Recently I looked through old entries of the Puffing Billy shop blog and noticed they mentioned using sacrificial anodes in their water tanks. To me this seems to be a very bright idea. They claimed to use it, because when a protective paint layer fails in one small area, it will receive heavily concentrated rust in short order.
Does anyone in the US have experience with this idea? How would this affect the water chemistry in relation to water treatment? Our group is very interested in this possibility to help extend the lives of our water tanks.

Hi,
I learned this in college (1973-1980 part time). As I recall, this is recommended civil engineering practice for any water based installation to protect steel bridges and piers when the metal is not encased in concrete.
It should work well for locomotive water carrying tenders or "canteens" (Southern Railway USA term - extra tender or tank car for used to carry extra water).
Doug vV

They use them on the hulls of ocean going vessels. I think they are zinc. I have read that pirates off the coast of Somalia will come alongside ships at night and steal them.

T7

When I had a steel yacht I used them. Works as promised but needs regular cleaning.
If the locomotive happens to have electricity that might be used also as the voltage needed is only 0.6V or so. Before applying you better consult a Kathodic protection company for the best type since you use boiler water which may have a treatment.
Kind regards
Jos Koopmans

Greetings:
In 1977, I inventoried the spare parts, etc. that were included in the sale of former Mobile & Gulf No.97 to Indiana Railway Museum.
Among all the "stuff" were dozens of small boxes each containing an anode about (as I recall) about 3 inches square.
Someone believed in them, although it didn't seem to have helped the boiler on No.97, it was a mess!
J.David
PS: That said, our riverboat, "Becky Thatcher" is equipped with them. They are replaced as needed when the boat is hauled out for it's 5 year hull inspection. JDC

Everybody that messes around in saltwater powerboats knows about zincs. Sooner or later.

More to the point, every domestic 'hot water heater' contains an anode rod that performs just this sort of duty to extend the life of a coated tank that sees relatively high throughput of water -- in fact the situation is a bit more extreme as there is heat rise within the heater vessel that doesn't occur in most tenders.

Part of the choice of a good anode for use inside a tank (as opposed to external corrosion) will be the relative innocuity of the 'neutralized' salts when that water is subsequently boiled. For instance you wouldn't want to use something that forms hard or adherent scale, or that adversely reacts with another water 'constituent' (While we are on this topic, note that the anode only protects corrosion of exposed metal in the cistern; it does nothing about the other dissolved ionic constituents in the water (which can and often do go on to make scale in the boiler just as they do "normally")

Note that the anodes generate their 'own' electricity by establishing a voltaic couple "away" from creating the wrong ionic species next to corrodible metal. You can achieve much the same action -- as noted -- with a low-voltage DC potential with the 'right' polarity; this might want to be implemented with some kind of constant-current power supply to limit the power requirement (anode rods are usually used because they are cheaper and 'automatic' until degraded or consumed; electricity has the advantage that no sacrifice chemistry is needed to produce the potential difference...)

It's possible that some of the equipment used to protect bridge steel (and the reinforcement or tendons in concrete bridges) could be adapted for locomotive-preservation purposes.

Firstly the sacrificial anode has to bolted or otherwise secured to the tank so as to form a circuit - just leaving it loose in the tank or boiler won't work. Secondly, whilst a zinc anode works to protect the steel in salt water, you'd have to use magnesium in fresh water. Personally I'd stick to a good quality tank sealer on properly prepared metal.
Ray.

Me too.

Here's a wikipedia article on the topic: Cathodic protection

"Firstly the sacrificial anode has to bolted or otherwise secured to the tank so as to form a circuit - just leaving it loose in the tank or boiler won't work."

Use of the term 'anode' necessarily implies the existence of an electric circuit. (The 'other end' of that circuit, whether dessiminated across all the little voids and gaps touched by the 'electrolyte' (here the tank water with its dissolved ionic constituents) is the 'cathode'.

As noted, just dumping a lump of metal into the tank does nothing but add stuff to the water when the metal reacts (corrodes) and dissolves. As a defective analogy, dropping a jelly sandwich at a picnic won't keep the ants away from the jelly jars nearby; you have to make it attractive for the ants near the jars to head for the sandwich instead of dithering.

Amazing if the people using 'all those little 3" pieces' did not recognize the need for a good conductive joint between anode and 'protected metal', or a good electric circuit (including the equivalent of 'ground straps' across any sort of "insulated" joint, including caulked or painted seams) to all the disseminated points of potential corrosion. I suppose there are some preservationists who are ignorant of electrochemistry (or who think that sympathetic magic or reliance on 'faith healing' potions or feedwater 'treatment systems' is a good substitute for scientific knowledge) but here is a set of principles and 'best practices' for Becky et al. that are easily documented in detail.

I was surprised with the topic title. I am familiar with the term "sacrificial anode" from my employment in the domestic water supply industry and exposure to other underground utility practice.

The problem in utilities comes from electrolysis caused by potential differences between soil conditions and metal pipes and similar differences between water and steel water tanks.

A "sacrificial anode" is a passive way to direct the electrolysis caused metal deterioration away from steel pipes. Here in Southern California I understand that the Gas Company will connect sacrificial anodes to its pipes. Also it is very concerned about other underground construction nicking the protective coating of its pipes -- if a hole and leak develop it will try to search out who caused the nicking and present a bill for the repair work.

The utility I work for uses an active system in its steel reservoirs. There an anode is hung within the water inside the reservoir and an induced electric current is applied to counteract the natural electrolysis. And besides this it makes use of an interior protective coating of the water reservoirs.

We had an in-the-ground reservoir with a unique steel liner instead of a concrete interior surface. This was so unique that along the way someone in our maintenance section did not maintain the active cathodic protection system. The result was pin-hole leaks in the bottom and water leaking into the underground, perforated witness drains. The company has started a multi-year, multi-million dollar program to remove this 7-million gallon reservoir and replace it with three steel tanks within its regraded excavation.

Hi,

Most of these ways we have discussed here are passive ways to make a battery out of the water supply and the surrounding metal.

I seem to recall that the other way to protect the metal is by activelt sending a DC current throught the water cistern. If I recall correctly, it is something like 0.5V and a few milliamps.

Since the DC current from the active source needs to be opposite the "battery" (in the form of the water cistern and metal), an effective zero current through both can be obtained and so no corrosive effect occurs. This is like taking two AA batteries and placing them in a radio or flashlight incorrectly so that the series batteries are positive to positive instead of positive to negative (normal installation).

Maybe someone who has experience with this can expand on this. I learned it (I have BSCE and BSEE) in college but I practiced in the electrical engineering field professionally. [I did get about 2 years full time and seven years part time in civil engineering professionally but it was in highway, railroad, office park, etc design - not structural.]

Doug vV

That is better than some contractors that did work for MassDOT. In fact in one of there meatings the person explaning some tunnel work being done emphasizing that they were useing all the same meatle because they learned from last time.

I have very little idea what this is meant to mean. Can someone define in particular what the 'meatle' is?

Metal*

All the West coast narrow gauge 5" scale, 15" gauge builders, starting with Erich Thomsen designed their boilers so they had holes in the back head that were to accept 2 - 3 anodes. These protruded into the boiler water space and offered great protection from corrosion

These anodes were over the counter hot water heater and were magnesium alloy based.

Last time I priced these were $15 each, and they last years.