You Spend More on Rust Than Gasoline (Probably)

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In July of 1995, Folsom Lake, a reservoir  created by Folsom Dam in Northern California,   reached its full capacity as snow continued  to melt in the upstream Sierra. With the power   plant shut down for maintenance, the dam’s  operator needed to open one of the spillway   gates to maintain appropriate flow in the  river below. As the gate began to rise,   one side suddenly collapsed and swung open,  allowing an uncontrolled torrent of water to flow   past the gate down the spillway. With no way  to control the flow, the water level of Folsom   Lake began to drop… and drop and drop. By  the time the deluge had slowed enough that   operators could block the opening, nearly half  the water stored in Folsom Lake had been lost. Forensic investigation of the failure revealed  that the gate malfunctioned because of corrosion   of its pivot mechanism, called the trunnion,  creating excessive friction. Essentially,   the gate was stuck at its hinges. When the hoist  tried to raise it, instead of pivoting upwards,   the struts buckled, causing the gate to collapse.  This gate operated flawlessly for 40 years before   the failure in 1995. However, corrosion is an  insidious issue. Because it occurs gradually,   it’s hard to know when to sound the  alarms. But, there are alarms to sound! It’s been estimated that we lose roughly  two-and-a-half trillion dollars per year globally   because of the collective corrosion of the things  we make and build. That is a colossal cost for a   simple chemical reaction, and there’s an entire  field of engineering dedicated to grappling with   the problem. So, this is the first in a series  of videos on corrosion engineering. Make sure you   subscribe to catch them all. You probably don’t  have a line item in your household budget for   rust, but you might add one after this video.  I’m Grady, and this is Practical Engineering.   In today’s episode we’re talking about  corrosion engineering for infrastructure. This video is sponsored by HelloFresh,  America’s #1 Meal Kit.. More on them later. It will come as no surprise to you that we build  a lot of stuff out of metal. Entire periods of   human civilization are named after the kinds  of metals we learned to use, like the bronze   age and the following iron age. These days nearly  every humanmade object is made at least partly of   metal or in a metallic machine, from devices and  vehicles to the infrastructure we use everyday,   including bridges, pipelines, sewers, pumps,  tanks, gates, and transmission towers.   Metals are particularly useful for so many  applications, and we humans have invented a   plethora of processes (like smelting, refining,  and alloying) to assemble metallic molecules in   various ways according to our needs. But,  mother nature is resolved to dismantle   (in due course) the materials we create through a  process called corrosion. It seems so self-evident   that structures deteriorate over time that it  might not seem worth the fuss to worry about why.   But, infrastructure is expensive and we  all pay for it in some way or another,   so we need it to last as long  as possible. Not only that, but   the failure of infrastructure has consequences  to life safety and the environment as well,   so keeping corrosion in check is big  business. But what is corrosion anyway? You’re here for engineering, not chemistry,  so I’ll keep this brief. Corrosion is an   electrochemical descent into entropy: a way  for mother nature to convert a refined metal   into a more stable form (usually an oxide).  Corrosion requires four things to occur:   an anode (that’s the corroding metal), a  cathode (the metal that doesn’t corrode),   a path for the electrical current between the  two, and an electrolyte (typically water or soil)   to complete the circuit. And the anode and  cathode can even be different areas of the   same piece of metal with slightly different  electrical charges. The combination of these   elements is a corrosion cell, and the process that  corrode metals in nature are nearly identical to   those used in batteries to store electricity.  In short, corrosion is a redox (that is,   reduction-oxidation) reaction, which  means electrons are transferred,   in this case from the metal in question to  a more stable (and usually much less useful)   material called an oxide. For corroded iron  or steel, we call the resulting oxide, rust. Here’s a little model bridge I made from  steel wires in a bath of aerated salt water.   I added a little bit of hydrogen peroxide  to speed up the process so you could see   it clearer on camera. This timelapse ran for  a few days, and the corrosion is hard to miss.   