Generation and Elimination of Static Electricity in the Use of Loading Arms
Static electricity is a physical phenomenon where positive and negative charges on the surface of an object become separated. A substance becomes charged when it loses or gains electrons-positively charged when losing electrons and negatively charged when gaining electrons. When a statically charged object comes into contact with a zero-potential object (grounded object) or another object with a potential difference, charge transfer occurs, which is the spark discharge phenomenon we commonly observe.
The main cause of static electricity formation in loading arms is friction.
When two objects of different materials come into contact and then separate, static electricity can be generated. The most common way to produce static electricity is through frictional electrification.
During the loading and unloading of materials using a loading arm, friction occurs between the flowing liquid material and the inner wall of the loading arm pipeline, generating static electricity. In such cases, the anti-static belt equipped with the loading arm is needed to help eliminate static electricity in the pipeline used for loading and unloading materials.
Both ends of each swivel joint of the loading arm must be equipped with copper strips for bridging and conducting static electricity, and the outlet end must be connected to the tank truck with a static clamp for grounding to eliminate static electricity.
The presence of static electricity in the loading arm during use is obviously unacceptable, as it can cause immeasurable harm.
Attention should be paid to the following locations: the entry and exit points of railway loading arms into/out of installations or facilities; the boundaries of explosive hazardous areas; loading arms equipped with pipeline pumps, as well as permanent filters and buffers at pump inlets. Metal components of pipelines, equipment, buildings, and structures at loading/unloading platforms and terminals for flammable liquids and liquefied hydrocarbons (excluding those under cathodic protection), as well as railway rails, must be electrically connected and grounded.
Special grounding wires for static electricity must be installed at railway loading arms, railway tank car loading arms, and loading/unloading areas. In production, processing, storage, and transportation involving loading arms, if equipment, pipelines, operating tools, or the human body may generate and accumulate static electricity, leading to potential hazards, static grounding measures should be adopted. To eliminate static electricity from the human body at tank farm loading arms, a grounded metal rod should be installed at the entrance of staircases, or a 1-meter-long exposed metal surface should be left on already grounded metal railings.
The outer shells of fixed equipment (towers, containers, pumps, heat exchangers, filters, etc.) must be statically grounded. For equipment with a diameter of 2.5 meters or more and a volume of 50 cubic meters or more, there must be at least two grounding points, which should be evenly arranged along the periphery of the equipment with a spacing of no more than 30 meters. The enterprise's substation and distribution equipment, electrical equipment, electrical lines, as well as working grounding, protective grounding, lightning protection, and anti-static grounding systems must be intact, effective, and functional.
