TY JOUR TI CRITERIA FOR CLASSIFICATION OF IN-PIPE ROBOTS KW in-pipe robots KW classification criteria KW contact interaction type KW controllable friction KW contact element type KW motor type KW transmission type JO Bulletin of Belgorod State Technological University named after. V. G. Shukhov AU Vorochaeva, L.Y. AU Savin, S.I. PY 2018 IS 3 PB Belgorod State Technological University named after V.G. Shukhov