01. Equipment Overview
The Daniudi Gas Field X Station is located in Xiaohaotu Township, Yuyang District, Yulin City, with a designed natural gas processing capacity of 50 × 108m3/a. It was completed and put into operation in December 2013, with the main function of boosting and exporting natural gas after dehydration and dehydrogenation treatment.
The core equipment of the station is 11 domestically produced large electric driven reciprocating natural gas compressors. The 2 # natural gas compressor model is 6RDSA-1/YZYKK710-6G, with a power of 3000KW, and both use symmetrical balanced reciprocating piston compressors with six cylinders and one stage compression. The single machine design flow rate is 151.44-525 × 104m3/d. The intake pressure is 1.70-4.50MPa, the exhaust pressure is 4.85-6.00MPa, and the lubricating oil pressure is 0.35-0.42MPa.
According to statistics, the main oil pump of the 6RDSA type unit in the station was damaged 24 times, with the situation of compressors 5 #, 6 #, and 7 # being the most prominent, and the oil pump damage interval Z being as short as 1200 hours.
02. Event sequence
On November 5, 2018, based on the operating time of the compressor, the lubricating oil of compressor 2 # was sampled and tested. The test results showed that the copper content was as high as 15.610ppm, exceeding the standard for copper content in the oil (see Figure 1). State analysis was conducted on parameters such as oil pressure of the unit, and no abnormal situations were found. Switching the unit for inspection, it was found that the main shaft sliding bearing of the main oil pump was damaged, the end cover was severely worn, and the color changed at high temperature (see Figure 2). After replacing the main oil pump, all parameters were checked and found to be normal. The machine was started for trial operation and ran normally.
03. Handling measures
1. Switch the operation of the unit.
2. Open the compressor body and check the operating components of the unit. No abnormal conditions were found, and the clearances between each part were measured to be within the normal range.
3. Upon inspection of the main oil pump of the compressor, it was found that the sliding bearings of the main oil pump were damaged and the bearing end caps were severely worn.
4. Clean the oil tank and oil passage of the machine body. Replace the main oil pump of the compressor, replace the lubricating oil and oil filter, and start the machine for normal operation.
04. Cause analysis
1. Direct cause
There are design flaws in the lubrication of the sliding bearings of the main oil pump of this model, which can easily cause shaft jamming and disengagement, accelerate bearing wear, and lead to excessive copper content in the lubricating oil, resulting in bearing damage.
2. Indirect reasons
2.1 Due to the unqualified quality of the sliding bearing of the main oil pump, the sliding shaft of the compressor is subjected to increased thermal expansion and wear during operation, resulting in insufficient lubrication and damage to the sliding bearing of the main oil pump.
2.2 The sliding bearing of the main oil pump is stuck, causing high temperature friction and discoloration of the bearing end cover.
2.3 Insufficient detection of compressor operating parameter status during daily operation.
Figure 1: Lubricating Oil Monitoring Report
Figure 2: Damaged sliding bearing
05. Preventive measures
1. Use Type III main oil pump, extend the width and shaft diameter of the sliding bearing, and reduce the bearing pressure ratio; An inclined oil hole is opened on the shaft to introduce lubricating oil from the pressure chamber into the bearing, enhancing bearing lubrication and improving bearing service life. The gear shaft is precision machined and the surface roughness of the gear is reduced through grinding.
2. The maintenance operation strictly follows the quality control requirements and conducts a thorough inspection of the main oil pump.
3. Monitor the lubricating oil pressure and promptly shut down for inspection if any abnormal oil pressure is detected.
Regularly inspect compressor oil samples, analyze and apply the results of lubricating oil sample testing.
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