Saturday, January 18, 2014

The Bronze Fish

Metal is notorious for corroding in water applications.  The power packed combination of moisture, oxygen and salt, especially sodium chloride, is more deadly to metal than rust.  It corrodes or eats away at the metal by weakening it and eventually causing it to fall apart.  And if the metal is submerged in a salt water environment than count on your metal corroding five times faster than if it was in fresh water.

Considering we rely on metal in just about every "water-related" application out there, the above statistics sound a bit bleak.  Let's see, we need metal in plumbing, water filtration, sewage plants, hydro-electric power, oil & gas platform parts in the ocean, engine cooling, refrigeration, irrigation and the list goes on and on.  How could the world's economy and infrastructure have survived if metal wasn't used in water applications?  Well, since you and I haven't heard about the world's ongoing struggle to find a metal for water applications that means a solution must have been found. 

Steel in Water?

Traditionally, steel is not seen as a suitable metal for water applications.  Why?  Remember that moisture is highly corrosive to most metals including steel and zinc.  However, steel is indeed used in water applications. 

So, how do you get around the moisture problem?   OK, so here is my inner Comic Book geek coming out.  There is this character called The Green Latern.  For a visual reference see below:

The Green Latern is a unique comic book character.  He is green, flies through the air and creates objects with a special ring.  BUT what sets him apart from a lot of other Comic Book characters is his protective suit.  You see, he doesn't "suit up" like Batman or Superman.  Instead his protective suit is bonded to his DNA makeup.  So when he senses danger the suit magically appears on this skin. 

So what does Steel have to do with Green Latern's magic suit?  In order to make steel suitable for water applications, there is a process called Hot Dip Galvanizing.  This is where a "layer or protective suit" is metallurgically bonded to the steel ~ not added like Superman or Batman's suit.  This bonded layer is a complete, uniform coating that adds strength (apprx. 3600 psi) and long term durability to the part.

However before you go and select Hot Dip Galvanizing Steel (HDGS) as your "go to water metal", beware of some of the disadvantages.  You must know what type of water the part will be submerged in, such as; pure water (distilled or de-ionized water), fresh water, or seawater. Each water environment has different mechanisms that determine the ultimate corrosion rate.  For instance, studies show that HDGS will corrode up to ten times faster in a pure water environment than in a fresh water environment.

Also, one of the most corrosive areas for HDGS is in Agitated Waters, such as; wash zones and tide lines.  The agitation accelerates the corrosion rate of the zinc.  Often the “washing” motion removes the passive scales which are forming on the surfaces, exposing fresh zinc which tries to redevelop more scales/patina. This leads to rapid erosion of the zinc coating resulting in increased corrosion rates.

So what are the alternatives?

Introducing The Bronze Fish

Well by now I'm sure most of you were beginning to wonder what is this Bronze Fish all about.  After all, that's the title of the blog post.  While it's true that other metals can be used in water, there is a Bronze Alloy group that is naturally suitable for water applications.  They are chemically and mechanically designed for water (and of course other applications as well).   Hence, the Bronze Fish reference.  

This group is the Aluminum Bronzes.  

Aluminum Bronzes are most commonly used in water applications because of their great resistance to corrosion in a variety of water environments.  This makes them preferable to other engineering materials.  The Aluminum Bronze group contains a variety of choices,  but for the sake of time I will highlight three:
        1. C63000 Nickel Aluminum Bronze
        2. C95400 Aluminum Bronze
        3. C95800 Nickel Aluminum Bronze 


The 630 Fish - the strong & tough fish

C63000 Aluminum Bronze is an extruded or forged Wrought Alloy that contains Nickel (nominal 5%). As an aluminum bronze, C63000 has an excellent resistance to salt water corrosion and displays exceptional strength and toughness as well.  C63000 is typically used where higher mechanical properties are required.  It is used in equipment for marine applications, such as:  valve stems, high strength bushings, valve guides and seats, gears, cams, ship propellers, as well as propeller nuts and shafts.



The C95400 Fish - the popular fish

C95400 Aluminum Bronze is a Cast Product that is considered the most popular of all the Aluminum
The "Nemo' fish
Bronzes.  It is regularly stocked in a variety of shapes and sizes, such as, Solid Bar, Cored Bar and Plate and Rectangle; thus making it the "go to" Aluminum Bronze. C95400 is suitable for fresh water and salt water (if heat-treated) applications as well as agitated waters.  In fact, C95400 is nearly impervious to attack from seawater when properly heat-treated.  However note that improper heat-treatment of C95400 castings can result in a finished product susceptible to a unique form of galvanic corrosion commonly called de-aluminization.  


The C95800 Fish - the dirty fish

C95800 Nickel Aluminum Bronze is a Cast Product that also contains 5% Nickel (much like C63000). However, unlike C63000 it contains slightly less Aluminum & Copper and a bit more Iron. Additionally, due to it's Method of Manufacture (or the way its made) it possesses different mechanical properties. 

C95800 as a Centrifugal for pumps will stand out as being ideally suited for  saltwater, as well as brackish or dirty water, waste water and pollution control applications.  The overall corrosion / erosion resistance this alloy displays
has been deemed far superior to stainless steel -- and costs less!! (always a benefit) 

It is amazing how Bronze stands out against the "big guys", like Steel and Stainless Steel in certain environments and applications. Even though annual Bronze consumption accounts for such a small percentage of all the metal consumed in the world - it is clear that Bronze has a major part to play in the Metals Industry.  I am finding that it is a unique, diverse and adaptable underdog. 

Until next time...enjoy your week!


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