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For any seawater cooling system, fuel oil transfer line or fire main system, an unjustified drop of pressure leads to trip alarms and degrades the equipment to decrease performance and to threaten critical machinery performance. Thus, an unnecessary trip and costly drydock would be avoided for vessel engineer and technical superintendent to trace to the point with reliable results. Benefitting from the support of our 100+ E&M Technicians and our 5000m workshop in Nantong City, SME Group engaged itself in engineering Marine Equipment projects and serviced for over 500 projects per year on average since the establishment in 2000, and holding ISO 9001/14001/45001 certificates (ANAB/IAF/UKAS) as well as serving worldwide. In this section, let's share a quick approach on troubleshooting of pressure drop of marine equipment and system.
Identifying the Root Cause: Filtration and Strainer Blockages
Blocked strainers or filters account for the highest cause of pressure drop in marine piping systems. As a rule, all your foreign materials from marine growth, sand, mussel shell, etc and in some cases, pieces of rust, would typically collect in the baskets of your strainer in seawater systems. As the basket continues to become more and more fouled, the differential pressure across the strainer increases as the pressure on the downstream side falls, but remains constant or somewhat elevated on the downstream side. It is important to check strainers and ensure they haven't clogged prior to making other considerations. One simple test involves checking the strainer differential pressure gages for there reading and noting any differences. We recommend using duplex strainers as you can swap between strainers and take your basket out for cleaning, as the second strainer would continue to work properly. If your filters and strainers are functioning normally it's time to review your internal process or consider contacting one of the SME Technical Engineers about installing and an additional monitoring systems that can identify when your strainers require cleaning.
Valve Malfunctions and Partially Closed Gate Valves
Pressure loss due to human error or failure of valves is a common occurrence. Valves that operate in a "full open" position such as globe or gate valves or butterfly valves are partially closed at sometimes resulting in great flow restriction. This can happen with a worn stem or indicator or normal operating or calibration error. Check valves have failed due to corrosion of or debris on the disc or worn hinge pin with the disc held in partially open instead of closed position. To check, the operator should examine physically each valve on the circuit in question, compare each valve with the line diagram of that circuit, working through each valve sequentially. On check valves it is often possible, (taking appropriate safety measures) to tap the body of the check valve with a hammer to release a stuck disc but a sticky or failed check valve will probably require replacement or stripping. It is also prudent to examine bypass lines in case of an operator accidentally leaving a bypass valve partially or full open causing unexpected pressures. The highly competent team at SME performs this function as part of routine maintenance and inspection packages thus minimizing the risk from this invisible problem.
Pipework Scale, Corrosion, and Internal Fouling
In time the components will begin to build up with internal scale deposits, corrosion products and biological foul layers inside the piping in marine environment all of these consume pipeline cross section area. Particularly true in seawater cooled applications the precipitation of CaCO3 (calcium carbonate) or mussel growth within pipes over time could effectively reduce their bore size. An internal fouling develops and manifests itself over a period of time as a progressive loss in pressure, that it can go unnoticed by the operation until the vessel performance begins to decline at a crucial stage, this situation can best be monitored using comparing current pump discharge pressures and flow rates with those published on original sea trial records/ performance data. Significant blockage indicated by for example, a15-20% reduction at a particular operating speed should lead you to investigate any blockage of this order. Ultrasonic thickness and borescope inspections will help to relate the scaling back to pipeline conditions. Chemical cleaning (acid descaling) or the removal by high pressure water jetting can remedy this, most typically when dry docked. On other occasions the offending pipework sections will just have to be replaced. We at SME regularly utilize and install ICCP with pipework condition evaluation surveys while the evaluation information allows our customers to preempt future in service fouling which might later occur, becoming a crisis for example in pressure drop and a real operational emergency for the vessel or plant.
Pump Wear, Impeller Damage, and Motor Performance Degradation
So if the strainers and valves upstream of the pump are checked out and determined to be working at 100%, the pump itself often causes the head loss. Wear is inevitable on any pump in a marine service environment, it is a common issue with the impeller vanes, Wear rings, the casing interiors and other component as well. This results in an increase in the internal leakage of the pump or internal recirculation increases the recirculation loss & so on. Impeller vane can also be lost due to low suction pressure, cavitation causes performance of the pump rapidly decrease & sometimes result in sudden collapse of pump output. So record the discharge pressure at the pump outlet flange stripping a suction pipeline &before the first isolation valve(which the can be isolated for test if applicable ),If pressure less Than that expected for the pump when it is under the rated suction pressure, then the pump is not running as the design capacity of the system may well be worn out, or one or two vanes gone. A comparison of the motor-load should be noted in addition: a lower current draw implies less load, possibly due to a worn pump or damaged impeller, versus the normal increased load to be expected from a choked system. Wear is most readily evident in terms of vibration and bearing temperatures. Our technicians in SME will help verify the pump performance curve on ship using calibration equipment such as flow metre and pressure sensors, etc. Troubleshooting a pressure drop problem requires a logical step-by-step analysis which begins with a simple strainer clearing and ascends to advanced monitoring and diagnostics of pumps. Using this disciplined methodology, marine engineers can achieve quick, efficient system diagnostics while reducing troubleshooting time and avoiding unnecessary component replacement. SME Group has more than 20 years of experience in the marine sector, a global base of support and a team who will always go the extra mile on behalf of customer needs and requirements.