Investigate Acid Escape to local water course
Finch was instructed to determine the root cause of a sulphuric acid escape to local watercourses of approximately 12,000 litres. The acid destroyed local fish stocks.
A 96% Sulphuric Acid dosing system was used to adjust the PH of the incoming water. The dosing system consists of the following elements:
- 20m³/20,000 litres bulk storage tank manufactured from High-Density Polyethylene (HDPE);
- 22m³/22,000 litres tank bund (integral) manufactured from HDPE;
- concrete spill bund;
- dosing kiosk – including 2 dosing pumps, control panel, emergency stop function, isolators, incoming mains distribution panel, lighting and heating; and
- safety shower/eyebath.
The system was installed in 2003. The bulk storage tank had two low-level flanged outlets, located outside of the integral bund but within the concrete spill bund.
One flanged outlet was the feed pipe between the bulk storage tank and dosing kiosk, the other was the bulk storage tank drain valve.
Usual Inspection Regime
Daily visual inspections of the spill bund and flanges; remove any rainwater that may have accumulated; confirm that the flange bolts are present.
Cause of Failure
Gradual leaking of acid through the flange caused an acid environment to occur leading to the corrosion of the bolts. Additional stresses at the bolts that remained in the flange connection led to a slow deterioration over time that resulted in sudden failure.
Upon closer inspection, the leak originated from the main feed flange from the bulk storage tank to the dosing kiosk. There was evidence of corrosion on the backing ring and surface corrosion on the bolts and nuts and 2 bolts missing from the bottom of the flange.