Exploration • Drilling • Field Services
filled with a mixture of potable water or poly propanolglycol (antifreeze) with corrosion inhibitors. Te windings, which are permanently immersed in water, are insulated either with PVC (for standard applications) or PE2 with a protective layer of PA for higher demands.
possibly through a defective mechanical seal, water flows out of the system. Tis leakage is signalled by one or two level controllers in the header tank. Te whole system is, therefore, protected against the ingress of the surrounding medium. Te installation of submersible pumps on offshore platforms and vessels is very straightforward. Te complete unit comes to site fully assembled with auxiliary parts fitted to the pumps, along with power and control cables. Te unit is lifted into a vertical position by crane and lowered into the planned installation position. Once there, it can be secured onto a caisson foundation using mounting ring clamps. Te remaining installation work involves the erection of the discharge column and securing the power and control cables to the discharge pipe. On average, and depending on the
All stator windings are subject to a Hi-Pot test that proves a high winding insulation resistance suitable for windings directly embedded in the motor liquid. On account of the electro-magnetic considerations, the internal parts of the motors, namely the rotor and stator package, are made from cast iron and are paint protected, but are not in contact with seawater. Any ingress of seawater may not result in motor failure, but could cause corrosion to take place. For this reason, an electrolytic conductivity sensor can be fitted in the motor and this will detect any change in conductivity in the motor fill water. Or an overhead water tank with a level indicator can be added, which will show liquid loss in the motor. Should there be the possibility of the smallest ingress of the pumped medium into the submersible motor, then this can be prevented by the presence of a header tank. Tis is installed on the deck and connected to the submersible motor with a hosepipe to form a totally enclosed system within the inner section of the water-filled motor. Te water pressure in the system is maintained at a higher pressure than the seawater surrounding the motor, and in the event of any leakage,
Fig. 2. Assembling a submersible pump motor.
pump size and installation depth, it takes between six and 20 hours for a two-man team to undertake the installation work. When it comes to maintenance, submersible motor pumps are described as being maintenance free. KSB’s response to questions about service intervals for its UPA pump range is not to have a planned maintenance regime but to keep the equipment under surveillance and to record all results as they occur. Recommended routine checks during normal operating conditions include: pump capacity, delivery head, motor current, motor fill temperature, electrolytic conductivity or water level in the header tank, vibration and axial displacement if a sensor is fitted. Under normal working conditions,
Corrosion is of prime importance and KSB’s UPA submersible pump range is constructed from materials that offer the highest protection against seawater corrosion. These materials are typically Nickelaluminiumbronze, Duplex and Super Duplex, particularly where high salinity is encountered, and should there be problems anticipated from sand, bearings will be constructed from silicon carbide.
the service life of a KSB UPA pump is between 16,000 and 25,000 hours. During this time, the pump will remain fully operational at all times. In the Arabian Gulf, KSB has operated submersible pumps for water lift duties for up to 25,000 operating hours in seawater temperatures of up to 35°C, before being removed. Only the wear parts needed to be replaced and all other components were in perfect condition, demonstrating that even under arduous conditions submersible pumps provide excellent service performance. ●
KSB Aktiengesellschaft is based in Frankenthal, Germany.
www.ksb.com
www.engineerlive.com 31
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