Instrumentation design specifications for major hazard sources

It’s not the case that only systems involving major hazard sources require SIS; currently, all hazardous processes in the chemical industry have SIS.

Chain conditions need to be specified in the process, to be implemented through the SIS system

I’m puzzled – why can’t the process leader put forward any conditions?

Hehe, just a few jars. There is no interlocking. Therefore, interlock conditions cannot be established.

Yes, I think too that it’s only needed for new projects. The problem is that mine is an old unit, and it already has a DCS system.

Old installations can be upgraded; whether to install a SIS depends on the requirements of the project owner and the local safety supervision authorities.

Just a few jars can be made at night! High liquid level high-limit alarm: the emergency shut-off valve closes or the emergency discharge valve opens. Actually, it’s the same as DCS – it’s designed to create a specific system. It is activated and operated by one-key interlock.

For something so critical, it should not be the department in charge of operation that proposes technical upgrades; this is not a matter of minor repairs. It is best for the design firm that created the overall design to identify the key aspects of the process and related requirements, and then hand them over to specialized manufacturers who can refine them based on their engineering experience.

To design a SIS system, the following tasks must be carried out first: 1. HAZOP analysis 2. SIL level assessment. Only by completing these two tasks can a proper SIS system be designed. Currently, in the petrochemical industry, HAZOP analysis is already a standard practice, but SIL level assessment has not been carried out on a widespread scale; it is only applied to a very small number of projects. Foreign-owned projects generally conduct SIL analyses. The SIS systems we design currently have their SIL levels determined by drawing analogies from previous SIL analyses, but they are not developed strictly in accordance with the requirements for those SIL levels. At present, only logic controllers meet the SIL requirements, and some field transmitters also satisfy these requirements. The vast majority of actuation mechanisms have not been designed in accordance with SIL standards, as this involves significant investment costs. Additionally, there is a lack of awareness in this regard among decision-makers; they have not yet realized the importance of safety in this context. It is not possible to design everything in strict compliance with SIL standards right away – it requires a process over time. Also, once the SIS system has been designed, it is necessary to conduct SIL level verification to determine whether the designed SIS system truly meets the required SIL level. If it cannot be achieved, the design still needs to be modified.

　　SIS is first and foremost a set of reliability standards. Next are specialized computers that enable the control system to meet SIS standards. 　　So using the SIS process does not introduce additional control conditions. Only reliability requirements are specified, to be implemented by the automation team. This is a bit similar to the question of whether explosion protection is needed; the process only sets requirements, while it is up to the instruments to ensure their implementation. 　　Due to the existing instrumentation, it is extremely rare for them to meet the reliability requirements of SIS. Even if the instrument itself meets the requirements, its manner of use (such as power supply and wiring) often causes it to fail to meet those requirements. So, the primary method to meet the SIS reliability standards at present is redundancy, redundancy, redundancy.