Accelerated Stress Rupture Testing for Creep Life Prediction—Its Value and Limitations

1998 ◽  
Vol 120 (2) ◽  
pp. 105-115 ◽  
Author(s):  
R. Viswanathan ◽  
J. Foulds
Keyword(s):  
Elevated Temperatures ◽  
Stress Rupture ◽  
Creep Damage ◽  
Operating Conditions ◽  
Remaining Life ◽  
Accelerated Tests ◽  
Accelerated Test ◽  
Research Activities ◽  
Creep Life Prediction ◽  
Stress Rupture Testing

Accelerated stress rupture testing has become a common method for determination of the remaining life of in-service components subject to creep damage at elevated temperatures. Stress and temperature increases have both been used to cause accelerated test failures, although the temperature accelerated tests have been preferred during the last decade. Remaining life estimation schemes have essentially involved extrapolation of results of the accelerated tests to the operating conditions. The accelerated test approach has found such widespread acceptance that most users today are unaware of its limitations and have started using the results in a definitive and quantitative way as a direct prediction of the remaining life of the component. EPRI (Electric Power Research Institute) investigators have examined the application and validity of a number of aspects of accelerated testing, as well as the underlying assumptions in the extrapolation procedures. This paper reviews the current practice, describes results from a number of research activities, and provides general guidelines for accelerated rupture testing.

High-Temperature Failures

2012 ◽  
pp. 415-459
Keyword(s):  
High Temperature ◽  
Stress Rupture ◽  
Creep Life Prediction ◽  
Creep Curves ◽  
Creep Fatigue ◽  
Temperature Fracture ◽  
Underlying Mechanisms ◽  
Thermomechanical Damage ◽  
Stress Rupture Testing ◽  
Related Design

Abstract This chapter compares and contrasts the high-temperature behaviors of metals and composites. It describes the use of creep curves and stress-rupture testing along with the underlying mechanisms in creep deformation and elevated-temperature fracture. It also discusses creep-life prediction and related design methods and some of the factors involved in high-temperature fatigue, including creep-fatigue interaction and thermomechanical damage.

scholarly journals Design, Fabrication, and Testing of Ceramic Joints for High Temperature SiC/SiC Composites

2000 ◽  
Author(s):  
M. Singh ◽  
Edgar Lara-Curzio
Keyword(s):  
Silicon Carbide ◽  
Shear Strength ◽  
Elevated Temperatures ◽  
Stress Rupture ◽  
Ceramic Matrix Composites ◽  
Matrix Composites ◽  
Carbide Matrix ◽  
Sic Composites ◽  
Stress Rupture Testing

Various issues associated with the design and mechanical evaluation of joints of ceramic matrix composites are discussed. The specific case of an affordable, robust ceramic joining technology (ARCJoinT) to join silicon carbide (CG-Nicalon™) fiber-reinforced-chemically vapor infiltrated (CVI) silicon carbide matrix composites is addressed. Experimental results are presented for the time and temperature dependence of the shear strength of these joints in air up to 1200°C. From compression testing of double-notched joint specimens with a notch separation of 4 mm, it was found that the apparent shear strength of the joints decreased from 92 MPa at room temperature to 71 MPa at 1200°C. From shear stress-rupture testing in air at 1200°C it was found that the shear strength of the joints decreased rapidly with time from an initial shear strength of 71 MPa to 17.5 MPa after 14.3 hours. The implications of these results in relation to the expected long-term service life of these joints in applications at elevated temperatures are discussed.

