Wastewater Conveyance - Wastewater Operators - page 162

brass, copper, and various alloys. Wastewater maintenance operators
who work with metal piping must be knowledgeable about the character-
istics of individual metals, as well as the kinds of considerations com-
mon to all piping systems. These considerations include the effect of
temperature changes, impurities in the line, shifting of pipe supports,
corrosion, and water hammer.

In this section, we present information about pipes made of cast
iron, steel, copper, and other metals. We also discuss the behavior of flu-
ids in a piping system, and the methods of connecting sections of pipe.

4.8.5.1 Characteristics of Metallic Materials

metallurgy (the science and study of metals) deals with the extrac-
tion of metals from ores and with the combining, treating, and process-
ing of metals into useful materials. Different metals have different
characteristics, making them usable in a wide variety of applications.
Metals are divided into two types: ferrous , which
includes iron and iron-based alloys (a metal made up
of two or ore metals that dissolve into each other
when melted together), and nonferrous , covering other
metals and alloys.

Key Point: Mixing a metal and a
nonmetal, such as steel, which
is a mixture of iron (a metal)
and carbon (a nonmetal), can
also form an alloy.

A ferrous metal is one that contains iron (Fe). Iron is one of the
most common of metals but is rarely found in nature in its pure form.
Comprising about 6% of the Earth's crust, iron ore is actually in the
form of iron oxides (Fe 2 O 3 or Fe 3 O 4 ). Coke and limestone are used in
the reduction of iron ore in a blast furnace, where oxygen is removed
from the ore, leaving a mixture of iron and carbon and small amounts
of other impurities. The end product removed from the furnace is called
pig iron —an impure form of iron. Sometimes the liquid pig iron is cast
from the blast furnace and used directly for metal castings; however, the
iron is more often remelted in a furnace to further refine it and adjust its
composition (Babcock & Wilcox, 1972).

Note: Piping is commonly made of wrought iron, cast iron, or steel.
The difference among them is largely the amount of carbon that each
contains.

Remelted pig iron is known as cast iron (meaning the iron pos-
sesses carbon in excess of 2% weight). Cast iron is inferior to steel in
malleability, strength, toughness, and ductility (i.e., it is hard and brit-
tle); however, cast iron has better fluidity in the molten state and can be
cast satisfactorily into complicated shapes.

Steel is an alloy of iron with not more than 2.0% by weight carbon.
The most common method of producing steel is to refine pig iron by
oxidation of impurities and excess carbon—both of which have a higher
affinity for oxygen than iron. Stainless steel is an alloy of steel and
chromium.

Note: When piping is made of stainless steel, an “S” after the schedule
number identifies it as such.