On the surface, polyethylene storage tanks can look pretty similar. It’s tough to tell a more expensive, well-designed and constructed tank from a cheap, inferior tank. Many customers are unaware that there is a standard for tank construction based upon resin properties and testing, or they simply assume all tank manufacturers follow the ASTM D 1998 standards.
Is your chemical storage tank designed and built to ASTM D 1998 standards?
Don’t depend upon the manufacturer to certify the standard of safety for the polyethylene chemical storage tank you choose for your operations. It’s important to verify that your storage tank has been manufactured according to ASTM D 1998 standards. For example, polyethylene producers generate the mechanical properties of their resin used from samples compression molded. This process optimizes the material’s mechanical properties, however doesn’t represent polyethylene processed using rotational molding. To provide the proper factor of safety, ASTM has lowered allowable usable ratings provided by resin producers. This provides you with a margin of safety and provides peace of mind knowing that your storage tank is designed and manufactured to withstand potential tank impacts, weight of the chemical being stored, and pressures under storage of the chemical.
What does this mean in simple terms? Here is one basic component of the ASTM D 1998 guidelines. When calculating wall thickness manufacturers are only allowed to use 600 PSI for a hoop stress rating even though the resin manufacturer states at a given thickness the material could withstand over 1200 PSI. If no standard is applied to the tank manufacturer, they could in theory select any hoop stress rating from 0-1200 PSI. This explains why two tanks designed to store up to a 1.9 specific gravity rating can vary so greatly and perform so differently.
The ASTM D 1998 standard determines through testing how various materials are processed together to form the finished rotational molded product. For example, in polyethylene storage tanks the mechanical properties of the resins used are factored in to accommodate the weight of the material being stored to determine acceptable tolerance levels. ASTM has calculated the maximum pounds per square inch of pressure at a real-life level to determine performance numbers.
It’s important to examine the hoop stress tests, understand how stress is actually calculated, and review wall thickness data sheets from the tank manufacturer to determine if the manufacturer is meeting ASTM D 1998 testing parameters. The tank manufacturer you are considering should have these technical documents and data sheets available for your verification so you are assured the tank is designed and manufactured to the highest safety standards. Saving a couple thousand dollars on the up-front cost of a tank could cost you tens, hundreds, or even millions of dollars in the event of a catastrophic tank failure resulting from a cheap, poorly constructed tank.