Structural Connection Fatigue Evaluation Methodology Using Time Domain Approach

2021 ◽  
Author(s):  
Sagar Samaria ◽  
Bob Zhang ◽  
Sudhakar Tallavajhula ◽  
Johyun Kyoung
Keyword(s):  
Time Domain ◽  
Evaluation Methodology ◽  
Fatigue Evaluation ◽  
Structural Connection

Fatigue Effect of RCS Branch Line by Thermal Stratification

2003 ◽  
Author(s):  
Hag-Ki Youm ◽  
Kwang-Chu Kim ◽  
Man-Heung Park ◽  
Tea-Eun Jin ◽  
Sun-Ki Lee ◽  
...  
Keyword(s):  
Thermal Stratification ◽  
Nuclear Power ◽  
Power Plants ◽  
Evaluation Methodology ◽  
Element Analysis ◽  
Branch Line ◽  
Reactor Coolant ◽  
Stratification Effect ◽  
Fatigue Evaluation ◽  
Coolant System

Recent events reported at a number of nuclear power plants worldwide have shown that thermal stratification, cycling, and striping in piping can cause excessive thermal stress and fatigue on the piping material. These phenomena are diverse and complicated because of the wide variety of geometry and thermal hydraulic conditions encountered in reactor coolant system. Thermal stratification effect of re-branched lines is not yet considered in the fatigue evaluation. To evaluate the thermal load due to turbulent penetration, this paper presents a fatigue evaluation methodology for a branch line of reactor coolant system with the re-branch line. The locations of fatigue monitoring and supplemented inspections are discussed as a result of fatigue evaluations by Interim Fatigue Management Guideline (ITFMG) and detail finite element analysis. Although the revised CUF was increased less than 50 %, the CUF values for some locations was greater than the ASME Code limits.

Applicability of Seismic Fatigue Evaluation by JSME Code Case, NC-CC-008

2019 ◽  
Author(s):  
Akihito Otani ◽  
Izumi Nakamura ◽  
Tomoyoshi Watakabe ◽  
Masaki Morishita ◽  
Tadahiro Shibutani ◽  
...  
Keyword(s):  
Evaluation Method ◽  
Shaking Table Test ◽  
Shaking Table ◽  
Evaluation Methodology ◽  
Response Analysis ◽  
Analysis Method ◽  
Seismic Evaluation ◽  
Fatigue Evaluation ◽  
Conservative Result ◽  
Current Rule

Abstract A Code Case, JSME S NC1, NC-CC-008, in the framework of JSME Nuclear Codes and Standards has been published. New seismic evaluation methodology for piping by utilizing advanced elastic-plastic response analysis method and strain-based fatigue criteria has been incorporated into the code case. It can achieve more rational seismic design than the current rule. This paper demonstrates validity and applicability of fatigue evaluation method proposed in the code case. Experimental results of a shaking table test for a piping model is used for comparing the evaluation by the current rule with one by the code case. As a result, it is confirmed that the code case can provide a rational and conservative result in the fatigue evaluation of piping. Moreover, cycle counting in the fatigue evaluation was examined for further progress of the code case.

Code Aspects Related to Combination of Stresses due to Hydrogen Detonations: Local Effects

2012 ◽  
Author(s):  
John C. Minichiello ◽  
Stephen D. Ahnert ◽  
Thomas C. Ligon ◽  
David J. Gross
Keyword(s):  
Fatigue Damage ◽  
Pipe Wall ◽  
Axial Strain ◽  
Evaluation Methodology ◽  
Local Effects ◽  
Bending Waves ◽  
Piping Systems ◽  
Asme Code ◽  
Fatigue Evaluation ◽  
Hoop Stresses

