Frequently asked questions on ELFIT!
It is important to select the right material used to make certain components that will be installed in either industrial environments or areas at risk of explosion due to the presence of gas. This decision is allocated to the designer of the system where the products will be installed, who is the person most familiar with the process variables and the presence of gases, which, in addition to having a specific ignition temperature, also have a certain aggressiveness such as to possibly trigger a corrosive process.
Hence why it is important to select materials able to withstand such aggressiveness.
For example, if stainless steel is used in the presence of gas or concentrated sulphuric acid vapours, it will not be subject to corrosion, but if the sulphuric acid is diluted to about 70%, the stainless steel will start to corrode. In this case, it will be necessary to use carbon steel, insofar as safe against corrosion.
Similarly, if the choice falls back on aluminium, it must be protected against corrosion with a passivation process before being painted, if in the presence of salt mist.
For various reasons related to the presence of substances such as firedamp, the ideal material is cast iron, or alternatively, carbon steel.
Read the insight “Constructive materials for classified zones”.
The maximum surface temperature implies the maximum detectable temperature on the outer surface of the equipment in normal operating or fault conditions, whereby this last aspect is specifically required by the protection technique. The maximum surface temperature is of crucial importance when the place of installation is classified by the presence of combustible dusts. Dusts are in fact deposited on the outer surface of the equipment. In the case of gases, however, it is necessary to consider the equipment temperature class, that is, a parameter which also considers the temperatures of the internal parts with which the gases may come into contact. Gas, in fact, unlike dusts, penetrates the inside of the equipment.
Those responsible for classifying the plant areas, being familiar with the substances therein, determine the temperature class required by the classification of the areas. With regard to the temperature classes, the installable equipment in those areas must have an equal or higher temperature class.
Correspondence between Temperature class required by area classification and acceptable Equipment temperature class [CEI EN 60079-14:2014 TABLE 3].
For more information, see the “Guide to the Ex world”.
If the thread is cylindrical, the number of threads must be greater than 5 (see Table 4:60079-1), if the thread is conical, the number of threads must be greater than 5 on each part of the threading, guarantee a firm hold and the NPT requirements of ANSI/ASME B1.20.1.
When the equipment has a “mixed” constructive form, that is, the with the sparking part in the ‘Ex db’ enclosure and the non-sparking part in the ‘Ex eb’ enclosure, the cable glands can be the increased safety type with protection technique ‘Ex eb’ or with double marking ‘Ex db eb’.
When the constructive form of the equipment is in an ‘Ex db’ enclosure, the cable glands must have a protection technique ‘Ex db’ or double marking ‘Ex db eb’.
This family of “db” cable glands covers two types: cable glands with sealing ring and barrier cable glands. The choice of the most suitable type depends on the selection criteria indicated by the standard for electrical installations in hazardous areas IEC/EN 60079-14.
For more information, see the “Guide to the Ex world”.
This type of problem often arises due to the non-safety of the designer, who, in order to be able to make subsequent schematic changes, may need to introduce additional conductors in the passage between one enclosure and the next. Hence the request to seal the sealed fittings at a later stage.
In this case, the producer must be immediately informed of having delivered a product that is not fully compliant, and it must be ascertained whether or not said nonconformity is attributable to the above.
Then, if the manufacturer is unable to promptly tend to the machine’s functional needs, it is necessary to check whether the equipment was supplied with the sealing kit, and if so, proceed with sealing in strict compliance with the manufacturer's instructions.
The interconnection between the two enclosures, which must be installed in such a way as to guarantee the lamination of the flame to stop the fire from spreading outside the equipment itself (to this end, see point 14.2 of the standard 60079-14), can be made with barrier type (sealable) cable glands, which can in turn be connected to a threaded conduit tube in order to guarantee the mechanical protection of the cable.
Regardless, note that when adopting this system, only specific “conduit” cable-carrying tubes compliant with standard UNI 7683 and without welding can be used, in order to protect the cable against any abrasion during insertion, which may otherwise affect its insulation level.
Moreover, as provided for by standard 60079-14, point 9.4, the maximum allowable packing of the tube containing 3 or more cables must not be greater than 40% of the effective internal tube diameter.
The equipment is delivered in special protective packaging, which, depending on the destination, can be land-based or maritime with barrier bag.
The installer must first and foremost check its integrity and correspondence with the documentation attached to the packaging, then, after eliminating all the unnecessary parts, proceed with its physical installation.
They will then check its correct operation and the tightness of the internal fasteners on the electrical connections.
This being done, they can make the interconnections (cables) between the equipment and utilities in the field, using specific cable glands pre-installed by the manufacturer, or procuring certified cable glands suited to the threaded entries already present on the enclosures and which comply with the clamping diameters for the cables. The cable glands will be selected according to the selection criteria of standard 60079/14.
The cable glands must be sealed in accordance with the provisions imparted by the manufacturer of the cable gland in the assembly instructions, adopting all necessary measures to guarantee the mechanical protection rating declared on the equipment certificate plate.
The first digit of the IP6X marking indicates protection against the ingress of solid objects and dust, the second digit IPX6 or IPX7 indicates protection against the ingress of liquids.
IP6X = Totally protected against the ingress of dust.
IPX6 = Can resist water jets, which, if directed towards the enclosure from any direction, must not cause any damaging effects.
IPX7 = Protected against the effects of temporary immersion in water. The casing is protected against damaging effects when temporarily immersed in water in standardised pressure and time conditions, which must be declared by the manufacturer. For example: depth of 1 metre for 10 seconds.
When the equipment is marked with the double value, this means it is suitable for both specified conditions. Note that a device with IPX7 marking does not necessarily pass the IPX6 test, and the same applies to a device with IPX6 marking subjected to the IPX7 test.
Hence why the marking indicates both protection ratings.
The cable gland for armoured cable is the double seal type, made with a sealing ring around the outer armour covering sheath, and a sealing ring that clasps the sheath containing the conductors. The latter guarantees the lamination.
Use utmost care when selecting the cable gland, making sure to select one with a range of sealing ring diameters such as to guarantee correct mechanical clamping.