Ljubljana, Slovenia
Ljubljana, Slovenia

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Suban M.,Institute of Metal Constructions | Bozic S.,Institute of Metal Constructions | Zajec A.,Institute of Metal Constructions | Cvelbar R.,Institute of Metal Constructions | Bundara B.,Institute of Metal Constructions
Nuclear Engineering and Design | Year: 2012

For protection of steel pipes that are exposed to corrosion, cathodic protection is commonly used. Joint between steel surface and copper conductor is done by thermite welding. During the welding process and due to the nature of it, steel surface in the solid state comes in contact with liquid copper. Contact of steel with liquid metal (copper, zinc) in some cases cause phenomenon known as the liquid-metal embrittlement or LME. Phenomenon was previously studied in cases such as soldering or hot-dip galvanizing but for thermite welding no records were found in accessible literature. The purpose of this paper is to draw attention to some irregularities and consequences arising from it, which in this type of welding can occur. At the end of article some measures to reduce these risks are given. © 2011 Elsevier B.V. All rights reserved.

Suban M.,Institute of Metal Constructions | Cvelbar R.,Institute of Metal Constructions | Bundara B.,Institute of Metal Constructions
Materiali in Tehnologije | Year: 2012

This paper presents a methodology to detect plastic deformation at the micro level. The analysis is based on the statistical data describing the morphological and crystallographic textures of a sample microstructure. This data was obtained from optical microscopy using a digital imaging analysis. The important parameters necessary to describe the microstructure were identified as the grain-size and grain-orientation distributions. A change in the weighted product of these two parameters, the grain size as the area of grains and the grain orientation as the moment of inertia of grains, can represent a measure to identify plastic deformation on a small area. A demonstration of its applicability was performed on a real object as part of a ruptured-pipe-failure analysis in a thermal-power-plant boiler. The presented analysis leads to a fast identification of the local plastic deformation and, in the case of periodical analysis of the same sample, it can even be used as a measure to identify creeping.

Suban M.,Institute of metal constructions | Cvelbar R.,Institute of metal constructions | Bundara B.,Institute of metal constructions
Materiali in Tehnologije | Year: 2010

The occurrence of stagnant water is often the result of the incomplete or improper hydrotesting procedure of pipelines (e.g., the water installation in buildings) or improper design and construction of a pipeline with blind ends. The influence of stagnant water can also be observed in sprinkler fire-protection systems. Potable water, which is not additionally chemically treated, is commonly used for the hydrotest or as a medium in fire-protection systems. Water, therefore, contains bacteria that cause microbiologically influenced corrosion. This relatively unusual form of corrosion results from the interactions of bacteria with various metals and their alloys and can increase the corrosion rate up to 100-times above that in conventional types of corrosion. The article describes in detail the causes for the formation and progress of microbiologically influenced corrosion and its consequences for the case of galvanized water pipes. Some recommendations for a reduction of the risk concerning the microbiologically influenced corrosion in water pipes are stated in the conclusion.

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