Resources
Plastic Tank Life, Inspection and Maintenance
What affects how long a polyethylene storage tank lasts, the signs of an aging tank, an inspection checklist, and how to prevent stress cracking.
Tank life
How Long Does a Plastic Tank Last?
There is no fixed number of years. A polyethylene tank wears with use, and how long it lasts depends far more on how it is used and installed than on the calendar. Our tanks carry a limited three-year warranty, or one year for a few demanding chemicals such as sulfuric acid, bleach and caustic soda.
The chemical
Strong oxidizers and concentrated acids are harder on polyethylene than mild, water-based liquids. Concentration and temperature matter as much as the chemical itself. Check our chemical compatibility database.
Temperature
Plastic loses strength as it warms. Running a tank above its rated temperature is one of the fastest ways to shorten its life, and it voids the warranty.
Installation and piping
Rigid piping and unsupported valves are a leading cause of early failure. Pipe weight pulls on fittings, and the tank can’t expand and contract. Use flexible connections and support all piping independently.
Sunlight
UV light slowly makes polyethylene hard and brittle. Our resins contain UV stabilizers, but tanks in strong sun still age faster than tanks indoors or in shade.
How it is used
A tank that is filled and emptied many times a day, agitated hard, or moved from site to site works harder than a holding tank that sits still.
The base
A tank needs a smooth, firm, level surface that supports the whole bottom. Rocks, slopes and uneven pads create stress points.
Warning signs
Signs of an Aging Tank
- Hard, brittle walls. The plastic feels harder and less flexible than it did when new, especially on the side that faces the sun.
- Crazing. A network of fine surface cracks, often first seen around fittings, the bottom corner or the top of the tank.
- Cracks. Any crack in the wall, at a fitting or along the bottom corner.
- Whitening or chalking. Stressed or weathered areas can turn whitish or powdery.
- Bulging or warping. A wall that has bowed out or a bottom that has sagged.
- Weeping or staining. Damp spots, crystals or stains on the outside of the wall or below a fitting.
Checklist
Tank Inspection Checklist
Set a schedule that fits your chemical and site. As a minimum, give every tank a thorough inspection at least once a year.
| How often | What to check |
|---|---|
| Every fill | The vent is open and clear, the level reading makes sense, and nothing is leaking at fittings, valves or hoses. |
| Monthly | Walk around the tank. Look for leaks, stains, crystals, cracks, bulges and fitting strain. Check that piping is still supported and flexible connections are in good shape. Check the lid or manway cover. |
| Yearly | A close look at the whole tank, including the top, the bottom corner and around every fitting. Check the walls for crazing, whitening and brittleness. Check gaskets, bolts and valves. Inspect the base, stand and tie-downs, and the secondary containment. |
| After any event | An impact from a forklift or vehicle, an overfill, a freeze, a storm or an earthquake, or any change in the chemical, concentration, temperature or fill rate. |
Keep a simple log for each tank: the chemical and concentration, temperature, install date, inspections and any repairs or changes. The serial number and date on the tank label make it easy to track.
Stress cracking
What Causes Stress Cracking
Stress cracking happens when a tank is under physical stress while it is exposed to something that attacks the plastic. Remove either one and cracking is far less likely.
Chemical attack
Oxidizers, some corrosives, and surfactants such as detergents and wetting agents can weaken polyethylene under stress. Higher concentration and temperature make it worse.
Pipe and fitting loads
Unsupported pipe, heavy valves, rigid plumbing and over-tightened fittings put constant stress on the wall around the fitting.
Temperature swings
Daily and seasonal heating and cooling make the tank expand and contract. Rigid connections fight that movement.
Pressure and vacuum
A blocked or undersized vent lets pressure build during filling or pulls a vacuum during emptying, flexing the walls.
How to prevent it
- Match the tank resin to the chemical, concentration and temperature, and don’t switch a tank to a different chemical without checking with us first.
- Support all piping and valves independently and use flexible connections, especially at fittings low on the tank wall.
- Hand-tighten plastic bulkhead fittings; over-tightening can cause leaks and stress.
- Keep the vent clear and sized for your fill and discharge rates.
- Set the tank on a smooth, firm, level base and use seismic and wind restraints where needed.
Maintenance
Maintenance Tips
Flush out sediment
Some chemicals, such as sodium hypochlorite, leave sediment as they break down. Flush it out periodically through a low cleanout outlet.
Leave room to freeze
Cold does not harm polyethylene, but freezing liquid expands, so leave headroom in tanks that may freeze. Don’t move a tank that has frozen contents, and avoid striking a cold tank.
Protect it from impact
Keep forklifts and vehicles clear, and guard tanks near traffic. A hit is more likely to crack a tank when it is cold.
Replace worn parts
Gaskets, valves and hoses wear out before the tank does. Replace them with materials rated for your chemical. See fittings and options.
For handling, installation and filling, see our installation and use guidelines.
FAQ
Tank Life and Inspection Questions
How long will my plastic tank last?
It depends on the chemical, concentration and temperature, sun exposure, how the tank is installed and piped, and how often it is filled and emptied. A tank storing water indoors will usually far outlast one holding a strong oxidizer outdoors. Inspect it regularly and replace it when it shows signs of aging.
How often should I inspect a chemical storage tank?
Check the vent and look for leaks every time you fill it, walk around it monthly, and give it a thorough inspection at least once a year. Inspect it again after any impact, overfill, freeze or change in service.
Can a cracked plastic tank be repaired?
A tank in chemical service with a crack in the wall should be taken out of service and replaced, not patched. A leak at a fitting may only need a new gasket or fitting. Call us and we’ll help you tell the difference.
What is the most common cause of early tank failure?
Installation problems, especially rigid piping and unsupported valves that load the fittings. Flexible connections and independent pipe supports are required for a proper installation and to keep the warranty in force.
Can I reuse a tank for a different chemical?
Only after checking that the tank resin, SG rating, fittings and gaskets suit the new chemical, and that the tank is clean and in good condition. Often a new tank is the safer choice. Ask us before you switch.
Time to Replace a Tank?
Tell us the chemical, volume and fittings on your current tank. We’ll quote a replacement outfitted the same way.