How to effectively prevent cable damage in oil and gas applications
Eldon Kruger discusses how novel flameproof cable gland technology is effectively preventing cable damage in oil and gas applications.
Cable glands are a crucial component for ensuring the safety and reliability of electrical connections in hazardous environments, such as oil and gas applications. Their role is to provide sealing and protection against the elements, while preventing the ingress of moisture and dust into electrical enclosures. In particular, cable glands are vital in situations involving explosive atmospheres, where sparks could ignite flammable gases or dust.
The Taper-Tech flameproof gland range from Pratley features four distinct glands across two unique categories. The first category includes the Pratley Taper-Tech gland for armoured and braided cables, which is a ‘double compression’ gland, incorporating both an inner and an outer seal. The second category consists of the Pratley Taper-Tech single-seal flameproof gland, also for armoured and braided cables, but equipped with a unique “self-drying” durable rubber shroud that breathes out any residual moisture.
Additionally, the range offers two ‘double compression’ glands for unarmoured cables, one of which is a hose-tail version that includes a tail on the compression nut. This design is intended for use with flexible hosing, particularly in applications such as mining machines, where it protects the cable’s outer sheath.
TAPER-TECH TECHNOLOGY
A standout feature of the Pratley flameproof cable gland range is the incorporation of Pratley Taper-Tech flame seal technology. This technology utilises tapered seals made from high-quality, high-temperature, and low compression-set elastomers developed by Pratley. Each seal features a taper on the leading edge that effectively seals against the gland nipple taper on the inside. The differing angles of the taper on the bush and the cable gland’s nipple enhance sealing performance.
This design allows the bush to slide down the taper easily under thrust or pressure from the front when tightened, thereby reducing the force required to achieve radial compression.
UNDER PRESSURE
Flameproof cable glands installed on flameproof equipment are engineered to withstand extremely high explosion pressures, which can reach up to 30 bar in many instances. For optimal sealing performance, it is crucial to maintain adequate pressure between the seal and the gland bedding.
As the leading edge of the seal forms a taper directed towards the applied explosive pressure, an increase in this pressure results in a corresponding increase in the radial seal pressure on the cable bedding. Once the pressure is relieved, the bush reverts to its initial low-pressure state, ensuring that high seal pressure is only applied to the cable when necessary.
The range is also designed to accommodate soft-bedding cables, such as PVC, which are susceptible to creep. This allows for safe installation on flameproof equipment without concerns about cable damage or inadequate long-term sealing.
UNARMOURED CABLES
The technology is significantly enhanced in the cable gland designed for unarmoured cables. These glands must not only provide a seal against high explosion pressures but also withstand axial pull-out forces. This is accomplished through a mechanism like the sealing process, where the rear outer seal features a taper that aligns with the cable’s pull-force.
As a result, the contact pressures increase in proportion to the pull-force exerted on the cable, ensuring that high contact pressures are present only when the cable is under tension. Pratley’s Taper-Tech technology effectively prevents cable damage commonly associated with inferior weak-back seals while fully adhering to the stringent IECEx flameproof cable gland requirements.
Eldon Kruger is at Pratley.
