Izbor optimalnog dodatnog materijala za reparaturno zavarivanje vratila turbine hidrocentrale na licu mesta

Abstract

Najznačajniji delovi hidroelektrana, vratila turbina izložena su tokom rada visokim naprezanjima, puzamju, zamoru i koroziji. Zbog toga je korisno preduprediti oštećenja tokom rada, povećati pouzdanost i produžiti radni vek postrojenja. Eksploatacioni uslovi mogu da dovedu do prslina i loma u homogenom materijalu, tako da postoji potreba za reparaturom dela postrojenja. A ona može biti skupa ili dugotrajna. U okolnostima kada se reparatura izvodi na licu mesta, posebno pažljivo treba da se definiše tehnologija reparaturnog zavarivanja, parametri postupka, i izbor dodatnog materijala. U ovom istraživanju izbor dodatnog materijala je bio tema i dati su rezultati. Vratilo je izrađeno od čeličnog liva 20Mn5 i na njemu su metodama IBR, otkrivena oštećenja tipa prslina dužine do 400 mm i dubine do 20 mm. Kako je planirano da se reparatura izvede bez demontaže vratila, primena termičke obrade nije bila izvodljiva. Analiza zavarljivosti osnovnoog materijala urađena je korišćenjem analitičkih jednačina. Rezultati su pokazali da je zavarljivost ovog čelika ograničena. Za reparaturno zavarivanje izabran je postupak REL (111) i dve obložene austenitne elektrode sa ciljem određivanja pogodnosti za upotrebu kao potencijalnih dodatnih materijala za reparaturu. U ovom istraživanju ispitane su Fe-Ni-Cr-Mo elektroda i elektroda na bazi Ni i njihove osobine su upoređene. Ispitivanje zatezanjem, ispitivanje apsorbovane energije, ispitivanje savijanjem, merenje tvrdoće i ispiivanje osetljivosti kao što su 'CTS' i 'Y' probe, izvedeni su na ispitnim spojevima dobijenim zavarivanjem osnovnog materijala, 20Mn5, ispitivanje savijanjem, merenje tvrdoće i ispiivanje osetljivosti kao što su 'CTS' i 'Y' probe izvedeni su na ispitnim spojevima dobijenim zavarivanjem osnovnog materijala, čelika 20Mn5, sa ispitivanim dodatnim materijalima. Dobijeni rezultati su analizirani i na osnovu toga, odabrana je elektroda na bazi Ni kao pogodnija za reparaturno zavarivanje.

The most significant components of hydropower plants are turbine shafts and generator rotors which undergo time-dependent processes such as high stresses, creep, fatigue and corrosion. It is therefore desirable to prevent in-service damages, improve reliability and extend the operational life of the plant. Plant operation can lead to cracking and failures in homogeneous materials, therefore a need for repair welding on plant components, which can be expensive and time-consuming, exists. In the circumstances when repair welding has to be carried out on site, special care has to be taken in defining repair welding technology, process parameters and selection of filler materials. In this research a selection of filler materials for repair welding on site of hydropower turbine shaft was performed and results were presented. The shaft was made of the cast steel 20Mn5 and presence of damages in the form of cracks which were up to 400 mm long and up to 20 mm deep was detected through the use of NDT methods. As the repairing was planned to be carried out without disassembling of the shaft, application of heat treatment procedures was not feasible. Weldability analysis of the base material was performed through the use of analytical equations. Results have shown that weldability of this steel is limited. For the repair welding a MMA (111) welding process was selected and two covered austenitic electrodes were analyzed in order to establish the feasibility of their use as potential filler material for repairing. In this research a Fe-Ni-Cr-Mo electrode and Ni based electrode were tested and their properties were compared. Tensile testing, absorbed energies tests, bending tests, hardness measurements and sensitivity tests such as 'CTS' and 'Y' were performed on test joints obtained by welding of base material, 20Mn5 steel, with investigated filler materials. Obtained results were analyzed and a Ni based electrode was selected as most suitable for repair welding.