PROBABILISTIC FATIGUE INITIATION ASSESSMENT DIAGRAM PIPE STEEL X52 : INFLUENCE OF HYDROGEN

International audienceA probabilistic fatigue Assessment Diagram (fAD) is proposed as a tool to guarantee a prescribed number of applied fatigue cycles with a conventional low probability of failure. The fatigue failure assessment curve is given by a power law described by two parameters: the fatigue initiation resistance and the fatigue initiation exponent. From the targeted applied stress range, it is possible to find the probability of failure and its associated safety factor. An example of fatigue life duration of a pipe steel submitted to hydrogen embrittlement is given. Keywords: probabilistic fatigue failure assessment diagram, pipe steel Nomenclature b Basquin's exponent safety factor f r fatigue parameter partial safety factor for the number of cycles CV Coefficient of variation cath I cathodic polarisation current P r loading parameter N r the number of applied cycles to failure N u maximum number of cycles for the LCF domain N* number of applied cycles associated to a design probability of failure P failure probability P* probability of failure associated with assessment point total quantity of hydrogen N D the number of cycles for the endurance limit X parameter fatigue exponent stress range mean standard deviation ' i fatigue initiation resistance y Yield stress coefficient of Basquin's law ul Ultimate strength ev H

A probabilistic fatigue assessment diagram to get a guaranteed lifetime with a low probability of failure

In order to guarantee a fatigue lifetime with a conventional and low probability of failure, a probabilistic fatigue assessment diagram is proposed as a tool. The safe domain is limited by the fatigue failure assessment curve, which depends on material properties through Basquin's exponent, the endurance limit and low cycle fatigue domain. From the double-truncated distribution of the targeted maximum applied stress, it is possible to find the probability of failure and its associated safety factor. An example of an aeronautical component made of TA6V titanium alloy welded by laser and exhibiting an undercut at the weld toe is given

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

AbstractIn order to guarantee a fatigue lifetime with a conventional and low probability of failure, a probabilistic fatigue assessment diagram is proposed as a tool. The safe domain is limited by the fatigue failure assessment curve, which depends on material properties through Basquin's exponent, endurance limit and low cycle fatigue domain. From the double-truncated distribution of the targeted maximum applied stress, it is possible to find the failure probability and its associated safety factor. An example of an aeronautical component made of TA6V titanium alloy welded by laser and exhibiting an undercut at the weld toe is given

Određivanje stepena sigurnosti i faktora pouzdanosti kotlovskih cevi sa površinskom prslinom

In this paper SINTAP Level 1 procedure has been used to determine the safety factor and the reliability factor for a boiler tube exhibiting a longitudinal defect inside the tube weld. These factors are obtained using probabilistic FORM/SORM methods. The influence of temperature on the safety and reliability of factors is discussed.U radu je korišćen postupak SINTAP nivo 1 za određivanje stepena sigurnosti i faktora pouzdanosti na cevima parnog kotla kod kojih je otkrivena uzdužna prslina u zavarenom spoju. Ovi stepeni su dobijeni pomoću metode verovatnoće SORM/FORM. Razmatra se i uticaj temperature na stepen sigurnosti i faktor pouzdanost

A Probabilistic Safety Factor for Defect Assessment of Water Pipes Subjected to Water Hammer

The aim of this paper is to determine the probabilistic safety factors for water pipes exhibiting surface defects such as gouges. The pipes are located in a water network that consists of a pump, a reservoir, and five pipe sections. Three different materials usually used for water pipes have been studied: cast iron, pipe steel, and polyvinyl chloride (PVC). The water pipes are subjected to the water hammer phenomenon, which is considered to be the loading condition. The overpressure due to water hammer is calculated for each pipe connection with a software program. The circumferential stress induced by the overpressure is then evaluated. Probabilistic safety factors associated with low failure probability are determined using a notch failure assessment diagram (NFAD). Fracture toughness, yield stress, and gouge depth are assumed to be randomly distributed to allow the determination of safety factors by Monte Carlo and FORM/SORM methods. A comparison of pipe material behaviour is then made by means of probabilistic safety factors. For the studied water network it is shown that the probabilistic safety factor is acceptable for steel and cast iron pipes but not acceptable for PVC pipes because its value is lower than 2. </jats:p