The case study presented within this article revolves around creating concepts of process control with the Functional Specification and S88.01 playing vital roles within the design process of engineering. This project used a certain methodology, which brought about several important benefits over the former process of engineering. In a nutshell, this study follows a multi-product biotech plant’s development through three different design phases. This particular discussion will start off with a short summary of the former process of engineering along with several of the disadvantages that came with it.
The Former Process of Engineering
Conceptual Design normally starts with the Process Description, which is created to showcase the major steps of the process as a whole. As its description states, Process Diagrams of Block Flow are created to showcase the main unit operations, the main ingredients, and the product flows. Afterwards, some notes are added onto the drawings to fully describe the concepts, workings and everything else that cannot really be graphically illustrated with ease. The clients then look at these documents of process design, after which they return their corrections and comments in the cycle of review, editing and approval. Once the documents are approved, another estimate is put together to compare the project with the expected return of investment and the overall budget.
Preliminary Design starts right after the completion of conceptual design and after the project’s feasibility has been completely justified. Based on the Diagrams of Block Flow, Diagrams of Process Flow are created here to illustrate the material flows and main equipment pieces. Once these have been approved, every unit operation gets fleshed out on an Instrumentation and Piping Diagram (I&PD), which usually illustrates every connection of the process from and to a vessel, such as the sizes of the pipe, the valves and the instruments. Usually, these drawings depict a certain strategy of control with ISA symbols, narratives, and dashed lines, as well.
Detailed Design
The client looks at the whole design package afterwards to get a more accurate estimate ready based on the material takeoffs and equipment expenses. This cost estimate supports a capital project appropriation requisition and project timeline and budget verification. After the project has been approved to go ahead, the documents are sent out and the detailed design can start.
Detailed Design works with what the preliminary design has to give. Instrument index and specifications, loop sheets, and equipment specifications are begun with help of the information at hand. A control system needs to be chosen and the entire architecture has to be studied to come up with control panels, assign the I/O points and make cable schedules. The engineering company can write a document on control strategy, as well, but usually, a systems integrator or the client himself will do this.
Suitable contractors have to be chosen and bid packages have to be developed for the entire construction by this point, though the cost estimate for it can be done after the detailed design. This estimate has to based on the contractor bids in order to confirm that there are enough funds to finish the whole project. Usually, this is when the systems integrators, and control system software and hardware suppliers are chosen, as well.
The Disadvantages of the Former Process of Engineering
The I&PD is Overworked – Complicated control algorithms and batch series are hard to draw with symbols and lines on I&PDs, most of all when numerous flow paths and unit operations for every vessel exist. And tracing lines in order to fully understand how each equipment entity relates to one another can be daunting and confusing, as well. Controlled SIP and CIP operations within the bigger system will be even harder to draw in an effective manner.
Imbedding the information of control strategy onto these drawings as control notes and valve matrix tables will just make the overall change strategy management more complicated, not to mention it will take up quite a lot of space on the I&PD. Since CAD machines aren’t very efficient as word processors, either, it would cost a lot to revise these drawings with them each time an update occurs while the design is being developed or during any of the review cycles thereafter, for that matter. Maintaining the text on these drawings while it exists will simply take up too much time and money, as well.
Documentation
ISA matrices, signs, and notes don’t address data management, operator interaction, and address timing, and they don’t describe any organized approaches for what the software developers have to do, either. In the end, the symbology will even have to be documented and interpreted in writing anyway. Also, with a lot of the strategy symbolized into drawings and the rest of it narrated into a document, it would practically be impossible to try and steer clear of information duplication – something that will complicate the change management significantly.
Since the I&PDs don’t have the entire story on them, their design will always be approved – even without a proper review of the entire control strategy. Therefore, any vital elements that might have been missed earlier on will be much harder to add later.
Next time we will start with the automation engineering aspect of S88.
