Recent Developments in the R5 Volume 2/3 Procedures for Assessing Creep-Fatigue Initiation in Defect-Free Components Operating at High Temperatures

Dean, David; Spindler, M. W.; Chevalier, Marc; Smith, N. Godfrey

doi:10.1115/pvp2013-98134

Cited by 3 publications

(5 citation statements)

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“…In view of the observed overconservatism of the ductility exhaustion approach and specifically because it was clear that there was an effect of stress on the calculated creep damage which was not being taken into account (as shown in Figs. 11b and 13b), it was decided to develop a 'stress modified ductility exhaustion' model [6][7][8] for Type 321 stainless steel.…”

Section: Results Creep and Fatigue Damage Calculations For Uniaxial Cmentioning

confidence: 99%

“…[6][7][8] The important features to note regarding the time fraction approach are that the best estimate damages calculated with time fraction were realistic (Fig. 10), although the upper bound estimates of time fraction creep damage are overly pessimistic (Fig.…”

Section: Discussionmentioning

confidence: 99%

“…Further details of the new R5 method to calculate fatigue endurance in weldments are given in R5 3 and in Ref. 8.…”

Section: Fatigue Damagementioning

confidence: 99%

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Creep fatigue behaviour of Type 321 stainless steel at 650°C

Spindler

Knowles²,

Jacques³

et al. 2014

Materials at High Temperatures

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Type 321 austenitic stainless steel has been used in the UK's advanced gas cooled reactors for a wide variety of thin section components which are within the concrete pressure vessel. These components operate at typically 650uC and experience very low primary stresses. However, temperature cycling can give rise to a creep fatigue loading and the life assessment of these cycles is calculated using the R5 procedure. In order to provide materials property models and to validate creep fatigue damage predictions, the available uniaxial creep, fatigue and creep fatigue data for Type 321 have been collated and analysed. The analyses of these data have provided evolutionary models for the cyclic stress strain and the stress relaxation behaviour of Type 321 at 650uC. In addition, different methods for predicting creep fatigue damage have been compared and it has been found that the stress modified ductility exhaustion approach for calculating creep damage gave the most reliable predictions of failure in the uniaxial creep fatigue tests. Following this, validation of the new R5 methods for calculating creep and fatigue damage in weldments has been provided using the results of reversed bend fatigue and creep fatigue tests on Type 321 welded plates at 650uC in conjunction with the materials properties that were determined from the uniaxial test data. This paper is part of a special issue on Creep-Fatigue Crack Development Nomenclature a 0 Crack depth used to define crack initiation in a specimen or structure a i Crack depth of 0?02 mm which is used to define crack nucleation in a specimen or structure A 1 , P 1 , m 1 , n 1 Parameters in the stress modified ductility exhaustion model, equations (14) and (15) b, B0 Parameters in the stress relaxation equation (2) d c Creep damage per cycle d f Fatigue damage per cycle D c Total creep damage per test D f Total fatigue damage per test E Young's modulus N Cycle number N 5% Number of cycles to a 5% decrease in maximum stress N 25% Number of cycles to a 25% decrease in maximum stress N 0 Continuous cycling fatigue endurance to create a crack of depth a 0 N f Number of cycles failure as defined by complete separation N9 g Number of cycles to grow a fatigue crack from the nucleation size of 0?02 mm to a 0 N i Number of cycles to nucleate a fatigue crack of size of 0?02 mm N pred Predicted number of cycles to the initiation of a creep fatigue crack N obs Observed number of cycles to the chosen failure criterion R p0?2% 0?2% proof stress R p1% 1% proof stress R m Tensile strength t Time t f Time at failure t h Dwell time T Temperature Z Elastic follow-up factor Ds Stress drop during the creep dwell s 0 2s e c Creep strain that accumulates during a creep dwell _ e e c Instantaneous creep strain rate e f Uniaxial creep ductility De T Total strain range e U Upper shelf total inelastic strain at failure s Instantaneous stress

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Section: Results Creep and Fatigue Damage Calculations For Uniaxial Cmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Creep fatigue behaviour of Type 321 stainless steel at 650°C

