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Ptujska, Slovenia

Zorc B.,Welding Institute Ltd | Zorc B.,University of Ljubljana | Nagode A.,University of Ljubljana
Engineering Failure Analysis | Year: 2015

Fatigue cracks were found in water-filter housings made of styrene-acrylonitrile. These cracks initiated on the external surface, along the sharp corner between the wall of the housing and the vertical external ribs or at a pre-existing crack in the base of the water-filter housing. The reason for the crack was the high stress concentration due to an inappropriate design or the poor quality of the filter housing in combination with water-pressure impacts during the operation of an electromagnetic water valve and taps. © 2015 Elsevier Inc.

Zorc B.,Welding Institute Ltd | Zorc B.,University of Ljubljana | Nagode A.,University of Ljubljana | Kosec B.,University of Ljubljana | Kosec L.,University of Ljubljana
Engineering Failure Analysis | Year: 2013

In fillet welds made of 18Cr-9Ni-7Mn austenitic stainless steel centerline cracks were established along the connection line of two solidification fronts in the weld. On the grain boundaries oxide and carbide films were identified. Hot cracks resulted from a combined activity of a large gap between plates and the resulting high tensile stresses occurring during cooling, free root surface of the weld in the large gap, and intergranular oxide and carbide films in the weld. Since the parent metal was cut with highly oxidating plasma and atmospherically corroded surfaces was not ground prior to welding, remelted surface oxides passed into the weld pool. The increased Cr content identified in intergranular oxide films results from Cr oxidation in the filler material. © 2013 Elsevier Ltd.

Wei Z.,Tenneco | Maleki S.,Welding Institute Ltd | Nikbin K.,Imperial College London
Journal of Pressure Vessel Technology, Transactions of the ASME | Year: 2014

A recently developed equilibrium based curve/surface fitting method is extended to linear function with heteroscedastic data (variable variance). The concept of equilibrium weighted "force" and "moment" is proposed to derive curve fitting formulae, which are exactly the same as that obtained with the traditional weighted least squares (LS) method for a linear function. Furthermore, a system of four equations, i.e., a "force" equilibrium equation, a "moment" equilibrium equation, an "equivalency" equation, and a "moment balance" equation have been established to solve both mean curve and the standard deviation simultaneously. Finally, the application of these methods to data of fatigue and creep lives is presented. Copyright © 2014 by ASME.

Zorc B.,Welding Institute Ltd | Zorc B.,University of Ljubljana | Bernetic J.,Acroni d.o.o. | Nagode A.,University of Ljubljana
Engineering Failure Analysis | Year: 2014

Due to residual tensile stresses acting through the material's thickness a cleavage fracture occurred in the central part of a thick steel plate during the cooling of a welded T-joint. Steel in the normalized rolled state, without non-metallic inclusions and with a very good contraction in the ". Z" axis, is brittle because of its banded, ferrite-pearlite microstructure, which is dependent on phosphorus segregation. A normalizing heat treatment greatly improved the toughness of the central part of the thick plate and prevented its cracking during the cooling of the welded T-joint. © 2014.

Zorc B.,Welding Institute Ltd | Zorc B.,University of Ljubljana | Imamovic M.,University of Zenica | Kosec L.,University of Ljubljana | And 2 more authors.
Materiali in Tehnologije | Year: 2014

A thick-walled casting of unalloyed cast steel with a high content of non-metallic inclusions was built up with the submerged arc-welding (SAW) process. Hot cracks were detected in the built-up, tough inner layer of unalloyed steel (near the fusion line alongside the edge of the prepared groove). The cause for it was an inappropriate "bead-to-bead" technique of building up, with a strong remelting of the base material and a strong contamination of the weld pool with non-metallic inclusions. The chemical composition of the inclusions also indicated an insufficient attention or technical difficulties during building, since some inclusions were based on the welding slag. The smallest possible content of the base-material admixture must be ensured, the welding slag fully removed and, if needed, before welding the next bead, the narrow and deep interpass groove must be widened and rounded off by grinding.

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