Effects of Primary and Secondary Creep Formulations on API 579-1 Residual Life Evaluation

2018 ◽  
Author(s):  
Lorenzo Scano ◽  
Luca Esposito
Keyword(s):  
Constitutive Equation ◽  
Residual Life ◽  
Creep Damage ◽  
Primary Creep ◽  
Secondary Creep ◽  
Time To Rupture ◽  
Life Evaluation ◽  
Omega Method ◽  
Material Constitutive Equation ◽  
Rate Formulation

A sound material constitutive equation is crucial for the residual life evaluation of pressure components operating in the creep range. In a previous work [1], the authors investigated how a secondary creep formulation encompassing both the dislocational and the diffusional range influences the assessment of damage according to API 579-1 [2] within the whole component stress range. In the present paper the work has been extended in order to include the effects of primary creep in the constitutive equation for the ASTM A335 P22 low-alloy steel used for the manufacturing of the HRSG header whose welded details were previously investigated. The creep damage was first calculated according to API 579-1 Section 10 via inelastic, time-dependent FEA and the Larson-Miller approach (LMP) with code-defined, minimum time-to-rupture data. This led to a first reckoning of the primary creep impact in terms of API 579-1 residual life for the components under evaluation. The API 579-1 time-to-rupture was then assessed with a detailed stress analysis implementing the Omega Method and its creep strain rate formulation. The obtained results were finally compared to those previously determined through the LMP procedure and the different creep correlations (secondary and primary+secondary).

Effects of Secondary Creep Formulation on API 579-1 Residual Life Evaluation

2017 ◽  
Author(s):  
Lorenzo Scano ◽  
Luca Esposito
Keyword(s):  
Life Prediction ◽  
Ad Hoc ◽  
Residual Life ◽  
Creep Damage ◽  
International Standards ◽  
Secondary Creep ◽  
Creep Life ◽  
Life Evaluation ◽  
Level 3 ◽  
The Impact

Although several ad hoc procedures are codified into main international standards, the creep life prediction remains a critical phase of each Fitness-For-Service assessment. Commonly, either a time-fraction or a ductility exhaustion approach can be used. In both cases, conservative predictions within a factor of 2 or 3 are expected [1]. However, since the procedures to determine the creep damage are based upon the results of a stress analysis, the residual life evaluation can be affected by the adopted creep formulation. The choice to use a simple modeling, only accounting for the dislocational creep range, could lead to overestimate the component creep life at low stresses, and this is also subtly true even at concentration points if triaxiality or deformation-controlled loading lead to marked stress relaxation over time. In this paper, the tube to header and the header to hemispherical end joints of a HRSG assembly were assessed by the API 579-1/ASME FFS-1 [2] Level 3 procedure, via inelastic FEA, changing the creep formulation to compare the results. The classical Nortons law was replaced by more sophisticated secondary creep models to account for the complex time-dependent stress-field. In particular, the primary and secondary stress re-distribution/relaxation in the creep range were investigated in order to evaluate the impact of the steady-state creep constitutive equation on the residual life prediction.

scholarly journals Creep Damage Repair of a Nickel-Based Single Crystal Superalloy Based on Heat Treatment

Metals ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 623
Author(s):  
Xiaoyan Wang ◽  
Meng Li ◽  
Yuansheng Wang ◽  
Chengjiang Zhang ◽  
Zhixun Wen
Keyword(s):  
Heat Treatment ◽  
Single Crystal ◽  
Creep Damage ◽  
Primary Creep ◽  
Single Crystal Superalloy ◽  
Secondary Creep ◽  
Creep Life ◽  
Phase Coarsening ◽  
Damage Repair ◽  
Creep Time

Taking nickel-based single crystal superalloy DD6 as the research object, different degrees of creep damage were prefabricated by creep interruption tests, and then the creep damage was repaired by the restoration heat treatment system of solid solution heat treatment and two-stage aging heat treatment. The results show that with the creep time increasing, the alloy underwent microstructure evolution including γ′ phase coarsening, N-type rafting and de-rafting. After the restoration heat treatment, the coarse rafted γ′ phase of creep damaged specimens dissolved, precipitated, grew up, and became cubic again. Except for the specimens with creep interruption of 100 h, the γ′ phase can basically achieve the same arrangement as the γ′ phase of the original sample. The comparison of the secondary creep test shows that the steady-state creep stage of the test piece after the restoration heat treatment is relatively increased, and the total creep life can reach the same level as the primary creep life. The high temperature creep properties of the tested alloy are basically recovered, and the restoration heat treatment effect is good.

