Last month we talked about the damaging effects
of water hammer, but there’s another state of H2O equally if not more dangerous when
put in pipes. Hey I’m Grady. Today on Practical Engineering we’re talking
about steam hammer and differential shock. This video is sponsored by Skillshare. More on that later. Unless you live in an home with an older radiator
or work in certain industrial settings, you probably aren’t as familiar with pipes that
carry steam as those that carry water. We don’t normally need access to steam in
our everyday lives like we do to its liquid analog. That’s not to say, though, that we don’t
rely on steam. In fact, it plays a critical role in our modern
society. We use steam for heating, cleaning, cooking,
and a vast array of industrial processes. About 90 percent of all electric power produced
in the world is through the use of steam turbines. If you didn’t see my previous video about
water hammer, here are the basics: water is heavy and incompressible. If you suddenly stop water while it’s moving
through a pipe, it can create a massive spike in pressure and break stuff like this pressure
gauge. Unlike water, steam is compressible. It’s “springy” and can absorb sudden
changes in velocity without a big change in pressure. The danger with steam is when it doesn’t
want to be steam anymore. In most places on earth, water exists naturally
as a liquid. Under the ambient temperature and pressure
conditions we consider habitable, most steam that happens to exist will condense. In a steam pipe, the water that forms from
condensation (also known as condensate) is the real danger. And I mean danger in the truest sense of the
word. Many lives have been lost in tragic accidents
resulting from misunderstanding or misapplication of good engineering principles for steam systems. There are several problems that condensate
can create, and we’ll talk about two of them in this video. The first one is thermal shock. Imagine this: you open a valve allowing steam
to flow into a steel pipe. As the steam comes into contact with that
cold steel, it condenses. The problem is that steam takes up about 1600
times more volume than its equivalent mass as a liquid. So, when it condenses, it literally shrinks. In a closed container like a pipe, or this
glass bottle that just came out of my microwave, that collapsing steam can lead to catastrophic
damage. Water rushes to fill the vacuum created by
condensation, cooling the steam even further and creating a runaway situation. This can happen extremely fast, and all that
water can accelerate and decelerate violently, hence the name steam hammer. If it’s violent enough, it can rupture the
pipe leading to an explosion like the one that happened in New York City in 2007. Check out Nick Moore’s video linked below
if you want to see this demo in slow motion. Thermal shock is a dangerous form of steam
hammer, but it’s easy to mitigate. When starting up a steam system, engineers
and operators expect condensation as the pipes warm up. So start-up procedures will include running
at reduced pressure with bleed valves open to make sure that condensation can’t form
a vacuum. The bigger danger happens during normal operations,
but to show how it works, first we need a steam pipe. Condensation in a steam pipe is always occurring
just from normal transfer of heat to the outside air. And this is roughly what that might look like. I’m using compressed air here in lieu of
steam for the obvious safety implications. Engineers manage this condensate by sloping
steam pipes and by installing devices that can get rid of condensate from the pipes called
steam traps. Steam traps are a fascinating topic on their
own, but occasionally they can get clogged or malfunction, allowing condensate to build
up. When water and steam flow together in the
same pipe, it’s known as biphase flow. In this situation, the velocity of the steam
is usually much higher than the velocity of the flowing liquid water. If there’s only a little bit of condensate
in the pipe, that’s really not a big issue. But, if condensate is accidentally allowed
to pool up, things can get dangerous. The steam passing over the top of the liquid
can create turbulence and waves. If those waves get high enough, the liquid
can create a complete seal inside the pipe with the full pressure of the steam behind
it. This seal of water becomes a slug or piston
and accelerates down the pipe like a the barrel of a cannon, picking up more condensate as
it travels. This slug of liquid eventually slams into
the end of the pipe, resulting in a dangerous pressure spike known as differential shock. Just like thermal shock, many people have
tragically lost their lives in steam pipe explosions caused by this phenomenon. Engineering of steam systems is an incredibly
complex topic in mechanical and chemical engineering, and I’ve just scratched the surface in this
video. Whether you realize it or not, many of our
modern conveniences are a direct result of steam systems, most notably electricity. So it’s critical that engineers can design
steam systems to be safe from dangerous phenomena, including thermal and differential shock,
also known as steam hammer. Thank you for watching, and let me know what
you think. Thanks to Skillshare for sponsoring this video. You probably won’t be shocked to learn that
Practical Engineering isn’t produced by a team of skilled writers, cinematographers,
editors, and artists. For the most part it’s just a nerd in the
garage, me. And they don’t teach this stuff in civil
engineering school, so I’m slowly improving my video production skills on my own. Skillshare is an online learning community
for creators with more than 17,000 high quality classes from experts working in their fields. I’ve been watching the DIY cinematography
class by Ryan Booth, and using it to improve how I use light and camera angles in my videos. If you’re trying to learn a new skill or
improve an existing one, click on the link in the description below and start your free
trial today. The first 300 people to sign up will get their
first 2 months free. Again, thank you for watching, and let me
know what you think!
Power engineer here. Stream has to be one of the scariest things I get to deal with on a daily basis. I have personally seen steel fittings explode like a freaking grenade due to steam hammer. Take it slow guys and girls! Be safe! Great video btw!
Is that a pollock?! Dude... thats the most awesome background EVER!
Armstrong International has a setup in Michigan for their training that shows this as well. Many clear pipes and steam traps on display in a classroom setting to demonstrate the distribution of steam and condensate and the affects of poorly designed systems, misapplied equipment, lack of maintenance..etc. This was one of the topics they discuss and demonstrate. Good video!
Process Operator here. This stuff is scary as fuck. Nothing like hearing a high pressure steam header blow out due to hammer.