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Integritet cevovoda i drugih elemenata opreme pod pritiskom je veoma važan za pouzdan i bezbedan rad postrojenja u procesnoj industriji. Otkazi opreme mogu, uz ugrožavanje sigurnosti zaposlenih i ekonomske gubitke, u nekim slučajevima izazvati ozbiljne ekološke posledice, ukoliko dođe do ispuštanja otrovnih, zapaljivih ili na drugi način opasnih fluida. Stoga, veoma je važno poznavati ponašanje cevi pri lomu ili drugim oblicima otkaza. Problem pri korišćenju standardnih epruveta predstavlja potrebna debljina uzorka, kao posledica zahteva za dominantnim ravnim stanjem deformacije. U ovom radu, otpornost prema lomu je određena primenom epruveta oblika prstena izloženih savijanju, kao nestandardnih epruveta predloženih u prethodnom periodu. Početni koncentrator napona (žleb ili zamorna prslina) je formiran u uzdužnom pravcu; opterećenje ove epruvete simulira dejstvo unutrašnjeg pritiska u cevi. Epruvete su izrađene od cevi za primenu na povišenoj temperaturi. Rezultati pokazuju da se epruvete oblika prstena mogu koristiti za karakterizaciju loma materijala cevovoda i posuda malih prečnika, posebno za tankozidne strukture koje nisu pogodne za izradu standardnih epruveta mehanike loma (poput elemenata sistema za skladištenje i distribuciju fluida -kiseonika, vodonika, azota, vode / vodene pare, tečnih i gasovitih goriva, itd.). Ključne reči: Otkaz nosivosti cevi; Epruveta oblika prstena za savijanje; Žilav lom; Stereometrijsko beskontaktno merenje deformacijaIntegrity of pipelines and other pressurised equipment elements is very important for reliable and safe exploitation of the process industry plants. Equipment failures can, in addition to endangering the safety of personnel and economic losses, in some cases cause serious ecological consequences, if some toxic, flammable or otherwise dangerous material is released. Therefore, it is very important to understand the behaviour of the pipes during fracture or other failure modes. The problem which arises if standard specimens are applied is the required thickness of the specimen, as a consequence of the plane strain requirement. In this work, fracture resistance is determined by application of ring-shaped specimens exposed to bending, as nonstandard specimens proposed recently. Initial stress concentrator (notch or fatigue pre-crack) is formed in axial direction; loading of this specimen simulates the internal pressure in the pipe. The specimens are fabricated from the pipes for usage on elevated temperature. The results show that the ring-shaped specimens can be applied in fracture characterisation of pipeline / small-diameter vessel material, especially for thin-walled structures which are not convenient for fabrication of standard fracture mechanics specimens (such as elements of systems for transport and distribution of fluids -oxygen, hydrogen, nitrogen, water / steam, liquid and gaseous fuels, etc.).

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Steel pipelines in industrial plants consist of different elements, including seamless and/or welded (seam) pipes. Properties of welded pipes, including their fracture behaviour, depend on the characteristics of both, the base metal, and the weld metal. In this work, two seam pipes are considered having different diameters and manufactured of P235TR1 steel. Hardness and microstructure were examined on the samples which contained the seam zone, to capture the influence of heterogeneity. Fracture resistance of the pipeline material, i.e. of both base metals and both seams, was determined by experimental examination of the recently proposed Pipe ring notch bending specimens with sharp stress concentrators. Differences between the two tested pipes, including the influence of the heterogeneity caused by the welded joint, were determined by comparison of the crack growth resistance curves. Effects of the initial stress concentrator shape, sharp machined notch or fatigue pre-crack are discussed.