One of the reasons aluminum oxide is protective is because it is an adherent oxide (the other reason being that aluminum oxide is such a stable compound). It is adherent because when it is converted to oxide, the volume doesn't change. Other oxides, such as the common hydrated iron oxide, grows. This is why you get rust scale on automotive iron that spalls off and isn't considered protective.

Strider, I still don't see where you disagree with me. It is commonly held that absolutely pure water will strip ions from unpassivated metal surfaces. Just the fact that you control the pH slightly acidic tells me you don't run pure water in your system. The water in itself does not passivate the metal. I believe you missed a step in your explanation. In fact, that is how one of my clients checks his product for proper passivation. After the passivation process and rinse, he rinses it in ultra high purity water (I believe he said one-millionth ohm water) and checks that the conductivity doesn't significantly increase.

How about a research assignment?
 

What does M-B use at the factory when they initially fill the radiator? :D

Best Regards,
Jim

I commissioned a pool type reactor a few years ago that required the pool chemistry to be absolutely free of ions or other impurities and to be neutral pH. The problems started when we discovered a construction mistake that had left the entire shutoff rod assembly pipework (hydraulically operated system, using pool water - all varieties of stainless) unpassivated. It took us a month to disassemble, passivate, then reassemble. The issue was a huge one for the regulating board as corrosion of unpassivated stainless in the required pool chemistry environment would have rendered the shutoff rods unreliable over time.
The material needed protection from the pure water, as purified water in an open environment cannot be controlled for dissolved oxygen. The MB coolant is most importantly, phosphate free. Phosphates will react with hard water to create scale deposits, possibly blocking small passages and inhibiting cooling, and also they will tend to form aluminum phosphate, which is inslouble in traditional glycol antifreezes, causing it to settle in the cooler areas. This corrosion of the aluminum feeds on itself until the mixture is replaced, thus renewing the inhibitors that are always mixed with glycol (hence the recommended renewal interval of traditional mixtures).
That being said, most engines have consisted of many aluminum pieces since the 70s, and most Japanese cars have never required a special coolant, just frequent changes. I can't help wondering if the MB (and other European manufacturers, by the way) recommendation is an attempt to remove another variable from the equation in order to attempt to gain a slight perceived reliability edge in the marketplace.

Not different chemistry for the systems at my plant, a Boiling water reactor (BWR). We make the steam in the vessel, which then goes through a steam separator, then a steam drier, then out 4 main steam lines at 99.8 % quality to our high pressure turbine. We don't have a secondary loop with pressurizors and steam generators and all. We have had some problems with errosion / corrosion and 'tiger striping' in our BOP lines... when identified our usual course of action is to replace the carbon steel piping with stainless.

Yeah in PWRs (Pressurized Water Reactors for those that don't know), the chemistry is REALLY different in the reactor core. They finely control reactivity by adjusting the concentration of boron ions in the water (boron absorbs neutrons). That boron is added by adding boric acid. Using boric acid has some serious risks. I refer to the Davis Besse event.

In the BWR we finely control reactivity by adjusting the rate of water recirculation. The slower the recirculation, the more voids (bubbles) are formed on the fuel surfaces. Water is a good moderator for neutrons (slows them down into the thermal range, and thus propigates the reaction), while air is not. So the more air bubbles, the reactor power goes down. Increase the recirculation, the bubbles get swept away, and power increases.

Of course our chemistry is really strange these days. We recently added a hydrogen water chemistry system, injecting hydrogen gas into the water to bind up any free oxygen and thus try and prevent corrosion, such as intergranular stress corrosion cracking (IGSCC) in the vessel internals. During our upcoming refueling outage we are going to be injecting nobel metals in the water as well.

Yeah, I missed a step that most people outside the nuclear industry never have to deal with, hydrolysis of the water by ionizing radiation. In the reactor, some water molecules are ionized or lysed due to the neutron field. These create OH- and H+ ions. For this reason, we have a hydrogen water system that injects hydrogen gas into the water. By driving the pH slightly negative and injecting H2, we hope to drive the reaction back, binding up the ions back into forming water molecules...(Le Chatliers principle or something like that? Its been oh, 15 years since I studied chemistry. I'm a mechanical engineer.)

