We get a lot of questions about the standard testing that is done at our facility. Vertical tanks larger than 500 gallons are extensively tested to ensure that they meet ASTM standards. Per customers’ requests, we offer additional testing on our chemical storage tank systems.
Let's take a look at the types of testing that PPC performs, how we do it, and why these tests are so important in the chemical storage tank production process.
Four Major Types of Testing
At PPC, we do standard testing on all Vertical, IMFO, Cone, and SAFE tanks over 500 gallons, per ASTM guidelines. There are four major tests that we do.
- The ASTM Gel Test takes a sample from the tank after it is molded. To meet the ASTM standard, the sample must be 60 percent or higher to be considered XLPE. To perform this test, we take a small sample from the innermost 1/8” of the tank wall, weigh it on a gram scale, and then put it into boiling Xylene for 16 hours. At that point, the sample is dried and then reweighed. The Xylene dissolves the linear polyethylene from the sample and what is left is the weight of the cross-linked resin material only. This indicates the percentage of cross-linked polyethylene (XLPE) in it.
- The ASTM Impact Test: Much like the gel test, a sample of the tank is taken but here, we want to determine the tank's structural integrity through impact. The goal is to verify that the material can withstand mechanical stress and other challenges associated with long-term chemical storage. The sample is frozen overnight at -20 degrees F. It is then placed in a machine where a “dart” is dropped at a certain foot-pound to create the appropriate impact. The wall thickness of the tank sample determines the required impact in foot pounds. As an example, a 1/4" thick tank must be capable of withstanding a 90 foot-pound impact. This threshold increases as the tank wall thickness increases.
- The Hydrostatic Test: This one-hour test is done on all tanks 500 gallons and above and any tank with fittings installed to ensure that the tank and fittings are leakproof. ASTM certification requires that the tank sits for 30 minutes to verify that there are no leaks. At PPC, our internal standard is to test for one hour. In all of these tests, we use the entire tank and not just a sample so that we can verify both the fittings and the tank itself are able to withstand hydrostatic pressure.
- The Ultrasonic Test verifies the thickness of the walls of the chemical storage tank. We use a sonar instrument to send out measurable sound waves and measure the amount of time it takes for the waves to travel back. That allows us to calculate the thickness of the walls. This test is performed at various points around the diameter and up the tank sidewall. Standard wall thickness readings are done at 0 degrees, 90 degrees, and 270 degrees at 1-foot, 2-foot, and 3-foot elevations. The ultrasonic test ensures that the walls have a consistent thickness around the entirety of the tank and that same thickness falls within the upper and lower parameters of the design specifications.
Additional PPC Testing
Poly Processing does all of the above testing at no charge but there are additional tests that customers can request for a small fee. While there is no standard for horizontal tanks, we can test those as well. Here are some other testing options offered:
- Longer Duration Hydrostatic Test: While PPC's hydrostatic tests are an hour long, it's common for customers to request that the tank sits for longer periods of time. This testing is done just as the standard hydrostatic test, but for up to 48 hours.
- Barlow Wall Thickness Test: This certification goes beyond the ASTM standard. For this test, we take the standard thickness readings from around the entire tank and send them to our engineering group for third party verification. This test confirms through a third-party that the entire tank meets the thickness standard.
Ultimately, these tests allow Poly Processing to ensure that all of our tanks meet or exceed ASTM standards.