The problems of estimating a fatigue service life with a low probability of failure

1976 ◽  
Vol 8 (1) ◽  
pp. 205-215 ◽  
Author(s):  
Sam C. Saunders
Keyword(s):  
Service Life ◽  
Probability Of Failure ◽  
Low Probability

Change of Steel’s Yield Stress Over Ship’s Service Life and its Effect on the First Yield Hull Girder Bending Moment - Technical Note

2013 ◽  
Vol 155 (A3) ◽  
Keyword(s):  
Service Life ◽  
Tensile Stress ◽  
Laboratory Test ◽  
Yield Stress ◽  
Bending Moment ◽  
Probability Of Failure ◽  
Technical Note ◽  
Bulk Carrier ◽  
Shipbuilding Steel ◽  
Hull Girder

The publication deals with the decrease of the yield and tensile stress of high tensile shipbuilding steel AH-32 over ship's service life and its effect on the first yield bending moment as a representative of the hull girder capacity. An example is given for a sample 25K DWT (25 thousand tons deadweight) bulk carrier. The probability of failure is calculated as the probability of the total hull girder bending moment exceeding the first yield bending moment. The probabilistic distributions of yield and tensile stress are obtained from laboratory test of the specimen of AH-32 steel (corroded plates of a 20 year old ship). It is found that although the decrease of yield stress may not be great, the increase of the probability of failure (i.e., the probability that the total hull girder bending moment will exceed the first yield bending moment) could be substantial.

Probabilistic Methods: Risk Based Design and Assessment

2019 ◽  
Author(s):  
H. Cathcart ◽  
G. Horne ◽  
J. Parkinson ◽  
A. Moffat ◽  
M. Joyce
Keyword(s):  
Monte Carlo ◽  
Damage Assessment ◽  
Structural Integrity ◽  
Probability Of Failure ◽  
Probabilistic Methods ◽  
Safety Factors ◽  
System Safety ◽  
Creep Fatigue ◽  
Low Probability ◽  
Integrity Assessments

Abstract Structural integrity assessments typically aim to calculate the integrity of a component under nominal or best estimate conditions. To account for potential variability and uncertainty present in the system, safety factors are often applied to assessment inputs and outputs. This approach does not allow the level of conservatism present to be quantified, often leading to over-conservatism or inadvertent non-conservatism. Probabilistic assessments explicitly calculate the probability of failure based on distributions of the input parameters and hence quantify the margin present in the assessment, leading to a greater understanding of the system. In this study a creep-fatigue damage assessment of a transiently loaded piping component is used as a vehicle to investigate some of the challenges and benefits of probabilistic assessments. A probabilistic assessment of the component life is compared to a lower-bound deterministic calculation to identify the mismatch in margin between the two results. The potential inaccuracies introduced when reducing the computational burden of Monte Carlo simulations with response surface methodologies are explored and tested. Finally, two challenges when attempting to underwrite a very low probability of failure are tackled: the inference of the shape of a distribution’s tails from limited experimental data and the uncertainty of extreme percentiles of finite Monte Carlo samples.

Benchmarking Probabilistic Code for LBB Analysis for Circumferential Cracks

2017 ◽  
Author(s):  
Robert E. Kurth ◽  
Cédric J. Sallaberry ◽  
Bruce A. Young ◽  
Paul Scott ◽  
Frederick W. Brust ◽  
...  
Keyword(s):  
Probability Of Failure ◽  
Primary System ◽  
Degradation Mechanisms ◽  
Detection Systems ◽  
System Pressure ◽  
Piping Systems ◽  
Primary Water ◽  
Low Probability ◽  
Assessment Procedures ◽  
Leak Before Break

NRC Standard Review Plan (SRP) 3.6.3 describes Leak-Before-Break (LBB) assessment procedures that can be used to assess compliance with the 10CFR50 Appendix A, GDC-4 requirement that primary system pressure piping exhibit an extremely low probability of rupture. SRP 3.6.3 does not allow for assessment of piping systems with active degradation mechanisms, such as Primary Water Stress Corrosion Cracking (PWSCC) which is currently occurring in systems that have been granted LBB approvals. There are several codes available for addressing the requirements of GDC-4. This paper addresses three of these codes: (1) xLPR 2.0; (2) PROLOCA; and (3) PROMETHEUS. Each of these codes is described and applied to a representative plant where active degradation mechanisms have been found. Conclusions about the design, results, and interpretation of the results is then provided. In all cases the probability of failure of the pipe is found to be extremely low when the crack inspections and leak detection systems are modeled.

scholarly journals A Probabilistic Fatigue Assessment Diagram To Get A Guaranteed Lifetime With A Low Probability Of Failure

