Analysis of coking problems in radial and thrust sliding bearings of axial flow centrifugal compressors?
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This post was last edited by Huang Zhao on 2020-7-12 at 11:32. Analysis of coking issues in the radial and thrust sliding bearings of axial flow centrifugal compressors. Model: Samsung SM6000; Power: 2100 Kw. Three-stage compression, with an outlet pressure of 0.88 Mpa. The first and second stages share the same shaft (rotation speed: approximately 13,000 r/m), while the third stage has its own separate shaft (rotation speed: approximately 25,000 r/m)； The coking areas in the thrust bearings are all on the main thrust surface; the radial bearings are tilting type: there are 3 lower bearings and 2 upper bearings, with coking occurring in 2 of them ； The lubricant is Mobil 1024, a specialized oil for compressors (very expensive), with a viscosity of 32 ； The temperature, pressure, and flow rate of the system’s lubricating oil are all within normal ranges; the compressor operates stably, and the vibration levels at each stage of the rotor are normal. This allows for a major overhaul every 4 years. The main goal is to analyze the causes of coking in sliding bearings ； I believe that too little lubricant reaches the sliding bearing area, so the heat generated by static and dynamic friction cannot be dissipated; as a result, the area remains at high temperatures. This causes the components in the lubricant to accumulate and coking at high temperatures. I would like everyone to help analyze this situation and to keep an eye on it. Thank you. Why can’t I add pictures? ? ? ? ?
Is it normal for there to be carbonization on the two sides of the lower bearing shells, or at a somewhat horizontal position? The main issue lies in the fact that the clearance between the tilting bearing shells is relatively small, and the oil contains a small amount of impurities. Just because it’s imported doesn’t mean it’s of the best quality; it is recommended to use filters with filtering elements
This post was last edited by Huang Zhao on 2020-7-10 at 10:07. There are 3 pieces of lower tiles: one is in severe condition, one is in a mild condition, and one has very little damage. It is mainly the thrust surface, the thrust bearing surface of the third stage, which is divided into 12 small sections by the oil return holes. Coking occurs on each of these sections; 9 of them have coking covering 70% of their surface area, while the remaining 3 sections have coking covering 30% of their surface area. I really want to add pictures, but I just can’t do it.
1. The oil needs to be analyzed; in particular, the oil currently in use should be compared and analyzed against the oil specified by the manufacturer. 2. Is the actual performance of lubricants as good as you might think? The data speaks for itself. Oil bath lubrication is used here, and it is required that the lubricating oil maintain a certain level so as to ensure proper distribution of the lubricant and enable it to fulfill its intended function. 3. Based on personal analysis, after coking, carbon provides a certain degree of lubrication and cooling effect; therefore, there is not much change in your operating parameters.
Images cannot be uploaded; you can try using a different browser – there should be no major issue.
Please conduct a paint film test on the lubricant
If it’s said that the oil temperature is normal, then why still does coking occur? It must be a problem with the quality of the lubricating oil
After 4 years of use, it’s performing well. Such sliding bearings rely on an oil film for lubrication, so it’s normal to experience such issues after such a long period of time. It is a special type of material deposition phenomenon. As for the issue with the images sent, it might be that the files are too large to be uploaded. It’s best to use screenshots, or phone photos should work as well. High-resolution photos from cameras are not supported. For reference.
After coking, the oil temperature is not necessarily abnormal; in the case of oil mist lubrication, the oil mist adheres to the bearings in the form of very small particles. The temperature may not be high, and a thin layer of substance similar to a carbon coating is formed, which possesses the basic properties of lubricating oil.
Is your compressor steam-driven or electrically driven? You need to analyze the compressor oil with regard to parameters such as emulsification resistance time, flash point, acid value, and solid particles. Normally, a plate-type filter and a vacuum oil filter should be connected to the oil tank to enable an oil circulation system
The oil circuit is equipped with precision filter elements, with an axial thrust clearance of 0.13–0.18 mm and a radial clearance of 0.06–0.08 mm.