Of course, we don’t keep our bridges  in aquariums full of salt water and   hydrogen peroxide, but we do expose  our infrastructure to a huge variety   of conditions and configurations  that create many forms of corrosion. You’re probably familiar with uniform  corrosion that happens on the surface of metal,   like the beautiful green patina of copper oxides  and other corrosion compounds covering the Statue   of Liberty. But corrosion takes many forms,  and corrosion engineers have to be familiar   with all of them. These engineers know the common  design pitfalls that exacerbate corrosion like   not including drainage holes, leaving small  gaps in steel structures, and mixing different   types of metals. Corrosion can occur from the  atmosphere or simply by allowing dissimilar   metals to contact one another, called galvanic  corrosion. Even using an ordinary steel bolt on   a stainless steel object can lead to degradation  over time. Corrosion can happen in crevices,   pits, or between individual grains of the metal’s  crystalline structure. Even concrete structures   are vulnerable to corrosion of the steel  reinforcement embedded within. When rebar rusts,   it expands in volume, creating internal  stresses that lead to spalling or worse. Just as there are lots of kinds  of corrosion, there are also many,   many professionals with careers  dedicated to the problem. After all,   the study of corrosion and its prevention is a  topic that combines various fields of chemistry,   material science, and structural engineering.  There’s even a major professional organization:   the AMPP or Association for Materials  Protection and Performance, that offers   training and certifications, develops standards,  and holds annual conferences for professionals   involved in the fight against corrosion.  Those professionals employ a myriad of ways   to protect structures against this insidious  force, that I’ll cover in this series. One of the simplest tools in the toolbox is just  material selection. Not all metals corrode at the   same rate or in the same conditions, and  some barely corrode at all. Gold, silver,   and platinum aren’t just used in jewelry because  they’re pretty. These so-called noble metals are   also prized because they aren’t very reactive to  atmospheric conditions like moisture and oxygen.   But, you won’t see many bridges built from gold,  both because it’s too expensive and too soft. Steel is the most common metal used in  structures because of its strength and cost.   It simply consists of iron and carbon. Steel  is easy to make, easy to machine, easy to weld,   and quite strong, but it’s also one of the  materials most susceptible to corrosion.   I’ve got another demonstration set up here in  my garage. This is a tank full of salt water,   a bubbler to keep the water oxygenated, and a  few bolts made from different materials. I’ll   let the time lapse run, and let you  guess which bolt is made from steel.   It doesn’t take long at all for that  characteristic burnt orange iron oxide to show up.   Even the steel bolt to the left that has a  protective coating of zinc is starting to rust   after a day or two of this harsh treatment. That  humanmade protective layer on the galvanized bolt   gives a hint about why the other ones shown are  able to avoid corrosion in the saltwater. Unlike   iron oxide that mostly flakes and falls off, there  are some oxides that form a durable and protective   film that keeps the metal from corroding further.  This process is called passivation. Metals that   passivate are corrosion resistant precisely  because they’re so reactive to water and air. In my demo I included several metals that undergo  passivation, including an aluminum bolt (or   aluminium for the non-north-americans), which is  typically quite corrosion resistant in air, but   struggled against the saltwater. I also included  a bronze bolt which is an alloy of copper and   (in this case) silicon. Finally, I included two  types of stainless steel, created by adding large   amounts, sometimes as much as 10%, of chromium  and nickel to steel. There are two major types   of stainless steel, called 304 and 316 in the US.  316 is more resistant to saltwater environments,   but I didn’t really notice a difference  between the two over the duration of my test. I should also note that there are even steel  alloys whose rust is protective! Weathering   steel (sometimes known by its trade name of Corten  Steel) is a group of alloys that are naturally   resilient against rust because of passivation. A  special blend of elements, including manganese,   nickel, silicon, and chromium don’t keep the  steel from rusting, but they allow the layer of   rust to stay attached, forming a protective  layer that significantly slows corrosion.   