Why Spillway Gates Don't Rust Out

An overview of cathodic protection, including a rust prevention shootout in my garage.
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Making a structure last as long as possible before it needs to be replaced isn’t just good stewardship of resources. It’s a way to keep the public safe and prevent environmental disasters too. Corrosion is one of the number one ways that infrastructure deteriorates over time, so cathodic protection systems are an essential tool for keeping the constructed environment safe and sound.
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Practical Engineering is a KZbin channel about infrastructure and the human-made world around us. It is hosted, written, and produced by Grady Hillhouse. We have new videos posted regularly, so please subscribe for updates. If you enjoyed the video, hit that ‘like’ button, give us a comment, or watch another of our videos!
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[@PracticalEngineeringChannel]

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[@C2K777]

These are used on boats as well. Both for the hull if it's steel and on/ near the shafts/ props/ engines depending on design. Different types ( metals) are used depending on if the boat is kept or used in fresh or salt water and just like in your examples they are designed to attract so that they degrade rather than the hull, props etc. You basically bolt them on and depending on quality, conditions the vessel is exposed to and if it's kept in or out of the water depends on how often you need to change them

[@Jacopski]

Love your videos but kinda disappointed that your advertising nebula to watch your videos early when this video came out on nebula only today aswell

[@johnspence2466]

I signed up for curiosity stream how do I access nebula

[@C2K777]

@@johnspence2466 Hi john. Give it like 5-10 mins then look out for an email from Curiosity Stream giving you a login ID and temp password.

[@Jacopski]

@@C2K777 for me I could instantly log in to nebula with the password and email I used for curiosity, I didn’t get a temp password Edit: I never even got an email from nebula but I have access anyway

[@dj_laundry_list]

This channel is just a financial justification for Grady to do awesome garage projects

[@wxwxsrg]

Isn't that true for all STEM youtube?

[@MereMeerkat]

He was definitely doing awesome garage projects before youtube, but now he can justify bigger ones.

[@hattielankford4775]

Not that it's a bad thing.

[@dj_laundry_list]

@@wxwxsrg Perhaps most

[@dj_laundry_list]

@@hattielankford4775 it's a very good thing

[@mikestackhousemusic]

I had a co-worker that swore (and told anyone listening) that putting a (like in singular) boat anode on the rear bumper of a truck would keep the body from rusting. He said it "neutralized" the road salt...I was in the marine industry, and we ran across and interesting situation once. A gentleman had bought a new boat with twin outboards. He'd leave it on the dock for weeks, so he had an onboard charger for the batteries that was plugged into shore power. We had to replace the charger as it had been submerged. Easy job. Just disconnect some wiring at the charger, install the new one, and reconnect. That fall we got a call from the boat yard that hauled it. "There's a problem with the boat." I went over to look at it and was shocked to find the stainless prop all chewed up and looking like some medieval weapon and the drain plug, also stainless, corroded right off. Turned out, the people that rigged the boat in the spring hadn't connected the two batteries together and, the way the charger was hooked up, it was sensing the port battery needed charging, sending charge, but the ground between the two batteries was missing so it went through the motor, out through the noblest metal (the stainless) and found it's ground at the starboard motor.

[@kklenov]

Is it was single wire 12v system? Negative via hull?

[@alexa.davronov1537]

@@kklenov Давай я помогу: "Was it a single wire power supply of 12v wired down to the hull?"

[@kklenov]

@@alexa.davronov1537 мгимо финишед :)

[@mikestackhousemusic]

@@kklenov twin 12 volt batteries but the positive from the charger went to one battery and the negative went to the neg. terminal of the other battery. When the boat was set up that spring, whoever did it didn't connect the ground for the two batteries together.

[@toahero5925]

I've used that technique to etch stainless steel water bottles

[@chriskelvin248]

I installed hundreds of passive cathodic protection systems on natural gas pipes in NYC (coatings + magnesium anodes), but only one active one (coatings+anodes+rectifier). The active one was on a section of underground high tension power line (345kv) in pipes bathed in oil. The field of anodes were like giant 12’ long candlesticks. The rectifier station looked exactly like the one you showed.

[@pierQRzt180]

could they modified to generate current/power? However little?

[@chriskelvin248]

@@pierQRzt180 they do create power. But pathetically little. And the fuel is a 10x millions of dollar steel pipeline coupled to 100x thousands of dollar anode array. And the added impressed current unit spends more power than the passive anodes make. There are better ways to make power. This is used to be a rust magnet for critical infrastructure.

[@FrozenHaxor]

I actually have active rust prevention anodes on the body of my 20+ year old car, it slowed down corrosion significantly, I have to sand down the anodes from time to time as they oxidize but it seems to be working.

[@domsquaaa4323]

e

[@PlayinWithMahWii]

@@FrozenHaxor Any info on these? It would definitely be helpful with my rust belt cars!

[@johnjohnson-gm3jh]

The way to show roughness on camera is to use side lighting so the peaks are highlighted and the indentations are in shadow. (That's how artists create a sense of depth in pictures - they draw a sphere by adding highlights and shadow to a circle.) And depending on the size of the features, you might need to bring the camera in close to make small features visible.

[@MichaelMastin]

And get a digital microscope camera.

[@mrosskne]

No, just do what John said.

[@oliverlane9716]

I remember being taught this age 12. 8 years later I found myself working on a container ship in a Dry Dock. The Chief Mate, trying to show me up asked me what these things were on hull were, and this random seemingly pointless science lesson from a decade earlier came back to me. Always pay attention in class, you never know what one day may become relevant.

[@officialspock]

Still waiting for the moment I can apply calculus in my everyday life

[@c31979839]

@@officialspock just because you don't use it, doesn't mean it hasn't been super useful for thousands of scientists and engineers around the globe. Learning calculus isn't some far fetched obsolete tool like Fortran or the slide calculator is. It's used all the time every day by people getting paid much greater sums of money than you.

[@WoLpH]

@@officialspock During the pandemic there were many charts, graphs and extrapolations that relied heavily on calculus. And don't forget about the exponential growth and all. Seems like you've missed the boat my friend ;)

[@neondemon5137]

What kind of sailor doesn't know what a sacrificial anode is?

