There is more than a tank to think about when configuring a polyethylene chemical storage system. As always, you have to think about your chemical first, then you have to choose the tank most appropriate for that chemical, then you need to choose the fittings and accessories that will ensure that your tank system is safe and effective. Another key consideration is the actual access point to the inside of the polyethylene tank. There are various points at which you can access the tank: from the top, or dome, and from the side. Each of these tank entrances must be protected with a manway cover to protect both the chemical itself and the surrounding environment and employees.
Let’s take a closer look at the side manway and its corresponding bolted side manway cover to learn about where it’s used, why, and considerations you should think through before choosing a side manway.
About Manways and Manway Covers
A manway is an opening in a tank big enough to allow a person to enter for inspection or cleaning purposes. Depending on the type of tank you’re using and the properties of the chemical that you’re storing, the manway can exist in different places on a tank. Some chemicals require a fume-tight manway cover, meaning the manway can be on the top of the tank and no person needs to enter the tank. Poly Processing offers many manway covers, like the SAFE-Surge® cover, that allow the chemical to be placed into the tank but no human entry is needed. A tank that contains less hazardous materials, such as water, can have a threaded manway cover for easy access. The chemical the tank is storing dictates the type of manway and cover used.
In a few cases, a side manway may be required, which means that the tank is in a position where the end user needs to have an access point on the side of the tank. In this case, a stainless steel or FRP bolted side manway is used to protect the opening on the tank, but it is also placed to protect the tank from the stress of the large hole that has to be cut into it to facilitate the side manway.
The Risk of A Thru-The-Wall Bolted Side Manway
There are indeed risk factors associated with incorporating a side manway on your chemical storage tank. Cutting a large hole in the side of a tank can compromise the integrity of the tank over time, and the many holes required to affix the manway cover also impact the tank, increasing the risk of leaks.
A chemical storage tank will most often leak from a fitting or accessory because of the nature of the gasket and bolting system. Adding a bolted side manway increases the risks and can put chemicals and employees at risk of exposure to dangerous fumes and corrosive chemicals if not designed and installed properly.
Things to Think About Regarding Manways and Manway Covers
There are some additional circumstances that can help you navigate through whether or not a bolted side manway is right for your specific application:
- If your chemical application requires the use of the OR-1000 system, which is a common FDA requirement, a bolted side manway is not an option because the bolts penetrate through the antioxidant system.
- If you are considering a side manway but need secondary containment such as a SAFE Tank® a side manway isn’t an option on this type of tank, because of the secondary tank that provides a second layer of containment to isolate chemicals.
- In instances where regulations require tanks to have two access points, a side manway is considered. There are options, however. You can have two top dome openings instead of a dome opening and a side manway, meaning that all the penetration to the tank is on the top, away from the hydrostatic pressure of the chemical.
- Poly Processing offers the Integrally Molded Flanged Outlet, or IMFO® system - an innovation that places a molded flanged outlet in the bottom knuckle of the tank while it is manufactured. This ensures a stress-free means of draining the tank, plus the flange is below the tank knuckle. A flange placed below the tank knuckle radius results in no need for tank entry and a full drain of the tank, keeping it safe for the next chemical delivery and virtually no maintenance.