How to Prevent Corrosion in Your Headworks
Your facility relies on its headworks to function as designed. Corrosion is one of the factors that can undermine this mission and affect the performance your entire wastewater treatment process.
In 1991, a US EPA report to Congress found that 32 cities reported sewer collapses, most of which were attributed to corrosion. The same corrosion was also present at the treatment plants. In this article, we’ll look at the reasons for that corrosion and how to prevent it from happening in your facility.
What causes corrosion
Metal is subject to different types of corrosion, but the primary ones are biogenic and chloride/pitting.
With biogenic corrosion, the pumped wastewater is biologically active. Because the water doesn’t come into contact with any air, bacteria grow and produce hydrogen sulfide, which is a gas. That gas can then corrode materials it comes into contact with, including concrete and steel.
Chloride corrosion often happens as a result of seawater. Areas that have extensive use of water softeners (regenerated with sodium chloride) and road salt can also have increased chlorides that causes pitting in stainless steel alloys.
How to prevent corrosion
Preventing corrosion starts with selecting the right materials. Those headworks materials should be:
- Acid resistant (to withstand biogenic corrosion)
- Chloride resistant
- Strong (to withstand hydraulic loading)
- Long lasting (20-year lifespan)
For these reasons, stainless steel is a good choice for most parts of the equipment. It is strong enough to take on large flow rates, plus it resists acid and chloride corrosion. The most commonly used steel is 304 and 304L (the L means “low carbon”), which have excellent resistance to corrosion. However, you must take a number of steps to protect the steel during the manufacturing process.
Hydro-Dyne’s process for manufacturing the equipment for your headworks
Because headworks are exposed to corrosive environments, screening equipment is made from stainless steel. Corrosion control depends in part on the quality of the steel. Higher grades of steels are needed as they are exposed to higher concentrations of chloride.
Other resistant materials in the headworks may include ultra-high molecular weight (UHMW) polyethylene and acetal polymer, both of which are non-ferrous polymers. These materials don’t corrode, have low coefficient of friction to move well through water, and have high strength. These materials are used in screening equipment parts like spacers and perforated plates.
Hydro-Dyne designs its screening equipment for maximum reliability and corrosion resistance. The HDE process involves the following:
- 3D model design (which enables efficient assembly)
- No key parts of the equipment are submerged
- Wear items are minimized (such as neoprene seals that can dry out)
- Solid stainless steel drive sprockets
- Equipment is designed to minimize the footprint
- Tight tolerances are maintained by using the right materials. This leads to high screen capture during operation.
How Hydro-Dyne protects your headworks equipment
Surface treatment is a key process to protect stainless steel from long term corrosion. Surface treatment involves removing iron deposited on the steel surface from welding and promoting the formation of a chromium oxide passivation layer. Pickling and passivation are common terms used.
- Pickling the steel removes impurities. It also limits the number of potential corrosion points. HDE uses a total immersion process that provides the best quality. This process involves immersion in cleaning solution, immersion rinse, immersion contact with acid and a final immersion rinse. Hydrofluoric acid immersion is the best way to remove impurities from the steel surface.
- Passivation is the process of adding a chromium oxide layer that protects the steel Nitric acid immersion is used passivate the steel surface for long term protection against pitting and crevasse corrosion.
Hydro-Dyne is one of the only manufacturers that takes this level of care in house.
Work with Hydro-Dyne to build the best headworks equipment available
Hydro-Dyne complies with the Infrastructure Investment and Jobs Act, which was passed in 2021 and has allocated $550 million in new spending to update our nation’s infrastructure, including roads, bridges, and wastewater.
To qualify for assistance, all the iron, steel, manufactured products, and construction materials used for these infrastructure projects must be made in the United States. Hydro-Dyne is uniquely positioned to meet requirements with ALL design, engineering, manufacturing, assembly and testing of our equipment performed at our Clearwater, Florida corporate headquarters and production facility. As you have seen above, we take our responsibility as a manufacturer seriously and follow a process that leads to the highest quality equipment.
If you are building a new headworks facility or need help in improving your current wastewater treatment plant, we are here to help. Contact Hydro-Dyne and we’ll be happy to answer your questions.