Comparison of new and old standards for anti-static hoses
In industrial production, the rapid movement of materials is a way to generate static electricity. Static electricity is an electric charge generated when two objects made of different materials or substances rub against each other. The accumulation of electric charge is called static electricity. When certain liquids (petroleum solvents, fuels) come into contact with other materials, electrical charges will accumulate. This happens when the liquid is pumped, filtered, and guided (flowed) through the hose. The amount of charge generated depends on the amount of liquid contained and the flow rate. The accumulation of static electricity can produce sparks, which can lead to fires or devastating explosions. Production accidents caused by static electricity occur from time to time at home and abroad. However, European countries earlier proposed the protection of static electricity, and also formulated a relatively complete protection standard-EN12115 standard. The current version is EN 12115: 2011 and IEC 60079-32-1: 2011. The requirements for anti-static hoses are clearly defined in the old and new standards.
We can see Ω, M, Ω/T, M/T signs on some anti-static hoses. These signs represent that the hose has the function of conducting static electricity, but what is the difference? ? The old version of EN12115 only had two standards, Ω or M, but EN12115:2011 added two Ω/T and M/T on this basis.
a, Ω/T u003d high security requirements. The entire hose is made of a mixture of conductive rubber. The resistance value between the tube walls is 10^9Ω. The mixture suitable for the inside is an explosive medium and is used in a hazardous area (all or the main part of the pipe assembly is in an explosive area). Suitable for explosive media higher than IIA (IIB or IIC). It is also suitable for key non-conductive chemicals such as toluene.
b, Ω u003d high safety. Made of conductive rubber compound. Suitable for normal use, such as filling liquid corresponding to IIA. If the hose is partially used in a hazardous area-for example, the explosion-proof area is limited to the joint area, this type of hose may also be acceptable.
c、M/T u003d In most cases, this type of hose can be used as an Ω/T hose. But comparing Ω and Ω/T hose assemblies, this kind of hose must be considered that its conductivity is achieved through metal conductors. The connection of metal conductors is subject to high fluid loads and can be disconnected in some cases. Therefore, it is necessary to regularly measure the electrical resistivity of the hose assembly. Furthermore, when there is so-called stray current in the environment, try to avoid using M/T (or M) hoses.
d, M u003d suitable for normal use. For example, filling the liquid corresponding to explosion group IIA, but this type has the same restrictions as the use of M/T hoses.
When we talk about the conductivity of a tube, we can’t think of a tube with a low resistivity as a good conductive hose. For example, a tube with a copper wire to conduct static electricity, because a low resistivity will generate a large current. There is a hidden danger of sparks. The inner wall does not conduct static electricity, but there is also a risk of static electricity conduction between the reinforcement layer and the outer rubber. When the external charge is high enough, the inside of the hose may be broken down. Therefore, the recommended choice is Ω/T hose (tube wall resistance <10^9Ω).