Application of Hot Hardness Test to the Evaluation of Creep Damage in Cr-Mo-V Turbine Rotor of Fossil Power Plant

2004 ◽  
Author(s):  
Shinsuke Sakai ◽  
Satoshi Izumi ◽  
Takashi Murakami ◽  
Akito Nitta ◽  
Junichi Kusumoto ◽  
...  
Keyword(s):  
Power Plants ◽  
Residual Life ◽  
Creep Damage ◽  
Hardness Test ◽  
Turbine Rotor ◽  
Constitutive Law ◽  
Life Evaluation ◽  
Site Evaluation ◽  
Fossil Power Plant ◽  
Hot Hardness

In residual life evaluation of fossil power plants, improvement of accuracy of creep damage evaluation is extremely important. One of the powerful non-destructive evaluation methods is hardness test. This method is effective because it enables us the on-site evaluation and the results are obtained without laborious work. However, in order to make it more powerful method, improvement of accuracy is inevitable. In this paper, the Vickers hardness test not at ambient but at high temperature is applied to the deteriorated rotor material and the method for the residual life evaluation with high accuracy is newly developed. In the method, creep constitutive law is determined from the results of hot hardness test first. Next, the variation of constitutive law with the creep damage is investigated. Finally, the dependency of exponent of constitutive law on the creep damage is shown and the method to evaluate the creep damage from this dependency will be proposed.

An improved nonlinear damage model of rocks considering initial damage and damage evolution

2020 ◽  
Vol 29 (7) ◽  
pp. 1117-1137 ◽  
Author(s):  
Wenlin Feng ◽  
Chunsheng Qiao ◽  
Shuangjian Niu ◽  
Zhao Yang ◽  
Tan Wang
Keyword(s):  
Damage Evolution ◽  
Least Squares Method ◽  
Damage Model ◽  
Creep Damage ◽  
Secondary Creep ◽  
Nonlinear Creep ◽  
Creep Failure ◽  
Initial Damage ◽  
Nonlinear Damage Model ◽  
Creep Damage Model

The experimental results show that the creep properties of the rocks are affected by the initial damage, and the damage evolution also has a significant impact on the time-dependent properties of the rocks during the creep. However, the effects of the initial damage and the damage evolution are seldom considered in the current study of the rocks' creep models. In this paper, a new nonlinear creep damage model is proposed based on the multistage creep test results of the sandstones with different damage degrees. The new nonlinear creep damage model is improved based on the Nishihara model. The influences of the initial damage and the damage evolution on the components in the Nishihara model are considered. The creep damage model can not only describe the changes in three creep stages, namely, the primary creep, the secondary creep, and the tertiary creep, but also reflect the influence of the initial damage and the damage evolution on creep failure. The nonlinear least squares method is used to determine the parameters in the nonlinear creep damage model. The consistency between the experimental data and the predicted results indicates the applicability of the nonlinear damage model to accurately predict the creep deformation of the rocks with initial damage.

scholarly journals Durability analysis of underground structures based on various creep models of the enclosing salt rock massif

2020 ◽  
Vol 201 ◽  
pp. 01007
Author(s):  
Mikhail Zhuravkov ◽  
Sergey Hvesenya ◽  
Siarhei Lapatsin
Keyword(s):  
Underground Structure ◽  
Primary Creep ◽  
Rock Massif ◽  
Initial Time ◽  
Creep Process ◽  
Secondary Creep ◽  
Salt Rock ◽  
Mine Shaft ◽  
Durability Analysis ◽  
Creep Models

The results of the durability analysis of a complex underground structure and surrounding multilayered rock massif are presented. The research is conducted based on an applied stress-strain state problem for a salt rock massif in the vicinity of an underground cavity of a large cross-section which is in conjunction with a mine shaft. The main aim of the research is to perform a comparative analysis of various mathematical models of the creep process. The problem is solved using finite element method to achieve this goal. Regularity in the development of deformation processes of the enclosing rock massif is established as a result of the study. According to this regularity, both primary creep and primary-secondary creep models show that the main increase of creep deformations occurs during a short initial time period after which creep strain rate decreases sharply.