Remaining Creep or Stress-Rupture Life Under Nonsteady Temperature and Stress

1979 ◽  
Vol 101 (4) ◽  
pp. 331-336 ◽  
Author(s):  
B. W. Roberts ◽  
F. V. Ellis ◽  
J. E. Bynum
Keyword(s):  
Elevated Temperatures ◽  
Rupture Life ◽  
Stress Rupture ◽  
Historical Review ◽  
Creep Damage ◽  
Empirical Methods ◽  
Stress Regime ◽  
Elevated Temperature Strength ◽  
Stress Rupture Life ◽  
Multiaxial Stress State

This paper presents a historical review of the assessment of remaining creep life for components operating under stress at elevated temperatures. Topics considered in this review include the effects of multiaxial stress state on creep deformation and rupture, empirical methods of summing creep damage, empirical methods of evaluating elevated temperature strength, testing of service exposed material, and microstructural observations of creep damage. While considerable understanding of the damage process has been gained in laboratory testing, only limited success has been attained in quantifying damage of service exposed materials designed to operate in the long time and low stress regime permitted by industrial codes.

scholarly journals Microstructural and Mechanical Effects of Thermo-Mechanical Processing on ATI 718Plus® Contoured Rings

2011 ◽  
Vol 278 ◽  
pp. 271-276 ◽  
Author(s):  
Octavio Covarrubias
Keyword(s):  
Elevated Temperatures ◽  
Stress Rupture ◽  
Ring Rolling ◽  
Nickel Base Superalloy ◽  
Present Contribution ◽  
Suitable Material ◽  
Nickel Base ◽  
Stress Rupture Testing ◽  
Base Superalloy ◽  
Precipitation Heat

ATI 718Plus® is a nickel-base superalloy designed to promote resistance and thermal stability at elevated temperatures. Beside these properties, this material presents superior formability during forging operations, making ATI 718Plus® a suitable material for the manufacture of non-rotating and rotating components for jet engine and land-based turbines. Present contribution summarizes main results when several contoured rings were produced by ring-rolling processes considering selected parameters as temperature and deformation ratio. Effect of solution and precipitation heat treatments on ATI 718Plus® microstructure and mechanical properties are also reported. These results include tensile testing at elevated temperature and stress-rupture testing. Microstructural evaluations performed by optical microscopy and electronic microscopy, complement reported results.

Use of CDM in Materials Modeling and Component Creep Life Prediction

2000 ◽  
Vol 122 (3) ◽  
pp. 281-296 ◽  
Author(s):  
Brian Dyson
Keyword(s):  
Damage Mechanics ◽  
Creep Damage ◽  
Inelastic Strain ◽  
Constant Load ◽  
Operating Conditions ◽  
Cyclic Plasticity ◽  
Rate Equations ◽  
Materials Modeling ◽  
Creep Life Prediction ◽  
Physically Based

Physically based continuum creep damage mechanics (CDM) has been reviewed and shown to provide a unifying framework for some seemingly diverse methods of predicting design and remanent creep lifetimes. These methods—theta projection, omega parameter, Larson-Miller parameter, and Robinson’s life fraction rule—exhibit certain strengths in common with CDM, but also weaknesses which CDM identifies and avoids. CDM consists of sets of coupled rate equations for inelastic strain, internal stress, and microstructural evolution (damage) which can then be integrated under boundary conditions appropriate to the test or service operating conditions: constant load/temperature for creep; constant total strain for stress-relaxation, variable stress/temperature, etc. Other state-variable approaches to creep and cyclic plasticity (for example, those due to Bodner, Miller, Chaboche, and Robinson), differ from CDM mainly in concentrating on the primary/secondary stages of creep (or cyclic work-hardening) and/or by their introduction of damage in an empirical Kachanov manner. The application of physically based CDM to LCF/thermal fatigue and its potential for predicting lifetimes of welded joints are also discussed. [S0094-9930(00)00903-3]

A Probabilistic Gas Touched Length Analysis

2011 ◽  
Author(s):  
Carl D. Skelonis ◽  
M. Brett Shelton ◽  
Glenn T. Burney
Keyword(s):  
High Temperature ◽  
Creep Damage ◽  
Oxide Thickness ◽  
Thickness Measurement ◽  
Operating Conditions ◽  
Life Assessment ◽  
Remaining Life ◽  
Analysis Model ◽  
Specific Test ◽  
Length Analysis

