Three questions about coking of air compressor oil

April 09, 2023

Air Compressor Oil is the "blood" that flows inside the air compressor and is crucial for the normal operation of the compressor.

Among them, coking is the most serious type of deterioration in air compressor oil. If not treated in a timely manner, it will inevitably lead to more serious accidents, such as severe carbon deposition, engine jamming, and detonation.

First: Why does air compressor oil coking?

Physical and chemical factors
Overall, coking is caused by a series of chemical changes in the air compressor oil.

Lubricating oil belongs to organic compounds. Taking mineral oil as an example, its main components are various hydrocarbons (including alkanes, aromatics, cycloalkanes, etc.). Hydrocarbon compounds undergo oxidation reactions under the action of heat, oxygen, and light. The higher the contact heat and oxygen intensity, the stronger the oxidation reaction rate. Oxidation can cause molecular chain breakage and may also cause cross-linking, both of which can cause changes in the properties of hydrocarbon compounds.

In practical applications, it manifests as an increase in oil viscosity, an increase in acid value, a change in color, an increase in insoluble substances, etc. When a deep oxidation reaction occurs, the increase in oil viscosity exceeds a certain range, resulting in coking phenomenon.

Of course, different types of air compressor oils undergo different changes in their properties during oxidation reactions. In practical applications, most coking accidents of screw air compressor oils are caused by the use of low-grade mineral oils.

Direct cause

1. Metal ions
The internal debris of the air compressor not only blocks the oil system, but also serves as a catalyst for oil oxidation. The presence of iron and other metal ions acts as initiators for the polymerization of certain hydrocarbons. The more water content in the oil, the higher the temperature, and the greater the tendency for metal catalysis. Therefore, metal debris in the oil should be removed in a timely manner.

2. Oxidation
Air compressor oil reacts with oxygen, sulfur and other substances in the air under high temperature and metal catalysis, generating alcohols, aldehydes, ketones, acids, and oxides. Under the long-term action of oxygen and high temperature, some hydrocarbon substances undergo polymerization, forming insoluble substances. The higher the pressure of the air compressor, the higher the oxygen concentration, the more severe the oxidation of the oil, and the shorter the service life of the oil.

3. Moisture impact
Due to the frequent contact between air compressor oil and the compression medium, the moisture in the air will condense and enter the oil after compression. In addition, the intense stirring during unit operation causes the two liquids, "oil" and "water", which cannot be mixed together, to mix together. When used for a long time without changing the oil, one phase of the liquid disperses into many particulate molecules scattered in the other phase, becoming an emulsion. The emulsified oil not only reduces the lubrication effect, but also causes hydrolysis reactions of additives or Base Oil, causing equipment corrosion. Rust gradually deposits, forming a portion of oil sludge or coking material seriously.

4. Impact of old oil
Most air compressors nowadays use mineral oil or semi synthetic oil based on mineral oil, with a lifespan generally between 2000 and 4000 hours. If this type of oil is not replaced, coking may occur after a maximum of about two years of operation. Even if it is a normal oil change, there will be slight such phenomena. Because it is impossible to completely discharge the sediment oil every time, the remaining old oil deposits at the low point of the oil circuit, and participates in a new round of oil circulation along with the new oil. After running for a certain period of time, the oil quality will deteriorate and coking phenomenon will occur.

Root cause
The coking of air compressor oil is not inevitable, and the root cause lies in "people" rather than "objects". The factor of 'human' can mainly be considered from two aspects: production and use.

1. Insufficient professionalism of the manufacturer
The quality of air compressor oil cannot be guaranteed. From the current market situation, many professional air compressor manufacturers do not produce matching air compressor oil products, and mostly rely on professional supply and cooperation from petroleum enterprises. Individual manufacturers and distributors are looking for small factories to supply in order to reduce costs. In this way, the quality of oil products will inevitably not be guaranteed, which is a major root cause of oil quality problems.

