A.8.1 Equipment description
The instrument air system of a power plant is equipped with 3 screw air compressors, with air compressor specifications of 110kW, water-cooled units, and exhaust volume of 20m³/min.
A.8.2 Accident description
The #3 instrument air compressor has been running for a total of 6000 hours. The maintenance personnel carried out maintenance work on the air compressor after processing the work ticket. After removing the oil separator during work, it was found that the bushing inside the oil and gas barrel was covered with oil and dirt, so it was decided to remove it for cleaning; the outlet pipe (DN50) connected to the oil and gas barrel was about 500mm long and above the oil and gas barrel, which affected the removal of the bushing and had to be removed; the other end of the outlet pipe was connected to a DN50 internal threaded check valve, and the other end of the check valve was connected to the air compressor outlet main pipe. Since the installation force of the oil and gas barrel outlet pipe and the check valve was too large to be removed, the maintenance personnel decided to remove them together with the check valve. When the check valve was about to be removed, there was a loud "bang" and the oil and gas barrel outlet pipe and the check valve "flew" forward and hit the air compressor soundproof cover, causing the soundproof cover to be concave about 10mm at the hit part. At the same time, it also hit a maintenance personnel working next to the oil and gas barrel, causing his arm to be fractured.
A.8.3 Cause Analysis
(1) The oil and gas barrel outlet pipe and the check valve "flew" together because there was pressure in the outlet main pipe. Although the work ticket was processed and the outlet door on the outlet main pipe was closed, the outlet door used a ball valve and the sign of closing was a horizontal line, which made it difficult to judge whether it was completely closed. Therefore, there was leakage. At the same time, the check valve on the outlet main pipe also leaked, causing a certain amount of pressure in the main pipe. Since the check valve at the outlet of the oil and gas barrel was tightly closed, no pressure leakage was found when the oil and gas barrel was removed.
(2) Although the maintenance personnel processed the work ticket and checked that the outlet door was closed, there was actually leakage, and they did not check the value of the main pipe pressure gauge to see if there was leakage at the outlet door, so they failed to find the leakage at the outlet door in advance.
A.8.4 Preventive measures
(1) Carefully analyze the dangerous points before work, and start work only after checking and confirming that the dangerous points are correct.
(2) Existing equipment hazards should be dealt with in a timely manner. In this accident, if the check valve of the main pipe is repaired and closed tightly, it can also be prevented.
