The Top Alloys For Use In Seawater Filtration Applications

a comparison of the top seawater worthy stainless steel alloys

Filtration of seawater is a necessity across a diverse range of industries – such as intake for a desalination plant, ballast filtration for an oil tanker, or to maintain pressure and the production rate. When running a complex operation there are plenty of unexpected expenses to deal with on a regular basis, and the last thing anyone wants is a preventable failure of their filtration equipment. This is especially pertinent when dealing with seawater because it is filled with corrosive elements that can lead to material failure like corrosion or strength degradation. Therefore it’s important to have a quality, durable filtration system.

desalination pipeAs part of the search for the best system, an often underappreciated but critical component to its success is dependent on which alloy the screen filter, the heart of the system, is made of. The filter screen is the physical barrier that prevents particles (organic and inorganic alike) that are larger that its pore size from passing through with the water. Corrosion to the screen can damage its ability to be cleaned, clog its open area and inhibit water flow, or degrade the screen’s structural integrity, letting particles larger than its pore size to get through and compromise the integrity of the system. Various seawater filtration industries struggle with the same decision as to which is the best

Seawater filters have unique and specific requirements: they need to be non-corrosive, as well as effective at removing debris of various sizes, which can harm down-stream processes. This is extra important in industries that rely on very fine filtration (100-5 microns), such as in desalination and ballast water filtration. In these cases, the screens must also be highly effective at removing phytoplankton and zooplankton from the water. Any seawater processing application requires a durable pre-filtration protection system so that time and money isn’t wasted over the years to repair poorly protected systems. With this in mind, let us look at the most common alloys used in seawater filtration and determine which alloy best suits your system.

316L

316L stainless steel, also known as “marine grade stainless steel,” is the second-most common stainless steel used in manufacturing today (after 304 stainless steel). This alloy is made up of iron, chromium (about 16%), nickel (10%) and molybdenum (2%), as well as trace amounts of quantities of silicon, phosphorus, and sulfur. Although it is a popular choice, the latest advice from the International Stainless Steel Forum is that AISI 316 and its derivatives “are no longer recommended for permanent contact with seawater.” We’ll see some of the reasons behind this decision in the Cons section.

Pros

316L stainless steel is a popular choice for seawater filtration. This is in part due to the alloy’s widespread use throughout many industries, making it widely available, as well as the benefits described below.

Some Corrosion-Resistance

Like all of the alloys discussed here, 316L stainless steel contains chromium. This element is an important part of the chemical makeup; it creates a thin film over the alloy when exposed to oxygen, which helps prevent the steel from becoming corroded over time.

The chromium in the alloy does provide a degree of protection that prolongs the steel’s – and by extension, the filtration system’s – lifespan. However, it is important to note that 316L does not provide complete protection from corrosion. While the alloy can offer reasonable protection in the short term, its particularly susceptible to pitting corrosion caused by inconsistent salinity levels in the seawater.

Tolerant to Higher Temperatures

Temperature fluctuations are most acutely felt in the shipping industry, as seawater can vary wildly in temperature between locations, seasons or even times of the day.  316L can tolerate water temperatures up to Celsius (68 degrees Fahrenheit), which means it is able to successfully stand up to most seawater.

Low Cost

One of the biggest benefits of 316L stainless steel is its relatively low cost and wide availability. Manufacturers can purchase 316L scrap relatively inexpensively, which makes it a highly accessible material for filtration system engineering.

Cons

Despite 316L’s popularity, there are some industry experts who believe that this stainless-steel alloy is inappropriate for use specifically in ballast water treatment systems. These professionals cite issues with the welding process as a major drawback – and the consequences of these issues certainly warrant a second look in other seawater applications as well.

High Ferrite Content

One of the biggest drawbacks in using 316L stainless steel for seawater filtration can occur during the welding process. 316L must be welded under very strict conditions, or else it might develop a high ferrite content in the weld seam.  Ferrite can diminish an alloy’s ability to resist corrosion. Even a small amount (around 2%) of ferrite content in a weld seam can result in a less effective finished product.

Since 316L stainless steel is prone to developing excess ferrite during production, it can make some filtration experts leery of using this alloy in their systems. In fact, some argue that the potential for high ferrite content in 316L stainless steel can lead to greater incidence of pitting corrosion or crevice corrosion. This kind of damage can require significant repair or even a completely new filtration system – effectively counteracting the reduced costs of using the 316L alloy.

