What are the reasons for abnormal noises during the operation of LNG high-pressure transfer pumps?
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The high-pressure LNG transfer pumps at a certain LNG receiving terminal are submersible high-pressure pumps installed atop elevated platforms. There are four such pumps in total, arranged in parallel. Initially, the vibration levels of the equipment were normal. Over time, however, the vibration acceleration values of 2 of these units increased gradually, and abnormal noises could be heard inside the pumps. Upon seeing this, the owner promptly stopped the equipment and carried out a thorough inspection. No abnormalities were found in the equipment itself, nor were any solid particles present in the pipelines; the pipelines were purged again. After the equipment was reassembled and restarted, abnormal noises appeared once more, and the vibration acceleration value reached around 1G. By reviewing the historical data on the DCS, it was found that there is no significant correlation between changes in vibration levels and changes in operating conditions such as temperature, pressure, and flow rate. All process parameters remained within the normal range during operation. Subsequently, the following checks were carried out: 1. The pipeline was purged thoroughly before operation, with no foreign objects present, but the inlet filter was not removed for inspection ； 2. The pump’s self-return pipe is far from the pump inlet, meeting the requirements ； 3. The filter screen is of T-type, which prevents low-inflow and high-outflow phenomena and meets the design requirements ； 4. The gases generated by backflow have been fully released ； 5. The pump inlet piping lacks a U-tube and is installed horizontally ； Based on the observations on site, it seems to be cavitation, but no significant evidence has been found to explain the cause at present. The following issues remain unresolved: 1. Was there stress that was not fully released during pipeline installation, resulting in low-temperature contraction and causing the pipelines to tilt? 2. The levelness of the pump body is within the standard of 0.05 mm/m. 3. The actual mesh size of the inlet filter is 40 mesh – is that too low? 4. If there are problems on the booster pump side, could that cause issues with the subsequent high-pressure pump? I hope the experts here can give me some advice!
This post was last edited by tomlinson on 2020-12-22 09:23. Based on the phenomena described by the original poster, you might consider checking whether there are any impurities or heavy hydrocarbons in the pump tank； Additionally, rapid cooling of the pipes can cause abnormal noises ； There is also resonance generated by the pipes and pumps, which is relatively difficult to analyze ； Additionally, in terms of the installation angle, is the connection between the submersible pump and the top plate secure? ； Installed on the ground; when wet, the levelness of the pump chamber must be maintained ； Regarding the original poster’s question: 1. This is possible; an inspection is required ； 2. This can meet the requirements, but it is necessary to check whether it will still meet the requirements after liquid is introduced ； 3. A 40-mesh filter screen can meet the requirements ； 4. If there is indeed an issue on the high-pressure pump side, it will affect the submersible pump itself, but it has little impact on downstream systems.
Hello, thank you for getting back to me. The pump is not installed below the water level but is suspended at a high altitude; therefore, there is no pump pool. If the pump continues to make noise, are there any other possible causes? Will long-term operation cause damage?
By pump pool, I do not mean the underlying structure, but rather the outer container of the submersible pump. If the pump keeps making noise, have you already checked the submersible pump itself? Have you checked the low-temperature bearings as well? By the way, whose submersible pump does your family use? Ebara? Nikkiso? J.C. Carter? Cryostar? The structures of different manufacturers vary slightly, and the potential for failures may also differ. If there is a problem with the pump itself, the continuous abnormal noise will definitely cause damage to the pump ； If the abnormal noise is caused by external structures such as pipes or insulation, it certainly will not have an impact on the pump.
The original poster is also from the industry, and their response was very professional; after confirming that the noise wasn’t coming from pipes, pump tanks, etc., it was necessary to check the actual equipment such as the pump shaft.
Hello, thank you for getting back to me. The pump is a Nikkiso device. After the equipment was disassembled and thoroughly inspected, no wear or damage to the equipment itself, nor any bearing failures were found. The magazines inside the pump tank were also purged, and no foreign objects were found; however, the filter has not been inspected yet. This issue will also be addressed by checking it during the next opportunity when the unit is disassembled. It is generally speculated that there might be some issue with the system; I hope experts can continue to provide guidance!
Four units are installed in parallel. Which two of them are vibrating? Is there an issue with uneven flow distribution at the inlet of the high-pressure pump? How are the inlet pipes arranged? Could you draw a simple diagram?
Is the vibration level high right now? What kind of sound is the abnormal noise? Could it be impact vibration caused by the flow of liquid exiting and getting entangled with cables, steel ropes, etc.?
Here’s a suggestion: collect the vibration spectrum and analyze it in detail. Disassemble and inspect all moving and stationary components for signs of friction. Check the dynamic balance of the impeller and the straightness of the shaft; if the pump shaft and motor rotor can be accessed, examine the dynamic balance of the rotor as well. Don’t believe that the straightness of foreign-made components is normal, or that there are no errors in the rotor’s dynamic balance. I’ve encountered two similar problems; feel free to message me if you have any other questions.
The pump shaft and the motor rotor can be separated; check the dynamic balance of the motor rotor. The internal pump of Nisshiki Seiki is disconnected. What we have is one unified whole. Also, the three low-temperature bearings will definitely work fine.
Did the vibration of this submersible pump occur at the beginning of operation or after it had been running for some time? If the vibration appeared in a newly installed system, then the pump needs to be inspected; if it occurred after the pump had been running for a while, then there is probably nothing wrong with the pump itself, and the issue is more likely to lie in the piping.