Field measurements of the steamside oxide thickness for high temperature (> 850F) boiler tubing subject to the accumulation of creep damage often are made to support deterministic assessments of the remaining life. Most often, these inspections are undertaken to understand the condition of the tubing at some particular location along a circuit, often as a result of a tube failure. The life assessment is based on relationships that have been developed between oxide growth kinetics and temperature. Unfortunately, because of variability in the oxide-temperature relationships reflecting different original data sets, and because of the inherent uncertainty in materials properties where heat-specific test data is not available, there typically exists a broad range of uncertainty in the deterministic assessment results. Large utility-type boilers typically contain a number of high temperature sections, including various stages of superheat and reheat, each of which will contain miles of tubing. Since the temperature derived from an oxide thickness measurement is relevant only to the specific location where the measurement was made, the deterministically derived life calculation is also specific to that location. As a result, the attempt to draw conclusions regarding the condition of an entire superheater or reheater section from measurements made at only one or two locations in those sections is fraught with difficulties. It is for this reason that the Probabilistic Gas Touched Length Analysis model has been developed. This model makes it possible to calculate creep damage accumulation/remaining life at any point along the steam path. Oxide thickness data and operating data are the primary operating inputs into the model, which performs heat transfer calculations at user-defined locations along the length of the tube circuit. The model applies statistical methods to evaluate variations in operating conditions as well as in physical and mechanical properties using a Monte Carlo simulation to generate values for the probability of failure at selected locations. This paper will discuss the limitations of the existing approach to estimating the remaining life of high temperature boiler tubing and present the underpinning theory of the gas touched length analysis model. A case study showing the analysis results is included.

Study of Prolonged Service Degradation of Superheater Tubes and its Effects on Remaining Life Predictions

2013 ◽  
Author(s):  
Khalid A. Al-Obaidi ◽  
Nesar Merah
Keyword(s):  
Stress Rupture ◽  
Petrochemical Plant ◽  
Remaining Life ◽  
Material Degradation ◽  
Long Time ◽  
Service Degradation ◽  
Life Predictions ◽  
Stress Rupture Testing ◽  
Prolonged Service ◽  
Plant Shutdown

This study investigates the degradation of superheater tubes that has been in service for very long time. It also discusses the degradation effects on tube remaining life predictions. The tubes, utilized in this study, belong to an industrial boiler that has been in service for 232 000 h in a petrochemical plant and generate steam at 47 barg and 410 °C. Outcomes of this study will contribute to better understanding and development of scientific procedures to make reasonable estimate of tube remaining life considering the tubes aging while in service. This is beneficial in preventing failures and forced plant shutdown when life is consumed. It also helps industry to avoid capital expenditures on premature replacements of boiler tubes that can still serve longer time. In this study, comparison is made between short-term life predictions and actual properties found after about 26.5 years of service. The tubes condition is assessed by metallographic, mechanical and stress rupture testing. According to the results, it is found that prolonged service degradation has strong effects on remaining life predictions. Both effects that would lead to overestimating or underestimating tube remaining life were found if existing procedures are used without consideration for material degradation during service.

Assessing the Condition and Estimating the Remaining Lives of Pressure Components in a Methanol Plant Reformer: Part 2 — Engineering Evaluation

2016 ◽  
Author(s):  
Carl E. Jaske ◽  
Brian E. Shannon ◽  
Gustavo Miranda ◽  
Thomas J. Prewitt
Keyword(s):  
Finite Element ◽  
Creep Damage ◽  
General Purpose ◽  
Operating Conditions ◽  
Remaining Life ◽  
Creep Life ◽  
Service Failures ◽  
Finite Element Software ◽  
Creep Stress ◽  
Non Destructive

Statoil Tjelbergodden operates a 2,400 ton/day methanol plant in Norway. Part 1 of this paper described the advanced non-destructive examination (NDE) technologies that were applied to obtain data for engineering evaluation of radiant catalyst tubes, outlet pigtails, and outlet collection headers. The inspection results were compiled along with data on materials properties and plant operating conditions for use in a series of life prediction studies. This paper describes the assessment methodologies that were applied in evaluating the remaining life of the in-service components. The special purpose WinTUBE™ finite element software was applied to predict remaining catalyst tube creep life based on the computed creep stress-strain response and creep damage accumulation under simulated future operating conditions. Outlet headers and pigtails were modeled using general purpose finite element software to compute stresses and strains during operation. Following the methodology of API 579-1/ASME FFS-1 the computed stresses and strains were used to predict remaining creep life. Using the remaining life estimates to decrease the potential of in-service failures and increase the reliability of future reformer operations is discussed.

