For level 3 major hazard sources, since interlocks are already in place in the SIS systems at the inlet and outlet, is it necessary to have interlocks also in the DCS system?
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As a Class III major hazard source for liquid ammonia storage tanks, with interlocks already in place in the inlet and outlet areas via the SIS system, is it necessary to have interlocks also in the DCS system? During the expert inspection, it was suggested that the SIS system should be interlocked with the DCS, and that the alarm and interlock values should be identical. I would appreciate it if the teachers could provide some guidance – is there any basis for this? As a protective layer, DCS is located within the protective layer of the SIS system; if interlocks are set up, then what’s the use of the interlocks in the SIS system? The role of a DCS is to achieve the objectives of process design, and it allows for taking action in response to alarms. In contrast, a SIS takes immediate action to shut off the material flow once there are no further actions that can be taken. (My personal understanding; please point out any mistakes, teacher.) I also found similar descriptions for 50074, and I wonder whether this can be used as a basis to justify the requirement that DCs must also have interlocks in place. Is that reasonable? GB50074-2014 \"Code for Design of Oil Storage Tanks\": 15.1.2 The following storage tanks shall be equipped with high liquid level alarms and interlocks; the high liquid level alarm shall be capable of simultaneously interlocking to close the control valve of the tank’s inlet pipeline: Storage tanks for Class A B and Class B liquids with a turnover rate of more than 6 times per year and a capacity of 10,000 m³ or more ； Class A B and Class B liquid storage tanks with a turnover rate of 6 times or less over 2 years, and a capacity of more than 20,000 m³ ； 3 Storage tanks for liquids of toxicity grades I and II. 15.1.4 The level measurement instruments used for high and low high/low level alarm signals in storage tanks shall be separate continuous level measurement instruments or level switches, and alarms and interlocks shall be provided in the automatic control system.
As a Class III major hazard source, the safety control measures for liquid ammonia storage tanks must be established in strict compliance with relevant standards and specifications. Setting interlocks in SIS and DCS systems is one of the important means to ensure the safe operation of storage tanks. Whether it is necessary to set up interlocks in the DCS system should be evaluated and decided based on actual conditions (optional but recommended, not mandatory). At the same time, it is necessary to ensure the independence and integrity of the SIS system, as well as its coordination and integration with other control systems.
Thank you. If chain links are set up for everything, then DCS will be the same as SIS. Is that really necessary? The SIS system is independent.
This post was last edited by Xiao Fu fu on 2024-6-4 16:07. If the SIL/HAZOP classification and analysis indicate a very high level, in order to ensure redundancy in safety controls, it is possible to install the same interlocks in the DCS system as those in the SIS system. This is because dual interlocking provides an additional layer of protection, reducing the safety risks associated with the failure of a single control system. It is not mandatory to set it, but a security analysis should be conducted
The SIS system should have interlocks that are independent of the DCS, while the DCS should also have its own safety interlocks. This ensures that the SIS can still operate independently in the event of a DCS failure.
The SIS interlock is designed to prevent situations where the DCS interlock fails to function; these two interlocks need to be independent of each other
The DCS alarm values can be set lower than those of the SIS, enabling earlier warning； Just check the grading report; the design institute provides the interlock logic table, so follow the design specifications
In clauses 15.1.2 and 15.1.4 of GB50074-2014 \"Code for Design of Oil Depots\", interlocks related to DCS are not mentioned; only SIS interlocks are referred to.
The expert opinion is inappropriate; the DCS alarm interlock values should not be the same as those of the SIS. The interlock of DCS should occur earlier than the SIS action, allowing for automatic recovery. A cascade in SIS requires manual reset.
Ask the expert about the issues; go ask the expert