Integrity assessment of bucket wheel excavator welded structures by using the single selection method

U cilju smanjenja troškova ispitivanja zavarenih spojeva na vitalnim konstrukcijama i gubitaka u proizvodnji zbog zastoja u radu bagera, razvijena je nova metoda za procjenu integriteta i pouzdanosti zavarenih spojeva u eksploataciji rotornih bagera. U radu je prikazan dio rezultata istraživanja stanja sučeono zavarenih spojeva na konstrukcijama strijele rotora, odlagajuće strijele i strijele protutega metodama bez razaranja, prije revitalizacije havariranog rotornog bagera Sch Rs 1760×32/5. Rotorni bager je prije havarije radio oko 85.000 sati (17 godina), odnosno bio je izložen promjenjivom opterećenju tokom približno 2 125 000 ciklusa. Hipergeometrijska raspodjela je primijenjena za izračunavanje vjerovatnosti da će za ispitivanje biti izabrano x zavarenih spojeva, koji sadrže n spojeva s greškom, od ukupnog broja spojeva Q. Procjena integriteta zavarenih konstrukcija rotornog bagera izvršena je na osnovu analize grešaka i analize rezultata ispitivanja rasta zamorne prsline u zavarenim spojevima. Primjenom ove metode, troškovi ispitivanja su smanjeni za 70 %, optimizacijom opsega ispitivanja i vremenskog razdoblja između njih.
In order to reduce the testing costs for structural welded joints and production losses due to excavator standstill, a new method for integrity and reliability assessment of welded joints during exploitation of bucket wheel excavators has been developed. In this paper, a part of non-destructive testing results for the butt welded joints on bucket wheel boom, counterweight boom and discharging boom is presented, prior to the repair of the collapsed bucket wheel excavator SchRs 1760×32/5. It has been in operational mode for 17 years prior to the collapse, in other words it has been subjected to aproximatelly 2 125 000 cycles of variable loading. Hypergeometric distribution has been used for calculation of probability that x welded joints, which comprise n welded joints with defects, would be selected for testing out of overall number of joints Q. The integrity assessment for welded structures of bucket wheel excavators has been performed on the basis of defect analysis and probabilistic assessment of the fatigue crack growth in welded joints. By using this method, the testing costs have been reduced by 70 % through optimized scope of the inspections and time periods between them.