Cause analysis of oil cross-contamination incident due to improper operation of the shut-off valve during power fluctuations in the tank area
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Recently, due to instability in the external power grid, the pumps in the tank area have experienced frequent sudden shutdowns. During these power fluctuations, the shut-off valves of some of the company’s tanks opened or closed without any command, which led to oil leakage incidents. The information currently available is described below; we would appreciate it if colleagues could help analyze the exact causes； The DCS control system used by our company is the Zhejiang University Zhongkong System JX-300XP; the cut-off valves that malfunctioned this time did not have any interlock logic. They were mostly valves used for oil blending, and the valves installed on site were of the electric or pneumatic actuation type (as confirmed on site) ； The cut-off valves that malfunction are no longer on the same cartridge; the cut-off valves that operate do not malfunction at the same time ； It is now determined that, in the absence of manual operation at the site, the valve can open only if the electromagnetic valve on-site is powered ； However, it is unknown how the cut-off valve obtains power. I would appreciate it if fellow sailors and experts could provide some ideas on how to conduct the inspection.
Is the air supply functioning properly? Is the power supply for the solenoid valve provided by a UPS?
Does DCS use a UPS? If a UPS is not used, will the DCS controller restart during power fluctuations? If it does restart, the output of the cards will remain at the pre-set safe level
It should be obvious. I also said it was caused by a spark. Then solve the flicker problem.
Do your DO cards directly control the valves, or do they control relays to regulate the power supply? If it’s the latter, I suggest you check whether your switch valves and relays are controlled by 24V positive or negative voltage.
Let’s first check the UPS and gas supply issues ?
Check the DCS to see if the cards have been restarted, as a restart can cause abnormal output.
The impact of gas supply pressure has been ruled out; the on-gas or on-electric valves designed for use in this application will not open abnormally even when the gas supply pressure is low； The solenoid valve is powered by the DCS system; the DCS system has two power supplies: one UPS and one mains supply.
Thank you for your reply. If the controller restarts due to a power fluctuation, all the shut-off valves connected to that same controller will act abnormally at the same time. In the case that occurred this time, although multiple shut-off valves were involved, their abnormal operation did not happen simultaneously.
Thank you for your reply. Power fluctuations cause abnormalities in the 220VAC supply. Our company’s DCS system is equipped with two power sources: one UPS and one mains supply. During power fluctuations, the monitoring screen of the DCS system showed no impact. Now, I want to analyze how surges cause the shut-off valve to malfunction, or in other words, what is the root cause of such malfunctions? Further investigation is needed to clarify this.
The on-site control valve is operated by a DO card that controls a relay, which in turn controls the opening and closing of the on-site solenoid valve. The relay should be controlled by the positive terminal of a 24V power supply. I also have a question: what is the difference between controlling the positive or negative terminal of a 24V power supply with a relay?