Spindler

Knowles²,

Jacques³

et al. 2014

Materials at High Temperatures

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“…The fatigue damage at the welds was calculated based on both weld and parent material properties. The new approach for assessing weldments as detailed in [7] has been used in this report. This new approach involves splitting the existing Fatigue Strength Reduction Factor (FSRF) into a Weldment Endurance Reduction (WER), which accounts for reduced fatigue endurance due to weld imperfections, and a Weldment Strain Enhacement Factor (WSEF), which accounts for material mismatch and local geometry.…”

Section: Bounding Weld Materials Locationsmentioning

confidence: 99%

“…As described in [7], the WSEFs in the following table have been derived such that the parent mean fatigue curve, factored by the WSEF and WER, provides a mean fit to the weldment fatigue data assuming a log normal distribution of fatigue life [8].…”

Section: Bounding Weld Materials Locationsmentioning

confidence: 99%

Structural Integrity Role in Plant Life Extension - A Case Study

Shi

2015

AMM

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The steam generators at Advanced Gas-Cooled Reactor (AGR) nuclear power stations in the UK are potentially life-limiting components. Enhancing the capability to monitor the steam generators has been identified as having the potential to provide key evidence in justifying the extension of the generating lifetime of the stations. It has been proposed to install new temperature measuring instrumentation to monitor reactor gas temperature and to provide additional data regarding steam generator operating conditions. The modification will be to introduce thermocouples to the bore of an intact steam generator tube to facilitate temperature measurement at or near to the locations of interest. The modified steam generator tube will be sealed at the feed header upstand. Between the upper surface of the superheater header tubeplate and the wall of the superheater header, the thermocouple bundle and sheath will be contained within a rigid stainless steel guide tube. The guide tube will be attached at both ends by welds, each forming a pressure boundary. At the tubeplate a weld will separate the bore of the sealed guide tube from the steam space within the superheater header; a weld between the guide tube and the superheater header will separate the steam space within the superheater header from atmosphere outside the header. In order to obtain a better design, three 3-dimentional finite element models have been created using ABAQUS. A series of cyclic pressure, and start-up and shutdown thermal transient stress analyses have been carried out to provide stress values for structural integrity assessments to be conducted using ASME III, Subsection NH and R5.

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Creep-Fatigue Crack Initiation Assessments of an Instrument Guide Tube Within a Superheater Header

Shi¹,

Dodia²

2014

Volume 1: Codes and Standards

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In order to extend the boiler lives at Advanced Gas-Cooled Reactor (AGR) nuclear power stations in the UK, new temperature measuring instrumentation to monitor reactor gas temperature has been proposed to install on the bore of an intact boiler tube to provide additional boiler operating data to support the station lifetime extension. This paper details a creep-fatigue crack initiation assessment of the proposed installation of an instrument guide tube within the superheater header using the latest R5 high temperature assessment procedures based on detailed finite element thermal transient stress analysis values for a bounding start-up and shutdown cycle. The fatigue damage at welds has been calculated based on both weld and parent material properties. The new approach for assessing weldments has been used in this paper. This new approach involves splitting the existing Fatigue Strength Reduction Factor (FSRF) into a Weldment Endurance Reduction (WER), which accounts for reduced fatigue endurance due to weld imperfections, and a Weldment Strain Enhacement Factor (WSEF), which accounts for material mismatch and local geometry. The creep assessments of the weld material locations have been carried out on both parent and weld material properties including the welding residual stress. The total creep-fatigue damage is then obtained as the sum of fatigue damage, Df, and creep damage, Dc.

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Recent Developments in the R5 Volume 2/3 Procedures for Assessing Creep-Fatigue Initiation in Defect-Free Components Operating at High Temperatures

Cited by 3 publications

References 0 publications

Creep fatigue behaviour of Type 321 stainless steel at 650°C

Creep fatigue behaviour of Type 321 stainless steel at 650°C

Structural Integrity Role in Plant Life Extension - A Case Study

Creep-Fatigue Crack Initiation Assessments of an Instrument Guide Tube Within a Superheater Header

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