[@RevCode]

@@officialspock I need to understand calculus in my professional life - it's all about what kind of career you are pursuing.

[@JCWren]

For most boats with outboard drives, the housings are made of aluminum. In a saltwater environment, usually zinc anodes are used. In freshwater environments it's more common to use magnesium anodes. The houseboat we lived on for 10 years had an aluminum hull, and had an impressed current system. It was powered by a 1.5V battery, and a meter and potentiometer. The meter had a scale to indicate which way current was flowing, and you'd adjust it with the pot to try to get it to zero. We replaced the battery every year, but it was rarely ever depleted (the amount of current is in the microamp range). When in the marina, if you noticed the meter had moved off zero, it was typically an indication there was an electrical problem with a nearby power pedestal or boat.

[@carllea-wilson7960]

What was the anode on that system?

[@JCWren]

I'm not 100% certain, but I think it was graphite. The houseboat was a 1976 Lazy Days Sportsman, and it was installed by the previous owner. We bought it in 1994, and in the 10 years we lived aboard, we had the boat pulled twice. Both times we did while we went on a trip, so I never actually saw the anode itself. I do know it was bolted to one of the two strakes that ran the length of the exterior of the hull. There was a thru-hull fitting for the lead that went to the anode, and I was always a little paranoid about breaking it when I would be down in the hull messing around.

[@thenameisalie6]

interesting! Thank you for sharing! 😊

[@asdfxcy]

Batteries are powered by a redox rection too, so you could say an impressed current system powered by a battery essentially just moves the corrosion to somewhere else, where it's easier to manage. How neat!

[@lelandlewis7207]

Aluminium anodes are used on motors run in brackish or run in brackish and salt waters.

[@anom794939393]

I was working on a project that required water wheels in salt water. the pushing surface of the wheel was fastened to the steel frame with aluminum rivits. I replaced so many of those rivets before figuring out what was happening. this video is the best explanation of that process I have ever seen!

[@crystalsoulslayer]

I absolutely love the Rust-O-Matic. Reminds me of the time I tried to do electrolysis for a science project and de-galvanized a bunch of washers by accident. Other fun potential uses: - Acid rain timelapse! Also etching, corrosion as a useful tool. Glass! Concrete! Circuit boards! - Thermal cycling fun times. Cold, hot. Cold, hot. Cold, hot... - Speaking of thermal things: mild steel vs. carbon steel vs. bronze and their respective hardening/annealing properties. Seems like a good way to dunk samples into quenching fluid all at the same time. - Put shapes into wind tunnels. Wheeeeeeee fluid dynamics - Don't know if this could be done on a reasonable timetable, but it'd be interesting to see biodegradable/non-biodegradable plastics in action. Do they actually break down and go away, or do they just go into smaller bits and hang around for ten thousand years? - Why you shouldn't just unplug high-voltage circuits. Bzzzzzzzzzzzt! - Pushing four (4) buttons at once, over and over - Donate it to Michael Reeves so he can gratuitously misuse it - Hot dip galvanizing at home! Just hold your breath around the molten zinc. - Impatient Fisherman Simulator 2022

[@joshyoung1440]

Ah yes, quenching, famously done by slowly lowering a piece of metal into liquid over the course of a minute

[@stevenlynch3456]

@crystlasoulslayer This is an amazing comment

[@willhikearizona]

Just curious if you weighed those samples before and after corroding them might be interesting to see what the percentage of metal loss is per day or hour.

[@KodakYarr]

Yeah, I was a bit disappointed that he seems to not have weighed them.

[@christopherhayes3328]

The problem is oxidation would actually add weight, so it's not a great way to get an accurate picture of how much metal is left. To do that, you'd want to fully dissolve each sample, convert it all to a stable salt, then dry and weigh that.

[@GameBoy-ep7de]

I was hoping that he would measure the volume of the metal plates before and after, and then an equivalent in weight. Maybe throw in a few percents. Would make the difference much more noticeable.

[@nilesbutler8638]

@@chriseffpunkt4333 A laboratory OR Grady´s garage. Estimates are for fieldwork! On multi-billion-dollar, one-of-a-kind-projects.

[@tinglin6121]

@@wojtek-33 Sure, can you think of an automated way that does this?

[@spencerwiltse2855]

Hey Grady, I work at Site C dam in Northern BC Canada. The construction budget of this dam has ballooned from a few billion to over 16B. Mostly from engineering challenges. Might make an interesting video if you felt like looking into it!

[@hhiippiittyy]

I'd like to know what the average budget overrun is for modern infrastructure projects. I feel like I could bet my house that they are NEVER on budget. Not even close for anything substantial.

[@spencerwiltse2855]

@@hhiippiittyy definitely. But an over run of 5 times the initial budget seems insane even with that in mind lol

[@David-bh7hs]

@@hhiippiittyy we're worse at building things. We always go over budget because we have superfluous workers and overhead. We need to justify employing an ever bigger population.

[@ITSecurityFTW]

Replying to help him see this comment.

[@IanBMorris]

​@@David-bh7hs Perhaps it is mostly due to everyone wanting the lowest bidder and very small buffers are put in place, causing unknowns to run up project costs. By changing the model from the lowest bidder to one that encourages technical and design prowls we'd probably get better estimates and less cost overruns.

[@NeilHaskins]

10:41 28.3 g of protection is worth 454 g of cure. Or, 62.5 g of protection is worth 1 kg of cure, if you're just concerned about the ratio.

[@tommydags1]

Grady I watch every video in its entirety because you deserve the boost in analytics for your wholesome, straightforward, and detailed approach to complex subjects. I enjoy every second and sitting through sponsor spots is my way of paying you back for such delightful content. Its got a vibe of serious business in a nonchalant but eager to teach you way that is TRULY appreciated. Among the greats!

