Environmental Engineering Reference
In-Depth Information
1
. aSTm ratings.
The American Society for Testing and Materials
(ASTM) publishes standards (codes) and specifications that are
used to determine the minimum pipe size and wall thickness for a
given application.
2.
manufacturer's ratings.
Pipe manufacturers, because of the pro-
priety design of pipe, fittings, or joints, often assign a pressure-
temperature rating that may form the design basis for the piping
system. (In addition, the manufacturer may impose limitations that
must be adhered to.)
Caution:
Under no circumstances shall the manufacturer's rating be
exceeded.
3.
nfPa ratings.
Certain piping systems fall within the jurisdiction
of the National Fire Protection Association (NFPA). These pipes are
required to be designed and tested to certain required pressures
(usually rated for 175 psi, 200 psi, or as specified).
4.
aWWa ratings.
The American Water Works Association (AWWA)
publishes standards and specifications that are used to design and
install water pipelines and distribution system piping. The ratings
used may be in accordance with the flange ratings of AWWA, or
the rating could be based on the rating of the joints used in the
piping.
5.
other ratings.
Sometimes a piping system may not fall within any
of these rating systems. In this case, the designer may assign a
specific rating to the piping system. This is a common practice in
classifying or rating piping for main steam or hot reheat piping of
power plants, whose design pressure and design temperature may
exceed the pressure-temperature rating of ASME B16.5. In assign-
ing a specific rating to such piping, the rating must be equal to or
higher than the design conditions.
When piping systems are subjected to full-vac-
uum conditions or submerged in water, they
experience both the internal pressure of the
flow medium and external pressure. In such
instances, piping must be rated for both internal and external pressures
at the given temperature. Moreover, if a piping system is designed to
handle more than one flow medium during its different modes of opera-
tion, it must be assigned a dual rating for two different flow media.
Key Point:
Ratings of every pressure-
containing components in a piping sys-
tem must meet or exceed specific ratings
assigned by the designer (Nayyar, 2000).
4.8.4.1 Code for Identification of Pipelines
Under guidelines provided by the American
National Standards Institute (ANSI A13.1), a
code has been established for the identifica-
tion of pipelines. This code involves the use
of nameplates (tags), legends, and colors. The
code states that the contents of a piping sys-
tem must be identified by lettered legend giving
Key Point:
Not all plants follow the same
code recommendations, which can be
confusing for those not familiar with the
system used. Standard piping color codes
are often used in water and wastewater
treatment operations. Plant maintenance
operators must be familiar with the pipe
codes used in their plants.
