scholarly journals Use of Elastic Follow-Up to Study the Effect of Displacement Controlled Loading on Plastic Collapse Pressures for Circumferentially Cracked Pipes

2015 ◽  
Author(s):  
Guiyi Wu ◽  
David J. Smith ◽  
Martyn J. Pavier
Keyword(s):  
Residual Stress ◽  
Long Range ◽  
Structural Integrity ◽  
Axial Displacement ◽  
Plastic Collapse ◽  
Integrity Assessment ◽  
Circumferential Crack ◽  
Displacement Condition ◽  
Global Collapse

Structural integrity assessments of pressurised pipes consider plastic collapse as a potential failure mode. This paper uses finite element analysis to explore the effect of the pipe end boundary conditions on the collapse pressure. Two end conditions are considered: a fixed axial load and a fixed axial displacement. The fixed axial displacement condition represents a long-range axial residual stress. In the R6 structural integrity assessment procedure long-range residual stress is associated with elastic follow-up. However, no guidance is given on whether the level of elastic follow-up is sufficient to justify treating long-range residual stress as a primary stress. In this paper, a method is proposed to estimate elastic follow-up of an internally pressurised pipe containing a fully circumferential crack. It is found that the elastic follow-up is related to the length of the pipe. A short pipe that contains a fully circumferential crack, subjected to a displacement induced axial stress, has a global collapse that is not modified by the fixed displacement condition. The short pipe corresponds to a small elastic follow-up factor, Z. However, as the elastic follow-up factor increases, the presence of long-range residual stress starts to make a contribution to global collapse. When elastic follow-up is significant, a long-range residual stress has the same effect on global collapse as does a mechanical stress.

The Influence of Long-Range Residual Stress on Plastic Collapse and Local Yielding of Internally Pressurized Pipes

2012 ◽  
Author(s):  
Gui-yi Wu ◽  
D. J. Smith ◽  
M. J. Pavier
Keyword(s):  
Residual Stresses ◽  
Long Range ◽  
Structural Engineering ◽  
Three Dimensional ◽  
Plastic Collapse ◽  
Displacement Control ◽  
Integrity Assessment ◽  
End Conditions ◽  
Global Collapse ◽  
Local Yielding

The determination of plastic collapse for cracked pipes is important in structural engineering design and component integrity assessment. Long-range residual stresses are usually treated as primary stresses which contribute to plastic collapse of pipes subjected to internal pressure. This paper explores the differences between load and displacement controlled conditions applied to the ends of thin- and thick-walled pipes. Both load and displacement control can represent long range or fit-up residual stresses if they are considered as primary or secondary stresses respectively. Both global collapse and local yielding for pipes containing partially and fully circumferential cracks are examined. Detailed three-dimensional (3D) finite element (FE) analyses are used to simulate the pipe and crack geometry and the boundary conditions. The cracked pipes are assumed to be open ended. For a defect free pipe the FE results for global collapse agree with analytical solutions for both load and displacement controlled end conditions. For high tensile end loads and displacements lower collapse pressures are found for displacement conditions, while it is the converse for high compressive end loading. However, when a crack is introduced it becomes evident that tensile or compressive displacement control has little impact on global collapse and therefore longrange displacement controlled (or residual) stresses do not contribute to collapse. On the other hand local net section yielding is strongly affected by either load or displacement controlled end conditions.

Determination of the Interaction Between Primary and Secondary Stresses Using an Idealised Model

2012 ◽  
Author(s):  
Graeme Horne ◽  
David J. Smith
Keyword(s):  
Residual Stress ◽  
Structural Integrity ◽  
New Approach ◽  
Integrity Assessment ◽  
Primary Stress ◽  
Reference Stress ◽  
Idealised Model ◽  
The Uk

When conducting an assessment of the integrity of a structure the user is directed to classify the stresses as either primary stress or secondary stress. Residual stresses are usually classified as secondary stresses unless they exhibit significant elastic follow-up. In this paper the authors have first summarised current methods and origins of the UK R6 structural integrity assessment methodology for combining primary and secondary stresses. Then, using an idealised model, a new approach has been developed to examine how fixed-displacement secondary stresses interact and redistribute; this model permits a combined reference stress to be determined directly. This combined reference stress is intrinsically linked to the effect of elastic follow-up within the structure and provides a direct measure of how the residual stress relaxes between the extremes of fixed-load and fixed-displacement conditions. The results have been compared with the existing approaches in R6 and it has been demonstrated that the R6 method can be either conservative or non-conservative, depending on the degree of elastic follow-up and residual stress redistribution.

Standardisation on Measurement and Interpretation of Residual Stress Data

2019 ◽  
Author(s):  
Ali Mirzaee-Sisan ◽  
P. John Bouchard ◽  
Foroogh Hosseinzadeh
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Practice Guidelines ◽  
Structural Integrity ◽  
Good Practice ◽  
Critical Assessment ◽  
Numerical Prediction ◽  
Specific Technique ◽  
Integrity Assessment

Abstract This paper highlights many unanswered questions relating to the characterisation of residual stresses in weldments and their treatment in engineering critical assessment and fitness for service assessment codes and standards. The need for an overarching standardisation framework is identified which goes beyond developing good practice guidelines for numerical prediction or measurement using a specific technique. The framework should cover all uncertainties and possible errors in measuring, simulating and interpreting residual stress in the context of structural integrity assessment.

