Analysis of the corossion condition of the steel pipe system after long period of exploatation

    Machines. Technologies. Materials., Vol. 13 (2019), Issue 10, pg(s) 433-436

    In this this research work, the results of investigation corrosion condition of the steel pipe system for the heated water transportation and distribution after long years of exploitation are presented. The analysis was performed on the pipe segments after their removing i.e. cutting. Thirty segments were taken for inspection. The outer and inner surface of the pipes was inspected. Plan for inspection was prepared basing of the literature revue and personal experience. All specimens were visually inspected. For the investigations of pitting corrosion measuring of depth of pits was done. Performed investigations confirmed that general corrosion, uniform and no uniform is represented on the pipe from the outer side. From the inner side are presented different types of pitting: narrow, shallow, and elliptical and corrosion under layer. Performed investigation confirmed that the most dangerous for the piping systems is corrosion on the outer sides of the pipes which their perforation. Measurement of the pits deepness showed that pitting corrosion is not so danger because pits deepness is in the range between 0.18-1.24 mm which is negligible compared with the pipes wall thickness.

  • Ion plasma nitriding of ferritic steel AISI 430 f

    Materials Science. Non-Equilibrium Phase Transformations., Vol. 4 (2018), Issue 4, pg(s) 138-141

    In this research work, results of the ion plasma nitriding of the ferritic steel AISI 430F are presented . From the raw material solid bar ф35 were machined specimens with the following dimension 20x20x15. Prepared specimens were plasma nitrided in the installation ION-20. According to research plan the temperatures of 430, 480 and 530 0C, and nitriding times of 3, 6 and 9 hours were used. Nitriding gas for this experiment was ammonia Pulsed direct current was used for the nitriding.
    After performing of the ion plasma nitriding process, experimental specimens were subjected to different investigations, mainly microstructural and tribological. Main facilities used for investigations are: device for determination wear resistance “ball-on-disc” (Nanovea), 3D profilometer for surface roughness determination, Optical Microscope Leits and SEM JEOL for microstructural investigations, XRD spectrometer (Rigaku RINT Ultima+) and Vickers microhardness tester for the microhardness measurement. Investigations confirmed that depending of the process parameters different characteristics of nitride layers were obtained. The following characteristic values important for the analysis of the nitride layer was obtained: specific wear rate, volume lost, friction coefficient, width of the wear path, type of wear, type of structure of the nitride layer and maximal hardness of the nitride layer. Performed investigations confirmed that ion plasma nirtriding improve surface properties of the investigate specimens compered with untreated specimen of the raw material. The effect of ion plasma nitriding is directly influenced by the nitriding parameters i.e. temperature and time of the nitriding process.



    Machines. Technologies. Materials., Vol. 12 (2018), Issue 3, pg(s) 136-138

    This practical research work is devoted to the adaptation of technology for ion plasma nitriding of mechanical parts (pins and gears). Formerly these parts were inductive hardened, and requirement of the purchaser was to replace inductive hardening technology with the chemical-heat treatment i.e. ion plasma nit riding.

    Procedure for ion plasma nitriding of pin hammers and gears made of 4M2CrMo4 steel was described. Starting from the heat treatment of the parts, their cleaning and charging of the parts in the chamber. Description of the chamber and complete installation for nitride in is described. Experimental nitriding parameters are given too. Finally, accuracy of obtained results was checked using hardness measured of nitrided parts. Hardness values were in accordance with purchaser requirement.



    Machines. Technologies. Materials., Vol. 11 (2017), Issue 9, pg(s) 470-472

    In this research work were analyzed the reasons for fracture of pin machined from 42CrMo44 steel. One pine build in TBU (Tread Brake Unit) of railway wagon breaking system was broken in exploratory condition. Reclamation from purchaser was sent to the producer concerning occurred fracture of pin. Producer sent request to the team of the Faculty of Technology and Metallurgy to perform investigations and to determine the reason of fracture (failure analysis). It was decided to perform the following investigations: visual inspection, determination of chemical composition, hardness measurement, metallographic investigations which include analysis of microstructure and quantitate determination of nonmetallic inclusions. For comparison of results, raw material for pin production i.e. solid bars φ50, and new none used bar from the same steel was investigated too. Performed investigations showed that the main reason for the fracture of pin is the quality of the raw material more concretely segregation of chemical elements and increased concentration of nonmetallic inclusions.



    Machines. Technologies. Materials., Vol. 11 (2017), Issue 4, pg(s) 183-185

    Pipe from the boiler of thermo power plant with diameter φ45was ruptured in exploitation conditions. In order to determine the reasons for this accident, very complex investigations of the pipe were performed.

    As first chemical composition was determined. Ovality and visual inspection of pipe were performed. Mechanical testing include tensile test at ambient and increased temperature of 350 0C. Thickness measurement of the wall pipe was made too. As technological testing flattening test of pipe segments was done. Metallographic investigations consist of determination of non-metallic inclusions, analyse of microstructure and grain size determination. Performed investigations didn’t indicate to defects in material and its processing. So, it can be concluded that working conditions in the boiler mainly overheating temperature caused damage of pipe.



