## 3 Materials and Methods
### Case Studies Conducted  
Case studies play a fundamental role in validating and demonstrating the applicability of new methodologies and tools developed in scientific research [89]. In this context, case studies were conducted that supported the development of the APM prototype and evaluated the effectiveness of the proposed solutions against the real challenges of maintenance and painting planning on offshore platforms.  
The case studies selected for this analysis employed specific selection criteria to ensure the relevance and applicability of the results in offshore contexts. The main parameters taken into account involve corrosion levels, categorised by their severity and specific location within the structure, along with environmental factors like humidity and temperature, which directly impact corrosion progression. These parameters were chosen through a preliminary analysis that identified the variables with the most significant impact on predictive maintenance and the structural integrity of offshore installations. Additionally, consistent parameters were used for each variable in the analysis, such as the number of personnel assigned per team and the duration of person-hours. In this case, each team had a specific number of painters and a set duration, ensuring that the planning criteria remained consistent across all simulations. Some criteria were used for specific advances, while others were applied according to the context of each study, thereby ensuring a robust and coherent application of the results in real conditions.  
The case study on the development of APM aimed to validate, test, and demonstrate the applicability of the methodologies and models developed in each research using real-world contexts of offshore oil platforms. A real-world major platform scenario was used to compare the painting plans generated by each strategy (PH limit, corrosion integrity, regulatory demand, and criticality), evaluating the results regarding the remaining corrosion, pending regulatory demand, the criticality of selected systems, and the required resources. Optimising maintenance planning through considering multiple criteria and constraints is a complex problem that demands advanced decision-support tools [90].  
Throughout these stages, various data sources were used: semi-structured interviews (with the interview tool updated according to emerging data), observations (e.g., shipments, participation in meetings), and documentary sources (e.g., documents from a large company  
Figure 3: Screen flow and user interactions for the APM tool.  
in the O&G industry). Several methods were employed to triangulate data from different sources to achieve greater data reliability and a have solid foundation for the constructs and propositions.  
A mix of exploratory and confirmatory focus groups was employed to assess the prototype's design. The exploratory focus groups gathered feedback for design changes and the artefact's refinement, serving as a formative evaluation procedure for iterative design improvement. Additionally, a confirmatory focus group was applied to demonstrate the utility of the artefact's design in the application domain. To this end, eight focus group workshops were conducted with painting planning specialists and maintenance managers (two to three participants per workshop, with an average duration of 60 min).