Fracture Assessment of Through-Wall and Surface Cracked Pipes by BS 7910 and API 579 Assessment Procedures: A Comparative Study

2004 ◽  
Author(s):  
Afshin K. Motarjemi
Keyword(s):  
Experimental Data ◽  
Comparative Study ◽  
Pressure Vessels ◽  
Plastic Collapse ◽  
Four Point Bending ◽  
Reference Stress ◽  
Fracture Assessment ◽  
Pipe Geometry ◽  
Assessment Procedures ◽  
The Comparative Study

Fracture assessment procedures such as BS 7910 and API 579 are formulated based on the Fracture Mechanics concept for assessing integrity of structures such as pipelines, pressure vessels, etc. In the current study those procedures are applied to through-wall and surface cracked pipe geometry under four-point bending. The predicted maximum tolerable applied loads are then compared with pipe full-scale fracture testing results published by Miura et al (2002). Other assessment schemes namely, GE/EPRI, Net-section plastic collapse, LBB.NRC and finally LBB.ENG2, as reported in the same publication are also included in the current paper for sake of comparison. The comparative study showed that BS 7910 and API 579 predict similar maximum tolerable load for through-wall pipes but different value for surface-cracked pipes. Difference in predictions for the latter geometry is owing to the use of different stress intensity factor/reference stress solution by BS 7910 than API 579. However, both procedures provided conservative results compared with the experimental data as well as other engineering routes mentioned in Miura et al (2002).

The Numerical Investigation of Plastic Collapse Loads in Cylinders Containing Circumferential Flaws Under a Combined Loading of Internal Pressure, Tension and Bending Moment

2013 ◽  
Author(s):  
Liwu Wei
Keyword(s):  
Surface Crack ◽  
Bending Moment ◽  
Limit Load ◽  
Plastic Collapse ◽  
Plastic Limit ◽  
Integrity Assessment ◽  
Reference Stress ◽  
Fracture Assessment ◽  
Plastic Limit Load ◽  
Assessment Procedures

Fracture assessment diagram (FAD) based fracture assessment procedures are universally adopted by standards/documents including BS7910, R6, API579-1/ASME FFS-1 and FITNET. In the use of a FAD for structural integrity assessment, one important consideration is to determine the load ratio (Lr) which is defined by two equivalent definitions: Lr is either defined as the ratio of reference stress (σref) to yield strength (σY) as in BS7910, or as the ratio of applied load to plastic limit load as in R6. The solutions of reference stress or limit load are given in the assessment procedures for commonly encountered flawed structures such as a plate containing a surface crack and a cylinder containing an external surface crack. Although the solutions given in the various standards are not all the same, they were invariably derived on the basis of analysis of the force and moment equilibrium with regard to a flawed section and few of them has taken into account the effects of bi-axial stressing on a flawed section, thus remaining a question whether these solutions are still valid in situations involving bi-axial loading such as the presence of pressure in a cylinder in addition to axial tension and bending. In this work, finite element analysis (FEA) of plastic collapse was systematically performed on circumferential internal surface cracks in a cylinder subjected to various combined loads, including combined tension and pressure, combined bending moment and pressure, and combined tension, bending moment and pressure. The focus was on understanding the effects of bi-axial stressing due to pressure on plastic limit load. The investigation of these cases has demonstrated a significant effect in plastic limit load arising from the application of pressure introducing a state of bi-axial stressing. Comparison of the results of plastic limit load obtained from FEA with those derived from BS 7910 reference stress solutions was carried out to assess the applicability when the standard solutions of plastic collapse are used in the applications containing bi-axial stresses.

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

Analysis of Strength Scaling Effect in Portuguese Limestone: Comparison between Three- and Four-Point Bending Tests

2010 ◽  
Vol 636-637 ◽  
pp. 1336-1341 ◽  
Author(s):  
Jorge Cruz Fernandes ◽  
Vera Pires ◽  
Pedro M. Amaral ◽  
Luís Guerra Rosa
Keyword(s):  
Experimental Data ◽  
Comparative Study ◽  
Surface Finishing ◽  
Intrinsic Volume ◽  
Cross Sectional ◽  
Weibull Statistics ◽  
Scaling Effect ◽  
Bending Tests ◽  
Four Point Bending ◽  
Cross Sectional Dimension

