Are any special precautions suggested by customers and installers against the discharge of static electricity during maintenance works?
PE pipe has a high electrical resistivity and static charge can accumulate on the surface of the PE pipe. Normal handling from pipe slings, cloths, etc generates the static charge, particularly in dry conditions.
Static occurs inside PE pipe in gas distribution systems because gas is electrically resistive. That means that electrons that have been scraped off gas molecules by friction as they flow against the PE pipe surface are resisted from reinserting themselves into gas molecules that have lost electrons. Instead, the free electrons build up on the interior PE pipe surface creating a negative charge with the ever-present possibility of arcing and igniting the gas any time the pipe is breached. Dust particles in gas also generate tension which needs to be discharged.
High static electric charges can develop on PE pipes during squeeze-off, when repairing a leak, purging, making a connection, etc. Safety procedures have been developed by the major gas utilities to prevent static electricity igniting the flammable gas-air mixture.
Ensuring good contact with the ground can easily dissipate the static charge, effectively earthing the PE pipe. This is achieved during normal backfilling operations or by wrapping a damp cotton cloth around the pipe and ensuring it is in contact with the ground.
The following precautions are often suggested to increase safe working where there is a risk of static discharge:
- Use an earthed wet tape conductor wound around, or laid in contact with, the entire section of the exposed piping.
- If gas is already present, wet the pipe starting from the ground end with a very dilute water and detergent solution. Apply tape immediately and leave it in place.
- Wet the tape occasionally with water. Where temperatures are below 0°C add glycol to the water to maintain tape flexibility. Earth the tape with a metal pin driven into the ground.
- Do not vent gas using an unearthed plastic pipe or tubing. Even with earthed metal piping, venting gas with high scale or dust content could generate an electric charge in the gas resulting in an arc from the dusty gas cloud back to the pipe which could ignite the gas. Vent gas only at a downwind location remote from people or flammable material.
- Dissipating the static charge build-up with wet rags, a bare copper wire, or other similar techniques may not be as effective as the above procedure.
In all cases, use appropriate safety equipment such as flame resistant and static free clothing, breathing apparatus, etc, and follow instructions from installers and our customers.