Evaluation of Groove Radius Assessment Criteria Based on Brittle and Ductile Local Failure Models

2016 ◽  
Author(s):  
Gregory W. Brown ◽  
Lucie Parietti ◽  
Brian Rose ◽  
Ted L. Anderson
Keyword(s):  
Ductile Failure ◽  
Metal Loss ◽  
Plastic Collapse ◽  
Loss Assessment ◽  
Element Analysis ◽  
Failure Models ◽  
The Difference ◽  
Collapse Failure ◽  
Tip Radius ◽  
Weibull Stress

API 579-1/ASME FFS-1[1] Part 5 (2007 edition) contains procedures for assessing local metal loss based on failure by plastic collapse. Equation (5.10) defines “acceptable” tip radii for grooves to ensure a plastic collapse failure mode. Grooves failing the radius check must be treated as a crack-like flaws. The validity of Equation (5.10) is questionable, and it may be excessively conservative. This paper presents new rules for groove assessment based on brittle and ductile failure models. Computation of the Weibull stress using finite element analysis (FEA) was employed to determine the minimum groove radius required to eliminate the possibility of cleavage fracture. The Bao-Wierzbicki ductile failure model was used with FEA to evaluate burst pressure and to determine a new groove radius criterion defining the plastic collapse regime, allowing categorization as metal loss. Groove-like flaws categorized as neither sharp cracks nor as metal loss are evaluated using an effective toughness concept. This concept quantifies the difference in fracture response between a sharp crack and a notch with a finite tip radius. The upcoming 2016 API 579-1/ASME FFS-1 rules remove the excessive conservatism found in Part 5 of the 2007 edition and avoid the abrupt transition between crack and metal loss assessment types based on groove radius.

Discussion on Plastic Collapse Criterion at High Temperatures in FFS Assessment Rules

2010 ◽  
Author(s):  
Kenji Oyamada ◽  
Shinji Konosu ◽  
Hikaru Miyata ◽  
Takashi Ohno
Keyword(s):  
Comparative Study ◽  
High Temperatures ◽  
Bending Moment ◽  
Flaw Size ◽  
Metal Loss ◽  
Plastic Collapse ◽  
Loss Assessment ◽  
Element Analysis ◽  
Diagram Method ◽  
The Difference

There are several Fitness-For-Service (FFS) standards with evaluation rules in terms of plastic collapse for a pressure vessel or piping component possessing a local metal loss area simultaneously subjected to internal pressure and bending moment. The authors have already reported the results of a comparative study of FFS rules, including the remaining strength factor (RSF) approach in Part 5 of API 579-1/ASME FFS-1 and the p-M diagram method, which pointed out that there could be significant differences in allowable flaw sizes. This paper describes an additional comparative study on the difference of allowable flaw size for local metal loss assessment between the RSF approach in Part 5 of API 579-1/ASME FFS-1 and the p-M diagram method, focusing on the effect of decreasing yield strength of the material at high temperatures, such as 350 degrees C. The allowable flaw depth at high temperatures derived from API579-1/ASME FFS-1 is larger than that derived by means of the p-M diagram method. However, it is verified by the finite element analysis that the allowable flaw size of the p-M diagram method is set on the stress state of general yielding near a local metal loss area if safety factor is not considered and it is possible to evade ratcheting due to cyclic bending moment in service, such as that caused by earthquake, etc.

Effect of Thickness Measurement Procedure on Stress Analysis of Pipes With Local Metal Loss

2013 ◽  
Author(s):  
Nobuyuki Yoshida ◽  
Atsushi Yamaguchi
Keyword(s):  
Decision Making ◽  
Measurement Procedure ◽  
Thickness Measurement ◽  
Burst Pressure ◽  
Metal Loss ◽  
Element Analysis ◽  
Fea Model ◽  
Laser Displacement Meter ◽  
The Difference ◽  
Corrosion Under Insulation

Fitness-For-Service (FFS) assessment using Finite Element Analysis (FEA) has been a problem in deciding yes-no which vary from evaluator to evaluator. The difference in decision making is caused by the degree of freedom in modeling a FEA model. In this study, burst pressures of pipes with local metal loss were calculated by using FEA in order to investigate the influence of thickness measurement intervals on FFS assessment. The analyzed pressures by FEA were verified by burst tests. A pipe specimen, which was thinned by corrosion under insulation in the actual plant, was used for the burst tests. Shape of the pipe specimen was measured by laser displacement meter and extracted at several types of interval. It is concluded that the analyzed pressures in various measurement intervals showed almost no difference, but were higher than the actual burst pressure of the specimen.

