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14249 Chemical accident in Australia with nitric acid
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General accident information
Class/Quality * * *
Year 1998
Summary A chemical was released from a
Nitric acid absorber tower
When inappropriate flange
Bolts failed due to corrosion
Country AUS
Activity STORAGE
Location FACTORY
Chemicals Nitric acid
Cause Technical-failure
Fatalities/Injuries 0 / 0
Occurrences or events Clean, Corrosion, Emergency-stop, Fire fighting/Emergency response,
Fire fighting/Emergency response, Mechanical failure, Pollution/Contamination, Release
 
 
Full accident information 
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Country: AUSTRALIA (AUS)
Date : 1998 0704


A spill of nitric acid occurred from a nitric acid absorber tower when a flange failed.
An operator noticed a small leak from the flange bolts and proceeded to climb the tower towards the top isolating valve. At this time the flange bolts failed and sprayed acid into the absorber tower bund.
The operator climbed to the next level and shut down the operation of the plant. Once the acid level had dropped to below the level of the flange, gaseous oxides of nitrogen were released and travelled in an east-north-easterly direction. The operator then used water spray to reduce the impact of gas and acid mist.
Industrial neighbours were notified of the release and the acid in the bund was neutralized with lime and sand, and later used in another onsite manufacturing process.

Cause
On investigation it was found that the bolts in the flange were mild steel bolts, which were not appropriate for use in nitric acid applications.
These bolts were found to be corroded, which lead to the leak.

Consequences
The company reviewed all of the bolts used in the process. Five other flanges were identified as having mild steel bolts rather than stainless steel bolts. It was found that these bolts had not been replaced since plant commissioning. All inappropriate bolts were immediately replaced with stainless steel bolts suitable for acid applications. The company has surveyed the area to ensure that no other inappropriate components have been used in the construction of the plant.

Lessons learned
To prevent a recurrence the company has also implemented quality control procedures and inspection test plans for new area projects and maintenance work.




 
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