The Influence of Residual Stresses on Small Through-Clad Cracks in Pressure Vessels

1984 ◽  
Vol 106 (4) ◽  
pp. 383-390 ◽  
Author(s):  
H. G. deLorenzi ◽  
B. I. Schumacher
Keyword(s):  
Residual Stresses ◽  
Pressure Vessel ◽  
Driving Force ◽  
Base Material ◽  
Pressure Vessels ◽  
Plastic Behavior ◽  
Material Interface ◽  
Crack Driving Force ◽  
Elastic Plastic ◽  
Stress Relieving

The influence of cladding residual stresses on the crack driving force for shallow cracks in the wall of a nuclear pressure vessel is investigated. Thermo-elastic-plastic analyses were carried out on long axial through-clad and sub-clad flaws on the inside of the vessel. The depth of the flaws were one and three times the cladding thickness, respectively. An analysis of a semielliptical axial through-clad flaw was also performed. It was assumed that the residual stresses arise due to the difference in the thermal expansion between the cladding and the base material during the cool down from stress relieving temperature to room temperature and due to the subsequent proof test before the vessel is put into service. The variation of the crack tip opening displacement during these loadings and during a subsequent thermal shock on the inside wall is described. The analyses for the long axial flaws suggest that the crack driving force is smaller for this type of flaw if the residual stresses in the cladding are taken into account than if one assumes that the cladding has no residual stresses. However, the analysis of the semielliptical flaw shows significantly different results. Here the crack driving force is higher than when the residual stresses are not taken into account and is maximum in the cladding at or near the clad/base material interface. This suggests that the crack would propagate along the clad/base material interface before it would penetrate deeper into the wall. The elastic-plastic behavior found in the analyses show that the cladding and the residual stresses in the cladding should be taken into acocunt when evaluating the severity of shallow surface cracks on the inside of a nuclear pressure vessel.

Residual Stress Effects on Cleavage Fracture

2007 ◽  
Author(s):  
A. H. Sherry ◽  
K. S. Lee ◽  
M. R. Goldthorpe ◽  
D. W. Beardsmore
Keyword(s):  
Fracture Toughness ◽  
Residual Stress ◽  
Residual Stresses ◽  
Cleavage Fracture ◽  
Driving Force ◽  
Compact Tension ◽  
Pressure Vessels ◽  
Crack Driving Force ◽  
Stress Effects ◽  
Definition Of

It is recognised that the driving force for the initiation and propagation of defects in materials may, under some circumstances, include contributions from both externally applied loads such as internal pressure in pressure vessels and piping and secondary stresses such as weld residual stresses. For non stress-relieved welds, residual stresses can provide a significant proportion of the crack driving force. This paper describes the results obtained from an experimental programme aimed at extending the understanding of residual stress effects on cleavage fracture. The paper describes the preparation and testing of standard and preloaded compact-tension specimens of an A533B pressure vessel steel at its Master Curve reference temperature. Standard tests on compact-tension specimens provide fracture toughness data which are broadly consistent with the conventional three-parameter Weibull model, with Kmin = 20 MPa√m and an exponent of about 4. The preloaded compact-tension specimens included a high level of tensile residual stress at the crack location. Fracture toughness data obtained using the test standards from these specimens fall significantly below the standard specimen data, since the contribution from residual stresses is ignored. However, when due account is taken of the residual stress on the crack driving force using a correct definition of the J-integral, the distributions of fracture toughness data from both specimen types are found to overlay each other. The definition of J used in this paper allows residual stress effects on fracture to be accounted for in a single fracture parameter.

scholarly journals Short fatigue crack growth in welded joints described by the effective cyclic J-integral

2018 ◽  
Vol 165 ◽  
pp. 09002
Author(s):  
Désiré Tchoffo Ngoula ◽  
Michael Vormwald
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Fatigue Crack Growth ◽  
Residual Stresses ◽  
Crack Growth ◽  
Welded Joints ◽  
Driving Force ◽  
J Integral ◽  
Crack Driving Force ◽  
Short Fatigue Crack

The purpose of the present contribution is to predict the fatigue life of welded joints by using the effective cyclic J-integral as crack driving force. The plasticity induced crack closure effects and the effects of welding residual stresses are taken into consideration. Here, the fatigue life is regarded as period of short fatigue crack growth. The node release technique is used to perform finite element based crack growth analyses. For fatigue lives calculations, the effective cyclic J-integral is employed in a relation similar to the Paris (crack growth) equation. For this purpose, a specific code was written for the determination of the effective cyclic J-integral for various lifetime relevant crack lengths. The effects of welding residual stresses on the crack driving force and the calculated fatigue lives are investigated. Results reveal that the influence of residual stresses can be neglected only for large load amplitudes. Finally, the predicted fatigue lives are compared with experimental data: a good accordance between both results is achieved.

