Accidents Waiting to Happen

March 14, 2009 01:57 PM

As you get ready for planting season, here's one job that will be fun to carry out: Take a felt marker and scribble on your polyethylene tanks. Then whack 'em with a baseball bat.
Sound silly? Well, we're dead serious. Inspecting your tanks—and making sure you have the right ones for each task—could prevent a chemical spill that could eat up hours of your time and untold dollars in cleanup costs and penalties, smack in the middle of planting or spraying season.

Like many farmers, Fred Whitford, Purdue University's coordinator of pesticide programs, never gave much thought to the disaster potential contained in an innocuous-looking plastic tank. That changed when he received a call from a farmer. "A 2,500-gal. tank actually exploded," he says.

Whitford set out to learn about poly tanks and educate farmers about the innocent-appearing containers. He shared his knowledge with attendees at the 2008 Farm Journal Corn College.

"Poly tanks have a limited useful life, depending on a number of factors. At some point, every one will fail," he says.

A tank's useful life, he explains, depends on the quality of the polyethylene material, the materials stored in the tank and whether it is used for storage or transport. Ultraviolet (UV) radiation from the sun is also a major enemy of tanks, making the tough polyethylene hard and brittle and ultimately setting the stage for a spill.

Which tank to buy. The first step in avoiding expensive and possibly catastrophic chemical spills is to buy a tank that is strong enough for the task.

Tanks are made from two materials, Whitford explains: high-density linear polyethylene (HDLPE) or high-density cross-linked polyethylene (XLPE).

"In general, both materials can be used to store and transport most pesticides and fertilizers," he says. "But XLPE is more chemical-resistant and durable and generally more expensive. Contact the chemical manufacturer if you are not certain whether a HDLPE tank will work for the products you store or haul."

The strength of poly tanks is rated in terms of specific gravity. A rating of 1.0 means the tank is designed to withstand the internal force of water, which weighs 8.334 lb. per gallon, or anything lighter than water.

A specific gravity rating of 1.5 means the tank is built to contain liquids weighing up to 12.5 lb. per gallon. That rating would include products such as 10-34-0 fertilizer, which weighs 11.67 lb. per gallon, and 28-0-0 fertilizer, which weighs 10.7 lb. per gallon.

"A good rule of thumb is to purchase a storage tank with a specific gravity rating at least one increment higher than that of the product you intend to put into it," Whitford
explains. "If a tank is to be used to transport chemicals, it's a good idea to buy one rated at 1.9."

You can't guess a tank's specific gravity rating based on its appearance or your experiences with similar tanks. It is important to know exactly what your tank is worth. "Sometimes the specific gravity rating is stamped on the tank, or it may be part of the product code," Whitford says. "If you can't figure out the specific gravity rating, check the spec sheet that came with the tank, or ask your dealer."

Transport tanks that are used for holding more than 1,000 gal. should have baffles inside to reduce the force of the chemical when it surges forward or backward into the end of the tank, Whitford notes. Make sure that tanks are mounted in the proper direction, so that the baffles will be effective.

The tanks must also be properly secured. "Vertical tanks are made for stationary use only, but many of them come with tie-down connectors," Whitford explains. "However, those connectors are not designed to secure loaded tanks to the bed of a truck or trailer for transport."

Horizontal tanks, designed to be placed on trucks, trailers and sprayers, come with more substantial tie-down features. "Horizontal tank tie-downs commonly are pipe hoops or metal bands capable of holding a loaded tank in place if the truck or trailer stops suddenly," Whitford says.

Inspect horizontal transport tanks every time you climb into the driver's seat. Be on the lookout for missing, broken and bent bolts on hoops or bands; leaks around tank valves, tank bungs, loose lids or plumbing; cracks or splits in hoses; improperly secured hoses and covers; and clogged vents in the lid or tank.

"Horizontal tanks on transport vehicles should be checked continually for movement, especially if they are held in place with metal straps, rather than metal hoops," Whitford adds. "Metal straps can cut into the tank if it shifts forward or backward."

The felt marker and baseball bat test comes into play during annual fall and spring tank inspections.

"Whether a tank is 20 years old or just a few years old, the only way to be sure it is structurally sound is to inspect it before use in the spring and again at the end of the application season," Whitford says. "Fall inspections give you time to purchase a new tank before you need it next spring."

Finding defects. There are three ways to check the quality of a tank, Whitford says. The first is to rub a felt marker over several 6"x6" sections on the sides of the tank exposed to sunlight, on the top of the tank and around fittings.

If you see crazing of the ink (a patchwork of fine lines) or cracking, use the tank only for water. "If the ink reveals cracking or spiderwebbing, with the lines going in all directions that indicates classic UV radiation damage," Whitford explains. "A checkered or ‘dry rot' appearance indicates advanced deterioration and loss of elasticity. Tanks like that should be replaced or at least not used for fertilizer and chemicals."

Parallel ink lines signal the early stage of UV damage and indicate a tank that requires constant inspection. Tanks with parallel lines in the plastic around fittings should be replaced immediately or used only for water.

You also can "candle" tanks by placing a bright, cool light source inside the tank. From the outside, defects and cracks will show up as areas or lines of different light
intensity. "Repeat the procedure holding the light outside the tank, while you look inside through the neck," Whitford says. "Or put a camera or camcorder inside."

If a tank shows UV cracking, that's where the baseball bat comes in. Hit the tank as hard as you can. "If it's a good tank, you won't hurt it; it's impossible to crack a good tank using this method," Whitford says. "If the tank cracks or breaks open, you may have saved yourself from a disaster."

Never try to repair a poly tank, Whitford says. And don't buy a used tank. "You should view replacing poly tanks at the end of their useful life just as you do changing tires, oil filters and hoses," he says.

For More Information: Purdue University's Fred Whitford and other tank experts felt so strongly about the dangers of poly tanks that they authored an 81-page book on the subject. Filled with large full-color photos, it provides addi-tional detail on everything discussed here and much more, including tank construction, proper siting, what to do with old tanks, insurance issues and what to do in the event of a spill. You can download it for free at Or you can order a copy for $5 at

You can e-mail Darrell Smith at

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