Page 20 - Reliability and Maintainability of In service Pipelines

Introduction 9

Stainless steel: Containing iron, nickel, and chromium content of various per-
centages, depending on the type of stainless steel. This type of metal is widely
used as it is stain and corrosion resistant.
Cast iron: containing 2% 6% carbon and 94% 98% iron content. Generally
is used for manhole covers and sewer pipes, this metal is very strong but
brittle.
Wrought iron: composed of almost 100% iron
Ferrous metals are known for their tensile strength and durability and their
characteristics recognized by their use in tall buildings and long bridges. They
also have magnetic properties, and their element content includes carbon, nickel,
and chromium. Ferrous metals are widely used in piping. Although high amounts
of carbon causes most of these metals an increased proneness to rust and corro-
sion, metals containing wrought iron (lack of sulfur and carbon) and chromium
content can resist oxidation and thereby provide protection against corrosion. It is
an understatement however to suggest that wrought iron does not corrode. The
lack of sulfur and carbon in wrought iron suggests that the iron is so pure that it
resists oxidation, which is a necessary process for corrosion to occur, however,
the wrought in iron only slows down corrosion and does not fully prevent it. In
fact, it is known that most ferrous metals are associated with rust and corrosion.
Considering both the characteristics of ferrous and nonferrous metals and their
uses in pipelines, it can be understood that the type of metals used in pipes
depends on the function of the pipe itself. Ferrous metals would be used in pipes
that are large and require sturdiness, due to their heavier weight, whereas nonfer-
rous metals would be used in pipes that require flexibility, light weight, and are
corrosion prone (Alton Materials, 2017).

Galvanized Iron Pipes
Galvanized iron pipes are wrought steel pipes which are often provided with a
zinc coating. They are applied to plumbing systems inside buildings and are used
in water supply and sewerage systems. These types of pipes are connected with
jointing methods using T-connectors branching off the main line and Y-joints to
split a single line into two and connectors to join the ends of pipes. The jointing
methods include screwed joints, welded joints, grooved joints, and flanged joints.
The fittings of these pipes are usually standardized, available in light, medium,
and heavy grades depending on the thickness of the metal. The sizes range from
DN 20 mm DN 300 mm which are supplied in standard lengths of 5.8 6 meters.
The advantages of these pipes include, long life span, toughness, durability,
availability in large diameters, and low installation and maintenance cost, which
make them useful for large construction projects. They are also rust resistant,
which makes these pipes very common in commercial buildings and households.