J-integral and crack driving force in elastic–plastic materials

2008 ◽  
Vol 56 (9) ◽  
pp. 2876-2895 ◽  
Author(s):  
N SIMHA ◽  
F FISCHER ◽  
G SHAN ◽  
C CHEN ◽  
O KOLEDNIK
Keyword(s):  
Driving Force ◽  
J Integral ◽  
Crack Driving Force ◽  
Elastic Plastic ◽  
Plastic Materials ◽  
Elastic Plastic Materials

Measurement and Modelling of Residual Stresses in Fracture Toughness Specimens Extracted From Large Components

2008 ◽  
Author(s):  
S. J. Lewis ◽  
S. Hossain ◽  
C. E. Truman ◽  
D. J. Smith ◽  
M. Hofmann
Keyword(s):  
Fracture Toughness ◽  
Residual Stress ◽  
Residual Stresses ◽  
Driving Force ◽  
Large Scale ◽  
Structural Integrity ◽  
Mechanical Load ◽  
Crack Driving Force ◽  
Neutron Diffraction Technique ◽  
Fracture Specimens

A number of previously published works have shown that the presence of residual stresses can significantly affect measurements of fracture toughness, unless they are properly accounted for when calculating parameters such as the crack driving force. This in turn requires accurate, quantitative residual stress data for the fracture specimens prior to loading to failure. It is known that material mechanical properties may change while components are in service, for example due to thermo-mechanical load cycles or neutron embrittlement. Fracture specimens are often extracted from large scale components in order to more accurately determine the current fracture resistance of components. In testing these fracture specimens it is generally assumed that any residual stresses present are reduced to a negligible level by the creation of free surfaces during extraction. If this is not the case, the value of toughness obtained from testing the extracted specimen is likely to be affected by the residual stress present and will not represent the true material property. In terms of structural integrity assessments, this can lead to ‘double accounting’ — including the residual stresses in both the material toughness and the crack driving force, which in turn can lead to unnecessary conservatism. This work describes the numerical modelling and measurement of stresses in fracture specimens extracted from two different welded parent components: one component considerably larger than the extracted specimens, where considerable relaxation would be expected as well as a smaller component where appreciable stresses were expected to remain. The results of finite element modelling, along with residual stress measurements obtained using the neutron diffraction technique, are presented and the likely implications of the results in terms of measured fracture toughness are examined.

Potential Detrimental Consequences of Excessive PWHT on Pressure Vessel Steel Properties

2012 ◽  
Vol 134 (2) ◽  
Author(s):  
Cédric Chauvy ◽  
Lionel Coudreuse ◽  
Patrick Toussaint
Keyword(s):  
Heat Treatment ◽  
Base Metal ◽  
Base Material ◽  
Heat Treatments ◽  
Pressure Vessels ◽  
Critical Parameters ◽  
Thick Wall ◽  
Pressure Vessel Steel ◽  
Vessel Steel ◽  
Stress Relieving

During fabrication of Pressure Vessels, steels undergo several heat treatments that aim to confer the required properties on the entire equipment, including welds and base metal. Indeed, the production heat treatment of the base material, which leads to achieve the target properties, is most of the time followed by post weld heat treatment (PWHT). The aim of such treatments is to insure a good behavior of the welded zones in terms of residual stresses and obviously properties such as toughness. Generally, many simulated PWHT (up to 4 or more) are required for the testing of the base material, which can affect its properties and even lead to unacceptable results. In some cases for fabrication purposes an intermediate Stress relieving treatment can be required. Special attention is paid on C-Mn steels (e.g., SA/A516 from ASME BPV Code) with the effect of thickness and Ceq (International Institute of Welding Carbon equivalent formula: see page 3) requirements on the final compromise between properties and heat treatments. In particular, toughness and ultimate tensile strength (UTS) are the critical parameters that will limit the acceptance of too high PWHT. Although micro-alloying is a mean to increase the resistance to PWHT, this leads to difficulties in softening the heat affected zones. This solution is therefore not the best one considering the whole equipment optimization. Finally, the manufacturing process can play a major role when specifications are stringent. Quenching and tempering (Q&T) can indeed provide better flexibility in terms of PWHT and improved toughness for given Ceq and thickness. The case of Cr-Mo(-V) steels, which are widely used in the energy industry, is also addressed. Indeed, PWHT requirements for increasing the toughness in the weld metal can lead to decrease the base metal properties below the specification limits. For example, the case of SA/A387gr11 is very typical of metallurgical changes that can occur during these high PWHT leading to a degradation of toughness in the base metal. Another focus is made on the Vanadium Cr-Mo grade SA/A542D that must withstand very high PWHT (705 °C and even 710 °C) because of welds toughness issues. Optimization has therefore to be done to increase the resistance to softening and to guarantee acceptable microstructure, especially in the case of thick wall vessels. Some ways for improvement are proposed on the basis of the equivalent Larson–Miller parameter (LMP) tempering parameter concept. The basic philosophy is to fulfil the need for discussion between companies involved in pressure vessels fabrication so that the best compromise can be found to ensure the best and safest behavior of the equipment as a whole. In particular, the tempering operation can sometimes be done at lower temperature than PWHT in order to offer the best properties to the final vessel.