[@robertlevine2152]

Grady, Ships have been using anodes and impressed current cathodic protection for decades. It has been over 50 years since I started training to be a naval architect and marine engineer. We were taught about the effects of corrosion on ships. Coatings, material selection, cathodic protection using both active (impressed current) and passive (anodes) andcombinations thereof. Shipping companies, depending on size and trade often have full time corrosion engineers to monitor corrosion and the performance of prevention systems. One of the strangest occurences I encountered was on a double bottom tanker that had recently entered the Alaskan North Slope trade. As was practice at the time the cargo tanks were not coated and except for the suction wells there was no cathodic protection. After a small amount of oil started appearing in the double bottoms the cargo tanks were cleaned and inspected. Small pits about 12 mm (1/2") in diameter were found. There was a higher concentration of pits near weld seams.The pits had water in them. If you put your finger in the pit and rubbed gently you could get them to shine brightly. It turned out the pits were a result of a combination of water settling out of the ANS crude, sulfur content of the crude and the uncoated mild steel. The concentration of pits near welds was due in part of the raised area of the weld seam causing the water to pool and the heat effected zone around the weld changing the properties of the steel. The end solution was, after repair of the pitting, to fit anodes and to coat the bottom 1 meter (36") with a 2 coats of epoxy paint.

[@noemierollindedebeaumont1130]

That's interesting ! Non native english speaker here. What does "pit" mean in this case ? Some sort of small depressions ?

[@robertlevine2152]

@@noemierollindedebeaumont1130 Yes. If you remove heavy rust from the surface of corroded steel you will see small holes commonly called "pits". The steel on the tank bottom was not heavily corroded. What we found were small holes filled with water. The holes we found were small hemispheres, similar to a small mellon ball. By rubbing the bottom of the hole with your finger the polishing action would leave the steel looking as if it had been sand blasted and was ready for painting. Bob

[@noemierollindedebeaumont1130]

@@robertlevine2152 Thank you very much Bob for your answer. It was just the precision i needed to understand !

[@DABrock-author]

Yeah, I was kind of hoping that since he lives in Texas, he would have had at least a brief mention of Battleship Texas, which was recently moved into a drydock for repairs, mostly for corrosion damage.

[@onradioactivewaves]

​@@DABrock-authorinteresting, I didn't know anything about the USS Texas. But my father was always into military vessels and wore his favorite USS Texas ball cap all the time before he passed away. I wore that hat until it was disintegrating, and was asked about the ship often, but I never knew much of anything about it. I did get to tour the USS Missouri once though, what a treat that was.

[@Jgardner2122]

I pulled an engine out of the river a couple weeks ago, crankshaft, cam, piston rods, wrist pins and piston rings were still in the engine. The piston heads were gone. Best I could figure is that the piston heads were some alloy that sacrificed itself to save the rest of the block.

[@nomms]

If I recall correctly, it's not uncommon for the heads to made of magnesium or an alluminum alloy, so you're apmost certainly right.

[@tybirous3417]

I read that as "pulled an engineer out of the river" and was really confused as the the context of engine parts.

[@cr10001]

Aluminium doesn't corrode in air as it forms a protective oxide film. However, in situations where the oxide film can't form, aluminium corrodes rapidly. Cast iron is actually surprisingly resistant to corrosion, way better than mild steel.

[@jamesengland7461]

...or the heads had been removed...

[@YouPlague]

@@jamesengland7461 By mermaids?

[@Insane247714]

in the swimming pool business, we have sacrificial anodes typically made of zinc. they are plumbed into the pool return lines and linked up to the pool equipment. just my two cents. awesome video

[@scottwithrow7791]

Super cool stuff! My Dad did cathodic protection for a natural gas pipeline for 40 years! I never really understood what he was doing every day but now I do. Thanks for the cool series and I look forward to more.

[@elizabethnicholson479]

Cathodic protection (CP) is a great tool that is under utilized. One of the main reasons is it does require occasional monitoring and maintenance. And it's often the first area to be cut when budget cuts are made as it has long-term consequences, not immediate ones.

[@JimAllen-Persona]

It's amazingly short sighted too- it's a relatively inexpensive item.

[@BicyclesMayUseFullLane]

@@JimAllen-Persona but you see, my quarterly profit and thus my bonus cheque do not care about your silly things like long-term outcome, so you are getting the axe :)

[@JimAllen-Persona]

@@BicyclesMayUseFullLane been there, got the severance to show for it. 😂😢

[@mikebarushok5361]

Nobody checks them in their domestic hot water tanks, but if they were maintained it's estimated to extend the life of the tank far beyond when the rest of the system will fail.

[@resurgam_b7]

I'm curious how large of an area each of those little anode pucks would protect. I guess it would depend on how electrically conductive the steel is, how far the charge could travel along it to reach the sacrificial anode.

[@IstasPumaNevada]

I too am curious. I know it's not an infinite amount of area, and that even 15-meter English narrowboats use them at multiple points along their length. I would suspect it's a case of diminishing returns.

[@wbfaulk]

The harder it is for the electron to move to the cathode, the more likely it will stay in the steel. The difficulty of the movement of electrons is known as electrical resistance. Steel is a conductor, but it does have some resistance, and that resistance increases with distance. So if the cathode is far enough away that the resistance between the point on the steel and the cathode is significantly greater than the point on the steel and some other point on the steel, the cathode becomes ineffective. This is actually a guess in the hopes that someone will come along and correct me.

[@olakoppe]

typically, steel in seawater needs a protection current of around 100mA/m^2, which the anode needs to supply. Anodes have a certain current capacity which can be delivered at any given time scince their protective current have to be supplied by corrosion of the anode. In addition, seawater has a resistance of around 0.3 ohm/m, so the current suplied times the resistance will cause a potential drop, which in turn will determine the furthest distance a anode can protect.

[@chrisevil7012]

there are engineering standards and calculations for this, should be a copy viewable at your local library so you dont have to spend 10grand buying them all =)

[@NavyDood21]

@@IstasPumaNevada That is funny. My first thought was thinking about them on narrow boats.

