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Medium and large scale industries typically consume large amounts of energy, and are under pressure to increase energy efficiency and reduce energy wastages. Conventional insight-based heat exchanger network (HEN) retrofit methods typically combine graphical visualisation and algebraic tools to manage different retrofit stages. These stages often involve repetitive calculations of approach temperature, enthalpy balance and heat transfer area to assess the HEN feasibility and cost-effectiveness. This paper extends the individual stream temperature versus enthalpy plot (STEP) methodology that was introduced for HEN synthesis, to HEN retrofit. The STEP retrofit method proposed in this work enables users to simultaneously diagnose and retrofit existing HEN by using only the STEP diagram that maintains the characteristics of individual process streams. Users can graphically perform individual stream mapping without having to calculate stream enthalpies or to check for minimum temperature approach ( Δ T m i n ) violation during retrofit. Application of the new STEP retrofit method on an industrial case study demonstrates its advantages in terms of user interactiveness, simplicity of use, flexibility to customise the methodology to achieve retrofit goals of plant owners, and the least amount of efforts needed to achieve comparable results as those of established retrofit methods. [ABSTRACT FROM AUTHOR]