Does static electricity occur in pipelines during welding?
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Raw materials (Category B) are scheduled to arrive at our workshop tomorrow. However, for various reasons, the pipes connecting the tank area to the workshop are still under installation. The raw materials are pumped into the large storage tanks in the tank area, and the pump’s outlet has a tee connection leading to the workshop (to deliver materials there; the two pipes are controlled separately by valves). The question is: what dangers can arise during the welding of these pipes, and how can they be prevented? Thank you!
Blind flanges should be installed behind the pipeline valves from the tank area to the workshop to achieve isolation (it seems the original poster intended to use individual valves to shut off the pipelines, but valves cannot guarantee a complete cut-off; therefore blind flanges are necessary). Additionally, proper grounding of the pipelines as well as leakage protection for the welding machines must be implemented.
Thank you. Our chief engineer said that when pipes are welded, electricity (or electric current) flows through them; if the flanges of the pipes are not insulated with anti-static materials, this electricity could reach the pump. I find it hard to understand this, which is why I came to ask for advice!
I’ve never heard of static electricity being generated during welding, and it doesn’t make sense either from the perspective of how static electricity is produced. During welding, if the overlap area is far from the welding zone, electricity flows between these two points. If there is a poor connection somewhere along this path, arcing or heating will occur, creating a source of ignition. Therefore, during welding, effective isolation is required (by removing or installing blind plates), flammable materials must be removed and cleaned thoroughly, and other pipeline equipment cannot be used as jumpers; the jumper point should be as close as possible to the welding point.
This post was last edited by lyhh9024 on 2010-9-11 07:43. If the pipeline is not disconnected during welding, current will flow in all circuits connected to that pipeline (either direct current or current induced by electromagnetic effects), and the intensity of this current depends on the specific circumstances. Your chief engineer is right. Therefore, isolation is required every time welding is performed, with direct disconnection being the most effective method. I have seen records of accidents in which a company experienced explosions in other workshops due to welding pipelines not being completely disconnected.
I originally thought that all that was needed was to loosen the flange and install a blind plate on the pipeline flange leading to the pump, but now the chief engineer requires us to use cardboard to seal it tightly off, with no contact between the two flanges. Is there any reason for this?
Reply to 6# cmhcmh1981: The blind plate is used to block the material, while the cardboard pad is used to block the electric current!
In practical applications, cardboard padding is generally not used as a shield; is it because the current tends to flow towards the ground first? Also, how can one determine the direction of the current flow?