2019-07-01_Discover

STEAM POWER

EVERYTHING

WORTH

KNOWING

66 DISCOVERMAGAZINE.COM

F

R

O

M

T

O

P

:^ C

H

U

C

K

S

TO

C

K

/S

H

U

T

T

ER

ST

O

C

K

;^ J

AY

S

M

IT

H

;^ R

E

U

T

E

R

S

/C

H

IP

E

A

ST

;^ J

A

Y

S

M

IT

H

(^2

)

When Things Go Wrong

The steam pipes beneath a city street operate under high

pressures. Explosions don’t happen often, but when they do,

they can be devastating. In July 2018, for example, a steam

pipe burst in New York’s Flatiron District, showering several

blocks with asbestos and other debris, and forcing the

evacuation of 49 buildings. A year earlier, an underground

steam pipe had exploded in Baltimore’s Camden Yards

neighborhood, spreading debris across an entire block and

injuring five people. And a steam pipe explosion near Grand

Central Station in 2007 shot a geyser of 400-degree steam

and mud as high as the top of the nearby 77-story Chrysler

Building.

Surprisingly, those structural failures usually aren’t caused

by old, worn-out pipes. “It doesn’t have anything to do with

the age of the system,” says Con Edison manager Cuomo. The

pipe that ruptured last July was put into service in 1924, but

when it was pulled it out, it was in “pretty good condition.”

So what causes the explosions? They’re all centered

around one thing: a water hammer.

Water Hammer Time

When heavy rain or leaks from water mains accumulate

around steam pipes, the steam inside cools and rapidly

condenses, creating a column of water. Pressure from

surrounding steam can accelerate the water column,

creating a liquid battering ram — a water hammer — that

ruptures the pipe. Unlike steam, liquid water is essentially

incompressible, meaning it doesn't absorb any power from an

impact, so a water hammer can batter pipes with devastating

force. Miniature versions of the phenomenon create the

knocks you hear in steam radiators.

Engineers in New York and other cities have deployed

monitoring systems to keep tabs on the “traps” designed to

prevent water from accumulating around steam pipes.

How Steam Powers a City

In every power plant, the

generation of electricity

begins in a boiler, which

heats water into steam

(1). The water must be

purified before it can be

used in most boilers, to

prevent the buildup of

deposits. Pipes then funnel the pressurized steam toward the blades of a turbine (2). The impact of the steam spins the

turbine’s blades, which are connected by a shaft to a generator (3). Inside the generator, attached to the spinning shaft,

are coils of copper wire positioned between magnets. The electromagnetic interaction between the spinning coils and

the magnets generates an electric current (4), which can then be sent to consumers (5).

Many cities now use remote

monitoring equipment to

prevent pressure buildup.

Transmitter

Steam

trap

Boiler

1

2

3

4 5

Steam

Generator

Power

Turbine

Condensate Liquid battering ram

(1) Steam cools and condenses (2) Condensate builds (3) Water hammer forms

Steam

An explosion in New York City in July 2007

sent a plume of steam into the air. Such

steam accidents are rare, but can cause

massive destruction.