Duplex 2205

Duplex 2205 is a stainless steel characterized by its strength. With a makeup of 22% chromium, 3% molybdenum, and about 5% nickel, it is about on par with 904L in terms of corrosion resistance. However, duplex 2205 is (as the name suggests) a duplex stainless steel; this means that it contains both austenite and ferrite phases in its metallurgical structure, giving the alloy a greater overall durability.

Pros

Duplex 2205 is the most popular of the duplex stainless steels, and it is often used in pipework systems for offshore oil and gas. This alloy’s strength and chemical composition, as well as its durability against
seawater in offshore uses, makes it a logical choice on paper.

seawater filtration for oil and gas applications

Good Corrosion Resistance

Duplex 2205 has a PREN average of 35.9 – just shy of 904L stainless steels average of 36.7. This indicates that this alloy would be able to fair just as well as 904L when dealing with pitting corrosion, crevice corrosion, or any other type of destructive wear and tear within the filtration system. Theoretically, duplex 2205 would be a reasonable alloy for a seawater filter.

Cons

While duplex 2205 has had plenty of success within the oil and gas industry when used as a solid structure such as piping, it’s not used often in complex manufacturing procedures such as a weaved screen mesh used in seawater filtration. This is likely due to two main issues: There are challenges when working with it and its lower temperature threshold for corrosion.

Hard to Work With

One of Duplex 2205’s assets, it’s strength, is actually a double-edged sword. Since the alloy is so strong, it makes it difficult to work with, and requires special heavy machinery that is not commonplace. In addition, it makes it very challenging to mold the steel into the very tiny and delicate structures, such as ballast water filters or desalination filters that require filtration down to 10 microns.

Corrodes Faster than 904L

While Duplex 2205 has better corrosion resistance than 316L, it still corrodes at a lower temperature than 904L (50C vs 55C for 904L).

904L

Another popular alloy used in seawater filtration is 904L stainless steel. This alloy contains many of the same elements as 316L steel, but it is comprised of higher levels of chromium (about 19%), nickel (23%), and molybdenum (4%).

904L stainless steel is most famously used in luxury watches (Rolex, for example, swears by this alloy), but it is also a popular metal for seawater filtration. This is because the high amounts of nickel in this alloy
makes it particularly corrosion resistant, protecting your seawater filter from damage.

Pros

Choosing the right alloy is essential for a durable and effective seawater filtration system. When alloys have similar compositions, like 316L and 904L, the decision may seem insignificant; however, 904L stainless steel has some major benefits that can make a big difference for a seawater filter.

Highly Corrosion-Resistant

As we mentioned above, 904L is highly resistant to corrosion due to the high levels of nickel in its composition. This means that seawater filtration systems made with 904L tend to have a longer lifespan than their competitors.

In fact, 904L stainless steel has an average pitting resistance equivalent number (PREN) of 36.7 – more than 10 points higher than 316L’s PREN average (26.1). This is an important parameter to consider when
designing seawater filters, as it will help determine how effective the filter’s corrosion resistance and durability will be over its life.

Widespread Availability

Another benefit 904L has to its credit is its availability in the market. This alloy is readily available from most suppliers, which means that engineers and manufacturers can procure the metal and produce filtration systems much more easily than they might with other metals.

Cons

While 904L stainless steel offers both practical and logistical benefits, it is not a perfect alloy. Some engineers or manufacturers may opt for another metal due to the one major flaw that accompanies using this metal: the cost to use it.

Higher Cost

The costs of most alloys vary based on the amount of chromium and molybdenum in the metal. As we’ve mentioned previously, 904L stainless steel has higher levels of both these elements compared to 316L – which means that it tends to be about 1.3 times more expensive.

This price difference might drive some budget-conscious manufacturers to a lower-quality alloy. However, it is important to mention that the greater strength and durability of 904L stainless steel means that filters made from this alloy are less likely to need repairs during their lifespan. The cost savings you will earn from this lack of repairs more than offsets the cost of the alloy itself.

254 SMO

Like the two alloys we’ve already mentioned, 254 SMO is an austenitic stainless steel. However, this alloy was originally developed for use in chloride-heavy environments – such as seawater cooling pipes, heat exchangers, pulp and paper plants and more. The metal contains a similar amount of chromium as 904L, but it has a greater amount of molybdenum (6% vs. 4% in 904L).

