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Compressor Failed. WHY?

posted on December 13, 2017 / IN Failure Analysis /

A Second Stage Compressor (SSC) failed at an air collection company. Prior to the incident, a power failure occurred on the same day at 1700 hours which caused the Main Air Compressor (MAC), which houses the SSC, to trip.

The power failure was rectified at 1900 hours and the plant process was restarted thereafter. The MAC was the first equipment to be restarted which later gave out an abnormal high reading of vibration from the SSC.

The high vibration subsequently caused the interlock system of the MAC to trip the MAC.

Personnel of the air collection company later dismantled the SSC and found that the balancing pin of the impeller of the SSC had dislodged from its original position.

Front view of the MAC. The red arrow indicates the location of the MAC.
Front view of the MAC. The red arrow indicates the location of the MAC.
A rust formation was observed on the surface of the shaft at the interconnection between the FSC (yellow arrow) and the SSC (red arrow) impellers. The exact location of the rust was on the shaft located closest to the FSC impeller. Slight oxidation mark was observed on the surface of the shaft adjacent to the SSC impeller. The gear set located in between the FSC and the SSC remains intact without any oxidation or corrosion.
A rust formation was observed on the surface of the shaft at the interconnection between the FSC (yellow arrow) and the SSC (red arrow) impellers. The exact location of the rust was on the shaft located closest to the FSC impeller. Slight oxidation mark was observed on the surface of the shaft adjacent to the SSC impeller. The gear set located in between the FSC and the SSC remains intact without any oxidation or corrosion.
The SSC impeller showed a layer of oxide throughout the impeller blades. The oxide layer was found formed along water marks on each of the impeller blade. Under original condition, there were two (2) balancing pins fastened at the centre body of the SSC impeller. However, during the team’s inspection, only one (1) remaining balancing pin.
The SSC impeller showed a layer of oxide throughout the impeller blades. The oxide layer was found formed along water marks on each of the impeller blade. Under original condition, there were two (2) balancing pins fastened at the centre body of the SSC impeller. However, during the team’s inspection, only one (1) remaining balancing pin.
The diameter of the balancing pin (red arrow) was found to be smaller than the diameter of the hole. Oxide layer was observed within the inner surface of the hole (yellow arrow). Water marks observed indicates that water had trickled into the balancing pin’s hole (blue arrows).
The diameter of the balancing pin (red arrow) was found to be smaller than the diameter of the hole. Oxide layer was observed within the inner surface of the hole (yellow arrow). Water marks observed indicates that water had trickled into the balancing pin’s hole (blue arrows).

The failed balancing pin was further tested under SEM for corrosion. Corrosion is defined as the degradation of a structural material by chemical reactions with the environment which usually by the process of oxidation.

The SEM analysis revealed a microstructure consisting of tungsten beads with large voids in between and traces of iron and nickel. This porosity was observed towards the perimeter of the failed balancing pin. Displayed below is the microstructure of the failed balancing pin under SEM.

AGI's Finding

Porous area (red arrow) of the failed balancing pin
Porous area (red arrow) of the failed balancing pin

The finding indicates that a selective corrosion which attacked the binding phase, iron-nickel, had occurred on the outer surface of the failed balancing pin.

By Rosadli Rosli

During the course of his work, Rosadli Rosli has carried out various cases of accidents and system failures involving fire, explosions, vehicle accident investigation and reconstruction, vehicle engine identification, failure analysis of electrical, electronic and mechanical equipment in power plants and in machines, failure cases in metallurgical industry, spontaneous combustion in agricultural industries, lightning damage and hot works investigation.

AGI’s Professional Restoration