The most dramatic failure is called a waterhammer

April 15, 2025 12:21 AM

New York City’s municipal steam system is an iconic anachronism: a fascinating part of the city’s daily life and visual language, a foundational part of its history, and a system that has been exported and refined worldwide. It was an essential technology for its time as the buildings of Manhattan began to reach up and nudge the sky even higher. from Steam Networks [Works in Progress]
posted by chavenet (20 comments total)

"But the most dramatic failure is called a waterhammer. Sometimes the condensate can form a ‘slug’ of water that fills the entire cross-section of the pipe. When a slug comes into contact with the high-pressure steam, it gets pushed through the piping and accelerated to ridiculous velocities, often reaching over 100 miles per hour (50 meters per second). When this fast-moving water reaches a closed valve, sharp bend, or other obstruction in the pipe, it crashes into whatever it has found, producing a spike of pressure much higher than the standard operating pressure of the system. This can cause significant damage and in some cases total system failures."

Fluid-hammer is it? [cw: one death, many injuries, many more survivors] One hypothesis for the catastrophic (but survivable) destruction of the fuselage of Flight Aloha 243 in April 1988 is that a fast moving object [Purser CB Lansing] reached an obstruction [a containable-by-design 25cm x 25cm fatigue failure in the roof of the plane] causing a spike of pressure aka an explosive decompression which ripped 5.6m off the roof of the fuselage just in front of the wing.
posted by BobTheScientist at 1:19 AM on April 15 [4 favorites]

Too grim? Grady Hillhouse has a piece on the beneficial use of water-hammer to pump water up hill in ram-pumps. Using some of the energy of flowing water to drive some of the water against gravity. Enough from me, already.
posted by BobTheScientist at 1:26 AM on April 15 [7 favorites]

Steam heat evangelist here. Although after a few winters my ardor, unlike my apartment temperatures, has cooled.

I learned recently that in my building's construction era, the heaters were sized to keep the place warm with every window fully open on the coldest day of the year, standards influenced by the Spanish Flu.

They take some maintenance, but considering the last time I think anyone who cared worked on the radiators in my apartment, the internal seems to be a good 20 to 70 years. I've repacked, re-valved, adjusted port sizes, and at least in our unit, we get nice quiet heat.

The part that cooled my ardor was the realization of just how much the whole system moves around due to heat expansion and seasonal wood movement. All my nicely scribed panels to repair the flooring damaged by movement and ancient leaks now look almost as bad as what I was repairing...

Still love radiant heat over convection.
posted by jellywerker at 5:32 AM on April 15 [8 favorites]

No mention of W.I.S.O.R.? Bah.

(To be fair it looks like WISOR has been thoroughly memory-holed; aside from the 2001 documentary there's almost no mention of it online.)
posted by phooky at 5:33 AM on April 15 [1 favorite]

Seattle still has a steam provider downtown. Almost 200 buildings still use it.
posted by funkaspuck at 6:56 AM on April 15 [4 favorites]

Omaha has centralized steam too and seems to serve most of the major buildings downtown.

Also, if anyone wants to find out more about Aloha 243, Admiral Cloudberg has a great detailed report.

For that matter, she (Cloudberg) has a a bunch of really well written summaries of the crashes. Note that some of the summaries show 45min - 1hr reading times, but her writing is always well worth the time.
posted by furiouscupcake at 7:13 AM on April 15 [3 favorites]

This got me wondering if it would still make sense to build steam transmission infrastructure today in any context. And… probably not. Other energy transmission technologies are much more efficient. Steam loses 10-25% of its energy in transmission. Electricity 4-6%. Natural gas 2-3%. Maybe it makes sense if you can’t put a furnace or heater at the end point.
posted by qxntpqbbbqxl at 8:10 AM on April 15 [1 favorite]

For years, I’ve seen steam being vented around the city center plaza in San Francisco. Didn’t think about it though. A few years back, I was walking on one of the weird little streets south of Market Street (the main street downtown) and saw this building tucked between much larger buildings. It had this tall “smoke stack” and steam being vented. There was a worker guy outside the building and I asked him what this building was. He said it was a steam generator that feeds the city buildings at the city center plaza, a number of blocks away. Oh…. I guess I was under the assumption that steam heat was an old timey thing and wasn’t really used anymore. Nope… still used. There are other similar steam generator like buildings here and there around downtown, but they don’t look active anymore. I don’t really know how extensive centralized steam heat is in this town, but it’s still here.
posted by njohnson23 at 8:11 AM on April 15 [1 favorite]

A little research, and here is a description courtesy of the company that runs San Francisco’s steam system. It’s pretty big. Two steam plants, over 180 buildings, and big water recovery system. The water boiled to make steam has to be purified better than drinking water.
posted by njohnson23 at 8:23 AM on April 15 [2 favorites]

Water hammer is very familiar if you have older plumbing but a newer HE washing machine. Modern washing machines sip water, and open and close their valves much more frequently. If your water piping is particularly rigid, the whole house thumps when the valve closes. There are suppressors you can add to your system to hush it a bit. But these aren't steam related.

