Oxidation is loss
In college, for a brief span, I decided I wanted to major in chemistry. I have always been intrigued by how and why different elements and molecules react with each other. However, the mathematic and testing side of being a chemistry major didn’t go as well as I had hoped.
Recently, I read "Rust: The Longest War" by Jonathan Waldman. The book is all about the never ending battle with oxidizing metal, which rekindled my interest in chemistry. According to a special division of the U.S. Department of Defense, The Corrosion Prevention Office, rust costs the U.S., “Something like $480 billion dollars a year – more than fifteen hundred dollars for every man, woman, and child in the country.”
Rust would quickly crumble something like a naval fleet without diligent maintenance work. Just like in plumbing and heating systems, staying vigilant in upkeep and maintenance may not be the primary focus of all property owners. Out of sight, out of mind. Unfortunately, rust doesn’t stop if you stop paying attention to it.
O.I.L. R.I.G. was one of the mnemonics that stuck with me from taking chemistry classes. It stands for, "Oxidation is the loss of electrons;. Reduction is the gain of electrons." It is a way to keep track of the misleading terminology relating to where electrons are coming and going in a chemical reaction. A metal oxidizes when it loses electrons to other elements it comes in contact with.
The metal-to-metal oxidation/reduction issue is why we put dielectric unions on water heaters. Dissimilar metals in direct contact are sacrificing electrons one direction or the other. Water facilitates this process. These unions keep the metals out of direct contact, which is effectively an electron trade embargo. The Galvanic Corrosion Chart helps determine how forcefully one metal will steal electrons from another. This corrosion chart also explains why the copper shell of the Statue of Liberty was literally eating the iron frame it was built around.
Some of the topics in Waldman's book are success stories against corrosion. The aluminum can that we use for carbonated drinks is a modern marvel. One of the most popular drinks in the world has a pH of 2.75. The pH, or power of hydrogen ion, scale is from 0-14. For reference, milk has a pH of 6, lemon juice is 3, and battery acid is just above 0.
There are some things that we like to drink that are so destructive that internal coatings need to be sprayed into the aluminum cans before they are filled to avoid rotting through their vessel in a matter of a few days. Can manufacturers have taken liquids that should chew right through metal and harnessed them to unbelievably high leak resistant standards.
The internal can coating is interesting for potential heating industry applications. What if we coated the inside and outside of a steel tank with a plastic internal coating instead of making it out of more costly stainless steel? Glass lined tanks use this model. The internal coatings used for aluminum cans are almost invisibly thin and would cost less to ship than glass based models. Developing a coating that could keep water and glycol out of direct contact with metals without hindering the heat transfer would be a great goal for all sorts of boiler components.
We could also avoid corrosion by building boiler systems with noble metals, although this may not be entirely realistic from a financial aspect. Metals that are most resistant to corrosion on the Galvanic Corrosion Chart are deemed noble metals. Unfortunately, piping a full heating system with gold or platinum may not be in the budget. We use copper, stainless steel, and brass for the majority of our components. None of these metals are perfect vessels for water, but they are improvements from some of the materials we used in the past.
The citizens of Flint, Michigan have seen that subtle differences in water chemistry can cause major harm. To save money, the city of Flint switched their water supply from coming from Detroit to coming from the Flint River. What they failed to catch is that the chloride to sulfate mass ratio (CSMR) for the two water supplies were very different. The 0.45 CSMR of Detroit water isn’t very corrosive. The 1.60 CSMR number of the Flint River water is very corrosive. High chloride levels are attributed to road salt in the watershed and FeCl3 used to combat E. coli.
What that means is that the high chloride levels in the Flint water attacked the lead pipes used throughout the city. If they switched back to Detroit water, the lead pipes wouldn’t be corroded the same way, because the chlorine levels are lower.
Not all pipes are neglected and forgotten. The Trans Alaska Pipeline runs the entire length of the state carrying oil to a port in Valdez. This 4-foot diameter steel tube is relentlessly monitored to prevent leaks from rust pitting. They actually send mechanical monitoring machines called pigs all the way through the pipeline continuously to look for weak spots in the line. The pigs use hundreds of magnetic sensors to measure all seven billion square inches of the pipe. This would be another cool crossover for our industry. Imagine being able to drop a device in 1-inch copper in order to catch a weak spot in a fitting before it sprung a pinhole leak. Unfortunately, $2 million may not be in your tool budget this year.
Plastic piping materials are the general direction our industry is headed. This doesn’t mean copper, steel, brass, stainless and even lead aren’t acceptable products to use. All metals can be used, if the proper water quality precautions are taken to protect from corrosion and ensure drinkable water. However, if they dug up Flint and repiped the entire city with a mix of PEX, polypropylene random, and other plastics, we would avoid the possibility of drinking lead. Plastics aren’t perfect, but they don’t fight each other like a mixture of metals piping can.
It would be interesting to go 100 years into the future and see what they use for heating and plumbing piping. Metal components may continue to be replaced by plastics as the polymers get stronger and better at controlling linear thermal expansion. Continuing the trend we are on, metal systems will need an infusion of technology to keep up with the plastics.
I ended up changing majors in college and getting a degree in Behavioral Science and Health. Having a small background in chemistry helped me figure out why different metals and plastics were used for heating systems. Oddly enough, the degree in Behavioral Science shed a light on the human desire to avoid change.
An installzrs comfort with a piping material trumps most other factors, except for possibly price. As an industry, we really only change our piping and components when we determine the current method to be poisonous, obnoxiously prone to leak, or harmful to humans. Will the next pipe you buy be chosen because it is the best way to transport water, or because it is what you are accustomed to?
Max Rohr has worked in the hydronics and solar industry for 10 years in the installation, sales and marketing sectors. Rohr is a LEED Green Associate and is Radiant Professional Alliance’s (RPA) Education Committee chairman. He can be reached at firstname.lastname@example.org and @maxjrohr.com.