DISLOCATION STRUCTURES IN COPPER SINGLE CRYSTALS DEFORMED IN HIGH TEMPERATURE CREEP

1967 ◽  
Vol 45 (2) ◽  
pp. 1213-1220 ◽  
Author(s):  
V. P. Gupta ◽  
P. R. Strutt
Keyword(s):  
Strain Rate ◽  
Single Crystals ◽  
Initial Strain Rate ◽  
Primary Creep ◽  
Secondary Creep ◽  
Etch Pit ◽  
Structure Changes ◽  
Initial Stage ◽  
Copper Single Crystals ◽  
Distribution Of Dislocations

The etch-pit technique has been used to study dislocations and substructures in copper single crystals deformed in primary, and into secondary creep at 550 °C at a CRSS of 250 g.mm−2. Etch-pit structures in crept specimens were observed parallel to the primary (111) plane and also the (111) plane to reveal "forest dislocations" and primary and other dislocations. In the initial stage of primary creep, the dislocations formed well-defined cells. Subboundaries began to form later on in primary creep. When a steady-state creep ensued, a well-developed subboundary structure was evident, with a random distribution of dislocations within the subgrains. The mean subgrain diameter was approximately twice that of the original cells and the dislocation density decreased by a factor of 2 during primary creep. Since the general form of the dislocation structure changes during primary creep, it is concluded that the decreasing strain rate cannot be ascribed to any one particular mechanism. However, the high initial strain rate probably results from the escape of dislocations from the cell walls in the initial type of structure.

Codes and Standards for Managing Degradation of Boilers in Service

2020 ◽  
Author(s):  
Corrado Delle Site ◽  
Emanuele Artenio ◽  
Gennaro Sepede ◽  
Matteo Chini ◽  
Francesco Giacobbe
Keyword(s):  
Service Time ◽  
Power Plants ◽  
Residual Life ◽  
Creep Damage ◽  
Pressure Vessels ◽  
Steam Boilers ◽  
Critical Components ◽  
Set Up ◽  
Effective Use ◽  
Life Consumption

Abstract Degradation of pressure equipment is becoming an important issue due to increasing asset service time in process and power plants across Europe. For this reason it is important to assess life consumption of these assets to avoid catastrophic failures. Therefore it is necessary to refer to national/international normative on this subject. At present time the Italian thermotechnical committee (CTI) has drawn up a comprehensive set of norms which help the user to set up an inspection plan to investigate and assess degradation of pressure vessels and boilers. In the first part of this paper creep damage of Steam Generators is analyzed. For this purpose results of INAIL (Istituto Nazionale per l’ Assicurazione contro gli Infortuni sul Lavoro) database of steam boilers with 100’000 service hours or more is illustrated. Critical components are identified with reference to materials, geometry and operating parameters (pressure, temperature and time). At the end of the design life cycle, components of pressure equipment operated in creep regime must subjected to specific checks to estimate their residual life and the suitability for further use in safety conditions. The procedure allows to define reinspection intervals keeping acceptable the risk associated with the further use of the component related to creep even in evidence of defects in progress. The first check must be performed after 100,000 hours of effective use. Then, residual life evaluations must be repeated according to period of time that are defined as function of the results of all the checks carried out. In the second part of this paper boiler degradation is discussed with reference to NDT results and in-field inspection campaigns which are carried out traditionally after 45 years of service time, to minimize the risk of pressure components failures. In this paper results of different case studies are discussed with reference to degradation mechanisms and applicable standards.

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