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.

New Safety Assessment System for Corroded Underground Pipelines

2009 ◽  
Author(s):  
Szabolcs Sza´vai ◽  
Gyo¨ngyve´r B. Lenkey
Keyword(s):  
Safety Assessment ◽  
Safety Margin ◽  
Assessment System ◽  
Metal Loss ◽  
Safety Factors ◽  
Element Analysis ◽  
Underground Pipelines ◽  
Corrosion Defects ◽  
The Difference ◽  
External Corrosion

The most important question for the user is if pipelines having metal loss defect could be operated safely, if any pipe sections should be repaired or replaced, and how much is the reserved safety against a possible failure. There are several engineering methods for determining the safety margin of operation but those are usually quite conservative. For this reason Lenkey has proposed safety diagrams based on finite element analysis of external corrosion defects in underground pipelines [4]. These safety diagrams could be used to determine safety factors in a less conservative way for critical situations during the pipeline operation. The FEM calculations have been verified by burst tests carried out on several pipe sections. In the present paper the results of some further analyses are presented about the difference between the measured, numerically and analytically determined failure pressure values.

Safe Operation and FFS Assessment for Pressure Equipment: Updated With Study for Local Metal Loss Assessment

2006 ◽  
Author(s):  
Atsushi Ohno ◽  
Yoshiaki Uno ◽  
Takayasu Tahara
Keyword(s):  
United States ◽  
Finite Element Analysis ◽  
Finite Element ◽  
Metal Loss ◽  
Assessment Procedure ◽  
Loss Assessment ◽  
Safe Operation ◽  
Element Analysis ◽  
Assessment Procedures ◽  
Design Margin

Recently, Codes and Standards for FFS assessment has been developed and applied in United States and other countries such as API RP579 as a series of maintenance procedures for pressure equipment. Activities developing FFS assessment procedures in conjunction with new safe inspection standards are also progressing in Japan. In order to prove applicability of the FFS procedure for assessment of damaged pressure equipment, it is also important to validate how much of inservice safe margin is derived from the FFS assessment procedures in compared with design margin of pressure equipment. Local metal loss assessment procedure specified by API RP579 is studied using finite element analysis and discussed how much of in-service safe margin will be sufficient as standardized FFS assessment procedure.

Finite Element Analysis of Creep Damage Behavior Near the Cavity on Bimaterial Interface

2006 ◽  
Vol 324-325 ◽  
pp. 951-954 ◽  
Author(s):  
Qing Min Yu ◽  
Zhu Feng Yue ◽  
Yong Shou Liu
Keyword(s):  
Finite Element ◽  
Elastic Moduli ◽  
Elastic Stress ◽  
Creep Damage ◽  
Ductile Material ◽  
Bimaterial Interface ◽  
Modulus Ratio ◽  
Element Analysis ◽  
Damage Law ◽  
The Difference

Fracture along an interface between materials plays a major role in failure of material. In this investigation, finite element calculations with Kachanov–Rabotnov damage law were carried out to study the creep damage distribution near the interface cavity in bimaterial specimens. The specimens with central hole were divided into three types. The material parameters of K-R law used in this paper were chosen for a brittle material and ductile material. All calculations were performed under four load cases. Due to the difference between elastic moduli of the bounded materials, the elastic stress field as a function of the Young’s modulus ratio (R=E1/E2) was determined. At the same time, the influence of model type on elastic stress distribution near the cavity was considered. Under the same conditions, the material with larger modulus is subjected to larger stress. The creep damage calculations show that the location of the maximum damage is different for each model. The distributions of creep damage for all three models are dependent on the material properties and load cases.