scholarly journals Design, Fabrication, and Testing of Ceramic Joints for High Temperature SiC/SiC Composites

2000 ◽  
Vol 123 (2) ◽  
pp. 288-292 ◽  
Author(s):  
M. Singh ◽  
E. Lara-Curzio
Keyword(s):  
Silicon Carbide ◽  
Shear Strength ◽  
Elevated Temperatures ◽  
Stress Rupture ◽  
Ceramic Matrix Composites ◽  
Matrix Composites ◽  
A Value ◽  
Carbide Matrix ◽  
Sic Composites ◽  
Stress Rupture Testing

Various issues associated with the design and mechanical evaluation of joints of ceramic matrix composites are discussed. The specific case of an affordable, robust ceramic joining technology (ARCJoinT) to join silicon carbide (CG-Nicalon™) fiber-reinforced-chemically vapor infiltrated (CVI) silicon carbide matrix composites is addressed. Experimental results are presented for the time and temperature dependence of the shear strength of these joints in air up to 1200°C. From compression testing of double-notched joint specimens with a notch separation of 4 mm, it was found that the apparent shear strength of the joints decreased from 92 MPa at room temperature to 71 MPa at 1200°C. From shear stress-rupture testing in air at 1200°C it was found that the shear strength of the joints decreased rapidly with time from an initial shear strength of 71 MPa to a value of 17.5 MPa after 14.3 h. The implications of these results in relation to the expected long-term service life of these joints in applications at elevated temperatures are discussed.

Fitness for Service and Remaining Life Assessment for 1-1/4Cr-1/2Mo Reactor System Piping on a Catalytic Reformer Unit

2006 ◽  
Author(s):  
Ayman M. Cheta ◽  
Ray Konet ◽  
F. Skip Hoyt
Keyword(s):  
Creep Damage ◽  
Pressure Vessels ◽  
Operating Conditions ◽  
Life Assessment ◽  
Low Alloy Steels ◽  
General Corrosion ◽  
Remaining Life ◽  
Reheat Cracking ◽  
Remaining Life Assessment ◽  
Welded Pipe

Fitness for service and remaining life assessment were performed on high temperature reactor piping to verify mechanical integrity for a desired remaining life. The NPS 20 1-1/4Cr-1/2Mo piping, which is the subject of this paper, was built in 1968 to the 1966 edition of ASA B31.3 for design conditions 465 psi at 950 °F / 365 psi at 1000 °F (3.16 MPa at 510 °C / 2.48 MPa at 538 °C) for hydrogen and naphtha service. The actual operating conditions are 400 psi at 900 °F / 330 psi at 950 °F (2.72 MPa at 482 °C / 2.24 MPa at 510 °C). Due to numerous reported failures in the industry in the 1980’s, the ASME codes for piping and pressure vessels lowered the allowable stresses for low alloy steels operating in the creep range, mainly above 900 °F (482 °C). Piping systems designed prior to changing the allowable stress do not satisfy today’s codes. The operating stresses which can lead to failure from potential damage mechanisms, e.g. creep, reheat cracking and general corrosion, are defined and their impact on fitness-for-service and remaining life evaluated. Acceptance criteria for different types of defects were established prior to the unit maintenance turnaround by: 1. Finite element modeling of assumed different degrees of weld peaking and pipe out-of-roundness for longitudinally welded pipe. 2. Piping flexibility / stress analysis to identify areas with the highest operating stresses. 3. Stresses from 1 and 2 above were used to calculate the creep life based on Larson-Miller parameter (API 530). Acceptable flaw sizes were limited by the desired remaining life. Inspection plans were developed to inspect for reheat cracking, creep damage, peaking, out of roundness, as well as general corrosion.

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