Toronto still has a very large downtown steam system, with Enwave's Pearl St station upgraded to be slightly less grotty than it used to be. Toronto's deep lake district cooling system is bigger, though, and gets most of the neat press.
posted by scruss at 9:02 AM on April 15 [1 favorite]

Water hammer is a result of designing a single-pipe system. One pipe is both the steam supply line and the condensate drain. The dynamics of that system are very hard to predict. They can be tuned, however. Professionally installed and tuned thermostatic steam traps do wonders. But steam traps degrade, fall out of tune, and take a lot of maintenance.

Modern radiator systems are two-pipe systems: I.e. separate supply and drain lines. And modern systems use hot water, rather than steam. Not going through a vapor/liquid phase transition is a big energy savings.
posted by Headfullofair at 9:08 AM on April 15 [2 favorites]

The little note at the end of the article

This piece has been updated to correct a statement that understated the energy capacity of steam versus water.

was likely added after an incensed steam power engineer wrote in and complained about a technical error. I have worked with steam engineers, and they tend to be extremely precise about this wildly complicate subject, and do not take the imprecision of others lightly.
posted by scruss at 9:20 AM on April 15 [5 favorites]

What the fuck is happening here?
What is coming out of the ground?
posted by TheWhiteSkull at 9:54 AM on April 15 [3 favorites]

The water boiled to make steam has to be purified better than drinking water.


Then additives to prevent rust and scaling are usually put in, and through those valves on radiators those can be vented into the heated spaces where they smell terrible and have given me many severe headaches.
posted by jamjam at 10:11 AM on April 15 [1 favorite]

There are suppressors you can add to your system to hush it a bit. But these aren't steam related.

In many (all?) places in the US those suppressors are required. It used to be acceptable to just use a vertical stub of pipe near the valve serving the appliance, those are disallowed now because the gas trapped inside the stub gets absorbed over time and the stub stops doing it's job. you have to drain the lines periodically to keep them working. purpose built water hammer arrestors are required now.
posted by Dr. Twist at 11:51 AM on April 15 [1 favorite]

→ additives to prevent rust and scaling are usually put in

Historically, some of those rust prevention/oxygen scavenging chemicals can be extremely nasty. Several workers at the Drax power station in England died after routinely making tea from the low-pressure turbine steam bleed. The water had been treated with hydrazine to remove dissolved oxygen.

→ purpose built water hammer arrestors are required now.

I should remind my inlaws of that, then. Their whole house goes kaThump every few minutes when the washer's going
posted by scruss at 1:41 PM on April 15 [2 favorites]

Lansing, Michigan, my own metro area, heats "nearly 200 residential, business and industrial steam customers from the REO Cogeneration Plant," with 9.7 miles of pipes.
posted by Well I never at 1:56 PM on April 15 [1 favorite]

additives to prevent rust and scaling are usually put in

How pure is the steam Con Edison uses?

The steam produced by Con Edison is very pure and is even used by some customers for the sterilization of hospital equipment. Steam may also be used for humidification purposes, for example, in museums, to help protect the art. There is nothing toxic in the steam.

posted by 1970s Antihero at 3:54 PM on April 15 [1 favorite]

Plainly Difficult just did a video on the 18th July 2007 failure in Manhattan of part of their steam system, creating a crater at Lexington and 41st.
posted by maxwelton at 5:04 PM on April 15 [1 favorite]

Hydrazine is really bad stuff.

Not only can fairly low level exposures kill you, sublethal exposures can cause psychosis:

Hydrazine-induced psychosis is a psychiatric disorder that can occur as a result of exposure to hydrazine, a toxic chemical. Symptoms can include hallucinations, delusions, and other signs of psychosis, along with central nervous system effects like lethargy, dizziness, and seizures. According to WikEM, hydrazine exposure can lead to a functional B6 deficiency due to its reaction with pyridoxine (vitamin B6), and it also inhibits GABA production, which may contribute to the neurological and psychiatric effects. [Google AI summary,]

It's used as rocket fuel, and exposure to it is my preferred explanation for what happened to poor Lisa Nowak, who was arrested after a bizarre attempt to kidnap and do who knows what to a fellow officer she considered a romantic rival some seven months after sitting on the rocket through several scrubbed launches on successive days and then complaining of nausea when she finally did get into space.
posted by jamjam at 7:28 PM on April 15 [1 favorite]