An Energy-Based Residual Stress Field Reconstruction Approach Using Limited Measurements

2015 ◽  
Author(s):  
H.-B. Liu ◽  
Y.-P. Li ◽  
Y.-Q. Wang ◽  
X.-J. Sheng
Keyword(s):  
Residual Stress ◽  
Stress Distribution ◽  
Stress Field ◽  
Structural Integrity ◽  
Spline Interpolation ◽  
Residual Stress Field ◽  
Strain Compatibility ◽  
Integrity Assessment ◽  
Field Reconstruction ◽  
Initial Stress Field

To characterize the residual stress distribution is very crucial for workpiece fatigue lifetime and structural integrity assessment. An energy-based residual stress field reconstruction approach using limited measurements is proposed. Firstly, the Ferguson spline interpolation technique is employed as the stress interpolation base of the 2-order stress tensor. Then, an initial stress field can be reconstructed using the overall boundary conditions by minimizing strain energy. Further, the stress distribution is modified according to strain compatibility equation. At last, a typical stress unit from the artificial stress field constructed by FEM, was picked up as an input set to verify the validation of the developed model and algorithm numerically. It was demonstrated that the energy-based scheme was efficient and reliable to reconstruct the residual stress field from limited measurements.

Application of the Linear Matching Method to the Integrity Assessment for the High Temperature Response of Structures

2003 ◽  
Author(s):  
Haofeng Chen ◽  
Alan R. S. Ponter
Keyword(s):  
Residual Stress ◽  
Stress Field ◽  
Temperature Response ◽  
Assessment Method ◽  
Life Assessment ◽  
Residual Stress Field ◽  
Matching Method ◽  
Integrity Assessment ◽  
Linear Matching Method

The paper describes a first attempt to produce a complete system of calculations that cover the entire range of assessments required in the Life Assessment method R5 based on a new programming method, the Linear Matching Method, and using shakedown and related concepts. We show that two solutions types are possible, the first assuming a constant residual stress field that provides shakedown and related limits. The second method involves the evaluation of the amplitude of the changing residual stress field. This provides the first stage for the ratchet limit and the amplitude of plastic strain. By adaptation the elastic follow-up factor corresponding to creep dwell periods may also be evaluated.

The Validation of Weld Residual Stresses for Use in Structural Integrity Assessment

2011 ◽  
Vol 70 ◽  
pp. 297-302 ◽  
Author(s):  
Steve K. Bate ◽  
P. John Bouchard
Keyword(s):  
Residual Stress ◽  
Finite Element ◽  
Residual Stresses ◽  
Structural Integrity ◽  
Measurement Techniques ◽  
Element Analysis ◽  
Integrity Assessment ◽  
Modelling Techniques ◽  
High Level ◽  
Assessment Procedures

The continued safe and reliable operation of plant invariably has to consider the assessment of defects in welded structural components. This requires some estimate of the residual stresses that have developed during the welding fabrication process. For as-welded structures these stresses can be of yield magnitude. Engineering critical assessment procedures such as R6, BS 7910, FITNET and API 579-1 provide simplified estimates, bounding profiles or advice on detailed analysis or measurement which can be applied to provide conservative estimates of the remaining life of plant. The use of finite element analysis (FEA) is being applied more frequently to predict residual stresses in welded components for assessment purposes. This calculation involves complex non-linear analyses with many assumptions. As a consequence, the accuracy and reliability of solutions is variable. In order to improve the consistency of weld modelling, and hence the accuracy and confidence in their use, a set of Guidelines covering the calculation of residual stresses have been developed. The residual stress calculations need to be validated before the results can be used in assessments and guidance on how to demonstrate the required standard of validation proof is provided with these Guidelines. The level of validation required, depends on the problem being solved and the sensitivity of the assessment to the presence of residual stress. For example a high level of validation may be required for assessments of safety critical plant. To support these calculations, measurements are required and a series of ‘Weld Residual Stress Benchmarks’, describing welded mock-ups which have been measured using various measurement techniques, are being collated which the users can then refer to when validating their finite element modelling techniques and thus provide a greater confidence in the predicted results.

A Study of the Effects of Scaling on Structural Integrity Assessment

2015 ◽  
Author(s):  
Paulo Orrock ◽  
David J. Smith ◽  
Christopher E. Truman
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Scaling Laws ◽  
Structural Integrity ◽  
Driving Forces ◽  
Scaling Law ◽  
Stress Fields ◽  
Complex Nature ◽  
Integrity Assessment ◽  
And Performance

For nuclear welded components the complex nature of the residual stresses involved means it is often advantageous to produce mock-ups in order that the structural integrity and performance may be assessed. The weight and size of these components can make the production of mock-ups prohibitively expensive, and so the use of scaled models is considered here. Numerical analysis and finite element simulations have been carried out to investigate the scaling laws encountered affecting the applied loads, stress fields and crack driving forces that are of interest in the full sized component. To illustrate the effects of scaling we consider the introduction of a residual stress through prior plastic deformation in rectangular beams of different sizes. A simple scaling law provides the loads required to introduce the same magnitude and distribution of residual stresses in different sized specimens. This is pertinent to uncracked beams. In contrast, if a crack is introduced this scaling law is no longer applicable and the stress intensity factor associated with residual and applied stresses differ for different sized specimens. Alternatively, to create the same crack driving force in different sized specimens different initial residual stress fields are required. The implications of these findings are discussed in the context of future work.

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