Effects of Weld Geometry on Residual Stress and Crack Driving Force for Centerhole Control Rod Drive Mechanism Nozzles: Part I — Weld Residual Stress

2005 ◽  
Author(s):  
Wentao Cheng ◽  
David L. Rudland ◽  
Gery Wilkowski ◽  
Wallace Norris
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Driving Force ◽  
Nuclear Regulatory Commission ◽  
Crack Driving Force ◽  
Control Rod ◽  
Drive Mechanism ◽  
Weld Geometry ◽  
Weld Residual Stress ◽  
Regulatory Commission

The U.S. Nuclear Regulatory Commission (NRC) has undertaken a program to assess the integrity of control rod drive mechanism (CRDM) nozzles in existing plants that are not immediately replacing their RPV heads. This two-part paper summarizes some of the efforts undertaken on the behalf of the U.S.NRC for the development of detailed residual stress and circumferential crack-driving force solutions to be used in probabilistic determinations of the time from detectable leakage to failure. In this first paper, the finite element (FE) simulations were conducted to investigate the effects of weld geometry on the residual stresses in the J-weld for a centerhole CRDM nozzle. The variables of weld geometry included three weld heights (weld sizes) and three groove angles for each weld height while keeping the same weld size. The analysis results indicate that the overall weld residual stress decreases as the groove angle increases and higher residual stress magnitude is associated with certain weld height. The results also reveal that the axial residual stresses in the Alloy 600 tube are very sensitive to the weld height, and that the tube hoop stresses above the J-weld root increase with the increasing weld height.

Displacement Controlled Stress Intensity Factor Solutions for Structural Integrity Assessments of Welding Residual Stress Distributions

2008 ◽  
Author(s):  
Adam Toft ◽  
David Beardsmore ◽  
Colin Madew ◽  
Huego Teng ◽  
Mark Jackson
Keyword(s):  
Residual Stress ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Residual Stresses ◽  
Weight Function ◽  
Driving Force ◽  
Welding Residual Stress ◽  
Crack Plane ◽  
Crack Driving Force

Within the UK nuclear industry the assessment of fracture in pressurised components is often carried out using procedures to calculate the margin of safety between a lower-bound fracture toughness and the crack driving force. Determination of the crack driving force usually requires the calculation of elastic stress intensity factor solutions for primary loads and secondary loads arising from weld residual stresses and/or thermal stresses. Within established UK assessment procedures weight function solutions are available which allow the stress intensity factors to be calculated from the through-wall opening-mode stress distribution in an uncracked component. These weight-function solutions are generally based on models where either no boundary condition is applied, or where one is applied at a distance either side of the crack plane that is very long compared with the crack size and wall thickness. Such solutions do not take into account any reduction in the stress field that might occur as the distance from the crack faces increases. Weld residual stress fields may often be expected to reduce in this manner. A separate, earlier study has shown that the stress intensity factor for a cracked plate loaded in displacement control decreases substantially as the loading plane is moved closer to the crack plane. It would therefore be expected that a similar reduction in stress intensity factor would be obtained for a residual stress analysis when displacement boundary conditions are imposed at a distance relatively close to the crack plane. This paper describes an investigation of the differences, particularly in terms of a reduction in calculated stress intensity factor, which may arise from application of displacement controlled stress intensity factor solutions, as compared with load controlled solutions, when considering weld residual stresses. Consideration is also given as to how new displacement controlled stress intensity factor solutions could be developed by modification of existing load controlled solutions.

scholarly journals Residual Stresses in Weld-Deposited Clad Pressure Vessels and Nozzles

1999 ◽  
Vol 121 (4) ◽  
pp. 423-429 ◽  
Author(s):  
D. P. Jones ◽  
W. R. Mabe ◽  
J. R. Shadley ◽  
E. F. Rybicki
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Pressure Vessel ◽  
Fatigue Testing ◽  
Pressure Vessels ◽  
Flat Plates ◽  
Spherical Head ◽  
Layer Removal Method ◽  
Ring Segment ◽  
Cladding Material

Results of through-thickness residual stress measurements are provided for a variety of samples of weld-deposited 308/309L stainless steel and Alloy 600 cladding on low-alloy pressure vessel ferritic steels. Clad thicknesses between 5 and 9 mm on samples that vary in thickness from 45 to 200 mm were studied. The samples were taken from flat plates, from a spherical head of a pressure vessel, from a ring-segment of a nozzle bore, and from the transition radius between a nozzle and a pressure vessel shell. A layer removal method was used to measure the residual stresses. The effects of uncertainties in elastic constants (Young’s modulus and Poisson’s ratio) as well as experimental error are assessed. All measurements were done at room temperature. The results of this work indicate that curvature plays a significant role in cladding residual stress and that tensile residual stresses as high as the yield stress can be measured in the cladding material. Since the vessel from which the spherical and nozzle corner samples were taken was hydrotested, and the flat plate specimens were taken from specimens used in mechanical fatigue testing, these results suggest that rather high tensile residual stresses can be retained in the cladding material, even after some mechanical loading associated with hydrotesting.

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