With this composition in mind (not to mention the alloy’s intended use), it is no surprise that 254 SMO is an alloy that generates lots of interest among seawater filtration engineers. There are unquestionable benefits that come with using this alloy – but there are also a few drawbacks that can complicate its use.

Pros

The greatest benefit of using 254 SMO for seawater filtration is its corrosion resistance. The chemical composition of this alloy makes it highly resistant to both microbiologically induced corrosion and chemical corrosion – making it incredibly durable against seawater even after prolonged exposure.

Excellent Corrosion Resistance

254 SMO has a PREN average of 43.8, which means it has the greatest protection against corrosion of all the alloys studied here. It also has a low carbon content (around .02%), which means that there is little risk of ferrite development during production. These two facts mean that 254 SMO is one of the best alloys for protecting your seawater filtration system from the corrosive effects of seawater.

Cons

The excellent protective qualities of 254 SMO might make it seem like the gold standard in seawater filtration materials. However, at least in their ballast water treatment systems, few developers use it – why? 254 SMO is often passed over due to two flaws in its practicality.

High Cost

As we mentioned earlier, alloy costs vary depending on the amount of chromium and molybdenum in the steel. 254 SMO contains higher levels of these elements than both 316L and 904L stainless steel – which means that it tends to cost much more than its competitor alloys.

254 SMO can cost as much as three times more than 316L, and many manufacturers are unwilling to spend more to produce their filtration systems. This cost is above the threshold deemed “acceptable” by most industry professionals (unlike 904L stainless steel, which has a slightly higher cost but offsets the cost of maintenance).

Limited Availability

One of the hinderances that limits 254 SMO from being suggested for more seawater filters is that this alloy is not produced regularly due to its higher costs.

Which Alloy is Best?

radar diagrams for common stainless steel alloys

Due to the nature of seawater filtration and its association with heavy industry, engineers of all applications endeavor to build filtration systems standing up to the ravages of seawater — all without costing you too much money. At the same time, the cost of using a lower-quality alloy will corrode more easily and lead to expensive problems – specifically more frequent maintenance and reduced filtration capabilities as corrosion overtakes the screen. These outcomes will, in the long run, increase operating costs, as equipment owners will have to pay for more frequent servicing, and where applicable such as in regulated industries like ballast water management systems (BWMS), potential fines for non-compliance of malfunctioning systems.

The solution? Invest in a filtration system that’s made from a durable, yet cost-efficient material. And when it comes to choosing the best alloys for seawater filtration without consideration of cost – SMO 254 is definitely the favored alloy. When dealing with a high end application where even the smallest downtime can be very costly such as in the oil & gas or desalination sector, the initial investment in using a Filter with an SMO 254 screen pays off in the long run. However, when a cost-effective solution is required, there is one option that stands head and shoulders above the competition: 904L stainless steel.

904L stainless steel is the ideal marriage of strength, corrosion resistance, and accessibility – all at a reasonable cost to manufacturers. Seawater filters made from this alloy will stand up to corrosion and keep your filtration system running effectively for many years, saving you thousands in fees and maintenance costs.

For a deeper investigation into the alloys discussed above for use in seawater applications please download our peer-reviewed white paper on the topic – Overcoming Corrosion of Stainless Steel Screens in Seawater Applications.

Filtersafe’s Smartweave Screen: Water Filtration at a Whole New Level

filtersafe default image with logo

Most eCommerce clicks not only put new clothes or appliances in your virtual shopping cart, they also are putting your packages on cargo ships for delivery. The continued dependence on online shopping has meant more work for  international shipping vessels, which are constantly moving from one corner of the globe to another – and they’re discharging ballast water in every port they visit.

This can be dangerous for our oceans, as zooplankton, phytoplankton, and other microorganisms that hitch a ride in ballast tanks can damage the native ecosystems if they are deposited into a new body of water. Therefore, it is essential that ships filter their ballast water before releasing it back into the sea.

As a company founded by engineers, Filtersafe has been dedicated to finding innovative solutions to filtering sea water. The current seawater screens often suffer two main problems: blockage, which can result in pressure depressions and a decreased flow rate, and an inability to filter out smaller microorganisms.

