Application of the CEGB Failure Assessment Procedure, R6, to Surface Flaws

2009 ◽  
pp. 525-525-20 ◽  
Author(s):  
GG Chell
Keyword(s):  
Assessment Procedure ◽  
Failure Assessment ◽  
Surface Flaws

Elastic-Plastic J-Estimation for Circumferentially Cracked Pipes Under Combined Mechanical and Thermal Loadings

2013 ◽  
Author(s):  
Chang-Young Oh ◽  
Yun-Jae Kim ◽  
R. A. Ainsworth
Keyword(s):  
Finite Element ◽  
Thermal Gradient ◽  
Order Effects ◽  
Assessment Procedure ◽  
Element Analysis ◽  
Elastic Plastic ◽  
Defect Assessment ◽  
Failure Assessment ◽  
Two Parameters ◽  
J Estimation

This paper addresses load order effects on elastic-plastic J estimation under combined mechanical and thermal loads for circumferentially cracked pipes. The load order effects, for various thermal gradient types and mechanical loading, are evaluated for a range of magnitudes of the loadings, crack sizes and material hardening. Variations of elastic-plastic J obtained by finite element analysis are compared with existing and proposed methods for use with the R6 defect assessment procedure. The load order effects are presented on the R6 failure assessment diagram (FAD) by calculating the two parameters Kr and Lr from the finite element results. It is shown that there are significant load order effects at large secondary stress cases but these are successfully treated by simplified methods proposed for use with R6.

Some Fundamental Aspects of High Temperature Defect Assessment

2005 ◽  
Vol 297-300 ◽  
pp. 428-434 ◽  
Author(s):  
Shan Tung Tu ◽  
Fu Zhen Xuan
Keyword(s):  
High Temperature ◽  
Assessment Method ◽  
Damage Effect ◽  
Assessment Procedure ◽  
Continuum Damage ◽  
Creep Failure ◽  
Failure Assessment Diagram ◽  
Defect Assessment ◽  
Failure Assessment ◽  
Dependent Failure

Current research efforts in the development of high temperature defect assessment procedure are summarized. Creep exemption criteria are proposed for the assessment of defective structures at high temperature in consideration of the effects of loadings, operating temperature and service time. Time-dependent failure assessment diagram (TDFAD) is developed that covers major failure mechanisms of defective high temperature structures. Challenges due to the welding effect are discussed. TDFAD for weldments is derived for various combinations of materials. In order to develop a unified assessment method to cope with material and loading complexity, a new failure assessment diagram based on continuum damage concept is proposed to reflect the damage effect on ductile creep failure and brittle creep fracture.

Fitness-For-Service Assessment of the Pipelines with Localized Geometric Imperfections such as Buckles and Wrinkles

2008 ◽  
Vol 385-387 ◽  
pp. 173-176
Author(s):  
Zheng Mao Yang ◽  
Shashi Bhushan Kumar ◽  
Jens P. Tronskar
Keyword(s):  
Plastic Strain ◽  
Fracture Resistance ◽  
Assessment Procedure ◽  
Test Results ◽  
Single Edge ◽  
Large Plastic Strain ◽  
Failure Assessment ◽  
Critical Flaw ◽  
Edge Notch ◽  
Girth Welds

In this paper, FFS assessment procedure for the buckle damaged pipeline with cracks in the girth welds is presented. For FFS assessment the tensile and J R-curve data from a pre-strained pipeline material, API 5L X65 were obtained in the laboratory to study the influences of the large plastic strain on the material properties and the fracture resistance of the pipeline girth welds. Tensile and single edge notch bend specimens in as-received, 10% pre-strained and 20% prestrained conditions were tested. The test results show significant increase in yield and tensile strength in the pre-strained specimens. Generally, the elongation and fracture resistance decreased after pre-straining. In FFS material specific failure assessment diagrams (FADs) generated based on the stress-strain curves obtained from testing were used. The critical flaw sizes of the pipeline girth welds were calculated, and the influence of the large plastic strain on the FFS results was discussed.

Assessment Procedure for Multiple Cracklike Flaws in Failure Assessment Diagram (FAD)

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
Shinji Konosu
Keyword(s):  
Body Force ◽  
Pressure Vessels ◽  
The Body ◽  
Assessment Procedure ◽  
Failure Assessment Diagram ◽  
Reference Stress ◽  
Body Force Method ◽  
Failure Assessment ◽  
Common Problems ◽  
Shielding Effects

Assessment of multiple discrete cracklike flaws is one of the most common problems relating to pressure vessels and piping components. Under the current fitness for service (FFS) rules, such as ASME, BS, and so on, multiple cracklike flaws are usually recharacterized as an enveloping crack (defined as a single larger crack), following their assessment rules. The procedure, however, varies significantly in these FFS codes. In this paper, the interaction between nonaligned multiple unequal cracks is clarified by applying the body force method. Based on the interaction that indicates the magnification and shielding effects and the reference stress solutions, a newly developed assessment procedure for multiple discrete cracklike flaws in the failure assessment diagram is proposed.

