B1 Intermediate US 35 Folder Collection
After playing the video, you can click or select the word to look it up in the dictionary.
Report Subtitle Errors
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

That's not to say, though, that we don't
rely on steam.

In fact, it plays a critical role in our modern

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

Unlike water, steam is compressible.
It's “springy” and can absorb sudden
changes in velocity without a big change in

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

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

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

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

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

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

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!

    You must  Log in  to get the function.
Tip: Click on the article or the word in the subtitle to get translation quickly!


What is Steam Hammer?

35 Folder Collection
wei published on December 14, 2018
More Recommended Videos
  1. 1. Search word

    Select word on the caption to look it up in the dictionary!

  2. 2. Repeat single sentence

    Repeat the same sentence to enhance listening ability

  3. 3. Shortcut


  4. 4. Close caption

    Close the English caption

  5. 5. Embed

    Embed the video to your blog

  6. 6. Unfold

    Hide right panel

  1. Listening Quiz

    Listening Quiz!

  1. Click to open your notebook

  1. UrbanDictionary 俚語字典整合查詢。一般字典查詢不到你滿意的解譯,不妨使用「俚語字典」,或許會讓你有滿意的答案喔