Materials used in hazardous areas
The safety that explosion-proof equipment provides in hazardous plants starts from the construction materials chosen for their realization.
These materials must be able to withstand the presence of aggressive chemical substances that could lead to the degradation of the product affecting its safety; furthermore they must be able to face other factors such as the high temperature: the exposure for a long time in a particularly hot aggressive and corrosive environment could affect the proper operation of the product.
Depending on the specific plant’s needs, Nuova ASP is able to propose the best construction solution, paying particular attention to the correct selection of the material.
The materials used for the construction of explosion-proof electrical and non-electric components are divided into ferrous materials and non-ferrous materials.
Specifically, the materials mainly used for the construction of electrical equipment such as lighting fixtures, enclosures and fittings are:
- Stainless steel
- Glass fiber reinforced polyester
- Nickel-plated brass
- Borosilicate glass
Aluminum is a light but resistant metal with a generally excellent corrosion resistance: a protective oxide film on its surface prevents the corrosion. Due to these characteristics, aluminum is one of the main materials used for the construction of explosion-proof equipment: thanks its light weight it is used both during assembly and maintenance activities.
Moreover, compared to stainless steel it is cheaper.
Because of its low mechanical strength, it is not used pure, it is always mixed with other compounds which improve the performances. Nuova ASP uses low copper content aluminum which allows:
- high mechanical strength;
- good ductility;
- good compactness;
- high resistance to corrosion;
Stainless steel is an alloy based on iron, carbon and chromium which combines the typical mechanical properties of carbon steel with the characteristics of resistance to corrosion due to an intrinsic passivation property.
The main characteristics of stainless steel are:
- corrosion resistance
- heat resistance
- low maintenance cost
- recyclable at the end of life cycle
- ease manufacture and cleaning
- pleasant aesthetic appearance
Stainless steel is traditionally divided into three large families: martensitic, ferritic and austenitic.
In recent years the market is requiring more and more materials capable of resisting to chloride corrosion, for this reason, most of the Nuova ASP products are available in AISI 316L stainless steel (low carbon). The reduced percentage of carbon (less than 0.03%) is particularly useful also to overcome the problems of intercrystalline corrosion, typically present in welding processes, in which temperatures up to 850°C can be reached. To improve corrosion resistance, at the end of the mechanical processing, the stainless steel can also be subjected to a galvanizing process.
Glass fiber reinforced polyester
Glass fiber reinforced polyester is a composite material, consisting of at least two different fundamental elements: resin and glass fiber. The performances offered by each of these elements are combined to achieve a lasting overall effect by using the resin, which represents the binding element. Low weight combined with high solidity performance are essential features that make the material suitable for use in hazardous areas.
This type of material, which has a good resistance to corrosion, is mainly used for the construction of Ex cable entries (typically cable glands). In addition to the copper and zinc alloy, there is a low percentage of lead which facilitates the operations. The product is subjected to the surface treatment of electrolytic nickel plating, in order to improve the aesthetic aspects and the corrosion protection.
From a technical point of view, the chemical inertia against acidic or alkaline solutions is the most important chemical property of borosilicate glass.
The hydrofluoric acid, the concentrated solutions of sulfuric acid and the combinations of caustic solutions with high pH values and high temperatures are the sole chemical compounds that can create some corrosion problems.
Rubber (silicone and EPDM60) is the material of which gaskets are typically composed. This material offers important features, such as:
- A wide temperature application
- Flexibility, resilience and steady sealing properties at a wide range of temperatures
- excellent resistant to atmospheric agents
- Long-lasting and excellent insulating properties
- Natural resistance to fire and toxic-free combustion products
- Wide hardness range
- Chemical and biochemical inertia