◽  
Creep Properties ◽  
Landslide Hazards ◽  
Accelerated Creep ◽  
Strain Relationship ◽  
Ratio Condition ◽  
Slow Moving

AbstractIn addition to the shearing behavior of soil, the creep character is also considered crucial in determining the long-term shear strength. This especially holds true for the loess that possesses the metastable microstructure and is prone to landslide hazards. This study explored the potential application of straw reinforcement to enhance the shearing and creep properties of the Quaternary loess. The mechanism responsible for the straw reinforcement to elevate the peak shear strength was revealed. Furthermore, three creep characters, namely attenuating creep, non-attenuating creep, and viscous flow were identified in this study. The unreinforced and reinforced specimen behaved in a different manner under identical shear stress ratio condition. The reinforced specimen was superior in limiting the particle relative movement within the shear plane than the unreinforced specimen. The chain reaction of interparticle contact loss, accompanied with excessive viscous displacement, rapid weakening of creep resistance, and eventually accelerated creep displacement, provided an evidence for the formation mechanism of slow-moving landslide. The long-term shear strength using the isochronal stress–strain relationship may be used for optimising the design of high-fill embankment works.

Comparison of Results of Accelerated and Conventional Creep Tests of Dissimilar Weld Joint of Steels FB2 and F

2017 ◽  
Vol 891 ◽  
pp. 322-329 ◽  
Author(s):  
Josef Kasl ◽  
Dagmar Jandová ◽  
Stan T. Mandziej ◽  
Ivo Schindler
Keyword(s):  
Weld Joint ◽  
Rupture Strength ◽  
Creep Damage ◽  
Point Of View ◽  
Creep Testing ◽  
Creep Tests ◽  
Creep Resisting Materials ◽  
Dissimilar Weld ◽  
Accelerated Creep

The recently developed simulative accelerated creep testing (ACT) on a Gleeble thermal mechanical simulator allows the microstructural transformation of creep-resisting materials in a relatively short time (less than 100 hours) to a state resembling that of multiyear application under creep conditions. This contribution deals with the comparison of long-term conventional creep testing (CCT) with ACT on a dissimilar weld joint prepared from steels COST FB2 (X13CrMoCoVNbN 9-1-1) and COST F (X14CrMoVNbN 10-1). Creep tests to rupture were carried out at temperatures from 550 °C to 650 °C in a stress range from 70 MPa to 220 MPa. Creep rupture strength was evaluated using the Larson-Miller parameter. Evolution of the microstructure, changes of precipitates and dislocation of the substructure in different zones of the weld joint (Fig. 1) were correlated with the position of fracture and the creep strength. The fine grained part of the heat affected zone of steel COST F was found to be a critical zone of creep damage. ACT of samples machined from various positions in the weldment was performed at 600°C under 100 MPa. Changes in the hardness and the microstructures of the samples, which underwent both types of creep tests, were compared. The results of both creep testing methods are compared from a point of view of the potential for utilization of ACT in industry. It seems that microstructural processes taking place during creep exposures are accelerated by ACT, however, further experiments have to be performed to improve the accuracy of fracture prediction and verification if long-term CCT is to be replaced by ACT.

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