Knowledge graphs (KGs) structure knowledge to develop intelligent systems in several application domains. Industrial maintenance support requires knowledge and expertise on a variety of aspects of the factory, machinery, and components. However, the actual creation and maintenance process of KGs has remained unelaborated. We review the KG literature to integrate previous models into one process model also incorporating knowledge engineering principles within. The literature review and a subsequent case study together represent the problem and objectives definition phases of a design science project. The contributions include the integrated process model for KG creation and maintenance and the initially observed design challenges in the KG process operationalisation in a context of supporting industrial maintenance.