Development Engineering International Ltd (DEI) carries out fire pump performance testing on a significant number of offshore Oil and Gas installations in the UK sector of the North Sea, forming part of the routine condition monitoring programme. The pumps typically are of two types: "Line Shaft" and "Electrically Submersible" (ESPs). The line shaft type consists of a diesel engine driving a pump via a 90-degree gearbox, the pump being tens of meters below the deck level, and below the surface of the sea. The ESP is an integral motor pump unit, which again is tens of meters below the deck level, and below the surface of the sea.
These tests involve measurements of flow, pressure and rotary speed across the operating range of the pumps using non-intrusive methods. These readings are then compared against the "as built" performance curve and, in the case of fire water pumps, is used to determine whether the unit meets the installation's safety case. If an unacceptable level of deterioration is evident, the unit is overhauled or replaced. Testing of this type has been used successfully to alleviate the need for costly routine pump overhauls and has saved operators large sums of money over the life cycle of their production facilities.
Offshore installations use a series of isolation valves to divert the flow from the pump on test from the ring main to a test loop with an overboard dump. One of the main reasons a pump can fail a test is if the test loop and ring main isolating valves are passing. DEI has recently begun testing isolating valves using the Ultraprobe 2000 to ensure that pumps are not being pulled for overhaul unnecessarily. Overhaul of an isolating valve costs significantly less for a client than undertaking an unnecessary pump major overhaul.
Testing of the valves is planned in advance and a table is produced to collect the upstream and down stream readings. For the purposes of repeatability, the 50% dial readings were recorded and converted to dB using the transfer curve supplied with the Ultraprobe. The upstream readings were noted to be lower than the downstream in all cases. No leak sounds were heard at the upstream side of any of the valves. These results can then be compared/trended with subsequent readings on a routine basis.
DEI recommend that the Ultraprobe be used on all pump tests of this nature in future to monitor the condition of isolating valves so that measures can be taken during testing to eliminate valve leakage as the cause of pump performance deterioration.
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