2016 ◽  
Vol 2 ◽  
pp. 2447-2455 ◽  
Author(s):  
S. Jallouf ◽  
G. Pluvinage ◽  
K. Casavola ◽  
C. Pappalettere
Keyword(s):  
Probability Of Failure ◽  
Fatigue Assessment ◽  
Low Probability

scholarly journals Assessment of the strength reliability of high-temperature heat exchangers with long service life at the design stage

2020 ◽  
Vol 15 (55) ◽  
pp. 136-144
Author(s):  
Vyacheslav Popov ◽  
V.V. Kashelkin ◽  
A.S. Demidov
Keyword(s):  
High Temperature ◽  
Service Life ◽  
Heat Exchangers ◽  
Statistical Data ◽  
Operating Time ◽  
Element Model ◽  
Probability Of Failure ◽  
Design Stage ◽  
Coefficients Of Variation ◽  
Temperature Heat

The article describes a method for assessing the strength reliability of high-temperature heat exchangers with service life of several tens of thousands of hours at the design stage, when there is not enough statistical data on the operating time of elements and material properties. The method shows, how to determine the missing coefficients of variation for calculating reliability and build the function of the probability of failure-free operation, considering the change of the properties of the structural material over time. The method of visualizing the distribution of zones, both satisfying and not satisfying reliability criteria at the nodes of any finite element model, is also described.

How to determine the remaining life of machine parts

2020 ◽  
pp. 50-57
Author(s):  
Vyacheslav I. Chernoivanov ◽  
Vyacheslav A. Denisov ◽  
Aleksey A. Solomashkin
Keyword(s):  
Service Life ◽  
Residual Life ◽  
Interval Estimation ◽  
Probability Of Failure ◽  
Technical Condition ◽  
Research Purpose ◽  
Interval Estimate ◽  
Remaining Life ◽  
Maintenance And Repair ◽  
Machine Parts

The article presents three strategies for maintenance and repair of machines that control the pre-selected and justified parameters of the technical condition of the machine, as well as the costs of eliminating failures for these strategies and the possibility of reducing them. (Research purpose) The research purpose is to identify the most effective way to determine the residual life of machine parts. (Materials and methods) The article proposes a strategy for maintenance and repair of machines, in which a special place is occupied by ways of reducing the mechanical friction losses, increasing the efficiency of the machine and the service life of its parts. The article notes that in order to meet the service life, it is necessary to monitor their remaining life visually or using appropriate sensors. In order to determine the remaining resource in more accurately way, we suggested that it would be measured several times, preferably using different methods or devices. Authors designed a computer program that allows to estimate the remaining resource using an interval estimation of random values for a given probability of failure-free operation of the machine part. The plunger pairs of a high-pressure fuel pump were chosen as the object of research. As a diagnostic parameter that characterizes the technical condition of the pump, its starting cycle feed was used, the value of which was determined on different stands. (Results and discussion) Article presents the values of the average resources of the plunger pairs, their dispersion around the corresponding average values, and calculated their average residual resource as an interval estimate for a given probability of failure-free operation. (Conclusions) The research results have shown a possibility of using the residual resource as the basis of the proposed strategy for maintenance and repair of machines based on minimizing the residual resource of their parts. The most important unsolved task for this strategy remains the selection and justification of primary diagnostic sensors for assessing the residual life of machine parts.

CHANGE OF STEEL’S YIELD STRESS OVER SHIP’S SERVICE LIFE AND ITS EFFECT ON THE FIRST YIELD HULL GIRDER BENDING MOMENT

2021 ◽  
Vol 155 (A3) ◽  
Author(s):  
Lyuben D Ivanov
Keyword(s):  
Service Life ◽  
Tensile Stress ◽  
Laboratory Test ◽  
Yield Stress ◽  
Bending Moment ◽  
Probability Of Failure ◽  
Bulk Carrier ◽  
Shipbuilding Steel ◽  
Hull Girder

The publication deals with the decrease of the yield and tensile stress of high tensile shipbuilding steel AH-32 over ship’s service life and its effect on the first yield bending moment as a representative of the hull girder capacity. An example is given for a sample 25K DWT (25 thousand tons deadweight) bulk carrier. The probability of failure is calculated as the probability of the total hull girder bending moment exceeding the first yield bending moment. The probabilistic distributions of yield and tensile stress are obtained from laboratory test of the specimen of AH-32 steel (corroded plates of a 20 year old ship). It is found that although the decrease of yield stress may not be great, the increase of the probability of failure (i.e., the probability yield bending moment) could be substantial.

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