“Ninety-nine percent of pump failures on board are not caused by pump failures. Instead, they are due to lack of knowledge or skills,” said John Nielsen, an experienced sales engineer at DESMI. This is a list of John’s suggestions.
John Nielsen, DESMI’s sales and application manager in China, sent a message to shipowners around the world: “Please pay attention to how your pump system is installed. Make sure it works well!”, he said. “That is the bottom line. There are too many outfits and lack of practical experience.”
Therefore, shipowners must ensure that their field teams follow key guidelines to install the pumps correctly. John said: “Because in most cases, pump failure is not caused by pump failure.”
“Ninety-nine percent of the time, the failure is related to lack of installation knowledge during the installation process. Or missing parts. Or incorrect operation (such as starting the pump without liquid) is a fatal killer. He said:” This is related to many things. ”
John Nielsen has worked at DESMI for a few years and has worked in the shipbuilding industry for more than 20 years. He knows what he is talking about. He provided the shipowner, the person in charge, the field team and the shipyard with a list of “dos and don’ts” in pump installation. He said: “You need to be aware of these things.” “The pump is just a component that will operate exactly as it was designed. However, if it is not installed correctly, you can destroy it. It’s a bit like Murphy’s law: if something goes wrong, That will definitely happen. In the end, the shipowner will have to bear the cost”
The solid pump foundation is John’s top spot. “It is very important to complete these tasks correctly. The foundation must be supported, so there is no chance of shaking.” In other words, do not install the pump on a soft board – a steel plate with no or lack of support underneath. “There is an old shipyard saying: The same amount of steel is needed under the steel plate as above the steel plate.”
If the equipment team wants to use counterweights or spring supports, they must first check the design with DESMI or steel engineers. John said: “This is not determined by the equipment team.” “Most pumps today are vertical. Two-thirds of the pump weight is actually an electric motor. Some pumps are four and a half tons, which means that the electric motor is three tons. All this requires a very good foundation to avoid vibration and so on.”
Image: The motor is two-thirds of the weight of the pump. Ensure a solid foundation under the pump
For pipe wiring, there are standard ISO rules, but due to limited space, following these rules on a ship can be tricky. John said: “So, this means you have to make another choice.” On ships, make sure that the piping design allows the liquid to flow to the suction side pump at a maximum speed of 1 meter per second (m/s). This is a rule of thumb, so you can avoid water vortex or cavitation, which will eventually damage the pump.
Then there are valve options. On ships, a large number of valves are butterfly valves, mainly because this is an inexpensive valve type. But the butterfly valve only works in the pumping direction. This is why there is always a check valve in series with the butterfly valve on the pressure side of the pump. Otherwise, if the pumps are running in parallel and one pump is dormant without a check valve installed, the active pump will pump liquid to the other pump regardless of whether the butterfly valve is open or closed.
In addition, it is important that the valve must be full bore (full port). This means that when the valve is opened, it has the same diameter as the pipe. Do not use valves with a diameter slightly smaller than the pipe. This will create a small vortex inside the pipeline and eventually destroy the pipeline and valve.
Image: If the pumps are operated in parallel, make sure to install the check valve in series with the butterfly valve.
Ensure that the size of the boundary line for water supply from the ship’s sea tank is appropriate. John Nielsen sometimes says that its design is too close to the limit. This will affect the flow rate and may cause the pump to lose suction. If this happens to the ship’s main seawater cooling pump, it may cause the main engine to shut down and lose power, putting the ship and crew at risk.
When the crossover is fully loaded, according to the rule of thumb, the liquid velocity should be at most 0.7m/s. This ensures a stable flow to the suction line of the pump.
Depending on the liquid being pumped and the surrounding conditions, it is also important to carefully plan the pump materials used. The material choices of the pump include bronze, nickel aluminum bronze (NiAIBz), gun metal, cast iron, cast steel, stainless steel 304, stainless steel 316 and duplex stainless steel. “All these materials have their own advantages and disadvantages. It is important to consider these,” John said.
For example, DESMI usually uses 316 or duplex stainless steel for alkaline or acidic liquids. “But you must handle these materials very carefully. You need to know what you are doing. Otherwise they will corrode.”
The sea water pump designed by DESMI is usually NiALBz, and the design sea water temperature is 32°C. Sea water above this temperature becomes more corrosive. Similarly, in warm areas, cast iron is not a good choice for sea water pumps. “If you work in Greenland, the cast iron pump can last a long time, but if you work in the tropics, you can’t.”
For cryogenic fresh water pumps, DESMI design uses a cast iron casing and NiAlBz impeller, and the design water temperature is 36°C. “The problem with fresh water on board is that you need to use additives to remove oxygen to avoid corrosion/rust. But there are many different types of additives, some of which make the water very viscous, and as a result the water may leak everywhere. Additives Another problem is that these chemicals change the pH of the water. This also needs to be considered when choosing materials.”
When considering materials, pay attention to the possibility of galvanic corrosion (also called bimetallic corrosion). This phenomenon occurs when two different materials (such as copper and iron in salt water) are put together. The salt water will act as an electrolyte. John said: “This is a slow killer.” “It takes a long time to discover the problem.”
