scholarly journals Reference Stress Approach for Fracture Assessment of Extrados Circumferential Through-Wall Crack at the Interface between Elbow and Pipe Subjected to Internal Pressure

2018 ◽  
Vol 22 (6) ◽  
pp. 151-163
Author(s):  
Jirapong Kasivitamnuay ◽  
Pairod Singhatanadgid
Keyword(s):  
Internal Pressure ◽  
Reference Stress ◽  
Fracture Assessment ◽  
Reference Stress Approach

Validation of Plastic Collapse Assessments Using BS 7910:2013 and R6 Procedures

2013 ◽  
Author(s):  
Şefika Elvin Eren ◽  
Tyler London ◽  
Yang Yang ◽  
Isabel Hadley
Keyword(s):  
Finite Element Analysis ◽  
Limit Load ◽  
Plastic Collapse ◽  
Element Analysis ◽  
Metallic Structures ◽  
British Standard ◽  
Reference Stress ◽  
Fracture Assessment ◽  
The Difference ◽  
Reference Stress Approach

The British Standard, BS 7910 Guide to Methods for Assessing the Acceptability of Flaws in Metallic Structures is currently under revision [1]. Major changes have been undertaken, especially in the fracture assessment routes, and this paper specifically addresses the assessment of proximity to plastic collapse, usually expressed as the parameter Lr via either a reference stress or limit load approach. In the new edition of BS 7910, the reference stress approach has been retained for the assessment of many geometries, mainly for reasons of continuity. However, new limit load solutions (originating in the R6 procedure) are given for use in the assessments of strength mismatched structures or clad plates. In general, a reference stress solution and a limit load solution for the same geometry should deliver the same value of Lr. However, recent comparative studies have shown differences in the assessment of plastic collapse depending on whether the reference stress solutions in BS 7910:2013 or the limit load solutions in R6 are used for the calculation of Lr. In this paper, the extent of the difference in the assessment results with respect to the choice of solutions and boundary conditions are discussed. The results of the assessments in accordance with BS 7910 and R6 are compared with the results of numerical assessments obtained via Finite Element Analysis (FEA). The collapse loads observed in various wide plate tests conducted in the last 20 years are also compared with the collapse loads predicted by BS 910:2013, R6 and FEA. Finally, observations regarding the accuracy of different Codes and FEA are discussed.

Reliability Assessment of Piping With Cracks Using Advanced First-Order Second-Moment Method

2009 ◽  
Author(s):  
Shinji Yoshida ◽  
Hideo Machida
Keyword(s):  
Safety Factor ◽  
Reliability Assessment ◽  
Limit Load ◽  
Service Level ◽  
Assessment Method ◽  
J Integral ◽  
Reference Stress ◽  
First Order Second Moment ◽  
Fracture Assessment ◽  
Second Moment Method

This paper describes applicability of the 2 parameter assessment method using a reference stress method from the viewpoint of reliability. The applicability of the reference stress method was examined comparing both the GE-EPRI method. As a result, J-integral and limit load at the time of fracture evaluated by the reference stress method is almost equivalent to that by the GE-EPRI method. Furthermore, the partial safety factor (PSF) evaluated by reliability assessment has little difference between two methods, and the required safety factor is enveloped by the safety factor for Service Level-A and B defined in fitness for service (FFS) codes. These results show that of the reference stress method is applicable for J-integral calculation in fracture assessment.

On Determining Reference Stresses for High Temperature Thin/Thick Tube Bends

2005 ◽  
Author(s):  
Abheek Basu ◽  
Khosrow Zarrabi ◽  
Lawrence Ng
Keyword(s):  
High Temperature ◽  
Internal Pressure ◽  
Explicit Expression ◽  
Finite Volume ◽  
Limit Analysis ◽  
Volume Analysis ◽  
Reference Stress ◽  
First Time

It is well known that tube/pipe bends have some degree of ovality caused during their manufacture. For the first time, based on limit analysis, the authors previously presented an explicit expression for calculation of the reference stress of tube/pipe bends with varying degrees of ovality that are subjected to uniform internal pressure. The present paper assesses this expression using an elastic-creep finite volume analysis. This is due to availability of an in-house finite volume code. It is shown that the references stresses predicted by proposed expression correlate well with those computed using elastic-creep analyses for tube/pipe bends with various degrees of ovality.

