Some examples how an experienced fabricator can manage in-field alteration of critical equipment in order to satisfy new customer needs are presented and relevant implications evidenced. 1) Site modification of a Cr-Mo-V Reactor A high thickness, large diameter 2.25Cr-1Mo-0.25V Hydrocracker Reactor was completed in field by performing three circumferential seams and related LPWHT. Since the Customer decided to modify the process and to add a new catalyst bed, design changes were implemented to add a new catalyst bed and a new 8” quench nozzle. 2) Rehabilitation of existing Reactor An existing reactor no more in operation for several years was rehabilitated in field to comply with a new process unit layout (debottlenecking) to comply with current law requirements. 3) Site Assistance during schedule Turnaround activities Reactors are designed for extended life cycle up 25 to 30 years, but severe operating conditions may require reconditioning after onsite inspection during scheduled turnaround. Fabricator has been involved jointly with End User and Process Licensor for design changes and has responsible for the onsite execution activities.