Archives pour la catégorie Publications

Les emboutis profonds ne sont pas si fragiles

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&Emboutis profondsDès 1988, le CETIM s’est attaché à définir les limites de déformation pour lesquelles une pièce emboutie à froid ne présente aucun risque de fragilité et peut donc être exemptée de traitement thermique. L’article paru en avril 1989 dans le numéro 110 de la revue CETIM-Informations vient d’être mis en ligne dans la Mecatech.

Lire l’article : Vintage – Les emboutis profonds ne sont pas si fragiles

Fracture analysis of wind turbine main shaft

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Read on Engineering Failure Analysis. Shaft fracture at an early stage of operation is a common problem for a certain type of wind turbine. To determine the cause of shaft failure a series of experimental tests were conducted to evaluate the chemical composition and mechanical properties. The results show that stress concentration on the shaft surface close to the critical section of the shaft due to rubbing of the annular ring and coupled with high stress concentration caused by the change of inner diameter of the main shaft are the main reasons that result in fracture of the main shaft. The contribution of this paper is to provide a reference in fracture analysis of similar main shaft of wind turbines.

Leak-before-break for piping systems of fast breeder reactor

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The Leak-Before-Break (LBB) concept has an effect on the safety design of Fast Breeder Reactors (FBRs), and thus its assessment has been one of the most significant issues. In the case of a commercial-scale FBR, since the main loads are the thermal expansion and thermal transient stresses, ferrite steel with a low thermal expansion rate has been a candidate material. A conventional LBB assessment method is insufficient to consider these characteristics, thus an advanced method is required.

  • The LBB assessment to ferrite pipes with thin walls and large diameters is proposed.
  • The surface resistance correction factor was improved for low-pressure.
  • The R6 method was applied to an unstable fracture assessment for postulated cracks.
  • A buckling assessment was introduced for the critical crack length for elbows.

More information on http://www.sciencedirect.com

Service fatigue cracking in an aircraft bulkhead exposed to a corrosive environment

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This paper presents a supporting case study that examines fatigue cracks that were detected in an F/A-18 Hornet bulkhead during post-service testing and teardown. The in-service phase of the cracking had significant evidence of oxidation on their surfaces which indicated an exposure to a mildly corrosive environment. Both the service and laboratory phases of the cracking were the subject of quantitative fractography and estimates of the crack growth rates were made. A comparison of the in-service and the in-test phases of crack growth indicated that no notable effect on the service part of the fatigue crack could be attributed to its exposure to the service environment.

Read the article on http://www.sciencedirect.com

Stress corrosion and hydrogen induced cracking of a control valve body

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The control valve body failed due to combination of SSC and HIC cracking in wet H2S environment. According to HIC and SSC laboratory tests the best alternative for the valve body alloy is A217-WC9 steel.Anodic polarization curves clearly shows a considerable improvement in pitting resistance.

More information on http://www.sciencedirect.com

Corrosion properties of AISI 321 stainless steel

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The main aim of this study was to analyze the pitting corrosion and stress corrosion cracking which is initiated on prototype cold-formed outer exhaust sleeves during the testing of different cleaning procedures before chromium plating. Various microscopic methods were used to identify the initiation of corrosion and its propagation.

  • Severe corrosion occurred in the cleaning solution containing H2SO4 at elevated temperature.
  • Pitting corrosion has formed on the titanium nitride inclusions.
  • Stress corrosion cracking was caused by deformation martensite.

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Erosion of heat exchangers due to sootblowing

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The erosion rate of convection surfaces is crucial for boiler reliability. This paper presents the impact of the action of a sootblowing stream (steam and air) jet on the sustainability of tubes. The model investigations described here compared the erosion rates of a tube bank while turning on or off an additional jet stream of compressed air that simulates the operation of a sootblower. This paper presents calculations for the erosion loss of a heat exchanger built in the actual object.

Failure analysis of solenoid valve components

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Valve had failed as a result of particles of material becoming trapped between the valve seat recess and the valve seat ball, leading to erosion of the valve seat recess, valve seat ball and the valve operating pin; this allowed hydraulic fluid to flow when the valve was nominally in the de-energised position.The material of construction of the valve seats was not compliant with engineering drawings.The investigation demonstrated the importance of maintaining the cleanliness of hydraulic systems and of the need to control the materials of manufacture in safety critical applications.

Read more at : Failure analysis of solenoid valve components from a hydraulic roof support.

Rupture d’un tuyau d’égout sous pression en PVC

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Le document décrit l’analyse de défaillance d’un tuyau d’égout en polychlorure de vinyle non plastifié (PVC-U) de diamètre nominal 200 mm, classe de pression 12, qui s’est rompu prématurément après 34 ans de service. L’étude devait permettre de savoir si la défaillance était due à un défaut de fabrication ou bien à une dégradation des propriétés du PVC sous l’effet de l’environnement agressif.

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Publication – Analyse des modes de défaillance : application aux équipements sous pression

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logo CetimUn article publié par le Cetim, présente différentes méthodologies innovantes, telles que la compensation élastique (ECM, LMM), l’analyse par diminution de la limite d’élasticité suivant le concept de Gockfeld (UMY, LDYM), ou encore l’analyse cyclique directe (DCA). Pour différents modes de ruine étudiés, un Benchmark est réalisé et permet de vérifier les performances de ces méthodologies en termes de précision et de temps de calcul, par rapport aux techniques codifiées. Un bilan final met en évidence les gains potentiellement atteignables en matière de qualité et de précision d’analyse.

Plus d’information : Analyse des modes de défaillance – Cetim – Centre technique des industries mécaniques.