Critical Speed of Flawed Rotors: Global vs Local Approach

2014 ◽  
Author(s):  
L. Scolavino ◽  
S. Beretta ◽  
M. Madia ◽  
U. Zerbst
Keyword(s):  
Critical Speed ◽  
Operating Conditions ◽  
Assessment Procedure ◽  
Local Approach ◽  
Element Analysis ◽  
Normal Operating ◽  
Safety Margins ◽  
Surface Flaws ◽  
Definition Of ◽  
Sphere Of Influence

The burst of a disc in rotating machinery can cause catastrophic damage of the equipment and, more importantly, it can represent a mortal threat to anyone in the sphere of influence of the event. In order to minimize the danger associated to a rotating component failure, burst testing is required by the authorities in order to set safety margins to the normal operating speeds. Moreover more accurate predicting tools are required for designing the components. This paper presents the results of a numerical and analytical study on the assessment of the crack driving force for discs containing surface flaws. The aim is to provide a simple, though reliable, tool in order to be able to calculate the possible dangerous in-service speed for a rotating component and, therefore, to set burst margins above the normal operating conditions of the equipment. An R6-like flaw assessment procedure is adopted considering different assumptions in the definition of the critical speed and the analytical predictions are compared with the results of elastic-plastic finite element analysis of disc. In particular, the validity and potentiality of the method is proved for surface flaws in different positions in the disc.

Continuing Development of a Simplified Method to Account for the Interaction of Primary and Secondary Stresses

2008 ◽  
Author(s):  
Peter M. James ◽  
Dennis G. Hooton ◽  
Lorna A. Higham ◽  
Colin J. Madew ◽  
John K. Sharples ◽  
...  
Keyword(s):  
Crack Opening ◽  
Full Range ◽  
Nuclear Industry ◽  
Assessment Procedure ◽  
Average Characteristic ◽  
Failure Assessment Diagram ◽  
Failure Assessment ◽  
Simplified Method ◽  
Out Of Plane ◽  
The Look

The R6 defect assessment procedure, used commonly in the UK nuclear industry to assess the significance of defects in structures, uses the Failure Assessment Diagram to evaluate limiting parameters whilst accounting for the effects of plasticity. The interaction of primary and secondary stress is accounted for within R6 through the use of the ρ, or an equivalent V, term. ‘Look-up’ tables are provided in order to evaluate parameters required to derive the ρ or V terms. In some circumstances, the current methodology has been shown to be excessively conservative and the use of the ‘look-up’ tables is somewhat complex and cumbersome anyway. Previous work has shown that an Alternative Method derived from the Time-Dependent Failure Assessment Diagram approach of the R5 high temperature procedure could potentially be considered. This has since been further modified and termed the Simplified Method. This Simplified Method has the benefit of being less conservative than the current R6 method and of not requiring ρ (or V) factors, and hence not requiring the use of the ‘Look-up’ tables. This paper presents the Simplified Method through comparisons within an extended range of Finite Element Analyses upon both an axial and circumferentially cracked pipe and a centre cracked plate. In addition to the use of the Simplified Method, further work is presented in order to include both out of plane primary and secondary stresses when determining the combined reference stress. A full range of crack opening and out of plane forces, as well as a full range of thermally induced secondary stresses, have been included to provide a broad basis upon which to compare the different methods investigated. Through comparing the full range of cases, some of the assumptions made within the R6 procedure have been reassessed. This has led to an average characteristic length, a¯, being defined to account for differences in loading type and in and out of plane ratios. However, within this paper further positive evidence for the use of the Simplified Method has been demonstrated.

scholarly journals Treatment of residual stress in failure assessment procedure

2006 ◽  
Vol 73 (13) ◽  
pp. 1755-1771 ◽  
Author(s):  
Hyeong-Yeon Lee ◽  
Farid R. Biglari ◽  
Robert Wimpory ◽  
Kamran M. Nikbin
Keyword(s):  
Residual Stress ◽  
Assessment Procedure ◽  
Failure Assessment

A Procedure for the Assessment of the Structural Integrity of Nuclear Pressure Vessels

1983 ◽  
Vol 105 (1) ◽  
pp. 28-34 ◽  
Author(s):  
J. M. Bloom
Keyword(s):  
Structural Integrity ◽  
Pressure Vessels ◽  
Assessment Procedure ◽  
Plastic Collapse ◽  
Failure Assessment Diagram ◽  
Linear Elastic ◽  
Failure Assessment ◽  
Deformation Plasticity ◽  
Margin Of Safety ◽  
Two Parameters

This paper presents a simple engineering procedure that the utility industry can use to assess the integrity of typical nuclear-grade pressure vessels. The procedure recognizes both brittle fracture and plastic collapse and is based on a set of proposed failure assessment curves which make up a safety/failure plane. The plane is defined by the stress intensity factor/fracture toughness ratio as the ordinate and the applied stress/reference plastic collapse stress ratio as the abscissa. The failure assessment procedure is based in part on the British Central Electricity Generating Board’s R-6 failure assessment diagram and the deformation plasticity solutions of the General Electric Company. Two parameters, a plastic collapse parameter (Sr′) and linear elastic fracture mechanics parameter (Kr′) are calculated by the user. The point (Sr′, Kr′) is plotted on the appropriate failure assessment diagram. If the point lies inside the respective curve, the structure is safe from failure. Moreover, for a given pressure and a postulated or actual flaw size, the margin of safety of the structure can be simply determined. Consistent with Appendix A of Section XI, (Division 1) of the ASME Boiler and Pressure Vessel Code the procedure presented in this paper is limited to ferritic materials 4 in. (102 mm) and greater in thickness. Details of the derivation of the proposed set of failure assessment curves are provided along with a sample problem illustrating the use of these curves.

Sign in / Sign up

Export Citation Format

Share Document