To address these issues, the Filtersafe engineers created the Smartweave screen. This unique technology is a weave-wire screen specifically designed to tackle the challenge of seawater filtration. By using a combination of weave wire filtration screens, protective screens, and a reinforcement layer — as well as the automated cleaning power of our Everclear system — this innovative, highly effective screen filters out sediment and microorganisms, protecting native marine life in every port. Its combined efficacy and durability make the Smartweave screen a filtering element ships can rely on for years.

 

How It’s Made

Filtersafe understands the unique challenges facing ballast water filtration (one of the most challenging seawater applications). Seawater contains microscopic particles that can cause harm when transferred to other ecosystems and encourage the creation of corrosion within the ships’ interior. Filtering out elements this small requires a complex and multi-layered system, so the Smartweave designers created exactly that.

The Smartweave screen is made up of three stainless steel weave-wire screens and a fourth reinforcement layer to enhance the screen’s integrity. This includes one filtration control layer, two protective layers on either side, and one reinforcement layer. We then take this combination of screens and sinter them together, creating one mega-screen that is durable enough to filter without additional support.

These screens are available in a variety of sizes, from 500 microns down to 10. This allows ship owners to choose a Smartweave screen that best suits their vessels’ unique needs. The Smartweave seawater screen is also made from 904L stainless steel: an stainless steel that offers high corrosion resistance, higher quality, and a longer-lasting screen than the standard 316L stainless steel and other options in the market today.

The innovation and careful design work behind Smartweave have made it one of the top weave-wire screens for seawater filtration today. This screen offers enhanced strength and top performance, so shippers can trust that their ballast water is safe to discharge and is compliant with the IMO G8 requirements.

 

How Does It Work?

All the innovation in the world doesn’t matter if a product doesn’t work. The engineers at Filtersafe know how important seawater filtration is, and so they’ve spent years testing and perfecting the Smartweave screen. As a result, Smartweave is one of the most effective filtration systems available today, keeping zooplankton, phytoplankton, and sediment out of ballast water across the world.

The term “zooplankton” refers to small microorganism and the immature stages of larger species. It is vital to filter these from ballast water, as they can be detrimental to the native ecosystem at a port of call. According to tests from Filtersafe and other research groups, the Smartweave screen removes 99.95% of zooplankton from ballast water – more than any other filter available today.

Shippers also need to filter phytoplankton from their ballast water before releasing it into the sea. Phytoplankton, or microscopic marine algae, are an important food source in the ocean’s ecosystems – but only if they’re in the right location. While phytoplankton can be very small (as small as 10 microns), Smartweave is an effective filter for them, too. that the Smartweave screen removes 100% of phytoplankton larger than the micron of your selected screen.

Finally, a filter must be able remove sediment and other suspended solids from any ballast water. Once again, Smartweave delivers here:  A series of tests we conducted on our filter show that even in extreme conditions when the TSS levels reached 2500 ppm, we were able to decrease the decrease suspended solids from 2500 ppm to 100 ppm – a removal rate of 98%.

 

Constantly Improving

Today, Filtersafe treats 25% of the world’s ballast water – and all because of unique, innovative, and effective products like the Smartweave screen. For some teams, the Smartweave screen’s impressive filtration rates would be enough to call the filter a success. But Filtersafe is dedicated to making the ballast water filter even better.

The team is constantly innovating and perfecting our ballast water treatment systems. We’ve outfitted our Smartweave screens with our Everclear cleaning sequence, which automatically returns your filter to its original operating parameters. This ensures peak performance and an optimum flow rate – and provides the user with peace of mind.

Each Smartweave screen is used in conjunction with Filtersafe’s patented nozzles – the Nozzlex system. This uses suction technology to clean the screen thoroughly and completely with each use(without damaging it). These features help maintain the Smartweave’s exceptional performance, so captains can focus on their cargo and getting to their next location and not just about meeting USCG or IMO water treatment standards.

*Efficacy is dependent on the size and distribution of the TSS.

Filtersafe’s NozzleX: An Innovation that will Save Your Filter Screen

filtersafe default image with logo

At Filtersafe, we understand that water filtration is essential to helping many industries run smoothly. However, we also understand that today’s filtration technologies can always be improved — which is why we strive to be a leader in the world of water filtration. Our engineers have decades of experience in the industry, and they’re dedicated to creating the top technologies for automatic filtration.