This paper presents a comparative study between 3- and 4-point bending tests applied to five Portuguese limestones. The study has been conducted on sawed limestone specimens, all showing the same surface finishing. The materials were compared for two distinct situations: i) using a 3-point flexure loading configuration in batches of materials with larger cross sectional specimen dimension (50 × 30 mm2); and ii) using a 4-point flexure loading configuration in the same batch of materials but with smaller cross sectional dimensions (30 × 25 mm2). In all situations, the materials have broken due to intrinsic volume defects. Formulae for the effective volumes and effective surfaces for rectangular beam specimens loaded in flexure were reviewed in order to analyse the strength scaling effect. The results show the applicability of the Weibull statistics to explain the differences in the results of the 3-point and 4-point bending tests, even when different cross sectional sizes are employed. Among other important remarks, in all the different limestone specimens used it was possible to confirm that the strength values determined experimentally via 3-point bending are of the same order as those estimated for the same loading configuration but via experimental data of 4-point bending tests using the Weibull strength scaling approach, even if employing a different cross-sectional dimension.

scholarly journals THE ANALYSIS OF INTELLECTUAL PROPERTY RIGHTS IN CHINA

2016 ◽  
Vol 3 (3) ◽  
Author(s):  
Edwin Agung Wibowo
Keyword(s):  
Experimental Data ◽  
Intellectual Property ◽  
Comparative Study ◽  
Intellectual Property Rights ◽  
Experimental Studies ◽  
Legal Framework ◽  
Accurate Information ◽  
Economic Culture ◽  
Administrative Procedures ◽  
The Comparative Study

This paper has used a comparative study for the key findings of the experimental studies.  The several aspects such as the legal framework, economic, culture and macro environment are subjected to be compared to measure the main gap as the issues between theoretical legal framework and IPR administrative procedures in China.  In addition, this paper includes several sources of experimental data from library, journals and Internet in order to obtain the accurate information for the comparative study.

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.

The Future of the BS 7910 Flaw Assessment Procedures

2010 ◽  
Author(s):  
Isabel Hadley ◽  
Bob Ainsworth ◽  
Peter Budden ◽  
John Sharples
Keyword(s):  
Weld Strength ◽  
Assessment Procedure ◽  
Metallic Structures ◽  
Damage And Failure ◽  
Reference Stress ◽  
Fracture Assessment ◽  
Crack Tip Constraint ◽  
The Uk ◽  
Assessment Procedures ◽  
Industry Sectors

BS 7910, the UK procedure for the assessment of flaws in metallic structures, was first published some 30 years ago in the form of a fracture/fatigue assessment procedure, PD6493. Since then it has been regularly maintained and expanded, taking in elements of other publications such as the UK power industry’s ‘R6’ procedure (in particular the Failure Assessment Diagram or FAD approach), the creep assessment procedure PD6539 and the UK gas transmission industry’s approach to corrosion assessment of locally thinned areas in pipelines. Work is currently underway to prepare another major revision, this time incorporating many elements of the European flaw assessment procedure FITNET. Like its predecessor, the new BS 7910 is intended for use by a range of industry sectors for virtually any type of metallic structure or component. The procedures will cover damage and failure by fatigue crack growth, fracture, creep and corrosion, including Environmentally Assisted Corrosion. The objective in revising the procedures is to support the use of more advanced assessment methods, whilst preserving compatibility with previous editions of BS 7910 and retaining methods for preliminary analyses based on simple, conservative inputs. Features of the new BS 7910 will include adoption of new advanced fracture assessment procedures (taking account of crack tip constraint and weld strength mismatch where appropriate), revision of the residual stress annex, preparation of a new annex covering guidance on NDE, an enhanced library of K-solutions and reference stress solutions and greater compatibility with procedures such as R6 and FITNET.