[@joel-py3fc]

I have lived in the west most of my life where humidity is rare. I worked out east one year and heard people talking about underground cathodic lines buried like if it was normal. I did understand that it was corrosion control but had absolutely no clue how it worked. This video really helped me understand! Thank you!!!

[@eboal2]

Loved how you set up experiments and tests that are fairly real-world yet simple/repeatable.

[@CP_Guy]

From a retired corrosion engineer with 40 years of CP experience...at minute 3:40 you state that the anode is low potential versus the cathode having high potential. The CP industry uses the reverse descriptions. In fact, better quality magnesium anodes are marketed as having high potential versus lesser quality standard alloys. This is also consistent with the Practical Galvanic Series as magnesium anodes have the "highest" electrochemical potential versus more noble metals that are typically cathodic in a CP system. You also never mentioned that CP is only effective when BOTH the anode and cathode occupy a common electrolyte such as soil, water, or concrete. Otherwise, your presentation was very informative. Thanks for engineering the Rustomatic 3000!

[@dwaynepenner2788]

I think that you are both correct. Grady is referring to the actual unprotected corrosion mechanism and your industry deliberately reverses the process, effectively changing the cathode to the anode which reverses their role in the corrosion process; it follows their definition changes as well.

[@CP_Guy]

The reversal of these terms also confused me when I started in the business in 1981. An addition nomenclature issue is that corrosion (CP) engineers track ion flow through the electrolyte and not electron flow through the metallic circuit. This makes explaining the entire CP process even more confusing!

[@richardharvey8529]

I was wondering whether anyone else was surprised by those conventions! My experience in biomedical engineering is similar to yours; implanted electrodes in the heart, brain, or nerves are anodic if they're high-potential, cathodic if low. Tangentially: you might enjoy reading about the various voltametry techniques used in neuroscience; it's all aqueous electrochemistry. I'm sure you'd have an easier time understanding it than I did! As of a few years ago, cyclic voltametry was the only technique we had to get real-time measures many high-profile neurotransmitters in living systems.

[@thekinginyellow1744]

Yeah, well. Blame the early physicists who got the current direction wrong. :) a high negative is a low positive. And then there's the convention that in most environments it is the negative terminal that is ground, but in naval convention, it is the positive. Semantics matter!

[@iaial0]

I believe, but I might be wrong, that those potentials are based off of the standard hydrogen electrode, which, as a convention, is set to be 0V. All the other electrodes are measured against that to determine their potentials

[@Modna89]

Fun fact! They make zinc "spray paint" and it actually works wonders. I use it on iron pipe fittings all the time, makes a huge difference (and it's very easy to reapply)

[@mikebarushok5361]

Especially handy afterwards where preparation for welding involves removing an area of zinc from galvanized steel.

[@JorgeFernandez-kj1io]

Working in the oil and gas industry, mainly in pipelines, this video finally opened my mind what cathodic protection is on our midstream equipment. Thanks!

[@TheRonHockman]

I just want to say how much I love this series. Infrastructure is so poorly understood, and so many people don't realize how important it is and how much work goes into it.

[@michaelandersen7535]

There's a cool technique where you put a sensor that measures the voltage caused by the sacrificial anode and then alert when it drops too low (indicating the anode is too corroded to protect the structure and needs to be replaced)

[@spacekee9071]

Oh wow! that timelapse of the corrosion is amazing! as someone in metallurgical engineering who never had the opportunity to take classes on corrosion during undergrad, this series has been very fun to watch. great work as always!

[@Deepak_Kocharla]

Absolutely correct

[@stankeebals713]

Very cool. My dads boat had a zinc sacrificial anode, and for years I never understood how it worked, but now it makes sense! Thanks Grady!

[@Soundhound101]

Another awesome thought provoking video Grady, thank you kindly. I have worked with sacrificial anodes in municipal water systems many times before. Impressed current anodes are new and fascinating to me. I'm loving this series and hope to learn more about them.

[@evanlucas8914]

I experienced the effects of corrosion in a unique way when I went to replace my brakes and rotors a month ago. My wheel lug nuts should have required a 19mm socket. Only the 21mm socket would fit, but it kept slipping. Eventually I rounded off the lug nut and had to use a special tool to get it off. I was frustrated and confused. I later discovered that the OEM lug nuts use a mild steel core for the threads with a stainless steel cap for the shiny look. The slight difference causes a small amount galvanization between the two layers. Since the inner layer is pressed against the threads of the lugs, the outer layer swells.

[@kbail5108]

Is it a dodge?

[@evanlucas8914]

@@kbail5108 nope, a Ford

[@mungtor]

@@evanlucas8914 Yup. Ford actually has 21.5mm and 19.5mm sockets to work through this issue, the larger fitting the swelled cover and the latter being the nut once the cover comes off. Jeep, Dodge, Infiniti, and Honda cars in my family have all had this issue. Now the first thing I buy for a new car is a set of chrome lug nuts.

[@animefreak5757]

that type of lugnut are the devil! I always swap that style with a regular chrome plated type. Sure they don't look pretty, but the caps also don't expand and get twisted off.

[@ireallyreallyreallylikethisimg]

That's why at my work I despise selling capped lugs to clients. I always recommend getting filled steel one.

[@dougkahl8124]

I am a research scientist and I love your channel. It often surprises me how engineers distill what are incredibly complex science into straightforward decisions about how to build/maintain something. And I love your experimental displays, just fantastic.

[@JCtheMusicMan_]

Engineers are experts at finding a sliding scale of solutions to a problem that allows decision makers to chose between the best solution, the least expensive solution, and the quick fix. Engineers definitely think differently than scientists. When I am presented with a problem, my brain wants to tackle the very complex. My engineering friend will find the easiest solution. Years ago I couldn’t figure out why my VCR display kept resetting to flashing and it bothered me. His solution was to put tape over the display. 😂 My scientific brain didn’t understand this solution for many years. That is why scientists and engineers are very different 😂

[@andydelle4509]

The reason the American analog telephone network designed in 1934 used -48 volts, meaning a positive ground. This was to protect the underground steel conduits.

