International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

Pelton mini hydro-turbine, more concretely its turbine circle buckets was completely damaged during explotation conditions i.e. working time of about two years and half. Because turbine was ensured in ensured company, representatives of the company engaged court expert prof Cvetkovski to perform investigations (analysis) and to determine the reasons for these accidents. Normally working time of the Pelton turbine is about ten years, but there is examples that it can work even twenty years if construction and maintains of turbine was properly done. Therefore, the purpose of the conducted expert examination is to analyze the causes, effects and potential solutions for the damaged Pelton turbine. This report covers the technical aspects, the mechanisms that contribute to the appearance of defects, that is, damage of the buckets of the Pelton turbine. In order to find the reason of failure of the turbine buckets, as first complete visual inspection of the turbine wheel was performed. As additional investigation was performed chemical analysis of the buckets, measuring of its hardness and metallographic investigation (determination of type and quantity of non-metallic inclusion and microstructure).

The main reason to perform this research investigation was to find a reason for appearing failures in exploratory condition of a part holder of breaking shoe beam. This part is incorporated in an assembly in railway wagon. This part together with few others was damaged in exploratory condition. It means that cracks were noticed on these parts. Some parts were completely broken. Because of that purchaser of parts complained of received parts to the producer. One of these parts was delivered to Prof Cvetkovski to find a reason and to give opinion about the reason for failure. The damaged parts are made of cast steel SG60/SE300. Many types of investigation was performed in order to solve this problem. As first visual control was done. After that, radiographic control was made. Investigations continued with determination of chemical composition and macro and micro metallography and determination of non-metallic inclusions. Finally mechanical testing like tensile testing, hardness measurement and impact toughness were performed too. Performed research confirmed that typical casting defects in the investigated part like the hot tears, slag inclusions, shrinkage porosity and segregation are the main reasons for failure of the delivered parts, holder of breaking shoes i.e. appearing of cracks or their completely fracture.

Steel wire rope was breaked in exploratory conditions i.e. during hoisting the load. The requirement of the purchaser of the investigations was to find a reason which caused breaking the steel rope. In other words to check fitness for purpose of the used steel wire rope. Because of that all necessary investigations to solve this problem were performed. As first, quality of delivered rope was checked. More concretely it was checked chemical composition of the base material (steel strands and wires). Besides, quality of the base material i.e. presence of non-metallic inclusions, microstructure, segregation and decarburation of the rope wires was done. This investigation showed that base material is high carbon steel. Its quality fulfill necessary requirement. Therefore, the next step was to make failure analysis of the rope after long period of exploitation. These investigations contain visual inspection of the rope, metallographic investigations, fractographic analysis and tensile test.
Visual inspection was performed according ISO 4309 and ASME B30.30. Standards [1-3]. This inspection was performed to all segments of the rope. To perform visual inspection segments were unwinded and separately tested. It was found that the most serious damaging was detected near the breaking point of the rope.
Performed investigations clear confirmed that wear of the rope is the most often detected type of failure. Besides corrosion of the rope was detected at many locations too. Metallographic investigation detected the wear damage too. Scaning electron microscope (SEM) confirmed that shear and fatigue are the most often found types of fracture in the rope wires.
It was concluded from the investigation to too that lubrication of the rope is different at different locations. It means that at some position there is no lubrication.
It is obvious that defects (failures) which caused breaking of the rope appeared in the rope during exploitation.
Metallographic investigations of the wires and visual control of the ropes segments and strands confirmed that all defects in the ropes are results of improper installation, manipulation and handling of the rope.
Nominal value of the load, which can be hoisted by steel rope, became lower during exploitation. More concretely remained load, which can be hoisted, is in relationship 5:1 with nominal load [4-6]. So if higher load was hoisted, the rope will be breaked as it happened in our case.