Recent Studies Towards Updating the BS7910 Flaw Interaction Rule

2018 ◽  
Author(s):  
Bostjan Bezensek ◽  
Harry E. Coules
Keyword(s):  
Aspect Ratio ◽  
Rule Based ◽  
Crack Driving Force ◽  
Reference Stress ◽  
Surface Flaws ◽  
Close Proximity ◽  
Fracture Assessment ◽  
Assessment Procedures ◽  
Work Done ◽  
Interaction Rule

Fitness for service assessment procedures rely on flaw interaction rules for assessment of multiple flaws in close proximity. Such rules are aimed at avoiding excessive amplification of the crack driving force that may result in a non-conservative fracture assessment. In BS7910, the 2013 edition [1] introduced a new flaw interaction rule for the co-planar flaws where the proximity of adjacent flaws is judged based on flaw height (i.e. s = 0.5*max(a1,a2) for surface flaws). The rule was introduced for flaws with aspect ratio of a/c < 1 for both flaws, while for other flaw shapes and combinations the earlier rule from the predecessor document PD6493:1993 [2] was retained. This paper summarises the recent work done by the authors and work from literature to examine the applicability of the s = 0.5*max(a1,a2) rule to flaws with aspect ratio a/c ≥ 1 and dissimilar flaw combinations. It is shown that the current BS7910 rule based on s = 0.5*max(a1,a2) produces a conservative flaw assessment with the use of BS7910 solutions for stress intensity factor and reference stress. An exception are cases of two deep surface flaws where the rule is proposed to change to: s ≤ max(a1, a2) for two surface flaws with a1/t & a2/t > 0.5

A Reference Stress Approach to Creep Bending of Straight Tubes

1974 ◽  
Vol 16 (3) ◽  
pp. 125-138 ◽  
Author(s):  
J. Fairbairn
Keyword(s):  
Entire Range ◽  
Creep Behaviour ◽  
Tensile Creep ◽  
Bending Moments ◽  
Stress Distributions ◽  
Creep Tests ◽  
Reference Stress ◽  
Hyperbolic Sine ◽  
Rotation Method ◽  
Reference Stress Approach

Reference-stress parameters, based on the Norton constitutive equation, are developed for creep bending of circular and elliptical tubes. The parameters are presented in the form of a design chart. The reference stress methods apply also to other simple constitutive equations of the power law, exponential and hyperbolic sine forms, and also to two complex equations describing creep behaviour over the entire range from primary to tertiary. In these equations the functions of stress and time are not separable and reference stress techniques provide a convenient method of evaluating stationary stress distributions and investigating the variation of these stresses with time. Aluminium alloy tubes were creep tested with cyclic uniform bending moments. Creep strains to fracture were measured by an end-rotation method. The creep behaviour of the tubes was well predicted by reference-stress cyclic tensile creep tests.

Development of LBB Assessment Method for Japanese Sodium Cooled Fast Reactor (JSFR) Pipes: 3—Fracture Assessment Methods Considering Compliance at a Crack Part

2010 ◽  
Author(s):  
Takashi Wakai ◽  
Hideo Machida ◽  
Shinji Yoshida ◽  
Yasuhiro Enuma ◽  
Tai Asayama
Keyword(s):  
Thermal Expansion ◽  
Internal Pressure ◽  
Fast Reactor ◽  
Load Balance ◽  
Assessment Method ◽  
Assessment Methods ◽  
Piping System ◽  
Thin Wall ◽  
Fracture Assessment ◽  
Leak Before Break

This paper presents a fracture assessment methods used in leak before break (LBB) assessment of sodium piping system in the Japanese sodium cooled fast reactor (JSFR). Use of thin wall pipes and compact layout of piping system are features of the design in JSFR. Since the internal pressure of piping of JSFR is low, the critical load is thermal expansion. Supposing a through wall crack (TWC) in such piping, the stiffness of the crack part will decrease, the load balance of the piping system will change from the condition without crack. The fracture assessment methods paying attention to this stiffness change at the crack part were proposed and these methods enabled rational LBB assessment. The proposed methods are much effective to loosen LBB conditions for the piping system of which the compliance is low. These methods applied to the LBB assessment of the piping system of JSFR which has the compact layout, and it was checked that the validity of these methods to loosen the LBB conditions.

scholarly journals J Predictions for Defective Pipe Elbows via the Reference Stress Method

2021 ◽  
Author(s):  
Yuebao Lei ◽  
Peter Budden
Keyword(s):  
Structural Integrity ◽  
Three Dimensional ◽  
Local Limit ◽  
Limit Load ◽  
Load Model ◽  
Reference Stress ◽  
Failure Assessment ◽  
Fracture Assessment ◽  
Global And Local ◽  
Integrity Assessments

Abstract In R6, the J-based failure assessment diagram (FAD) method is used in the fracture assessment, and is underpinned by the reference stress J scheme. Therefore, an assessment using the R6 FAD method is equivalent to a J prediction using the reference stress method. In this paper, the effect of global and local limit load solutions for defective elbows on the reference stress and hence the J predictions is investigated using published three dimensional elastic-plastic finite element (FE) J results, in order to create guidance for users to follow when performing structural integrity assessments of defective elbows using the R6 procedure. The results show that using the global limit load solutions recommended in this paper can lead to good and reasonably conservative J predictions. However, the availability of global limit load solutions is very limited. The results also show that using the local limit load evaluated from the local limit load model recommended in this paper can lead to conservative J predictions for most of the cases considered.

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