[@alexanderwoodley8987]

Glad you mentioned ICCP. Very common for protecting the steel hulls of large ships

[@srdsrd16]

Another great example of cathodic protection that many people may have in there house is the anode rod found in tank-style water heaters, which helps to protect the glass lined steel tank. Also, as demonstrated in the video, the rod will deteriorate over time, which is why it should be replaced every 5 years or sooner to extend the life of a water heater.

[@Linusgump]

It would be interesting to see how Cor-ten, or “weathering” steel would hold up in comparison to your control and anode laden steel samples in your rusty contraption.

[@jwstocker1979]

I was just about to write the same comment.

[@tomdonahoe3539]

@@jwstocker1979 It's used extensively in shipping containers.

[@mytech6779]

CorTen is good in moist atmospheres but shows no significant advantage when submerged or in the continuous splash zone. The liquid water tend to wash away or otherwise bypass the protective layer of rust.

[@Linusgump]

@@mytech6779 could you elaborate on this? It is my understanding that through a red-ox reaction an oxygen layer is attached to the steel, which prevents further oxidization, similar to the oxygen layer that forms and protects aluminum. As long as the oxygen layer is not chemically or physically removed, the steel would be continually protected. Are you saying liquid water has the ability to overcome the bonds holding the oxygen to the steel and physically remove it, or is something else going on?

[@mytech6779]

@@Linusgump Mostly submersion is just a harsher environment physically and chemically and it is more than the oxide layer can tolerate. Mind you the rest of this is not in the core of my specialties so there may be some errors. That oxide layer protection works best on metals that have an oxide crystal packing similar in volume to the base metal crystal volume. But iron oxide crystals have much higher volume than the base metal which creates mechanical stresses which make the oxide layer cracked, poorly bonded, and friable. CorTen has minor alloying to reduce this issue by altering both the galvanic cells to favor certain oxide products and the bulk iron oxide crystal structure to make a slightly better bonded oxide layer. BUT it is still pretty weak and easily compromised. Being submerged may also favor a different oxidation level Fe+2 vs Fe+3 and crystal hydration.

[@saltaronlostapones2145]

That principle is very used in water heaters to prevent copper corrosion from the tank itself. There is usually a magnesium anode that needs to be changed between 1 or 2 years, protecting the heater. At least that's how it works in the systems used in southamerica to heat water before taking a bath. Very nice videos by the way, Grady!

[@scruggs.jonathan]

"The maintenance and rehabilitation of existing facilities is almost always less costly, uses fewer resources, and is less environmentally disruptive than replacing them." - Grady from Practical Engineering. I like it!

[@onradioactivewaves]

Now if we could only apply that logic to consumer products such as art or furniture, so they don't have to be consumables.

[@Zebra_M]

Back when I worked at a large scale saltwater aquarium, we had large magnesium anodes on all the underwater circulation/current creating pumps. It always blew my mind how effective this was. Also, that time lapse is absolutely beautiful.

[@mafarnz]

As a hobby I collect and restore old train locomotive air horns. Most locomotive horns in North America are cast aluminum, which means dealing with corrosion is a huge issue when it comes to restoring them. Most often the hardware used in the horns is grade 5 steel bolts, but on railroads that operate near the coasts or ones that use highly caustic wash solutions that often doesn’t last very long and bolts get stuck. Getting those apart is very difficult, and in extremely bad cases horns crack apart due to the corrosion. Some companies and collectors use stainless steel bolts and nuts but that just exacerbates the corrosion of the aluminum! The best thing to do and what I do on mine is to use zinc biased anti seize compound on the hardware. Learning about galvanic corrosion and the galvanic chart has been extremely helpful for me to know what to do to give the pieces in my collection the best preservation that I can. On a horn restoration most often it’s corrosion of the aluminum rather than the steel hardware that’s the biggest problem, and machining parts down to get them back in spec and helicoil inserts are needed to get things functional again.

[@andrewheld2475]

Never thought of using stainless... great idea! K5LA, P3, P2, M5, & S3 owner here!

[@andrewheld2475]

... oh, nearly forgot the A-200!

[@dbayboyds409]

That time lapse was awesome! Thank you! Thank you! I can tell it was a huge effort and I really appreciate it. I have an aluminium boat and I’m keen to check my anodes now! Thanks again.

[@vtbhanukiran1231]

Great video. Such a beautiful demonstration of the galvanic series and galvanic protection. Thank you Brady, for great clarity of information on all your videos.

[@dan725]

We always attach fresh zinc plates on our ship’s hull every dry dock for this very purpose! Thanks as always for sharing this with everyone with an amazing explanation and awesome demonstration!!!

[@th3d3wd3r]

Another way of looking at this is the problems it can cause when using mixed metals in cooling systems.

[@davida1hiwaaynet]

Excellent. Thank you! As an engineer on new projects for the offshore oil and gas industry; I really find the corrosion prevention aspect of the structural engineering to be fascinating. Also, as a restorer of antique machinery, I totally agree with your observation as to how preserving and prolonging is much better for all; versus replacing in a short time.

[@eugenedayney7848]

Well I guess as an engineer you must have an understanding of electrolysis add salt water

[@mataichi14]

Great video. I work offshore so rust and cathodic protection is something we see a lot but I never knew how exactly it worked beyond the zincs corrode instead of the steel. This video filled in the missing piece. There are a lot of big pieces with big anodes down there, you should see the corrosion on those zincs after they have been on bottom for 20 years or more. They do their job though, the steel is usually still fine while the zincs are encased in their own oxidation.

[@OttoTheWeim]

I used to design and install CP systems for everything from nuclear missiles and silos, ships, underground/above storage tanks using both sacrificial and impressed current systems. It is quite complex to the point I could tel you within a small window when an in coated tank would fail due to corrosion. It is called a MTCF (mean time to corrosion failure).

[@ProfessorJayTee]

Looking forward to receiving my pre-ordered copy of your book soon, Grady. Since university I haven't bought any other book on engineering, but I already knew yours will be both entertaining AND informative.

[@JimAllen-Persona]

Thanks for reminding me. I think I pre-ordered it.