This paper addresses the local effects of hydrogen detonations inside piping. It is the first in a two-part series of papers which assess the effects of detonations in piping systems relative to ASME Code allowables. The effects of internal detonations in piping systems are typically separated into two regimes: local effects and system effects. Local effects are often simplistically represented as pure hoop stresses resulting from the pressure acting radially on the inside circumference of the pipe. In reality, the interaction of the pipe wall and the propagating detonation wave is relatively complex, resulting in “waves” or “ripples” in the pipe wall. These areas of local, through-wall curvature lead to substantial axial stresses which may even exceed the hoop stresses. Furthermore, in the elastic regime, there is very little damping present in the pipe wall, leading to numerous stress cycles as the local bending waves move axially along the pipe wall. Fatigue effects of the combined hoop and axial cycling were evaluated using ASME Code Section VIII, Division 2 fatigue evaluation methodology. Analysis of strain gage data from a number of hydrogen detonation experiments in 2-inch and 4-inch Schedule 40 piping showed that the fatigue damage is generally driven by fewer than 10 large-magnitude fatigue cycles, which account for an average of 75% of the total fatigue damage. However, the results also demonstrate that for two detonation events with similar measured peak hoop or axial strain, the number of fatigue allowable events may vary dramatically depending on the shape of the strain response.

Structural Connection Fatigue Evaluation Methodology Using Time Domain Approach

2020 ◽  
Author(s):  
Sagar Samaria ◽  
Bob Zhang ◽  
Sudhakar Tallavajhula ◽  
Johyun Kyoung
Keyword(s):  
Fatigue Life ◽  
Fracture Mechanics ◽  
Fatigue Damage ◽  
Time Domain ◽  
Life Extension ◽  
Stress Range ◽  
Repair Work ◽  
Structural Fatigue ◽  
Structural Connections ◽  
Structural Connection

Abstract There is an ever-increasing demand for life extension of existing floating platforms worldwide. To adequately support these life extension projects there is a need to predict fatigue life of floating structures more accurately using a time domain approach. However, structural fatigue damage calculations using time domain response analysis can be very time consuming and challenging. An efficient and effective structural analysis methodology is developed to calculate accumulated fatigue damage for structural connections in a floating offshore platform using a response-based time domain routine. The methodology discussed in this paper can be applied to estimate fatigue life for hull critical connections in floaters such as Spars, TLPs or Semis as well as local structural supports such as mooring foundations and riser foundations. It also provides the option to generate stress histograms that can be utilized for Fracture Mechanics Evaluation (FME) of welds in structural connections. To calculate the accumulated fatigue damage at desired locations on a floating platform, the time domain analysis employs a Stress Intensification Factor (SIF) which correlates global loads with local stresses. In cases where a crack initiation is observed on a structural connection, fracture mechanics is used to evaluate the structural integrity of the weld. The FME requires fatigue stress range histograms as one of the input parameters. The stress ranges and cycles that are calculated and used to compute the fatigue damage using this methodology can be converted to stress range histograms which can then be used in the FME. The standard method to compute fatigue damage for a structural connection is by using an S-N fatigue approach under the assumption of linear cumulative damage (Palmgren-Miner rule). The methodology discussed in this paper uses a rainflow counting algorithm to effectively calculate the stress range and cycles which are then utilized for computing the fatigue damage. This methodology can be applied to green field projects involving a new design or for life of field studies of an existing platform requiring life extensions. It is particularly beneficial for brownfield projects where more accurate re-evaluation of fatigue life is needed. It can also provide Clients with reliable Engineering Criticality Assessments (ECA) and enable them to plan in-service inspections and repair work. As an application, a typical truss connection for a Spar platform is used to evaluate structural fatigue damage and generate the stress range histogram for FME. Also, a comparative study is performed for a typical truss connection fatigue damage result between the traditional approach used and the method discussed in this paper.