Probability of Plastic Collapse Failure

1969 ◽  
Vol 95 (8) ◽  
pp. 1743-1761
Author(s):  
James L. Jorgenson ◽  
John E. Goldberg
Keyword(s):  
Plastic Collapse ◽  
Collapse Failure

scholarly journals DEVELOPMENT OF THE CONDITIONS FOR STORING THALLIUM AMALGAM

2021 ◽  
Vol 447 (3) ◽  
pp. 65-70
Author(s):  
А.S. Mussina ◽  
G.U. Baitasheva ◽  
N.О. Myrzakhmetova ◽  
Zh.A. Tagabergenova ◽  
E.P. Gorbulicheva
Keyword(s):  
Reaction Rate ◽  
Decomposition Reaction ◽  
Metal Loss ◽  
Distilled Water ◽  
K Value ◽  
Long Term Storage ◽  
Rate Of Dissolution ◽  
Protective Medium ◽  
Zero Order Reaction ◽  
The Difference

It has been established that lNH2SO4 solution and distilled water can be used as a protective medium for a long-term storage (30-40 days) of thallium amalgam of eutectic composition (8.6 mas.%), without sliming of its surface and an insignificant change of its concentration. An inverse dependence between the decomposition reaction rate and the ratio of the solution volume per unit of the contact surface (V:S), which corresponds to the height of the liquid layer (h) above the amalgam, is observed. At h ~ 2.5 cm and higher, the reaction rate becomes stabilized. The value of metal loss during its storage for 10-15 days does not exceed 0.5-1.0 mas.% of the initial thallium content in the amalgam. It has been shown that the rate of dissolution of thallium from amalgam is rather low, and in sulfuric acid solution it is only slightly higher than that in water with all S:V ratios. A similar picture is observed upon thallium amalgam decomposition in the same media in an open vessel; the difference consists only in a higher K value (Table 4). Thus, with S:V = 1:2.5, in an open vessel K in lNH2SO4 makes up 10,5.1011 mol/cm2.sec, and in H2O – 7.3.1011 mol/cm2.sec, whereas in a closed vessel K in lNH2SO4 makes up 1,9.1011 mol/cm2. sec, and in H2O – 1.5.1011 mol/cm2.sec. For 40 days of thallium amalgam (8.54 mas.%) storage in 1NH2SO4 the loss of thallium has been 1.3 mas.%, and in the distilled water - 1 mas.%. The quantity of the dissolved metal increases in proportion to the experiment duration, which is characteristic for a zero-order reaction, and this dependence is observed for all S:V ratios from 1:1 to 1:7. Besides, a possibility to use some saturated hydrocarbons, wherein no sliming of thallium amalgam occurs, as a protective wash liquid has been shown.

scholarly journals Analytical Iron Loss Evaluation in the Stator Yoke of Slotless Surface-Mounted PM Machines

2021 ◽  
Author(s):  
Matteo Leandro ◽  
Nada Elloumi ◽  
Alberto Tessarolo ◽  
Jonas Kristiansen Nøland
Keyword(s):  
Core Loss ◽  
Lookup Table ◽  
Iron Loss ◽  
Estimation Methods ◽  
Design Stage ◽  
Loss Assessment ◽  
Stator Core ◽  
Element Analysis ◽  
Field Solution ◽  
Loss Models

<div>One of the attractive benefits of slotless machines is low losses at high speeds, which could be emphasized by a careful stator core loss assessment, potentially available already at the pre-design stage. Unfortunately, mainstream iron loss estimation methods are typically implemented in the finite element analysis (FEA) environment with a constant-coefficients dummy model, leading to weak extrapolations with huge errors. In this paper, an analytical method for iron loss prediction in the stator core of slotless PM machines is derived. It is based on the extension of the 2-D field solution over the entire machine geometry. Then, the analytical solution is combined with variable- or constant-coefficient loss models (i.e., VARCO or CCM), which can be efficiently computed by vectorized post-processing. VARCO loss models are shown to be preferred at a general level.Moreover, the paper proposes a lookup-table-based (LUT) solution as an alternative approach. The main contribution lies in the numerical link between the analytical field solution and the iron loss estimate, with the aid of a code implementation of the proposed methodology. First, the models are compared against a sufficiently dense dataset available from laminations manufacturer for validation purposes. Then, all the methods are compared for the slotless machine case. Finally, the models are applied to a real case study and validated experimentally.</div>

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