Our research is part of the cycle of research papers dedicated to modelling, running, and collecting scientific and engineering results from development and implementation of digital twins for industrial assets and whole process units, thus allowing to build and test the concept of digital twin for industrial enterprise. Authors introduce digital twin for steam turbine which is key equipment for many industrial applications and especially for most of power generation plants. This is one of key industrial equipment/asset types used in energy industry nowadays. This paper presents both asset performance management and efficiency optimization digital twins and process simulation digital twins for steam turbines. Paper makes special accent on how digital twin technology combines achievements of information technologies (IT) with achievements of operation technologies (OT) and creates digitization solution capable to increase effectiveness of production up to completely new level of optimization.