Development of Advanced Fatigue Evaluation Methodology for Monitoring Major Components in Nuclear Power Plant

2010 ◽  
Author(s):  
W. Kim ◽  
Jongjooh Kwon ◽  
Hong Tae Kang ◽  
Gyeong-Hoi Koo ◽  
Tae-Ryong Kim
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Nuclear Power ◽  
Evaluation Methodology ◽  
Coolant Temperature ◽  
Pressurized Water Reactor ◽  
Pressurized Water ◽  
Fatigue Monitoring ◽  
Improve Accuracy ◽  
Fatigue Evaluation

In an attempt to develop fatigue monitoring system, two improved fatigue evaluation schemes have been proposed to monitor fatigue degradation in major components and piping of the pressurized water reactor. Proposed methods are both aimed to obtain realistic fatigue usage factors for given plant transients. Developed schemes utilize plant operating signals such as coolant temperature, pressure and flow rate. Finite element method and an improved Green’s function approach were used to calculate stresses and fatigue usage. Case studies were performed to validate effectiveness of each proposed scheme. It has been confirmed that proposed schemes can effectively reduce excessive conservatism in estimating fatigue usage and improve accuracy in stress calculation.

Symptom Validity Testing

2018 ◽  
Vol 23 (6) ◽  
pp. 14-15
Author(s):  
Lee H. Ensalada
Keyword(s):  
Memory Deficits ◽  
Symptom Validity ◽  
Sensory Cues ◽  
Validity Testing ◽  
Symptom Validity Testing ◽  
Tunnel Vision ◽  
Blurry Vision ◽  
The Common ◽  
Fatigue Evaluation ◽  
Choice Testing

Abstract Symptom validity testing (SVT), also known as forced-choice testing, is a means of assessing the validity of sensory and memory deficits, including tactile anesthesias, paresthesias, blindness, color blindness, tunnel vision, blurry vision, and deafness. The common feature among these symptoms is a claimed inability to perceive or remember a sensory signal. SVT comprises two elements: a specific ability is assessed by presenting a large number of items in a multiple-choice format, and then the examinee's performance is compared to the statistical likelihood of success based on chance alone. These tests usually present two alternatives; thus the probability of simply guessing the correct response (equivalent to having no ability at all) is 50%. Thus, scores significantly below chance performance indicate that the sensory cues must have been perceived, but the examinee chose not to report the correct answer—alternative explanations are not apparent. SVT also has the capacity to demonstrate that the examinee performed below the probabilities of chance. Scoring below a norm can be explained by fatigue, evaluation anxiety, inattention, or limited intelligence. Scoring below the probabilities of chance alone most likely indicates deliberate deceptions and is evidence of malingering because it provides strong evidence that the examinee received the sensory cues and denied the perception. Even so, malingering must be evaluated from the total clinical context.

Impairment Questions and Answers

1999 ◽  
Vol 4 (4) ◽  
pp. 4-4
Keyword(s):  
Symptom Validity ◽  
Validity Testing ◽  
Symptom Validity Testing ◽  
Negative Results ◽  
Tunnel Vision ◽  
Questions And Answers ◽  
Blurry Vision ◽  
Fatigue Evaluation ◽  
Choice Testing ◽  
Rule Out

Abstract Symptom validity testing, also known as forced-choice testing, is a way to assess the validity of sensory and memory deficits, including tactile anesthesias, paresthesias, blindness, color blindness, tunnel vision, blurry vision, and deafness—the common feature of which is a claimed inability to perceive or remember a sensory signal. Symptom validity testing comprises two elements: A specific ability is assessed by presenting a large number of items in a multiple-choice format, and then the examinee's performance is compared with the statistical likelihood of success based on chance alone. Scoring below a norm can be explained in many different ways (eg, fatigue, evaluation anxiety, limited intelligence, and so on), but scoring below the probabilities of chance alone most likely indicates deliberate deception. The positive predictive value of the symptom validity technique likely is quite high because there is no alternative explanation to deliberate distortion when performance is below the probability of chance. The sensitivity of this technique is not likely to be good because, as with a thermometer, positive findings indicate that a problem is present, but negative results do not rule out a problem. Although a compelling conclusion is that the examinee who scores below probabilities is deliberately motivated to perform poorly, malingering must be concluded from the total clinical context.

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