How are the boundaries of a project defined? For example, how are ISBL and OSBL determined?

Generally, a single set of equipment defines a boundary zone; there are boundaries for both incoming and outgoing flows, and strict separation is required during piping

When a project is under construction, a boundary is established, namely the red line boundary. Areas within this red line boundary are considered ISBL, while areas outside it are considered OSBL. During normal operation, to prevent the wiring (pipelines or instrument wires) from being unable to be connected, ISBL is set back 1 meter as the interface point. Furthermore, if there is an external pipe gallery within the red-line area, sometimes part of that external pipe gallery is deliberately designated as “OSBL” in order to separate it from the equipment and make the equipment independent – that’s my understanding.

The project boundary is divided into an external boundary and an internal boundary. The external boundary is generally planned by the landscape design team based on the conditions of the approved plot, taking into account the boundary relationships with the surrounding environment as a whole. For example, if there is a gas pipeline in the vicinity, an appropriate safety distance must be maintained based on the grade of that gas pipeline. If there are upstream and downstream projects in the vicinity, and logistics routes need to be taken into account, the project boundaries will also be placed as close as possible to those corresponding upstream and downstream projects. In addition to these unified regulations and process requirements, certain local-specific requirements must also be taken into account, such as the distance from residential areas, requirements regarding logistics and traffic flow, and requirements for centralized discharge points. After taking all these factors into consideration, they are reflected in the site plan; the final result is the overall boundary of the project. There are also boundaries between different specialties within the project, which constitute internal boundaries. Typically, the chief designer is responsible for establishing an overall plan, making rough divisions based on the different process stages, after which process engineers from various specialties participate in discussions to evaluate and finalize the details. The goal of defining boundaries is to minimize any overlap between the design work within those boundaries and external design elements. Within my defined boundaries, what I say counts; even if there is interaction, it should take place in a few designated areas. This improves design efficiency. The above are my personal insights; my wording may not be perfect, please forgive me.