SOLVING RUST
Corrosion plagues the energy industry. Globally, the cost of corrosion is estimated to be?$2.5 trillion annually?– and this is before you factor in the employee safety and environmental costs into the equation. These high costs stem from maintenance, equipment downtime, asset replacement, and lost production, just to name just a few. For example, just the corrosion under insulation costs accounts for approximately one-half the pipe maintenance budget.
Each company in the industry has experts that are incredibly knowledgeable about the effects of corrosion, the varied unique mechanisms by which it occurs, and the many complex techniques to mitigate it. Unfortunately, as is the case with many things in life, by not understanding and focusing on the root cause, we make the problem of corrosion more complicated than it needs to be.
Listening to folks talk about the intricate details and complications reminds one of an accountant talking about tax strategies – the eyes glaze over. For example:
You get the eyes-glazed-over point!
The most important thing that the Georgia Institute of Technology taught me is that reducing the problem to its simplest form often causes the answer to fall out. When you reduce corrosion prevention to its simplest form,
SOLVING RUST = PREVENTING RUST
Preventing Rust is about stopping the loss of electrons. In this article is everything you need to understand rust – and how to permanently prevent it. Rust is a simple thing that is only made difficult when we talk about the complexities of things like galvanic corrosion, microbial-induced corrosion, and all the various technical details of applying a coating without understanding why we do it. However, if we forget about the complexity and focus on the basics, the problem becomes easy to solve
Corrosion?happens when a carbon steel atom loses an electron and bonds with oxygen to restore the charge imbalance.
SOLVING RUST = UNDERSTANDING THE PROBLEM
By definition, metals are good conductors of heat and electricity. They have these properties because they readily share electrons. Electrical current is just electrons moving in a path from high to low voltage.
This sharing of electrons makes extraordinary things possible, like electricity. Each atom gives electrons to the next atom in line and then accepts electrons from the atom behind it in the chain. Everything goes swimmingly until an atom loses an electron. Then there is a net shortage of electrons, and everything goes wrong after that.?If the iron atom that has lost electrons bonds with oxygen, you get rust.
SOLVING RUST = STOPPING ELECTRON LOSS
If the problem is the loss of electrons, how do we stop it? We do not want metal to stop sharing electrons – it would no longer be metal if it did that.
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Could we electrically insulate it somehow so the electrons travel down the middle of the metal but cannot leave the surface??EXACTLY!
Could we feed the metal a constant stream of electrons, so no atom ever runs short on electrons??THAT WORKS TOO!
SOLVING RUST = THE SCIENCE
A more permanent method of insulating steel is to form an alloy over its entire surface. We must create an alloy that does not share its electrons for this to work. In other words, the alloy must be non-conductive. Fortunately, there are several effective ways to do this. Take, for example, the poor atom that became short of electrons. The atom cannot be happy until it finds a replacement electron. The atom will bond with WHATEVER satisfies the need and takes the LEAST AMOUNT OF ENERGY!
In the case of the atom, this means bonding with another atom (or molecule) that has extra electrons it is willing to share. This new partner can be one of two types. One type will form a stable partnership that is welcome in the community of other similar atoms forming the metal, and?this is an alloy. The second type is a partnership that is not as stable and will not become part of base metal.?That unstable base metal is called corrosion – or rust.
There are also stable oxide bonds. For example, the chromium in stainless steel forms an amorphous layer of chromium oxide. The amorphous oxides stay bonded to the base metal and protect it. This is also possible with iron, but a catalyst is required to convert the iron oxide crystals to amorphous. Examples of unstable bonds include iron combining with oxygen – resulting in a crystalline iron oxide (FeO, Fe2O3, or Fe3O4), and these are the various forms of rust.?
As described, the Fe ion chooses which of these to bond with, based on what reaction takes the least energy. Engineers quantify the energy of formation using something called Gibbs Free Energy. We do not need to explain Gibbs Energy here but accept my word that the more negative the Gibbs Energy of a Reaction, the more likely it will happen. For example, the Gibbs Energy of the reaction of oxygen with iron is not as negative as the reaction with phosphate. Therefore, if sufficient phosphate is present – the Fe ion will choose to bond with phosphate instead of oxygen. In the process, we get an insulation layer of iron phosphate that is not conductive in nature and does not give up its electrons.
SOLVING RUST = THE PERMANENT SOLUTION
All we must do is put soluble phosphate next to steel in an aqueous environment, and it will create its own alloyed layer. The higher the phosphate concentration, the better this works, and the more corrosive environment the metal can endure and stay protected.
Many years ago, paint companies, recognizing the limitations of the plastic barrier, began employing both insulating methods mentioned above. They encapsulated phosphates in the plastic barrier. While the idea was a step in the right direction (polymers containing inhibitive pigments do work better than those without), the encapsulation of the pigment in the gooey resin of phosphates in a plastic barrier is counterproductive. The phosphate must fight its way out of the resin to reach the carbon steel to form the alloy. Additionally, adding a large enough volume of pigment to be effective in a highly corrosive environment is impossible. From a practical standpoint, polymers can hold only about 20 percent inhibitors.
HOW TO PREVENT EXTERNAL PIPELINE CORROSION
will be explained next Hopefully
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