[@SirFloofy001]

This gave me an idea, and after some research im happy to say someone has already had my idea. Some people have used Hot Zinc Spray to coat their steel hulls in a extremely thin layer of zinc which is then covered by a base cover paint and then an anti fouling paint. Some boats have seen 20+ years with the only maintenance on the coatings being the anti fouling and occasionally the base coat needs touching up.

[@utah133]

Every time I hear about cathodic corrosion protection I recall when I was tasked with replacing a bunch of big zinc blocks inside a boiler condenser. They were very heavy.... This plant also had some equipment with active protection where an electric current was applied to counter corrosion as you described.

[@naeem_bari]

This is one of your best and most dramatic experiment yet. And that's saying something, given your past high quality experiments. Great stuff, really did an excellent job covering cathodic protection, a phrase I hadn't even heard of before!

[@paulsim2605]

This is amazing. Learned this during high-school but this is the very first time seeing it out of the textbook's diagrams and tables. Thanks for sharing!

[@Dream.of.Endless]

On documentaries about ships undergoing maintenance on dry docks, I have seen that they use cathodic protection as well on the underwater part to slow down corrosion until next service. And those sacrificial materials were huge. Thanks Grady.

[@stepheneyles2198]

I've always been grateful to my late Father who was a Mechanical Engineer; he taught me about Cathodic Protection when we walked past a pipeline marker near our village. I was probably about 12 at the time. He told me what the three terminals on the marker post were for, we could measure a voltage between them, which was obviously the voltage between the pipeline and the anodes.

[@eugenedayney7848]

Did he ever explain to you about electrolysis

[@kailashbtw9103]

Hands down one of the coolest time lapses ive seen, and it sop perfectly shows off corrosion! I love the setup as well!

[@RichardLaughlin]

A new video from this channel is always a delight. Thank you for your hard work!

[@MariaLanger]

This video is incredibly timely for me. I just took delivery of a boat currently based in salt water. Boats like mine used “zincs” to help prevent corrosion on underwater parts such as props, rudder components, and side thrusters. Although I knew what zinc (the element) was, I had no clue what a “zinc” (the anode or sacrificial part) was until about two weeks ago. This video really helps explain HOW they work. Thanks!

[@RollerCoaster233]

Hi Grady. Great video about Cathodic Protection. You explained it very well. I did cathodic protection for 5 years for pipelines and tanks when I worked for Matcor. What I learned in 5 years you were able to compress to 13 min. When at Matcor I was the only drafter so I was a part of every project, did thousands of junction boxes and anodes. I know the life span of the anodes we installed was 100 years, and that monitoring the system is key in maintaining Cathodic Protection. Also sand is what we mostly used to carry the electric current.

[@onradioactivewaves]

Interesting aboit the use of sand. Upon investigating the topic using sand for cathodic protection, the forst result that came up was none other than MATCOR, saying that the industry is now moving away from oiled sand for tank corrosion protection, as it has been found to be creating more issues than it solves.

[@mrosskne]

sand conducts electricity??

[@onradioactivewaves]

@@mrosskne I believe the oil in the sand does more so. Everything conducts to some degree. If you take for example a AA battery, there is a self discharge and the battery eventually dies. We say it has an open circuit but really, there is that air surround the battery ( or even a vacuum ) that could technically be considered no conductive, but it still has a field and conducts some miniscule amount. So given a high enough potential (voltage) you can conduct some amount electricity though anything. The key to the cathodic protection is to by making thr material you want protected by making it the cathode with a high enough electronegativity compared to the other material., so you just need to be at equal or above, it doesn't need to be some large amount ( you're swapling the cathode and anode in your system by adding some extra potential to the otherwise would be anode). So really you just want to stop the current with just a slight tendency to to the other direction, for every part you want protected.

[@daveOnYouTube]

That was a fascinating experiment. You could see the galvanic series in the results!

[@Richardincancale]

That’s funny - I was photographing the sacrificial anodes on the rudder of a trawler that was grounded only last week! Sent you the photo just now via Instagram DM, feel free to use it if you want.

[@landonfinnerty2391]

Grady, thanks to you, I got in on that Curiosity Stream/ Nebula Bundle, and I use it all the time. Thanks. Peace.

[@andrewwmitchell]

Great explanation with an awsome demonstration. I've always loved your hand-built models, but this one is a step above the rest. Thanks for a great video.

[@vanish85]

Hello, Grady! I just wanted to say hi and tell you how much I appreciate your efforts on your garage experiments. This one was specially remarkable! Thanks a lot, and keep up the good work!

[@lvisser9648]

hello..the same water al metal ...plates..its better each plate own water ..real difference

[@2goober4u]

@@lvisser9648 hello ... why ... do you ... talk ... like this?

[@bf2wesley]

Grady, awesome video as per usual. Maybe after the rust series you can do a series on the new materials we've come up with to beat corrosion? Like basalt rebar, self-healing concrete, etc.

[@MrHamsto24]

I did some digitization work for an energy company once relating to pipeline corrosion. One of the major influences on that process is that transmission pipelines are frequently built along the same path (and therefore fields) as transmission powerlines.

[@minimoose1441]

Great timing, I've been watching some narrowboat videos recently and noticed a few times the cathodes they have on the hull but didn't know the science behind it!

[@suamme1]

I learned a bit about cathodic protection when I was in 6th grade after reading the stickers on our gas meter. I was curious about why this meant people weren't supposed to chain things to the gas meter (in that area and time, it wasn't uncommon to see dogs chained to them regularly ☹) and had to find out.

[@Tibor716]

This was such an awesome project. Thank you, I learned so much.

[@guymontag2948]

The time lapse is really nicely done. I was quite surprised by how severe the corrosion was after so short a time.

[@mikefrisby9233]

Coming back to comment after having watched this day it came out. I've been working the last two week doing safety for a crew performing cathodic protection on water mains. It was quite interesting seeing this process being done in person.

[@DerrangedGadgeteer]

Very cool! I've wondered if the "cold galvanizing" zinc paints you can get at the hardware store actually performed comparably to real galvanization. From your video, it sounds rather like it could. Like a spray-on cathode. Are you planning to take a look at those products in this series?

