Pipe can be provided with plain ends,
threads or mechanical connections.
Before the perfection of pipe welding
techniques 75 years ago, most piping
was supplied with threads on each end.
Through the use of couplings and
threaded pipe fittings, pipelines and piping assemblies were created. Making a
leak-free connection on a 40-foot joint
of 6-inch threaded pipe took quite a bit
of muscle power, a bucket of “pipe
dope” and a giant-sized pipe wrench!
Today, virtually all industrial piping
is welded. Properly welded pipe joints
have high integrity and they are much
faster to make than by threading fittings
to each piece of pipe. In the waterworks
industry mechanical connections are
used to join most large diameter water
and wastewater lines. These mechanical
connections employ a bell and spigot or
grooved-end design, combined with a
resilient seal and bolting mechanism to
lock the joint in place. Mechanical
joints are also popular because they
allow for a slight misalignment to permit pipe runs to dodge around obstacles
without the use of curved pipe or excessive use of elbow fittings.
From Homes to Industry
If you have walked through a house
under construction or made a wrong
turn down one of the big box store aisles,
you have probably seen white plastic
PVC piping. While not allowed in most
industrial plants, the plastic pipe forms
the basis of nearly all residential piping.
PVC pipe as used in home construction
is usually schedule 40, and it is welded
to PVC fittings and valves using a plastic
solvent. For some low-pressure, highly
corrosive industrial applications, plastic
CIRCLE READER RESPONSE #31
pipe made of exotic materials such as
Kynar and Kalrez is used.
Industrial facilities and power plants
require a maze of piping that twists and
turns in all directions. Small-diameter
pipe is welded to fittings to achieve
direction changes in the pipe runs, while
larger pipe is bent. Steel pipe of virtually any size can be bent to any angle.
This process creates what is called “
fabricated” piping that is formed to the
exact geometry called for in the piping
blueprints. The prefabricated pipe sections are then shipped intact to the job
site where they are joined with other
fabricated sections. This off-site fabrication saves time and money as well
ensuring more accurate construction.
GREG JOHNSON is president of United Valve
( www.unitedvalve.com), a valve service company
in Houston, TX. Reach him at greg1950@