Conduit

With regard to conduit, one of its disadvantages, particularly on offshore installations, is it‘s susceptibility to corrosion as a result of exposure to sea spray. Deterioration due to corrosion can occur relatively quickly and, as a consequence, can reduce the strength of the conduit. This is undesirable particularly where conduit is the method of entry to a flameproof enclosure because of the possible inability of the conduit to contain an internal explosion in the run of conduit between the enclosure and the sealing device.

Furthermore, corroded conduit may not meet the impact resistance requirements essential for use with Increased Safety apparatus.

The use of conduit in hazardous areas requires particular care, especially when used with flameproof enclosures.

In addition to maintaining the ingress protection (IP) rating of an enclosure - this applies to all types of protection - the integrity of the enclosure must be maintained, ie the conduit in the run between the enclosure wall and the conduit sealing device must also be able to withstand the force of an explosion within the enclosure so that the flames/hot gases are prevented from reaching the external atmosphere. Where two flameproof enclosures are connected by means of conduit, seals must be fitted to avoid pressure piling occurring during an internal explosion.

Sealing devices are also used to prevent the migration of gases from one hazardous location to another. Although not entirely gas-tight, they will limit, to an acceptable level, the quantity of gas which will pass at normal atmospheric pressure. Where positive or negative pressures are likely, appropriate measures must be implemented.

Appropriate installation practices must, therefore, be observed and this requires observation of the manufacturer‘s installation specification and the recommendations given in BS EN60079-14.

SELECTION OF CONDUIT

Conduit used with explosion protected apparatus will be that recommended by the manufacturer and selected from either:

• Screwed heavy duty steel, solid drawn or seam welded conduit manufactured in accordance with IEC 614-2-1; or
• Flexible conduit of metal or composite material construction, for example metal conduit with a plastic or elastomer jacket, of heavy or very heavy mechanical strength classification manufactured in accordance with IEC 614-2-5 Conduit entering flameproof enclosures is required to be engaged by 5 full threads.

SEALING OF CONDUIT

Conduit seals are required to be fitted:

• Where conduit leaves or enters a hazardous area;
• Within a distance of 450 mm from the wall of any enclosure which contains a source of ignition in normal operation;
• At all enclosures entered by conduit of 50 mm diameter or greater, which contain taps, splices, joints or terminals.

Instrument and Control Cables will be specified by the design engineer and indicated on the system documentation (see I.S. Section later).