Layers of Protection in a P&ID

Hi

In a P&ID, a process engineer should think about all expected upset scenarios. For example, he may ask these questions: 🤔

1. What if a control valve failed?
2. What if the operator closed some valve by mistake?
3. What if the cooling water system failed?
4. What shall happen in case of power failure
5. And so on

This video talks about some of the hazards an operator may face while operating the plant.

These questions should be asked when examining each system. This to ensure that the system has enough layers of protection against process upsets. 🦺

To address these questions, there are several approaches to be followed:

1. Make the system inherently safe, so if the upset scenario occurs, our system can still mechanically withstand it.
2. Consider operator's response: So we should warn the operator through alarms
3. Prevent the hazard from occurring through a shutdown action such as tripping the pump or closing shutdown valve
4. Finally, if we couldn't prevent the hazard, we shall mitigate it. A famous example is using a PSV or a pressure safety valve.

So which method shall we use? Or shall we use more than one method or even all of them? This depends on the nature of the system.

Analyze your Protection with HAZOP & SIL Sessions

So how can we check out if there is enough protection to the system on a P&ID? This is commonly done through HAZOP and SIL sessions.

Through this session, the project team from different backgrounds sit with each other, identify the risks and project deviations in each portion of the plant, check out if the design addresses the above scenarios with proper safeguards, and if it doesn’t, then it adds applicable recommendations.

For even more critical points, we may need to conduct a further study against the current layers of protection, check their reliability against the severity of the deviations they are addressing, and based on the result of this study, we end up determining the SIL rating of the shutdown protection system, instruments, and shutdown valves. 

Within the next few days, our P&ID course shall be ready. It shall talk about the different layers of protection and the methods used to ensure the plant safety. If you'd like to know more about the course, you can click the button below:

Learn More

Have a nice day / night !!

Boostrand