Tanks and Tank Appurtenances
What this domain covers
This domain covers the tank itself and the fittings that make it work: fill, vent, gauge, monitor, pump, overfill prevention, and corrosion protection.
Core rules and concepts
- Tank construction: fiberglass, coated or clad steel, or steel with cathodic protection (galvanic or impressed current). New and replaced tanks are secondarily contained with interstitial monitoring.
- Cathodic protection must be tested within six months of installation and at least every three years; impressed-current rectifiers are checked on a short cycle, commonly every 60 days, and the readings recorded.
- Overfill prevention must alert at 90% of capacity and stop flow at 95%. Automatic tank gauging, flappers, and ball float valves are the familiar devices; confirm which are acceptable locally before installing one.
- A fill pipe needs a spill bucket, a striker plate protects the tank bottom if a gauging stick is dropped, and the vent must be sized and piped per NFPA 30 or 30A and the manufacturer's instructions.
Worked example
A 10,000-gallon tank has its ATG high-level alarm set at 9,200 gallons. That is 92% - too late. The correct setting warns at 90% (9,000 gallons) and the 95% (9,500 gallons) device stops the delivery. Setting only one point means either no warning or no shutdown.
Traps that cost marks
- Setting overfill at a single point instead of 90% and 95%.
- Treating cathodic protection as maintenance-free.
- Forgetting buoyancy and anchoring where groundwater is high.
- Recording rectifier readings without acting on an out-of-range value.