First, case background

The air compressor of a cement plant uses a certain brand of coolant. In May 2015, the oil change process was carried out. Shortly after the oil change, the oil was cokeed. As shown in the figure, after a long shutdown, the start-up was difficult and could not be normal. run.

Oil coking

Second, detection and analysis

In August 2015, the customer sampled both new and faulty oils and wanted to find out the cause of air compressor oil coking through oil analysis. In this regard, Guangyan Testing has carried out a thorough testing program, and has carried out detailed testing and analysis on new oil and in-use oil.

From the test data, you can find:

(1) The infrared oil, nitrification and sulfide content of the old oil being inspected are very high, and the oil has been seriously oxidized;

(2) The content of B and Ba in the old oil is higher, and the content of the two elements in the new oil is lower, which indicates that the composition of the new oil and the old oil are different, and the air compressor has a mixed oil phenomenon;

According to the experience of Guangyan Testing, the 40°C viscosity of the brand coolant is typically 48mm2/s, the viscosity index is greater than 150, and there is Ba additive, and the viscosity and viscosity index of the new oil sent at 40°C is significantly lower than the typical one. The value, and does not contain Ba element, initially suspected that the new oil has quality problems.

For further confirmation, the new oil sent this time and the new oil in the Guangyan test database were compared in infrared, as shown in the figure.

It can be seen from the infrared spectrum comparison chart that the new oil (red map) sent for inspection is quite different from the typical map of the brand coolant (blue map) in the database. The brand coolant is a polyethylene glycol synthetic oil. (PAG), and the new oil submitted for inspection is a hydrocarbon oil.

According to the description of the site, the oil of the head cannot be completely discharged due to the incompleteness of the last oil change, and the mixing of new and old oil is inevitable. However, since the new oil added to the system is different from the original coolant base oil, the oxidation reaction occurs under the action of high temperature after mixing, resulting in the formation of a large amount of gelatinous substance, which ultimately leads to an increase in the viscosity of the oil and difficulty in starting the machine.

First, suggested actions

Through oil testing, it was found that the air compressor failure was caused by oil mixing, and the new oil used was completely different from the brand coolant composition. This aspect may be caused by the accidental addition of other types of oil during the oil change on the spot. On the other hand, it may be a quality problem with the new oil. It is recommended to check the oil change operation on the spot first. If other oil products are mistakenly added, if the oil change operation is confirmed to be correct, it indicates that the new oil purchased in the batch has serious quality problems, and the source should be identified.