Predviđanje životnog vijeka oštećene plinske cijevi PE 80

This paper deals with new approach to life estimation of damaged thick-walled gas pipes made of high-density polyethylene (PE 80). The most common approaches to polyethylene gas pipes durability prediction rely on methods of fracture mechanics, which involve defining the stress intensity factor experimentally. However, such tests are carried out on standardized specimens neglecting the influence of real pipe geometry and processing method. On the other hand, these data are not always available to gas distributors, which are responsible for installed pipelines durability. Investigations based on long-term experiments involving three parameters: pressure, length and depth of initial notch type crack gave empirical mathematical model for life prediction of polyethylene gas pipes.U radu je prikazan novi pristup za procjenu preostalog vremena uporabe oštećenih plinovodnih cijevi od polietilena visoke gustoće (PE 80). U praksi se najčešće primjenjuju metode mehanike loma za procjenu trajnosti polietilenskih plinovodnih cijevi koje uključuju eksperimentalno definiranje koeficijenta intenzivnosti naprezanja. Međutim takvi su testovi napravljeni na normiranim ispitnim tijelima pri čemu je zanemaren utjecaj stvarne geometrije i postupak proizvodnje cijevi. S druge strane, podaci o koeficijentu intenzivnosti naprezanja nisu uvijek dostupni distributerima prirodnog plina. Provedbom dugotrajnih ispitivanja temeljenih na distributerima dostupnim podacima: tlaku u cijevima, duljini zareznog oštećenja i dubini zareznog oštećenja dobiven je empirijski matematički model za procjenu preostalog vremena uporabe oštećenih polietilenskih plinovodnih cijevi

Primjena suvremenih materijala za brtvljenje cijevnih navojnih spojeva

This paper deals with application of contemporary liquid sealants based on methyl - methacrylate, so called anaerobic sealants. Applications include reliable sealing of threaded joints in pipeline installations (cold and hot water pipelines, steam pipelines, gas pipelines, cooling and air-conditioning, pneumatics and hydraulics). Economy of anaerobic sealants application as well as important advantages of this contemporary sealing technique in comparison with traditional one has been considered in particular.U radu je razmotrena primjena suvremenih tekućih brtvenih materijala na bazi metil-metakrilata, tzv. anaerobnih brtvila. Primjene obuhvaćaju pouzdano brtvljenje navojnih spojeva u svim vrstama cijevnih instalacija (vodovodi, toplovodi, parovodi, plinovodi, rashladna tehnika i klimatizacija, pneumatika i hidraulika). Posebice je razmotrena gospodarska opravdanost tih brtvenih materijala i značajne prednosti koje ta suvremena tehnika brtvljenja ima u odnosu na klasične postupke

Adhesive bonding of polymeric composites

Lijepljenje je suvremeni način spajanja dijelova, a primjenjuje se za povezivanje različitih materijala. Lijepljenje ima mnogobrojne prednosti pred mehaničkim postupcima spajanja dijelova. Lijepljeni spojevi prenose opterećenje cijelom površinom spoja, što osigurava veću postojanost djelovanju savojnih opterećenja i vibracija obzirom na druge načine spajanja materijala. Ljepila su tvari koje na osnovi kemijskog sastava i fizičkog stanja u trenutku nanošenja na površine omogućuju njihovo spajanje. Za povezivanje dijelova od metala, stakla, keramike, plastike i kompozita primjenjuju se ljepila koja mogu biti epoksidna, poliuretanska, akrilatna, itd. U tekstu će se prikazati ispitivanje smične čvrstoće lijepljenih spojeva kompozitnih tvorevina načinjenih postupcima obodnog namotavanja i izravnog prešanja, uz korištenje dvije vrste polimernih ljepila.Adhesive bonding is a modern method for joining parts and is applied for connecting different types of materials. Adhesive bonding has many advantages over mechanical joining, because in adhesive bonding load is carried over entire surface of joint thus providing better resistance to flexural stress and vibrations. Adhesives are substances that, based on chemical configuration and physical state, at the moment of coating the surfaces allow their joining. For joining parts of metal, glass, ceramics, polymers and composites adhesives are used, which may be epoxide, polyurethane, acrylate etc. The paper presents shear strength testing of the composite assemblies\u27 joints bonded by filament winding and direct pressing by using two polymer adhesives

Ispitivanje trajnosti membrana regulatora plina

Rad se bavi ispitivanjem trajnosti pomoćne membrane regulatora plina. Provedenim ispitivanjem ustanovljeno je razdoblje nakon kojeg pomoćna membrana gubi svoja početna svojstva. Kao referentni primjerak za praćenje svojstava membrana uzeta je nova, neugrađena membrana. Provedenim ispitivanjem rastezne žilavosti ispitnih tijela načinjenih iz pomoćnih membrana došlo se do zaključka da je preporučljivo provjeriti kvalitetu membrana svakih 8 godina

