Materijali povećane erozione otpornosti izloženi ekstremnim uslovima rada na termoenergetskim postrojenjima

Abstract

Produžetak radnog veka kritičnih komponenti industrijskih sistema je moguć kroz izbor i ugradnju pravilno projektovanog materijala. Pri jednom takvom izboru potrebno je izvršiti detaljnu karakterizaciju materijala i ispitivanje različitim metodama sa posebnim osvrtom na eksperimentalna ispitivanja u uslovima koji simuliraju radne uslove. Ovakva ispitivanja, uz dodatnu mogućnost izvođenja ispitivanja in-situ i uz određivanje optimalnog polaznog stanja materijala, predstavljaju osnovu pravilnog izbora, izrade i ugradnje projektovanog materijala. Istraživanja u okviru ove disertacije su usmerena na produžetak radnog veka kritičnih komponenti sistema za otpepeljavanje na jednom domaćem termoenergetskom sistemu. Cevovodi za pneumatski transport pepela su izdvojeni kao najkritičniji elementi tih sistema, gde su svakodnevni zastoji i otkazi bili prouzrokovani erozivno-abrazivnim oštećenjima materijala usled transporta velike količine pepela. Polazna smernica u rešavanju ovakvog problema je bila modifikacija hemijskog sastava postojećih legura belih livenih gvožđa legiranih sa ~15%Cr i ~25%Cr (HCCI legure) i ograničenje sadržaja uticajnih legirajućih elemenata kako bi se, uz pravilan izbor parametara režima termičke obrade žarenja, dobila austenitna duktilna osnova sa manjim sadržajem martenzita i sa čvrsto vezanim M7C3 karbidima u njoj. U cilju poređenja, ispitane su predložene HCCI legure u stanju nakon livenja i u stanju nakon termičke obrade, kao i prevlake na bazi Fe-Cr-C legura nanete plazma postupkom navarivanja. Takođe, u okviru ove disertacije, izvršena su i laboratorijska ispitivanja erozione otpornosti uzoraka od svih predloženih materijala, kao i do sada korišćenih komercijalnih materijala u cevovodima za otpepeljavanje na bazi bazalta i keramike. Erozioni test je sproveden u uslovima velikih brzina čestica i sa povećanim masenim protokom erodenta, simulirajući na taj način realne intenzivne eksploatacione uslove. Detaljna karakterizacija svih ispitanih materijala, na osnovu rezultata erozionog testa i prema mikromehanizmima erozije koji u intenzivnim uslovima rada dovode do erozivno-abrazivnih oštećenja, poslužili su da se izabere legura kandidat za izradu mašinskog dela i ispitivanje in-situ. Tako je u nastavku istraživanja ove disertacije, izrađen cevni luk od izabrane HCCI legure i isti je ugrađen na sistem za pneumatski transport pepela na domaćem TE postrojenju. Od posebnog značaja su rezultati ispitivanja in-situ i njihovo poređenje sa rezultatima laboratorijskih ispitivanja istih legura. Rezultati eksperimentalnih laboratorijskih ispitivanja erozione otpornosti HCCI legura, u okviru ove disertacije, su verifikovani publikovanjem u relevantnim međunarodnim naučnim časopisima.

Extending remaining life assessment of critical components of industrial systems is possible through the selection of properly designed materials. When making such a choice, it is necessary to carry out a detailed characterization of the material and testing with different methods, with special reference to experimental tests in conditions that simulate working conditions. Such tests, with the additional possibility of conducting in-situ tests and determining the optimal initial state of the material, represent the basis for the correct selection, production and installation of the designed material. The research in this dissertation is focused on extending the remaining life of critical components of the ash removal system on a domestic Thermal Power Plant (TPP). Pipelines for pneumatic transport of ash were singled out as the most critical elements of those systems, where daily outages and failures were caused by erosive-abrasive material damages, due to the transport of a large amount of ash. The initial guideline in solving such a problem was the modification of the chemical composition of the white cast iron alloys alloyed with ~15%Cr and ~25%Cr (HCCI alloys) and the limitation of the content of influential alloying elements in order to, with the correct selection of parameters of the annealing heat treatment regime, obtained an austenitic ductile base with a lower content of martensite and with tightly bound M7C3 carbides in it. For the purpose of comparison, the proposed HCCI alloys were examined in the state after casting and in the state after heat treatment, as well as coatings based on Fe-Cr-C alloys applied by the plasma transferred arc surfacing process. Also, as part of this dissertation, laboratory tests of the erosion resistance of samples of all the proposed materials, as well as commercial materials used so far in ash removal pipelines based on basalt and ceramics, were performed. The erosion test was conducted under conditions of high particle velocities and with an increased mass flow of the erodent, thus simulating realistic intensive exploitation conditions. Detailed characterization of all the tested materials, based on the results of the erosion test and according to the erosion micromechanisms that lead to erosive-abrasive damage in intensive working conditions, served to select a substitute alloy for the production of the machine part and in-situ testing. Thus, in the research of this dissertation, a pipe arch was made from the selected HCCI alloy and it was built-in on the system for pneumatic transport of ash at the domestic TPP. The results of in-situ tests and their comparison with the results of laboratory tests of the same alloys, are of particular importance. The results of experimental laboratory tests of erosion resistance of HCCI alloys, within this dissertation, were verified by publication in relevant international scientific journals.