If you keep an eye out, you’ll see weathering  steel used in many structural applications.   One of my favorite examples is the Pennybacker  bridge outside of Austin. The U.S. Steel Tower,   the tallest building in Pittsburgh, Pennsylvania,  was famously designed to incorporate corten steel   in the building’s facade and structural columns.  Rather than fireproof the columns with a concrete   coating, the engineers elected to make them hollow  and fill them with fluid so the corten steel could   remain exposed as an exemplification of the  material. Corten steel is in wide use today.   Architects love the oxidized look, engineers love  that it’s just as strong as mild steel and almost   as cheap, and owners love not having to paint  it on a regular schedule. That saves a lot of   cost. In fact, the cost of corrosion is the  main point I want to express in this video. In 1998, the Federal Highway Administration  conducted a 2-year study on the monetary   impacts of corrosion across nearly every industry  sector, from infrastructure and transportation   to production and manufacturing. They found that  the annual direct costs of corrosion in the U.S.   made up an astronomical $276 billion dollars, over  three percent of the entire GDP. Assuming we still   spend roughly as much today, that amounts  to over 1,400 dollars per person per year,   more than the average American spends on gasoline!  Of course, you don’t get a monthly rust bill.   Corrosion costs show up in increased taxes to pay  for infrastructure; increased rates for water,   sewer, electricity, and natural gas; increased  costs of goods; and shorter lifespans for the   metal things you buy (especially vehicles). But  corrosion has costs that go even beyond money. In 2014, the City of Flint Michigan began using  water from the Flint River as their main source of   drinking water to save money. The river water had  a higher chloride concentration than the previous   supply sourced from Lake Huron, making it more  corrosive. Many cities add corrosion inhibitors   to their water supply to prevent decay of pipe  walls over time, but the City of Flint decided   against it, again to save on costs. The result was  that water in the city’s distribution system began   leaching lead from aging pipes, exposing  residents to this extremely dangerous heavy metal   and sparking a water crisis that lasted for  5 years. A public health emergency, nearly   80 lawsuits (many of which are still ongoing),  government officials fired and in some cases   criminally charged, and upwards of 12,000 kids  exposed to elevated levels of lead all resulted   because of poor management of corrosion. Sadly,  it’s just a single example in a long line of   infrastructure problems caused by corrosion.  Metals are so necessary and important to modern   society that we’ll never escape the problem,  but the field of corrosion engineering continues   to advance so that we can learn more about how  to manage it and mitigate its incredible cost. You know what else is necessary  and important to modern society?   Good food! We are now in our fourth  year of my wife trying to film me   while I try to make dinner in  partnership with this video’s   sponsor, Hello Fresh. Spending time in the kitchen  is so important to us,   and HelloFresh converts the chore of cooking  dinner into our favorite evening activity. My family has grown by 2 over those past few  years, which means our dinners have changed as   well. HelloFresh has flexible plans that  can accommodate ever-changing schedules,   and they even have kid-friendly  recipes that are picky-eater proof. The meals are also pretty quick to make, with  most of them ready in 30 minutes or less.   Those evening hours are precious right now,   and the preproportioned ingredients and simple  recipe cards mean we have more time for trucks. And why say it when I can show  it? The meals are delicious.   We wouldn’t still be making them 4  years later if we didn’t love the food. Now is a great time to give it a try. Go to  HelloFresh dot com and use code PRACTICAL16   for 16 free meals across 7 boxes and 3 free  gifts. That’s HelloFresh.com and use code   PRACTICAL16. Thank you for watching,  and let me know what you think!
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Channel: Practical Engineering
Views: 2,352,041
Rating: undefined out of 5
Keywords: Folsom Lake, Folsom Dam, corrosion, corrosion engineering, rust, reduction-oxidation, oxide, galvanic corrosion, AMPP, passivation, stainless steel, Weathering steel, Corten Steel, U.S. Steel Tower, Pennybacker bridge, Flint Michigan
Id: 2RbiCOFffRs
Channel Id: undefined
Length: 13min 46sec (826 seconds)
Published: Tue Aug 02 2022
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