POWER September 2017 - 52

FUNDAMENTALS
using insulation with thermal conductivity
of 0.025 Btu/hr-ft-F. For cases with flowing
water, the tables also show the water mass
flow rate per unit length of exposed pipe to
prevent freezing based on initial water temperature
of 42F. In case it becomes impractical
to avoid freezing with insulation alone,
heat tracing is utilized to compensate for the
heat loss through the insulation.
Cold Insulation
Cold insulation refers to insulation installed
on piping and equipment operating below
ambient temperatures. The main difference
between hot and cold insulation is that with
cold insulation there is the possibility of
creating a water vapor pressure gradient,
which could drive the water vapor through
the insulation to the cold metal surface. This
could lead to accumulation of water within
the insulation and on the surface of the piping,
which could degrade the insulation and
pipe surface.
To counter the effect of water vapor migration,
closed-cell insulation material is
recommended for cold insulation applications
so that it resists moisture absorption or
wicking. In addition, moisture vapor stops
are used to isolate insulation sections and
limit the area of damage, if it occurs. Also,
a vapor retarder jacket is used but it must
be continuous and sealed at all seams and
joints to provide effective protection against
moisture ingress.
Insulation Jacket
The insulation jacket provides the outer
covering for the insulation and functions to
protect the insulation from mechanical damage
and moisture ingress. The commonly
used material for the insulation jacket is
aluminum. However, aluminum has a low
melting point and therefore is not suited for
use under fire conditions. For cases where
fire risk is present, stainless steel jacketing
is used, which has a significantly higher
melting point.
Aluminum jacketing is available with
various surface finishes such as smooth,
stucco-embossed, or corrugated. Ingress of
water has the potential to corrode the aluminum
jacket from the inside. Therefore, aluminum
jackets are often provided with an
inner layer of nonpermeable material (moisture
barrier), which protects the jacket from
moisture corrosion from the inside.
If jacket corrosion is an issue, other material
such as thermoplastics, fabrics, or
synthetic rubber can be utilized. The various
jacket materials have different emissivity
and this has an effect on heat transfer
performance. Polished metals have lower
emissivity whereas plastics, such as PVC
(polyvinyl chloride) or fabric-mastic layer,
have higher emissivity.
High emissivity results in higher heat
loss from the hot-source pipe or equipment.
In low-temperature systems, higher emissivity
jackets result in higher heat gain by
the cold pipe. For anti-sweat insulation and
personnel protection insulation, high-emissivity
jackets tend to reduce the required
insulation thickness.
Thermal insulation is also important for
noise control and for fire protection. Sound
attenuation is a natural attribute of insulation
material and jacketing. For fire protection,
metal jackets and bands, as mentioned
previously, are made of stainless steel, and
they are fixed to ensure that they can withstand
the impact from a firefighting water
stream. ■
-S. Zaheer Akhtar, PE is principal
engineer-mechanical with Bechtel Corp.
2018
SOLAR
POWER
EVENTS
Solar Power Northeast | Feb. 5-6 | Boston, MA
California Solar Power Expo | Mar. 27-28 | San Diego, CA
Solar Power Southeast | May 14-15 | Atlanta, GA
Solar Power Texas | June 4-5 | Austin, TX
Solar Power International
Co-located with: Energy Storage International
Sept. 24-27 | Anaheim, CA
Solar Power Midwest | Fall 2018 | Chicago, IL
Solar Power New York | Dec. 11-12 | New York, NY
LEARN MORE | events.solar
POWERED BY
Content Licensing for
Every Marketing Strategy
Marketing solutions it for:
* Outdoor
* Direct Mail
* Print Advertising
* Tradeshow/POP Displays
* Social Media
* Radio & Television
Logo Licensing |
Reprints
Eprints | Plaques
Leverage branded content from Power Magazine to
create a more powerful and sophisticated statement
about your product, service, or company in your
next marketing campaign. Contact Wright's Media
to ind out more about how we can customize your
acknowledgements and recognitions to enhance your
marketing strategies.
For more information, call Wright's Media at 877.652.5295
or visit our website at www.wrightsmedia.com
EVENTS
52
www.powermag.com
POWER | September 2017
http://www.wrightsmedia.com http://www.powermag.com
POWER September 2017

Table of Contents for the Digital Edition of POWER September 2017
