## 3 Learning by Building: Interactive Modular Piping 3D CAD Configuration System
### System Specification and Limitations  
The basic idea behind the industry use case of this study is not complete automation for routing designs, as shown in Figure 2, but to raise the efficiency in the design process with an interactive modular piping 3D CAD configuration system. Designers should have the ability to specify the position and orientation of the starting and ending connectors (represented by green and red cylinders, respectively), as well as define and subsequently modify the position and orientation of instrumentation or supports (represented by red spheres), and efficiently add routings between them.  
Figure 1: Correlation model for a steel platform (adapted from [16]).  
Figure 2: Example configuration with four adaptable routings to be realized by the modular configuration system.  
To specify the configuration system, a user group consisting of piping engineers, construction supervisors, a purchaser, and project managers was interviewed and invited to create user stories based on their experience and obstacles they observed in past projects (Figure 3). Before creating a feature list, the development team prioritized tasks, estimated effort, and then mapped user stories to features. (Figure 4). To simplify the implementation process, a modular architecture was chosen.  
In addition to the basic layout (user stories 1, 2, 3, 5, 7, 9, and 10), user story 4 from the construction supervisor is particularly relevant for this case. When planning meets the construction site, many routing modifications may occur due to terrain differences, support foundation positioning or obstacles. When the construction supervisor has access to the design data but is not the originator of the 3D CAD model, they usually just comment on the design and send it back to engineering. For such modifications, the feedback of the engineering department is necessary in many cases as restrictions need to be checked, e.g., pressure drop, necessary slope, and manufacturability.  
Figure 4: User story mapping (excerpt).  
Figure 3: Collected user stories (sample).  
A basic requirement was stated that modifications of the routing should be handled directly to avoid errors and save time by using the configuration system. In this case study, the modification of a routing should trigger two actions. First, after the update, the routing assembly is checked for basic manufacturability restrictions, such as minimum segment lengths and weldability. Secondly, the cut list should be updated and compared to the initial one to ensure that the same amount of semi-finished materials is kept.  
The configuration system is implemented directly into the CAD environment of Autodesk Inventor using its base functionalities. The initial release of the configuration system is defined as a technology demonstrator to show basic workflows and functionalities, and the following limitations are applicable:  
* Branches: If the routing contains branches, these are treated as instrumentation without flanges. The pipe tee is positioned and aligned directly on a drag point.
* Reducers: Reducers are handled in the same way as instrumentation and aligned on a drag point.
* Compensators: The check for length compensation due to thermal expansion is neglected and placing compensators is subject to subsequent manual refinement.
* Slope: The slope check is neglected. This could be included in the system either directly in the path sketches of the routing templates or in the parametrics of the layout.
* Intersection warning: Instead of a separate intersection analysis, the existing assembly interference analysis of the CAD system is used manually.  
Based on the concept of reducing interaction costs, the user group and developers refined the interaction functionality to be implemented as drag points.