QUESTION:
"What caused the crack to form in my poly tank, right above the outlet fitting, at the bottom of the tank?"
ANSWER:
The following are the main reasons that cracks and splits can for and develop in Polyethylene (Poly) Tanks:
Settling of tank & foundation.
- If the foundation sub-grade for your poly tank was not properly prepared, your tank can begin to settle over time. As it does, the rigid plumbing that is connected to your tank’s outlet drain fitting does not settle like the tank does. Then, as your tank settles, it creates a leveraged/binding force on the tank fitting that ultimately cases the tank to crack/split and fail.
Sharp edges, gouges, cutting marks, or burrs around the tank fitting hole (and bolt holes) were not removed when the tank fitting was originally installed.
- When tank fittings are installed, holes must be drilled for the fitting body and or any bolts that go through the tank wall (for bolted tank fittings). After these holes are cut and drilled, it is imperative that all holes are deburred and all gouges, cutting marks, sharp edges, etc. are completely removed. If this simple procedure is not done, these are the exact areas where stress cracks can form in the tank wall, leading to the failure of your poly tank.
Unsupported valves and piping on tank outlet fittings:
- When heavy valves and piping are installed and connected to the outlet fittings on poly tanks, the full weight of these items must be fully supported to prevent stress being placed on the tank wall and outlet fitting. If this is not done, the weight of these items will place downward force and stress on the tank wall and fitting. Over time, stress cracks will then form around the fitting body hole (in the tank wall) which can and will cause major leaks that are difficult to repair. In certain rare circumstances, a catastrophic vertical split can take place on the tank wall, rendering the tank and water system completely unusable until the poly tank is replaced.
Defects in the manufacturing of the tank.
- Though very uncommon in major manufacturer’s poly tanks such as Norwesco, Snyder, Bushman, Ace, Poly Processing, Etc., if the wall on the poly tank was rotomolded too thin, the tank can crack or split. This is very rare and would not usually happen upon installation but rather down the road after the tank has been subjected to additional detrimental forces such as settling, earthquake, pump vibration etc. Also, there have been cases where external embossing of the tank gallon markers or serial number have created a small stress riser that caused the tank to crack or split after it was filled with water.
