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Poly Got a Cracker?

Poly tanks are not designed to last forever. The life of a poly tank will depend, among other things, on the thickness and quality of the material and how much sunlight (UV) it is exposed to. UV protection slows but does not prevent tank aging.
Figure 1. Crazing is an early sign of tank deterioration

Figure 1. Crazing is an early sign of tank deterioration

When is the last time you made an evaluation of the condition of poly tanks that you use? There are three simple ways to test a poly tank:

  1. Take a water soluble marker and color several six by six inch areas on the tank. Rub the marker off with a rag and look for “crazing”, a patchwork of very fine cracks within the tank wall appearing as fine lines. Crazing is one of the first signs of deterioration.
  2. Hold a bright light inside the tank (candling) and look on the outside for defects or cracks that show up as different lines or areas of light intensity.
  3. Tanks that have signs of UV damage can be further tested (when empty) by taking a baseball bat and “swing for the fences”. “It might break!”, you may say. If it does, then you know that the tank might have failed because the material was too brittle. A tank in good shape should flex and rebound without breaking. You may have put the tank out of commission but you saved having a tank rupturing at some inopportune moment.

A weakened tank may be safe for water, but you probably can’t afford to lose several thousand dollars worth of fertilizer or a tank of spray mix.

What is the difference between a poly tank built for storage (vertical) and one made for transport (horizontal)? Transport tanks are usually built stronger, have baffles to slow water movement and are secured to a cradle, the truck or trailer bed with bands or hoops. Storage tanks are not designed for transport. They don’t have baffles built into them. The tie-down slots molded into the top of the tank are designed to allow for securing the tank in place on the ground from wind movement or for transporting the tank when it is empty.

Roping or strapping a storage tank onto a flat bed with too much force on the lines can cause the side of the tank below the tie-down slot to buckle and possibly crack.

Tank strength is rated in specific gravity. Water at 8.3 lbs/gal has a specific gravity of 1.0, so a tank with this rating should not hold heavier materials such as fertilizers. A fertilizer that weighs 11.7 lbs/gal would have a specific gravity of 1.4 (11.7/8.3) so the tank intended to hold that needs to be rated at least as high as that.

Excerpts from Purdue Extension PPP-77, Poly Tanks for Farms and Businesses were used in this article.

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Poly Got a Cracker?

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John Rowehl
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Phone: 717-840-7408