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Pipe and Pipe Installation Considerations 177

omitted in this chapter. The American Iron and Steel Institute’s
Modern Sewer Design is an excellent source for information on cor-
rugated steel piping systems.

Manufacturing Steel pipes used in municipal applications are man-
ufactured by an automatic welding process. There are generally
three types of steel pipe, each identified by the way in which it is
manufactured:
1. Rolled and welded pipe: This is one of the oldest methods of
steel pipe production, where plates of steel are rolled into
cylindrical pipes, usually 6 to 12 ft in length, then welded in
the circumferential and longitudinal directions. The pipes
used in casing applications for trenchless technology are of
this type. They are also used in other types of applications.
2. Electric resistance welded (ERW) pipe: ERW pipes are generally
manufactured and used in smaller diameters up to 24 in.
ERW is a single straight seam welding process where contin-
uous coils of treated, low-carbon steel, called skelp, are
shaped into cylindrical pipes by edge-forming, and then
welded at the seam. These pipes can be manufactured in
lengths of up to 100 ft. They are used in water systems, as
well as other industrial applications.
3. Spiral welded pipe: Starting with continuous rolls of steel simi-
lar to the type used for ERW pipe, the steel is fed into a
machine and spirally wrapped against buttress rolls to form
the pipe. The edges of the spiral pipe are then welded in and
out by a double-submerged arc process. Spiral welded steel
pipes are used in municipal water transmission applications
in diameters of up to 156 in. Trenchless processes such as
HDD have been used to install this type of pipe in the potable
water systems.

Corrosion Protection—General There have been many approaches to
corrosion-protection of all kinds of pipes through the centuries. There
are decades of practical experience with many applications and cor-
rosion-protection systems of iron and steel pipes, in particular. There
are field and laboratory studies of gray and ductile iron pipes in
widely divergent soil types, and also in some notably very corrosive
actual soil burial test sites, by the Ductile Iron Pipe Research Associa-
tion (DIPRA) working in many cases in close conjunction with the
utilities involved. Both unprotected iron and steel pipes will rapidly
corrode in some soil environments, and in these environments suit-
able corrosion protection must be provided. It is also being discov-
ered (in more recent applications of pipes that have not been around
as long) that other piping materials, such as variously reinforced