Discussion on unit shutdowns caused by welding or the use of electrical equipment in the unit building
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This post was last edited by zhenghongyong on 2022-9-26 at 16:43. Dear seniors and colleagues: Some time ago, while a petrochemical company was carrying out modifications and welding work on the inspection platform for compressor units in their plant, the interlock system related to the vibration monitoring modules of those units came into effect, resulting in the shutdown of the units located near that area. This incident triggered extensive discussions among various departments and teams involved in safety, equipment, instrumentation, electrical systems, and the operations itself. Based on on-site inspections, DCS curve analysis, and analysis of the unit’s operation records, it was concluded that during the welding of the steel structure, the secondary grounding wire of the welder was connected to the unit’s static grounding post, which caused surge impacts and magnetic field interference to the vibration damping module, leading to the shutdown of the unit as a result of instrument interlocks. So, what should we pay attention to when carrying out welding, temporary power usage, and other tasks inside the turbine hall? What are the items that must be prohibited? Which devices are prohibited from use? How is the safe distance for related operations determined? Wait, wait—I earnestly ask for the generous guidance of all my seniors and fellow sailors; I am extremely grateful.
The question raised by the poster is excellent; although I can’t come up with any good suggestions or comments either, I hope to see the opinions of experienced and knowledgeable users in the future. The only point is that the power used for maintenance, construction, or the grounding system should be completely separated from the power supply used for the production system.
When I was working in the compressor department, I did it this way: when performing hot work on site, it is essential to pay close attention. Process engineers should assess the impact of such work on the site, and the workshop must have plans in place for this situation! The key is the presence of technical personnel; process engineers should carry out sequential shutdowns, and pay close attention to various parameters. If the electronic signal transmission of the valves is affected, switch to manual control for those valves, reduce the load as appropriate, and keep a close eye on vibration and shaft displacement! If any abnormalities occur, they can be detected in advance; identifying the cause and taking appropriate action will suffice.
First of all, I would like to thank our seniors for their generous assistance. This solution is also within the scope of our discussions; perhaps in the future, when carrying out welding or other electrical tasks in the unit building that may generate surges or electromagnetic interference, we could consider disabling the interlocks and using on-site monitoring equipment. However, this approach does not address the root of the problem, and to resolve it completely, we need to work together to find a fundamental solution.
By the way, as a supplementary point, in situations like this, it’s usually sufficient to cut off the vibration interlock and the shaft displacement interlock, as well as the interlocks related to control valves such as circuit valves. In the past, during welding, there were instances where the operation of the circuit valves was affected, leading to an interlocked shutdown of the system.
Thank you very much for sharing your experience. What was your conclusion when analyzing the causes? Are there any other preventive measures besides the drastic step of removing interlocks?
Primarily, hot work interferes with the transmission of electrical and instrumentation signals. In my opinion, interlocks serve a protective purpose; sometimes, maintenance of on-site equipment requires temporary use of fire. If hot work indeed affects these electrical and instrumentation signals, it is necessary to act carefully in such situations. Additionally, operators should carry walkie-talkies (four-way one-valve) on site to make adjustments as instructed when needed.
Practical and useful suggestions, thank you very much
The DCS grounding wire is also important; attention should be paid to it when performing welding work near the control room
Senior, could you be more specific? I look forward to your detailed guidance