One such technology is the NozzleX suction scanner – an innovative tool that enables the cleaning of organic and inorganic material from your filter’s screen, without wearing down the nozzle or wearing out the screen. With a typical automatic screen filter, the nozzles sit on a bar called a raiser. The raiser moves the nozzle heads back and forth along the length of the screen, while also rotating the nozzles in a corkscrew motion. The nozzles scan the surface, and by using negative pressure, dislodge debris one square inch at a time. While this does help the screen filter water effectively in the short term, the force from the nozzle can damage the screen and shorten its lifespan.

NozzleX, by contrast, uses low head pressure (as low as 23psi) to clear off all the buildup on the screen without damaging it. First, the raisers move the nozzles in such a way that 100% of the screen is scanned and cleaned. Next, in contrast to other filters, NozzleX nozzles safely come into contact with the screen, utilizing gentle pressure to pull materials off of the screen without impacting the screen’s integrity. This results in improved performance and a longer lifespan for your ballast water filter or other filtration technologies.

 

How it Works

The NozzleX uses passive suction to remove organic matter like debris and sediment from the filter screen. Through an innovative combination of consistent force and passive pressure, whereby the nozzle both actively removes material from the filter while allowing the naturally occurring changes in pressure to carry it away, this nozzle makes cleaning your filtration system an easy and automatic process.

This patented system moves around the filter screen automatically, using as little as 1/32nd the force of typical cleaning nozzles to offer a thorough cleaning with minimal wear. Then, the nozzle disposes of reject water through the system’s flushing chamber, guaranteeing that buildup won’t remain on your screen.

NozzleX is part of Filtersafe’s Everclear cleaning system, which includes the Smartweave screen filter. Working together, these two technologies provide exceptional filtration power while minimizing space. This ensures that operators can use their filtration system as long as possible.

 

Benefits of NozzleX

In the world of water filtration, NozzleX is truly a revolution. This unique cleaning tool offers several significant benefits to an automated filtration system, which can make a real difference in the quality and longevity of a system. Here are just a few of the unique benefits you can get from using NozzleX:
  

    • Continual System Operation: Firstly, NozzleX runs as part of the automated filtration system. There’s no need to halt system operation and clean out your filtration screens; instead, NozzleX will clean your screens throughout the filtration process.
    • Minimal Surface Area: In addition to its consistent cleaning functionality, the NozzleX is exceptionally compact. The nozzle takes up a mere 1% of the screen area, which allows your filtration system to continue running even while it’s being cleaned, and without significantly hindering the flow rate. This will result in greater filtration capacity and greater overall efficiency for your system.
    • Improved Performance: Dirty or clogged filters can have a serious impact on a filtration system’s efficacy. In fact, Filtersafe testing has shown that some systems lose performance in as little as six hours. In that time, a system’s flow rate can drop from about 3,000 m3/hr to less than 1,900 — but NozzleX maintains a consistent flow rate throughout its operations. With NozzleX, you’ll be able to get the optimum performance from your filtration system all day long.
    • Zero Screen Wear: Finally, one of the greatest benefits NozzleX provides is the way it minimizes screen wear. Other nozzle-based cleaning systems use significant force to remove debris from their filters, which can lead to punctures and other damage that cuts the screen’s lifespan short. NozzleX, in contrast, equalizes system pressure to use far less force — around 1.6 Bar (23psi) of head pressure. This means your filter screens suffer next to zero wear, allowing them to operate much longer than other screens.

     

    Why It’s Important

    The importance of a properly functioning nozzle is simple – a water filtration system only works when it’s clean. Whether you are filtering ballast water before filling your tanks, protecting your oil and gas exploration equipment safe from organic oceanic materials, or prefiltering water for desalination, each filtration system should have the same thing in common  a reliable nozzle to clean your screen.

    So, why not let NozzleX do the job for you?

    NozzleX ensures that a filtration system stays clean throughout operations, thereby making sure that the system remains effective and efficient. As part of Filtersafe’s Everclear system, NozzleX will provide users with a completely clean filter screen — and that will help guarantee superior performance from your filtration system.

     

    To learn more about the NozzleX cleaning technology, contact Filtersafe today. Our team will be happy to answer questions and help you find the system that best suits your industry and your organization’s unique filtration needs.