“I think many people have experienced calcium accumulation in pipes etc.-this is also due to the effect of electrochemical elements.”
John’s main advice on material selection is to carefully study the materials that should be used under different conditions and listen to expert opinions.
“We have seen many customers specify bronze. Yes, we can use bronze, but we prefer to use nickel aluminum bronze because it is more rigid. And it can better avoid electrochemical element corrosion. Therefore, this It was DESMI’s choice.”
“The last sentence in this material section is related to how to improve pump efficiency. Most pumps have an efficiency of 75-80%,” John said. “Some shipowners need 80-83%. This requires more than just an update mechanism. Although there are many ways to do this, the most common method is to coat the pump with a glass-like coating internally. An electrical control system can also be used. To improve efficiency. More and more shipowners demand higher efficiency.”
John also made a short list of common mistakes-practical issues that must be considered. These are small problems around the pump. Although small-but still need to consider the following:
Image: Make sure you have the equipment to safely lift the pump onto the ship. Otherwise, maintenance will be difficult. This is a good example of not doing it!
Traditional electrical installations must follow the relevant rules and standards of the International Electrotechnical Commission (IEC), which is very important. This includes factors such as correct installation, correct cable size and correct cable temperature rating. “All this must be checked,” John Nelson said. “And in the event of a fire, you must have self-extinguishing cables. The cables must also be halogen-free. Large cables or small wires-they must all follow the same rules and regulations.”
The ground connection must be carefully made using the correct cable size. John said: “Don’t cheat.” “This means that the bottom line, the size of the ground wire must be almost the same as the main power cord. Therefore, if you are using a 3×50 mm2 power cord, you must at least use a 1x35mm2 cable for grounding. ”
A rule of thumb is to use the same wire cross section in the ground wire as the power wire of each component. John also wants to urge consideration of where to make potential grounding. “There must be no potential electrical differences between the grounding points of the same equipment.
This means that if you have a motor starter, the ground of the motor starter that drives the pump is connected to the ground of the motor. This is also called equipotential grounding. Because if they are 10 meters apart, you can ensure that there is a difference in potential. ”
He said: “It is generally believed that just because you weld something to the steel plate, there is no difference in potential. But they are big. It’s just that the welding itself will be different.”
Molded case circuit breakers (MCCB) must be adjusted and installed correctly. The setting on the MCCB is the maximum current marked on the motor.
Set the thermal relay according to the non-overload power of the pump, which is given by the pump test table.
The recommendations for the use of frequency converters and the rules and regulations follow the recommendations for traditional electrical installations above. But you must pay extra attention, because frequency generates electrical noise that must be managed. “When installing, make sure that at least a common mode filter is installed on the inverter. Larger installations may require du/dt filters.”
You must also correctly adjust the maximum current of the frequency converter-the same as the thermal relay in a traditional starter.
Then, when you want to use the frequency converter to operate the motor, you should seriously consider increasing the temperature level of the motor to a higher temperature level. “Usually, choose F class with a temperature of 135°C.
However, when running with a frequency converter, the motor will become hot due to the switching frequency of the motor power cord. Therefore, we recommend: rise to H level, which is 150°C. This will give you more leeway. In terms of price, this is a small amount of money.
In addition, set the internal winding temperature of the motor to be measured as a standard. This means that your motor should have a built-in PT100 sensor. Then, we can directly measure it. In addition, since this motor usually runs at a different RPM, make sure to install an electric cooling fan on the top instead of a standard mechanical fan. Because when running the motor at low RPM, you don’t have the same cooling capacity as when running at normal speed. However, if an electric fan is installed, the same amount of cooling will be obtained regardless of the speed of the load.
John Nielsen said: “When using a frequency converter, please carefully consider using a normal rated IE motor or a standard efficiency motor. The reason for this is that if the motor is connected to the frequency converter, by increasing the IE type on the motor No benefit will be gained. Since the aggregate efficiency of the grid will stop at the inverter, the grid efficiency on the grid is determined by the inverter. The price difference between IE2 and IE3 or IE4 is very large.”
John said that in addition to monitoring the winding temperature of the motor, “it is worth monitoring the bearing temperature, especially on important equipment. In addition, consider monitoring the vibration level at high and low frequencies.”
“The vibration level we see is 10 millimeters per second (mm/s), which is not uncommon. The pump limit (if we really want to stretch) is 7 mm/s. If the vibration level is too high, it may The pump must be stopped to avoid damage to the pump or pump parts. Remember that two-thirds of the total weight of the pump is still the motor, which is located above the pump casing, bearings, etc. Therefore, if you have a three and a half ton pump motor, it is literally The beating speed on the pump is 10 mm/s, which is like a huge hammer, knocking down some small bearings in some places. So – it’s only a matter of time before the pump stops on its own.”
There is also leakage monitoring. For large pumps with grease-lubricated bearings, if the shaft seal starts to leak, it will usually leak directly into the bearing. Grease and water are a bad combination. Therefore, to avoid this situation, please consider installing a leak detection sensor.
John Nielsen’s alpha and omega advice is: “Ensure good workmanship. That’s information. Especially on ships.”
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Post time: Jan-07-2021