[@olakoppe]

If they have a sufficient amount of zinc (>80% wt), and are applied properly, they should work pretty good. The problem with cold galvanizing is ofthen the layer thickness achieved, electrical connection with the substrate, and that it doesn't adhere as well to the substrate metal as hod dip galvanizing does

[@Mark_Bridges]

@@olakoppe Exactly right. Prepare the surface properly and spray multiple coats and you get good protection for the steel. Do what I've previously done and just spray it on without much surface preparation and it doesn't last long. I discovered it lasts even less time if you spray it on a weld before the weld cools.

[@tyrannosaurusimperator]

No it doesn't. Actual galvanizing uses the temperature of the molten zinc to form a zinc-steel alloy at the surface and then a zinc shell on top. However, the paint can be used to touch up a piece that has already been galvanized.

[@olakoppe]

@@tyrannosaurusimperatorYou are right about what the result of HDG is, but the zinc alloys and such in it self is not crucial, but yes, the process ensures better electrical contact and bonding between Iron and Zinc, which again provides better cathodic protection

[@dielaughing73]

I researched exactly this in my engineering undergrad thesis and found that a paint with a sufficiently high zinc content has significant benefit (greater than 80% Zn as someone else said - in our case it was 96% Zn in the dry film). The application was a galvanised structure that had been in service for some decades but had lost a lot of the galvanised layer thickness (through the normal protective mechanism). Applying the paint over this weathered surface was a cost-effective way of extending its service life. Not as effective as fresh galvanising of course, but that was not feasible. For a structure in service, the options really are either to apply remedial fixes like this or replace the whole thing. These paints are different from the 'cold galv' spraycan and need to be applied properly. But with a suitable layer thickness they can offer both galvanic protection and also a degree of physical barrier protection, as the pores in the paint become sealed by the products of corrosion. And in the case of small areas of damage they can 'reactivate' the galvanic mode of protection. Application of a thick layer or layers of organic paints over this system would no doubt extend the lifespan even further. In fact, triplex systems of primer and paint applied over hot-dip galvanising are in common use in new builds in high-corrosion areas.

[@multicoloredwiz]

Incredible work as always sir! I love your models so much!!!

[@UpLateGeek]

That was a pretty impressive demonstration with the timelapse. I'd read about cathodic protection before, but it's really interesting to see it in action.

[@Animosity00]

Wow I just happened across this video while preparing to attempt to get my NACE Cathodic Protection 1 certification and it is a great low level introductory primer. Excellent content, thanks!

[@philiptetherow71]

I love this! Back before I went to engineering school I worked in the Industrial and Marine division of Sherwin Williams and the properties of Zinc is incredible. Oh! And I recognize that rebar. Back before I sold paint at SW we used coated rebar in some of our projects. You see some neat stuff if you build foundations with a highly respected concrete company.

[@johnrymszewicz]

Did you measure the mass of the steel before and after? Also, I work on powerlines, and they are subject to corrosion. Does being part of an energized circuit help slow the processs?

[@gus473]

Wondered about that too!

[@giovane_Diaz]

hmm, if they are actually under a active forced protection it can make sense, but I'm more prone to think they have a reinforced galvanized coating, since they are mass built and certainly are worth the investment on more protection from rust.

[@ZE0XE0]

measuring the mass might not be as interesting as one might expect because of some key issues: When the steel is turned into rust, it gains mass because its capturing oxygen. He had to grind off the rust to see the surface pitting, this also grinds off some of the steel and affects its mass. If you had a way to perfectly remove only the rust, one may be able to get some good numerical insight into how protective each cathode was, but there are the previously listed challenges that would complicate the issue.

[@JeffreyBue_imtxsmoke]

@@ZE0XE0 true

[@matthewchambers817]

@@ZE0XE0 Thanks for that explanation of the challenges, I was wondering why he didn't report the change in mass, and you answered my question very succinctly.

[@JB-eg1tb]

I appreciate all your efforts in making the principles and application of engineering so practical, relatable, and understandable!

[@dleland71]

Fantastic demostration! I've always been of the idea that they should use stainless steel in the rebar in highly corrosive applications. I worked in a company a bunch of years ago that made exaust manifolds for vehicles using 409 stainless. They are probably still in use today. Also, this why manufactures use an anode rod in water heaters, to sacrifice and protect the heater.

[@christhorney]

I can't help but wonder if the stainless steel bolt would have thrown off your test a little bit, would be interesting to see if raw mild steel bolts would make a difference to the end results because the stainless would have been the more noble metal

[@olakoppe]

Probably negligable due to the small surface area of the bolt compared to the sample

[@lazz4205]

Would have been really interesting to weigh each of the slabs before and after the experiment, awesome video nonetheless!

[@JeffreyBue_imtxsmoke]

I was thinking the same thing.

[@KP11YT]

Oxidation adds weight. Plus sometimes rust stays on, sometimes flakes off and you would get a variation. If a sample is cleaned with wire brush, this may influence weight. An experiment like that would have to take much much longer to create much bigger differences.

[@lazz4205]

@@KP11YT Fair enough, but you could vary the test so that the results were more accurate, you could spray the samples with a high pressure hose, which can be used as a rust remover

[@tylerharris5606]

@@KP11YT I've done corrosion tests (chemist). Weigh before; test, clean (cleaning solution); weigh again; calculate the corrosion rate.

[@robertp881]

Tyler is right. Like internal corrosion coupons in pipelines are judged by metal loss. Weight.

[@stephenbritton9297]

I used to be a Merchant Mariner... We start painting at one end of the ship, when we were done at the other end, we started over again. The hull would have zinc anodes and often impressed current protection, since you can't paint it except every other year in dry dock. Impressed current becomes interesting when you are transferring oil products, especially ones like diesel that can build up there OWN charge. Have to make sure you're grounded to the shore facility!

[@angelserrano4272]

Grady for the win! This is the most detailed footage of rust I've seen on the internet!