Discussion on a Comparative Study Among FFS Rules

2009 ◽  
Author(s):  
Kenji Oyamada ◽  
Shinji Konosu ◽  
Takashi Ohno
Keyword(s):  
Comparative Study ◽  
Assessment Method ◽  
Metal Loss ◽  
Plastic Collapse ◽  
Correction Factors ◽  
Diagram Method ◽  
Reference Stress ◽  
Cylindrical Component ◽  
Failure Assessment ◽  
Surface Correction

Remaining Strength Factor (RSF) approach in Part 5 of API 579-1/ASME FFS-1 is an assessment method for a cylindrical component with a local metal loss based on surface correction factors. Also, reference stress solutions that are applied in the Failure Assessment Diagram (FAD) method for a cylindrical component with a crack-like flaw are provided in Annex D using surface correction factors. In the p-M diagram method that has been recently developed, reference stress solution for local metal loss evaluation in a cylindrical component is derived using bulging factors, which are similar but not identical to the surface correction factors used in API 579-1/ASME FFS-1. This paper describes the results of a comparative study among the RSF approach, reference stress solutions for the FAD method, and the p-M diagram method, in terms of plastic collapse evaluation of a cylindrical component. These results were compared with the FEA and experimental results to confirm how those estimated stresses could be validated. The results of the study also contain proposals for prospective modifications of API 579-1/ASME FFS-1.

The Effect of Bi-Axial Stress on Limit Loads of Structures Containing Surface-Breaking Flaws and its Influence on Structural Integrity Assessments

2012 ◽  
Author(s):  
Liwu Wei ◽  
Isabel Hadley
Keyword(s):  
Surface Crack ◽  
Structural Integrity ◽  
Axial Loading ◽  
Limit Load ◽  
Plastic Limit ◽  
Integrity Assessment ◽  
Reference Stress ◽  
Fracture Assessment ◽  
Plastic Limit Load ◽  
Assessment Procedures

Fracture assessment diagram (FAD) based fracture assessment procedures are universally adopted by standards/documents including BS7910, R6, API579-1/ASME FFS-1 and FITNET. In the use of a FAD for structural integrity assessment, one important consideration is to determine the load ratio (Lr) which is defined by two equivalent definitions: Lr is either defined as the ratio of reference stress (σref) to yield strength (σY) as in BS7910, or as the ratio of applied load to plastic limit load as in R6. The solutions of reference stress or limit load are given in the assessment procedures for commonly encountered flawed structures such as a plate containing a surface crack and a cylinder containing an external surface crack. Although the solutions given in the various standards are not all the same, they were invariably derived on the basis of analysis of the force and moment equilibrium with regard to a flawed section and none of them has taken into account the effects of bi-axial stressing on a flawed section, thus leading to the likelihood of an overly conservative assessment. In this work, finite element analysis (FEA) of various flawed geometries (plate and cylinder containing surface cracks) was performed to compute plastic limit load, with the focus on understanding the effects of bi-axial stressing on plastic limit load. The geometries assessed include a plate with a surface crack subjected to both uni-axial and bi-axial loading, and a cylinder with circumferentially internal and external surface cracks sustaining a combination of axial loading and internal pressure. The investigation of these cases has demonstrated a significant increase in plastic limit load arising from bi-axial stressing. Comparison of the results of plastic limit load obtained from FEA with those derived from BS 7910 reference stress solutions was carried out to assess the extent of conservatism when the standard solutions are used in the applications containing bi-axial stresses. The implication for structural integrity assessment due to bi-axial stressing was also addressed. A comparison between BS 7910 Level 2B (material-specific FAD) and Level 3C (based on a FAD generated with FEA) procedures was also made and it was shown that whether the Level 3C procedure can reduce the conservatism in an assessment is dependent on individual cases.

Differences in the Assessment of Plastic Collapse in BS 7910:2005 and R6/FITNET FFS Procedures

2011 ◽  
Author(s):  
S¸efika Elvin Eren ◽  
Isabel Hadley ◽  
Kamran Nikbin
Keyword(s):  
Boundary Conditions ◽  
Comparative Studies ◽  
Limit Load ◽  
Plastic Collapse ◽  
Reference Stress ◽  
Fracture Assessment

At present within the fracture assessment routes of different codes and standards, two different options for the assessment of plastic collapse, Lr, are available, namely reference stress and limit load approaches. Recent comparative studies have shown significant differences in the assessment of plastic collapse depending on whether the reference stress solutions in BS 7910:2005 or the limit load solutions in R6/FITNET are used for the calculation of Lr. In this paper, differences with respect to the choice of solutions and boundary conditions will be illustrated and observations regarding the route that the Codes should take with respect to a unified assessment will be discussed.

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