The water is as pure as we can make it, in a system that runs around 548 degrees F, with two phase flow (water and steam), flowing through a reactor producing 3486 Megawatts of heat, with all types of dissimilar metals and galvanic reactions throughout, and other ions like boron from the control rod blades. Our biggest problems are with our condensor, which is made from admiralty brass and badly needs retubing. (We just keep plugging more and more tubes.) Actually, a condensor leak shut us down prematurely before our last refueling outage. The nuclear steam side is of course under vacuum in the condensor, and we use recirculated river water to cool the condensor. (The circ water goes to 6 mechanical draft cooling towers, dumping over 2000 megawatts of heat into the air.) The river water got sucked in through the leak and the conductivity detectors went off. Conductivity went above our license limits and we then had a controlled shutdown.

For us, protecting the passive layer isn't just a matter of chemistry though. The passive layer gets 'mechanically' removed due to the forces of the flow through the pipes too. (Erosion Corrosion, as well as cavitation in some spots). The bottom line though is this: After the steam lines to the turbine, the rest of the piping is called BOP, or Balance Of Plant. None of that stuff is 'Safety Related'. Our primary concern is in protecting the pressure vessel and its internals like the reactor recirc jet pumps. The BOP piping, feedwater heaters, etc can and does get replaced, but we only have one vessel, and it is a legal, credited, safety barrier.

I saw the Davis Besse photos - Yikes! :eek:
Ah, for the simplicity of a BWR. We got us a positive void coefficient in this neck of the woods. :(

So you're at a CANDU reactor?

Yes. I currently work on 4 of 8 units at the plant I am at.

Strider, do you work at the Energy Northwest facility in Richland, Washington? About a year ago I did an analysis of the electrical generator bearing failure from the 2/27/03 shutdown at that facility.

Yep, that's right
 

Yes I do, but I'm not sure for how much longer :( (we're downsizing, 1 in 5 people are going to get laid off.).

To be fair and balanced for the audience, the bearing failure was not on our main generator, but on an emergency diesel powered generator that is one of three used for providing power to emergency loads if the grid collapses and we lose offsite power. We are required to have all three diesel generators capable of operating for 30 days straight at all times, and one DG had a bad bearing, so after trying to repair it within a tight window, the repair failed and we had to shut down the plant to continue the repairs.

Interesting cause that was, the grounding and electrical isolation of the bearing had failed, and as a rotating piece of metal in a magnetic field, it was building up charges and then arcing. The arcing caused eletrostatic discharge machining on the bearing surface.

Ah, so that would put you at Pickering?

Yessir, Pickering A to be specific. Massive rebuilding project.

That's exactly the story about the bearing. I hope I didn't alarm anybody with mention of the failure. The NRC is very stringent with having contingency plans for smooth shutdowns.

My contact at Energy Northwest was J. LaSalle.

I have used ordinary (green) antifreeze and tap water in my vehicles at a 50% ratio for many years. I change the coolant to include block draining every other year. There has never been a problem with any of my vehicles. Look at the models in my signature block. This should tell you something. I have owned all since they were built except the Porsche. And if you think Mercedes parts are expensive, try Ferrari parts. This is how much confidence I have with what I have been doing for years.

The distilled water argument amazes me.

Everytime it pops up, a group of folks with grad school degrees in chemistry/engineering jump in with all sorts of yack about what happens inside their nuclear reactors, etc. We're talking about a .79 cent bottle of water one buys at Wal-Mart.

The ultimate testimonial is not the college boys with their lengthy retorts, but the wisdom found inside radiator shops. Go ask the owners/employees in these places what to use. These folks don't deal with nuclear reactors or plasmic-bipolar-trionosphoric-metallosmosis. They deal with automotive cooling systems.

Geeeeez.