There are several important factors to consider if you are in the process of configuring a polyethylene chemical storage tank. Always start the configuration process with the chemical being stored, because the chemical’s properties affect the entire tank design, including fittings and accessories.
One important property is the chemical’s specific gravity. If your chemical tank isn’t rated for the proper specific gravity, you could be looking at costly maintenance and employee injuries.
What Is Specific Gravity and Why Does It Matter?
Specific gravity is the ratio of the density of a substance to the density of a standard—in our case, water. So if a chemical has twice the weight as water, its specific gravity is 2.0. If the chemical is 50 percent heavier than water, its specific gravity is 1.5. If it has half the weight of water, its specific gravity is 0.5.
Generally speaking, tanks that store water are built to handle a specific gravity rating of between 1.0 and 1.35. Chemicals with a fluid specific gravity outside of this range require a tank that is engineered to handle that type of chemical. If you use a water tank for chemicals with a specific gravity greater than 1.0, you are putting your equipment and your people at risk.
If you use a tank that isn’t rated for the chemical you’re storing, it can break down, leak, or even fail catastrophically—requiring costly maintenance and placing your employees in danger. When we build tanks to hold a chemical like hydrofluoric acid, we use a specific gravity rating of 1.9 with cross-linked polyethylene resin, instead of the linear polyethylene that is used to manufacture water tanks.
How Temperature Impacts Your Tank’s Specific Gravity Design Rating
A chemical’s specific gravity rating is especially important when you take into account the temperature of the chemical you will be storing. Many projects require chemicals to be stored at a slightly elevated temperature above room temperature. If this is a concern for your company, it is very important to understand how it affects specific gravity, and the design of your tank.
The thickness of a poly storage tank’s walls can vary to ensure that the tank system is safeguarded from the chemical itself. With some chemicals, such as sulfuric acid, the heavy weight of the chemical can cause damage to the storage tank’s walls if the tank is not made for the specific chemical. Simply put, a heavier chemical, especially at temperatures above 100°F, requires a thicker tank wall in comparison to simply storing something such as ambient temperature water.
When we design a standard tank, we design it to withstand a maximum temperature of 100 deg F. But in some cases, chemicals may be added to the tank at higher temperatures. These higher temperatures put greater pressure on the tank and increase the hoop stress. So it is critical that the tank wall is designed to withstand greater stress at higher temperatures.
Poly Processing offers four different standard tank wall thicknesses, depending on your chemical’s specific gravity. As the specific gravity increases, a storage system will require thicker walls to withstand additional stress from the increased temperature and weight. The maximum service temperature for our XLPE tanks is 150 degrees F, assuming your chemical’s specific gravity is 1.00. You can find out more information about your specific chemical’s fluid specific gravity by checking out our list of commonly stored chemicals.
How to Know Your Tank Design Works for Your Application
You need to be confident that your chemical tank storage system meets your tank requirements. Take the following steps if you know that you will be storing chemicals at an elevated temperature.Follow these steps to ensure that you have built a tank system capable of storing your specific chemical:
Know the exact chemical name of the substance you plan to store. At Poly Processing, we rely on the chemical’s material safety data sheet (MSDS) to build a tank that matches your specific needs.
Find out if the chemical’s temperature will be ambient, and what its variance will be. For substances with a relatively high level of temperature variance, we allow additional tolerance to make sure that the quality of the substance is not compromised.
Submit all relevant chemical and storage condition data to one of our tank specialists so that we can verify that you have selected the right tank based on your requirements. We have helped customers develop superior storage solutions for over four decades. Let us help you pick the right tank so that you have total peace of mind about your chemical storage.
Contact a chemical storage expert to determine the specific gravity rating required for your chemical storage application.