A Study of the Flexural Properties of PA12/Clay Nanocomposites

Polymer nanocomposites consist of a polymer matrix and reinforcing particles that have at least one dimension under 100 nm. The processing of nanocomposite polymers is the most important stage, determining the final properties of nanocomposites. Nanocomposites are now preferentially prepared by melt-mixing using conventional compounding processes such as twin-screw extrusion. Many processing parameters (polymer matrix type, content and type of nanofiller, barrel temperature, screw speed, number and shape of extruder screws, etc.) affect the properties of nanocomposites. This research work represents an investigation of the influence of processing parameters (amount of nanoclay filler, the screw rotation speed, and extruder barrel temperature) on the flexural properties of polyamide 12/nanoclay-reinforced nanocomposite. From the test results, it is apparent that an increase in nanoclay content from 1 to 8% significantly increases flexural strength. The obtained nanocomposite has a 19% higher flexural strength and a 56% higher flexural modulus than pure PA12. Mathematical models that show the dependence of flexural strength and flexural modulus on the processing parameters used were obtained as a result of this analysis

Istraživanje primjene anaerobnih brtvenih smjesa u plinovodnim sustavima

Contemporary approaches regarding to infrastructure are more and more directed to new materials development for natural gas and other installations. The most recent development and application of the new materials pertain to sealant materials for sealing of threaded joints in gas pipeline installations and installations for other media. Based on provided analysis, gas leaking on threaded joints in home metering and control units sealed with hemp was affirmed. Considering that in practical work in the case of hemp, sealing threads are made by a thread tool and during threading, the tool lubricates, the influence of impurities on sealing with anaerobic sealant compounds has been tested. Experimental work includes testing of three different anaerobic sealing compounds with three material combinations in threaded pipe joints (steel – brass, brass – brass and brass – aluminium) on three different temperatures (-20 °C, 25 °C and 100 °C).Trenutačni su pristupi, koji se odnose na infrastrukturu, sve više usmjereni na razvoj novih materijala za izvođenje plinskih i drugih instalacija. Najnovija dostignuća i primjena novih materijala prvenstveno se odnose na smjese za brtvljenje navojnih spojeva plinskih cjevovodnih instalacija, te cjevovoda za druge medije. Provedenim je ispitivanjima potvrđeno propuštanje prirodnog plina na navojnim spojevima kućnih regulacijskih stanica brtvljenih kudjeljom, što je potvrđeno provedenim ispitivanjima. U instalaterskoj praksi navoj na cijevima izrađuje se pomoću nareznica koje se prilikom narezivanja navoja podmazuju. Ispitivanjem se utvrdio utjecaj onečišćenja na brtvljenje spojeva pomoću anaerobnih brtvenih smjesa. Eksperimentalnim radom ispitana su tri različita anaerobna brtvila s kombinacijom tri materijala u navojnom spoju (čelik - mesing, mesing - mesing, mesing - aluminij), pri trima različitim temperaturama (-20 °C, 25 °C i 100 °C)

Evaluation of Boride Layers on C70W2 Steel Using a New Approach to Characterization of Boride Layers

In this study, boride layers on C70W2 steel, obtained by boronizing at temperatures ranging from 870 to 970 °C and durations from 4 to 8 h, were investigated. The characterization of the layers was carried out using a new approach based on the change in the volume fraction of the boride phase. Analysis of the change in volume fraction showed that an increase in temperature and duration resulted in thicker layers, with temperature having a greater influence. Based on the volume fraction of the boride phase, the layer is divided into compact and toothed parts. With increasing temperature, the thicknesses of both parts of the layer increased. The thickness of the toothed part was the highest after 6 h of boronizing and further prolongation of boronizing led to a decrease in the thickness. Regression equations were estimated for the prediction of the volume fraction of the boride phase, the thickness of the compact part, and that of the toothed part of the boride layer as a function of the boronizing parameters. This study has shown that characterization based on the volume fraction of the boride phase offers advantages over the conventional method based on the average thickness of the layer

A Study of the Flexural Properties of PA12/Clay Nanocomposites

Polymer nanocomposites consist of a polymer matrix and reinforcing particles that have at least one dimension under 100 nm. The processing of nanocomposite polymers is the most important stage, determining the final properties of nanocomposites. Nanocomposites are now preferentially prepared by melt-mixing using conventional compounding processes such as twin-screw extrusion. Many processing parameters (polymer matrix type, content and type of nanofiller, barrel temperature, screw speed, number and shape of extruder screws, etc.) affect the properties of nanocomposites. This research work represents an investigation of the influence of processing parameters (amount of nanoclay filler, the screw rotation speed, and extruder barrel temperature) on the flexural properties of polyamide 12/nanoclay-reinforced nanocomposite. From the test results, it is apparent that an increase in nanoclay content from 1 to 8% significantly increases flexural strength. The obtained nanocomposite has a 19% higher flexural strength and a 56% higher flexural modulus than pure PA12. Mathematical models that show the dependence of flexural strength and flexural modulus on the processing parameters used were obtained as a result of this analysis