[@exharkhun5605]

Fantastic video explaining this process. I'd have liked it if you'd expanded a sentence or 2 on the term "sacrifical anode". You mentioned it, but that's the way I, as a historical ship lover, exclusively come across this topic. Of course, historical ships aren't your brief and as I said, the explanation itself is fantastic. The Rust-O-Matic may at the same time be an historical achievement and even more futuristic than it's moniker of 3000 implies. Congratulations! 🙂

[@Kenionatus]

I'm pretty sure what he showed is exactly the concept of the sacrificial anode.

[@exharkhun5605]

@@Kenionatus He did, and the video is excellent. But I'd have liked a stronger "connection" of the term to the concept. I've come across the term "sacrifial anode" in books about ships, it then gets explained (poorly) by the writer who is probably a history major who has never seen a Rust-O-Matic 2000, let alone a Rust-O-Matic 3000. Someone looking up "sacrifial anode" may not see the connection to "cathodic protection" so I would have liked a confirmation early in the video that it is same process.

[@GarageSupra]

Something to look into may be the automotive version of electronic rust inhibitors. Here in Australia heaps of people use them however many people think it's just snake oil.

[@bshingledecker]

Dang, I was just thinking of that. I had just bought a car, (U.S.) in 1980. I was deluged with mail and magazines about electronic rust protection for your vehicle. It offered a lifetime warranty, but was also very expensive. It was a DIY kit that you installed, which was their 'out' for denying warranty claims saying you didnt install it correctly. It would also drain your battery if you didnt have a trickle charger on. I never took the plunge for that due to the cost, which was over a thousand dollars. I always wondered 'what if' since my pride and joy babied 320i slowly rusted into oblivion after 30 years in Ohio.

[@WhatTheHellIsWrongWithYouu]

For cars, snake oil. For a bridge? they could work.

[@SosirisTseng]

Doesn't the battery anode protect the car frame already?

[@elizabethnicholson479]

Snake oil. Electronic rust stopping boxes are a form of impressed current cathodic protection. Which requires an electrolyte to work such as water or soil. Air is an insulator and prevents the flow of the CP current. The boxes only work well if you bury your car or store it in a lake or pond. Not idea. For cars, annual oil spray is your best protection.

[@indeedgrasshopper]

This is so weird. Last weekend I spotted some odd contraptions on a concrete bridge: a bunch of stainless steel boxes attached about 20 feet off the ground/water level with conduit running to them. Each base had them. My first thought was to take a photo and see if I could send it to this channel as a topic idea.... and then this video drops. It's almost certainly an impressed current system. Thanks for the great content!

[@JustJanitor]

I lived in the area for 25ish years and I've never seen the Howard Franklin from that angle wow. Thank you

[@scottmilano2940]

Aluminum generally has an oxide coating that protects it from further oxidation. Does that interfere with Cathodic Protection?

[@viniciusmmd2282]

It's a good question. As far as I know, aluminum is the most used metal for cathodic protection in industry. I think that the layer of oxide is released to environment when positive charged, exposing the raw material. That's the reason of the consumption of the anode

[@elizabethnicholson479]

Yes. The oxide acts as a coating, preventing contact with the electrolyte (water) and stopping the cathodic protection. Aluminum is not commonly used in environments that cause passivation (aka oxide coating). Zinc is much more common for protection of ship hulls, pilings, and other sea water infrastructure.

[@giovane_Diaz]

@@viniciusmmd2282 amd in the test grady used it was under salt water, so the harsher conditions may have weaken the oxide formation allowing for constant exposure of some pure metal to react. but even without this it may work, since the surface of both metals is firmly attached and the oxide can still conduct electricity in some way, allowing the aluminum underneath to be further oxidized

[@hodor3024]

That oxide layer isn't impenetrable. Salt water will eat aluminium away.

[@elizabethnicholson479]

@@hodor3024 agreed, and a fast flow of water will also wash away the layer before it can build up. There are ways to use aluminum anodes, they just require a bit more awareness and engineering in some environments.

[@Toutou-vs8or]

You could have weighted the metal after you wire brush it, this would have made a great comparison 👍. Great video though 👌

[@hootinouts]

I love your presentations Grady. Other solutions against corrosion are what are known as weathering steels. One is called Cor-Ten. Another awesome solution in civl engineering is the use of rebar made of basalt which has incredible mechanical properties. The basalt rebar will last way longer than steel and is amazingly lightweight.

[@nickmcdonald42]

This hit my feed a year late, but I’m so glad it did. After changing out electric water heaters and a lifetime of boating, it was great to see the process in “reel” time. Many thanks! 😅

[@MikaTheAboveAverageDog]

Oh man, I *wish* we had before and after weights for those four samples, love your work!

[@Hexagonaldonut]

Really cool to now understand the fully details of how these work! Tom Scott mentioned the concept of sacrificial anodes in his video on the Thames Barrier, and I was kinda curious about the specifics.

[@MrPaulpph]

I am working in the shipping industry and we use impressed current systems and cathodic protection by zinc (or Aluminum for light weight) all the time! Great video :-)

[@glshim13]

I swear it said "Catholic protection" and took me forever to figure out what metal has to do it lolol

[@Arbys626]

this is very pog thank u

[@JThelen1031]

I learned this spending summers on my grandparent's boat. I spent plenty of time underwater scraping barnacles and checking the zincs to make sure they were still adequate for protecting the hull, propeller and propeller shaft.

[@standardannonymousguy]

Excellent work like always Grady. I especially like the time lapse at 6:57. This is great qualitative content. Cheers.

[@joren_combs]

Okay, did anyone else think it said "Catholic protection" and wonder what the practical engineering angle on religion was? 😅🤣

[@AleHand_]

Amem bro

[@emmah1408]

Engagement

[@m-yday]

Ooh!! If you’re going to run this again, do weigh the samples before and after!!! That would be super interesting to see, and a great way to quantify the corrosion!

[@GuyChapman]

I drove over the Frankland bridge on a work trip to Tampa. It’s a really impressive structure, and takes you to the Dalí Museum in St. Pete, pleasing my head and heart at the same time!