1. Introduction The engineering companies operating in the petroleum, petrochemical, pharmaceutical, food sectors and also in all those...
The engineering companies operating in the petroleum, petrochemical, pharmaceutical, food sectors and also in all those areas where the maximum attention must be paid both to the dimensioning and to the maintenance problems of the plants, correctly select the types of equipment to be integrated into the production cycle and produce the documentation that, made available to the end user, provides precise indications on the management and the maintenance methods of these plants.
However, it often happens that the management of the plants is lacking in terms of preventive maintenance, an activity that is vitally important for the compliance with the constructive guarantees of all those electrical equipment installed respecting certain dimensional parameters such as: the belonging to a specific classification of the area in which they must be installed, the correspondence to the temperature class and to the ambient temperature to which they must work correctly without functional interruption.
Maintenance, which must be carried out daily to all the equipment, is one of the many activities necessary to comply with the regulatory requirements and for the safety of a correct operation.
Few people know that a device is designed and built taking into account specific regulatory and construction requirements, necessary for the safe operation.
The construction is defined on the basis of a series of tests that are carried out by a third certifying body, which has the obligation to verify that the equipment meets all the standards requirements, such as for example:
As written above, the maintenance is of fundamental importance for the correct equipment functionality but also to avoid an explosion.
If we analyse some of the possible causes of malfunction, we can understand how the non-cleaning of electrical and instrumental equipment can affect. In fact, the accumulation of dust on such equipment causes an insufficient or a total lack of thermal transmission, leaving the equipment in the condition of thermal insulation.
The devices, therefore, reach a state of overheating and incorrect operation. As a consequence of this, the air inside will tend to increase, raising the surface temperature which, by exceeding the expected limit of the maximum surface temperature, could cause a fire or an explosion based on the type and the concentration of gas present.
An initial (primary) explosion (Figure 2) in processing equipment or in areas where latent dust has accumulated may dislodge additional dust or damage a collection system (such as a duct, vessel or collector). This dust, if ignited, causes additional explosions (secondary explosion) which can cause damages more severe than the original explosion due to increased concentrations and quantities of dispersed combustible dust.
Dust explosions can occur in any activity in which solid materials are treated and finely divided (metals, organic substances, polymers, resins, coals, wood, etc.). Dust may be the end product of a process or an unwanted by-product. Even very common substances such as wheat flour, cocoa powder, icing sugar, tea, coffee, present an explosion hazard, often masked by their familiar appearance, when they are treated, in powder form, on industrial scale in milling, transport, separation, drying processes.
A myriad of small-sized particles is produced during the processes, thus creating dust. The particles with dimensions that are too large to remain suspended in the air are deposited, while the smaller ones remain suspended for an unlimited period.
The electrical and instrumental systems suitable for installation in environments with danger of explosion mainly comply with the international, EU and national regulations that are included in the 60079 series.
These systems are divided into zones such as Zone 1 and 2, with the presence of Gas, and Zone 21 and 22 with the presence of dust.
The reference standards for electrical and instrumental equipment installed in the presence of dust are: