Treatment of boiler feedwater

[Michael Kestner]

I'm active on several railfan message boards, and over the last several months there has been a lot of controversy over the Union Pacific Railroad Steam Program's decision to change their water treatment system 3-4 years ago, a change which some say was responsible for the buildup of scale and sludge in the boiler of one of their locomotives, which resulted in a costly and time consuming rebuild. That got me to thinking. Did the water boiler feedwater on Titanic need to be treated in order to prevent similar issues? Obviously, Titanic is not a steam locomotive, and did not vent exhaust steam to atmosphere. I'm sure there were unique concerns associated with the reuse of the water from the condensors. If the water was not treated chemically, then how was the buildup of scale and/or sludge prevented or managed?

 

[Stephen Carey]

Boiler water treatment is a contentious subject. I read today that one of the causes of the boiler explosion on the SS France/Norway was inattention to the boiler water, and have experienced similar problems off the coast of Nigeria where the chemicals required were not readily available. The boiler problems of "foaming, priming and carryover" are all conditions of poor boiler water purity.
I guess you know the reasons for adding chemicals and today's methods, and I could give a more concise answer if I had my "1927 Sotherns Marine Engineering" book with me, but unfortunately that's in another country at the moment...
As far as I remember from that book, boiler alkalinity (to reduce the acidic effects of corrosion and scale formation) was accomplished by dosing with sodium hydroxide (caustic soda as it was referred to then) and phosphates (potash in those days, or potassium compounds today) were added to control sludge formations on the tubes that could inhibit heat transfer. It wasn't the more exact science that it is today on modern ships, but the pressure was quite low - 220psi - and I would imagine frequent blowdown of the boilers was necessary to reduce sludge build up. As far as oxygen scavengers go, such as hydrazine, I don't think they were available at that time, and I remember a picture in the book that shows cracks between boiler rivets which exhibited a classic example of caustic embrittlement (from overdosing of caustic soda on the "chuck in a bucket full" principle) but the author did not know this term or its origin at the time! In early ships in my career at sea, and with open feed systems, we did not dose the feed system with hydrazine as it would just oxygen scavenge the air in the engineroom... We had no injectors to put chemicals directly into the boiler feed stream at that time (late 50s and early 60s built ships with low pressure fire-tube boilers). I would imagine that Titanic and her sisters would have gone in for a mechanical boiler clean at regular intervals to compensate for the lack of knowledge on boiler water chemistry at that time.
In the days before flash evaporators, ships I sailed on had a standard seawater/steam evaporator, and to get shot of the scale on the tubes, you fed live steam through it to heat it up nicely, then opened up cold seawater which cracked the scale off the tubes - dramatic! I don't see them doing that with a boiler though...
Stephen

 

[Michael Kestner]

"Boiler water treatment is a contentious subject."

Clearly so, if the discussions over UPs steam program are anything to go by! Thanks for the information. I'd never considered the unique challenges of boiler maintenance in marine applications before. If the chemicals couldn't be injected directly into the boiler feed stream, how were they administered? Did they just dump them in the tanks that housed the boiler water?

 

[TimTurner]

Chemicals were probably injected directly into the boiler feed, probably right before the pumps. That would give them a low-pressure opening in the system to just dump the chemicals in, and the pumps would ensure a pretty good mixing. It seems like a bad idea to dump chemicals into a feed tank, since the water would be stagnant and the chemicals would probably settle to the bottom/top of the tank. They also wouldn't be in the system doing their job.

 

[Penguin]

I think a marine boiler would need de-scaling much less often than a locomotive boiler because the water from the condensor would not contain any scale-forming salts. It would be contaminated with oil from the engine so an oil-separator would be needed. The only source of scale-forming salts would be from make-up water added to replace lost steam, e.g. from the safety valves, and this would be quite small.

 

[TimTurner]

Any steam engine will build up scale eventually, because no water is perfectly pure. However, you'd be foolish to put unpurified water in any steam engine, locomotive or marine. I wonder how much water fed through Titanic's steam system hourly?

 

[Penguin]

Here are two articles on water treatment for marine boilers Link 1 Link 2 but I don't know how much of this information would have been known at the time the Titanic was built.