Testing of welded and not welded flanges for water pipelines

Leteče prirobnice se v praksi uporabljajo za sestavljanje plastičnih cevovodov večjih premerov. Prirobnice morajo zagotoviti tesnenje pri določenih tlakih obratovanja. V tem delu smo se osredotočili na preizkušanje treh vrst letečih prirobnic, ki so se razlikovale po velikosti. Preizkušali smo dva tipa različnih prirobnic glede na način izdelave. Prve prirobnice so bile izdelane iz upognjenih trakov in varjene. Druge prirobnice so bile izrezane iz pločevine brez zvarih spojev. Preizkušanje prirobnic je potekalo s povečevanjem tlaka na prirobnične spoje. Pri preizkusu se je meril tlak preizkusnega medija in deformacije na kritičnih prerezih prirobnic. Deformacije so bile izmerjene z upornimi merilnimi lističi na mestu zvara in na mestu brez njega. Preizkusi so pokazali, da so opazne razlike pri deformiranju prirobnic na mestih, kjer imamo zvarni spoj v primerjavi z mestom, kjer ni zvarnega spoja. Preizkusili smo tudi prirobnične spoje z manjšim številom vijakov. V praksi se namreč dogaja, da v spoje ne vstavijo vseh vijakov. Ugotovili smo, da je tak spoj prirobnic vzdržal bistveno manjše obremenitve pred samo popustitvijo, tudi do štiri krat manj. Za natezne preizkuse pa so bili izdelani posebni preizkušanci, kjer se je preverila ustreznost nepopolno prevarjenega zvarnega spoja na varjenih prirobnicah.Slip-on flanges are used in practice for composing of plastic pipelines of bigger diameters. Flanges must reassure no leakage at specific working pressures. In this work we focused on testing three different types of slip-on flanges. Flanges had three different dimensions. We tested two different types of flanges by production process. First ones were made by forging of steel band and welding of them. Second ones were cut out of the steel plates without welding joints. Testing of the flanges was performed by increasing of the pressure on the flange joints. Pressure of the testing medium and strains in the critical cross sections were measured during testing. Strains were measured by strain gauges on the position of welding joint and on the position without welding joint. Testing showed some differences in deformation of flanges on positions with welded joints in comparison with positions without welded joint. Flanges were also tested with reduced number of screws in flange joint. Reduced number of crews in flange joints is commonly used in practice. Testing showed that that kind of flange joints sustain less capacity of loading before leakage, up to four time less. Special specimens were made for tensile testing, where suitability of non-cross welded joint were checked on welded flanges