Why this subject
Details of 5 incidents
1: Hydro-test of a new vertical vessel
The root cause of the incident is not fully known but there was some thought that hydrotesting with “very cold” water was a contributing factor. Fortunately no injuries occured.
Hydro-test of a new vertical vessel
2: Filling of a vertical tank
The filling of the tank was made with water from a fire hydrant. The top the tank blew off becuase the relief valve could not displace the air fast enough for the volume of water that was being pumped in. Fortunately no injury happened, but an operator was on top of the tank a few seconds before.
Filling of a vertical tank
3: Emptying of a vertical tank
The collapse of this tank happened while it was being emptied. A plastic sheet protecting the roof was trapped in the vent; hence a vacuum was caused. There was no injury. It should be noted that this type of incident is not that unusual.
Emptying of a vertical tank
4: Sphere collapse
The accident happened during the filling of a bar 2000 m LPG sphere. Its legs collapsed. One person was killed and one seriously injured.
At the time of the accident, the sphere was approximately 80% full of fresh water.
The vessel’s last hydro-test was 10 years ago and the last inspection of its legs was 5 years ago.
Severe corrosion of the legs under the concrete fire protection was the main cause. The corrosion occurred due to water ingress between the concrete and the steel legs.
The water protective cap located over the concrete was not sufficient to keep water out. After the accident, it was verified that the steel legs had thickness reductions of up to 8mm, with piting holes of up to 10cm .
After analysis and tests, it has been found that the following factors caused the collapse:
Water caps over the fire-proofing concrete were of poor design thereby letting water penetrate between the steel beams and the concrete.
Vertical cracks in the concrete let water in.
Repairs had been done to the concrete, but with poor workmanship.
The concrete had not adhered to the old concrete, again letting water in.
The deluge system had been tested with salt water, increasing the possibility of corrosion.
5: Emptying of a gear box
To speeed up the removal of 250l of oil from a gear-box, the guage hole was plugged and the breather was connected to the 6 bar air network.
The gear box exploded, and threw missiles around seriously damaging surrounding piping and structure. Fortunately there was no injury.
Emptying of a gear box