2. User's own reasons
Some users do not use the required oil according to regulations to reduce costs when using air compressors:

(1) The mixing of new and old oil products results in the failure of the new oil. Production enterprises do not change oil for a long time when using equipment. As long as the air compressor can rotate, add lubricating oil when there is not enough, causing pollution by mixing new and old oil, and thus losing the proper function of new oil;

(2) Mixing multiple brands of air compressor oil results in reduced performance. Little did they know that the formulas of air compressor oil additives from different manufacturers are not the same, and their compatibility with similar products is poor;

(3) Blindly adopting various alternative oil products. Replace with Gear Oil, hydraulic oil and other non air compressor special oil products. This not only wastes resources but also increases costs, and more importantly, it does not have the expected effect of specialized oil products.

3. During long-term high-temperature operation, the oil naturally evaporates and forms coking
The working environment of the air compressor is not good, the cooling water supply is insufficient, and the air cooling fins are blocked, resulting in a reduced cooling effect. This causes the equipment to work in a critical state of high temperature or high temperature for a long time, resulting in natural oxidation of the air compressor oil, accelerating the overall aging of the oil, and forming coking.

4. The quality of air compressor accessories is poor, and the product technical parameters cannot meet the requirements

The quality of the air compressor accessories purchased by some enterprises is poor, which cannot meet the technical requirements of the unit itself, resulting in the failure of the air compressor oil and the formation of coking. The main reasons are:

(1) The air filter quality is not good. The poor dust filtering effect causes the dust to be directly sucked into the oil in the chamber of the air compressor, directly contaminating the oil, causing the oil in the air compressor to age, obstructing the oil circuit, causing the air compressor to shut down at high temperatures, and causing coking of the oil in the air compressor;

(2) The oil filter quality of the air compressor is poor. Unable to prevent debris from entering the oil;

(3) The oil separation effect does not meet the technical specifications. The main manifestation is unclear oil separation, which causes the air compressor oil to evaporate with the compressed gas, resulting in a lack of oil in the air compressor body and the formation of high temperature phenomenon.

Second: How to prevent the lubricating oil from coking in the air compressor?

1. Be sure to use oil according to the regulations of the air compressor equipment

In some harsh working conditions, shorten the usage time of the oil appropriately. Before each oil change, the oil circuit of the air compressor should be cleaned to prevent debris and coking substances from blocking the oil circuit.

2. Ensure the quality of air compressor accessories and spare parts
Strictly control procurement and ensure the use of genuine air compressor accessories.

3. Maintain smooth heat exchange in the cooling system
The air-cooled unit should maintain the cleanliness of the cooler fins to ensure good heat dissipation. The water cooling unit should ensure the supply of cooling water. Every six months or one year, it is necessary to open the cooler for inspection, clean the scale, and perform descaling and maintenance treatment. Especially in the northern regions, many cooling water has a hard water quality, which can easily form scale and affect cooling efficiency. Therefore, special attention should be paid to descaling maintenance or cooling water softening treatment. The reason for this is to avoid poor heat dissipation of the air compressor. Long term operation at high temperatures can cause significant damage to the oil.

4. Adhere to the use of specialized air compressor oil
Do not replace air compressor oil with hydraulic oil, gear oil, base oil or other air compressor oil. In terms of oil function, hydraulic oil has good hydraulic transmission and wear resistance, but poor resistance to high-temperature oxidation. Gear oil has good shearing property, but high viscosity and poor high-temperature resistance. The base oil is not added with key additives, such as anti-wear, Anti Foam, anti-oxidation, etc., to help complete the function of the oil and cannot be used directly.

Third: What should I do if the air compressor oil is coking?

If coking is found (even if it is rare), it is necessary to undergo professional cleaning. Disassemble the host and soak it in a dedicated cleaning agent. Then clean and soak the oil and gas barrel, cooler, and main oil circuit components. After soaking, all sealing components of the machine need to be replaced.

After cleaning, the air filter, oil filter, and oil separator should be replaced in a timely manner. According to the coking situation and economic efficiency, carbon cleaning agents, acetone cleaning, Tena water, caustic soda, etc. can be selected for cleaning, and special attention should be paid to the safety of using cleaning solvents.

The above is the Three questions about coking of air compressor oil we have listed for you. You can submit the following form to obtain more industry information we provide for you.

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