In the operation of steam turbine units, the fire-resistant oil lubrication system is the core subsystem to ensure the stable operation of the rotor. As a key barrier to oil circuit cleanliness, the blockage of the return oil filter not only directly affects the oil quality, but is also likely to cause abnormal bearing temperature through a chain reaction, and even cause a burning accident. Taking the DL002001 type oil station return oil filter as an example, this paper discusses the correlation mechanism between its blockage and abnormal bearing temperature from the perspectives of oil circuit dynamic balance, heat exchange efficiency and system design defects, and proposes a systematic prevention strategy.

I. Cause system of abnormal bearing temperature

The essence of abnormal bearing temperature is the imbalance of lubrication and heat dissipation between the journal and the bearing. According to literature analysis, the main causes can be summarized as follows:

• Oil film stability destruction: uneven bearing load distribution, oil gap deviation or abnormal oil viscosity, resulting in insufficient or broken oil film thickness, causing local dry friction;
• Decrease in heat exchange efficiency: insufficient lubricating oil flow or excessive oil temperature, unable to effectively remove friction heat;
• External heat source interference: cylinder insulation failure or high-temperature steam leakage, direct radiation bearing;
• Monitoring system distortion: temperature sensor failure or compensation logic error, covering up the real working conditions.

Among them, the first two types of problems are directly related to the state of the lubricating oil system, and the blockage of the return oil filter element often becomes the hidden pusher of such problems.

II. Functions and causes of blockage of the return oil filter DL002001

As the terminal filtering device of the oil circuit circulation, the DL002001 oil return filter element has two core functions: filtering out metal debris, oxidized colloid and other particulate matter (>25μm), protecting bearings and oil pumps; balancing the return oil flow rate through the filter structure design to maintain the negative pressure of the oil tank stable.

Progressive characteristics of filter element blockage:

• Initial stage: Impurities deposited on the filter surface cause the pressure difference to rise slowly, and the oil flow rate drops by 10%-20%. At this time, the oil temperature can still be maintained normal;
• Mid-term stage: The filter is partially blocked to form a turbulent area, the gas content in the oil increases, the heat exchange efficiency of the oil cooler decreases, and the return oil temperature is 5-8℃ higher than the inlet oil temperature;
• Final stage: The filter is completely blocked, triggering the bypass valve to open, and the unfiltered oil directly enters the oil tank, the oil quality deteriorates rapidly, and the oil level in the main oil tank drops sharply due to overflow loss.

III. The association path between filter element blockage and bearing temperature rise

1. Insufficient oil leads to lubrication failure

When the pressure difference of the return oil filter DL002001 exceeds the design threshold, the circulation of lubricating oil decreases, and the oil supply pressure of the bearing decreases. Taking the 350MW unit as an example, the filter element blockage causes the oil inlet of the No. 2 bearing to drop by 30%, the oil film thickness drops from the theoretical value of 0.08mm to 0.04mm, the local contact pressure increases sharply, and the temperature rises from 85℃ to 91℃. At this time, if the unit is running at high load, the risk of oil film rupture will increase sharply.

2. Oil quality deterioration aggravates friction heat accumulation

The blocked filter element bypasses, allowing the unfiltered oil to carry metal abrasive particles into the gap between the bearings. These hard particles (such as Babbitt alloy debris) form a “micro-cutting” effect in the oil film, causing scratches on the journal surface and increasing the friction coefficient by 15%-20%. At the same time, the viscosity of the oxidized and deteriorated lubricating oil is abnormal (such as the viscosity of No. 32 turbine oil drops from 46cSt to 38cSt), further weakening the bearing capacity of the oil film.

3. System negative pressure imbalance induces cavitation

When the filter element is severely blocked, the negative pressure of the return oil pipeline increases abnormally, and the dissolved air in the lubricating oil precipitates to form microbubbles. These bubbles generate local high temperatures when they collapse in the high-pressure area, directly burning the black gold layer of the bearing. In an accident of a 300MW unit, the cavitation effect caused by the blockage of the filter element caused the black gold layer of 7 thrust bearings to melt and peel off.

4. Chain failures amplify the temperature rise effect

Filter element blockage is often accompanied by problems such as reduced oil cooler efficiency and main oil pump suction. For example, a case showed that filter element blockage caused the main oil tank oil level to be artificially high, the AC lubricating oil pump suction port was exposed, and the bearing temperature soared to 316°C within 7 minutes after the oil supply was interrupted, eventually causing multiple bearings to burn out.

The blockage of the return oil filter DL002001 is not an isolated incident, but a prelude to the collapse of the lubricating oil system. Its association with abnormal bearing temperature is essentially a comprehensive manifestation of the coordinated failure of oil circuit cleanliness, thermodynamic equilibrium and mechanical design. Only through the trinity strategy of dynamic monitoring, preventive maintenance and system optimization can this fault chain be cut off and the long-term safe operation of the steam turbine unit be guaranteed.

When looking for high-quality, reliable steam turbine oil filters, YOYIK is undoubtedly a choice worth considering. The company specializes in providing a variety of power equipment including steam turbine accessories, and has won wide acclaim for its high-quality products and services. For more information or inquiries, please contact the customer service below:
E-mail: sales@yoyik.com
Tel: +86-838-2226655
Whatsapp: +86-13618105229

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