EFFECT ANALYSIS OF AN ARC-STRIKE-INDUCED DEFECT ON THE FAILURE OF A POST-TENSIONED THREADBAR

A new article available online 10 November 2015 in « Case Studies in Engineering Failure Analysis ».

A temporary threadbar used for precast segmental construction broke during the post-tensioning stage before reaching the service load. Failure analysis showed that the premature failure of the bar was due to the presence of an arc strike. The arc strike effects on the material and threadbar integrity are studied. Read more….

 

Corrosion of Welded Joint in Alloy Steel Pipe

2015-11-15_10h33_54An interesting article published on 4 November 2015 in the International Journal of ELECTROCHEMICAL SCIENCE.

In this paper an investigation on corrosion behaviour of welded joints was performed to facilitate determination the causes of preferential degradation by corrosion of the welded metal (WM) and the heat affected zone (HAZ), in a welded pipeline of grade ASTM A355P5, used in a petrochemical plant as transfer line between a thermal cracking heater and a column which are part of an atmospheric distillation and vacuum (DAV) unit. It was found that the corrosion of the weld analyzed in this research has resulted due to its dendritic structure (pearlite, ferrite, complex carbide, bainite and martensite in localized areas), which reveals the lack of post welding heat treatment (PWHT). Read more …..

 

Essais et caractérisation des accessoires et équipements sous pression

Gaz-Liquefie-Industrie_Img_DetailReferenceCertains produits doivent être mis à rude épreuve avant d’obtenir leur mise sur le marché. Les réservoirs de gaz sont de ceux-là. Et rares sont les infrastructures capables de les brutaliser. Exemple de l’expérience de Gaz Liquéfié Industrie (GLI), menée avec le Cetim. Une équipe d’experts ESP (équipements sous pression) connaissant le métier !

Pour en savoir plus, lire le document.

Les compétences du Cetim s’expriment à travers sa capacité à maîtriser l’ensemble des technologies mécaniques. Les cas qui sont présentées ici exposent des exemples de réalisations menées pour ses clients tant à titre collectif qu’à titre individuel. Elles témoignent de la capacité du Cetim à proposer une offre globale et personnalisée de prestations autant pour les grands donneurs d’ordre que pour les petites entreprises.

Évaluer l’intégrité et la réparabilité

Stir_Img_DetailReference

La Société tunisienne des industries du raffinage (Stir) possède, entre autres, une sphère de stockage de 4000 m3 qui a présenté des défauts diamétralement opposés au niveau d’une soudure circonférentielle basse. La Stir a souhaité évaluer l’intégrité et la réparabilité de l’équipement et se prononcer sur sa requalification périodique. Le Cetim est intervenu à la demande du Centre technique des industries mécaniques et électriques de Tunisie (Cetime) afin d’effectuer un diagnostic global sur trois sphères de gaz. Un partenariat exemplaire !

Pour en savoir plus, lire le document.

Les compétences du Cetim s’expriment à travers sa capacité à maîtriser l’ensemble des technologies mécaniques. Les cas qui sont présentées ici exposent des exemples de réalisations menées pour ses clients tant à titre collectif qu’à titre individuel. Elles témoignent de la capacité du Cetim à proposer une offre globale et personnalisée de prestations autant pour les grands donneurs d’ordre que pour les petites entreprises.

Mechanics of Collapse of WTC Towers

A telechargementpaper published in september 2016 on www.civil.northwestern.edu .

Abstract : The previously formulated model of the gravity-driven collapse of the twin towers of the World Trade Center on 9/11/2001 was shown to match all the existing observations, including the video record of the crush-down motion of the top part of tower during the first few seconds, the seismically recorded duration of collapse, the size distribution of particles caused by impact comminution of concrete floor slabs, the loud booms due to near-sonic lateral ejection velocity of air and dust, and precedence of the crush-down collapse mode before the crush-up. Nevertheless, di↵erent degrees of ductility, fracturing and end support flexibility of WTC columns could lead to an equally good match of these observations and remained uncertain, due to lack of test data. Recently, Korol and Sivakumaran reported valuable experiments that allow clarifying this uncertainty. They reveal that, under the assumptions of rigid end supports and unlimited ductility (or no fracturing), the energy dissipation in the WTC columns would have been at maximum 3.5-times as large as that calculated by the plastic hinge mechanism normally considered for small deflection buckling. This increase would still allow close match of all the aforementioned observations except for the first two seconds of the video. The proper conclusion from Korol and Sivakumaran’s tests, based on close matching of the video record, is that the fracturing of columns and the flexibility of end restraints must have significantly reduced the energy dissipation in columns calculated under the assumptions of no fracture and no end restraint flexibility.

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Undercutting Formation Mechanism in Gas Metal Arc Welding

2016-06-04_07h59_57A vision­based sensing system was improved to acquire 2D images of weld pool shape and tracer particle movement simultaneously. …..

Based on analysis of tracer particle movement, roles of different associated forces, such as gravity, arc drag force, Maragoni force, magnetic force, droplet impact, and viscous force, were investigated. The results show that liquid metal under the arc decreases to a thin liquid layer if the welding speed is more than 1.0 m/min. This phenomenon makes viscous resistance increase in the thin liquid layer, which impedes transverse spreading of liquid metal. Thus, it is difficult for the weld toe to be filled by molten metal. Meanwhile, experiments revealed the amount of forward molten metal can be ignored in the front and middle of the weld pool. Therefore, it is difficult for the weld toe to be filled by the backward molten metal. As a result, undercutting defects appear during high­speed welding……..

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