    Machines. Technologies. Materials., Vol. 10 (2016), Issue 12, pg(s) 12-15

    In this research work the Welding technology that implements high frequency contact welding process (HFCW), is presented as a method for automatic steel pipes production. The pipes produced by the HFCW are meant to be used for natural gas transportation.
    X60M steel coils with thickness of 6.5 mm are used as a raw material. The outer pipe diameter is φ508 and the length is 12000 mm. The preliminary welding procedure is based on the personal experience, technical knowledge and the expert judgment. A special attention has been paid to the most important welding parameters such as: current frequency, voltage and welding speed. After the welding was finished, an additional heat treatment (normalization) of the welded pipes (joints) was performed at the temperature of 900oC.

    In order to justify the proposed welding technology a complex analysis is applied. The first analysis was the chemical analysis of base metal. The next was the nondestructive testing consisted of a visual inspection, and ultrasound testing of the pipes. The destructive testing was consisted of tensile testing, bend testing and the hardness measurement. Besides the analysis of the micro and macro structure of the welded joints, a metallographic analysis is performed as well. Moreover a hydrostatic test and a flattening test were performed as an integral part of the entire testing process. The test results confirmed that the pipes produced with the predicted welding parameters completely fulfilled standard requirements. The manufacturing process for the pipes for natural gas transportation is ready to begin.


    Machines. Technologies. Materials., Vol. 10 (2016), Issue 6, pg(s) 55-57

    This investigation was performed on the request of the Company for production of the solar systems collectors. Subject of the investigation is the segment of the solar stainless steel collector for the heating water in the swimming pool. The system was installed in the private property and was in use until August 2015 (about one month after installation) when it was disconnected for a period of about one month. After that system was restarted again and it was noticed that many cracks appeared in vertical tubes φ8 mm of collector manufactured of S304 stainless steel. In the horizontal pipes made of S316 steel cracks were not detected. This investigation should give the answer what is the reason for appearing of cracks in stainless steel pipes for pretty short period of exploitation.


    Machines. Technologies. Materials., Vol. 10 (2016), Issue 6, pg(s) 25-28

    Zing galvanized panels were ordered and delivered for the fencing of the factory yard. But immediately after receiving the panel from the deliverer, it was concluded that their quality is suspicious. These panels must fulfil strict standards requirement concerning their quality. To confirm this purchaser engaged the team from the Faculty of Technology ad Metallurgy in Skopje to perform investigation and to check if the panels satisfy quality requirement. The performed investigation consists of the following testing’s: chemical composition of base metal (wire), wire diameter and tolerances, tensile test, weld shear strength test, mesh size and tolerances, coating, visual inspection of panels. Performed investigation confirmed that delivered panels didn’t fulfill necessary requirement for this type of fencing.


    Machines. Technologies. Materials., Vol. 10 (2016), Issue 1, pg(s) 33-35

    The results of performed analysis and the study of analytical methods for assessing the precision of the measuring system are presented in this paper. Studies are related to the methods for assessing the precision based on the range calculation and the method of variances analysis (ANOVA).The importance of each factor in variation inducation in the measurement process is estimated by applying both methods in the analysis of the same measured sample. In order to assess the accuracy and efficiency of the applied methods, the obtained results are compared, which is the basis for obtaining specific conclusions.Reliability of the obtained results from the investigations are verified by applying the tools of programming package MINITAB.


    Machines. Technologies. Materials., Vol. 9 (2015), Issue 4, pg(s) 3-7

    In this paper is analyzed situation in the world casting industry starting from the 2008 i.e. period of global economical crisis, trough recovery period untill the current time. The top leading countries in the world and their casting production is presented. Special attention is devoted do the products cost of castings, influence of casting production to the environment and perspective of casting as a industry branch are discused.


    Machines. Technologies. Materials., Vol. 8 (2014), Issue 12, pg(s) 48-51

    In this research work, procedure for certification process of dissimilar welding between austenitic stainless steel S316 with structural steel grade 300NZS according EN 15614 standard was explained. Shielded metal arc welding process (SMAW) was used. Welding was performed in PA position with EIS 309 Mo electrode. Qualification test has to confirm that the preliminary welding procedure fulfil quality requirement, and welded joint will satisfy the exploitation conditions. The following investigations were conducted to welded test plate; Visual testing (VT) has to show existence of surface defects in the welded joints. Next step was radiographic testing (RT) in order to check eventually appearing of volumetric defects inside the weld. Finally the plate was cut for mechanical testing. All conducted tests fulfilled requirements except one probe of bend test. Because of that qualification procedure was not successful, and it was completely repeated after two weeks. The repeated welding procedure specification (WPS) was qualified.


    Machines. Technologies. Materials., Vol. 8 (2014), Issue 2, pg(s) 3-8

    In this paper short reviue about the most important Macedonian foundry companies is given. During prepariation of this work autors visited production units of of the foundry companies and discused with their menegament about the most important things concerning their current work and the plans for the future. It was found that six of the companies are the most important for Macedonian industry. All of them are private companies. They are founded before transition period, and their production is mainly intended for the foreign market. It is important to say that they have very ambitious plans for improvement of technological processes and increase of production.