Steel pipes are long, hollow
tubes that are used for a variety of purposes. They are produced by two
distinct methods which result in either a welded or seamless pipe. In
both methods, raw steel is first cast into a more workable starting form. It is
then made into a pipe by stretching the steel out into a seamless tube or
forcing the edges together and sealing them with a weld. The first methods for
producing steel pipe were introduced in the early 1800s, and they have steadily
evolved into the modern processes we use today. Each year, millions of tons of
steel pipe are produced. Its versatility makes it the most often used product
produced by the steel industry.
Steel pipes are found in a
variety of places. Since they are strong, they are used underground for
transporting water and gas throughout cities and towns. They are also employed
in construction to protect electrical wires. While steel pipes are strong, they
can also be lightweight. This makes them perfect for use in bicycle frame
manufacture. Other places they find utility is in automobiles, refrigeration units,
heating and plumbing systems, flagpoles, street lamps, and medicine to name a
few.
History
People have used pipes for
thousands of years. Perhaps the first use was by ancient agriculturalists who
diverted water from streams and rivers into their fields. Archeological evidence
suggests that the Chinese used reed pipe for transporting water to desired
locations as early as 2000 B.C. Clay tubes that were used by other
ancient civilizations have been discovered. During the first century A.D. ,
the first lead pipes were constructed in Europe. In tropical countries, bamboo tubes were used
to transport water. Colonial Americans used wood for a similar purpose. In
1652, the first waterworks was made in Boston using hollow logs.
Development of the modern
day welded steel pipe can be traced back to the early 1800s. In 1815, William
Murdock invented a coal burning lamp system. To fit the entire city of London
with these lights, Murdock joined together the barrels from discarded muskets.
He used this continuous pipeline to transport the coal gas. When his lighting
system proved successful a greater demand was created for long metal tubes. To
produce enough tubes to meet this demand, a variety of inventors set to work on
developing new pipe making processes.
An early notable method for
producing metal tubes quickly and inexpensively was patented by James Russell
in 1824. In his method, tubes were created by joining together opposite edges
of a flat iron strip. The metal was first heated until it was malleable. Using
a drop hammer, the edges folded together and welded. The pipe was finished by
passing it through a groove and rolling mill.
Russell's method was not
used long because in the next year, Comelius Whitehouse developed a better
method for making metal tubes. This process, called the butt-weld process is
the basis for our current pipe-making procedures. In his method, thin sheets of
iron were heated and drawn through a cone-shaped opening. As the metal went
through the opening, its edges curled up and created a pipe shape. The two ends
were welded together to finish the pipe. The first manufacturing plant to use
Welded pipe is formed by
rolling steel strips through a series of grooved rollers that mold the material
into a circular shape. Next, the unwelded pipe passes by welding electrodes.
These devices seal the two ends of the pipe together.
this process in the United
States was opened in 1832 in Philadelphia.
Gradually, improvements were
made in the Whitehouse method. One of the most important innovations was
introduced by John Moon in 1911. He suggested the continuous process method in
which a manufacturing plant could produce pipe in an unending stream. He built
machinery for this specific purpose and many pipe manufacturing facilities
adopted it.
While the welded tube
processes were being developed, a need for seamless metal pipes arouse.
Seamless pipes are those which do not have a welded seam. They were first made
by drilling a hole through the center of a solid cylinder. This method was
developed during the late 1800s. These types of pipes were perfect for bicycle
frames because they have thin walls, are lightweight but are strong. In 1895,
the first plant to produce seamless tubes was built. As bicycle manufacturing
gave way to auto manufacturing, seamless tubes were still needed for gasoline
and oil lines. This demand was made even greater as larger oil deposits were
found.
As early as 1840,
ironworkers could already produce seamless tubes. In one method, a hole was
drilled through a solid metal, round billet. The billet was then heated and
drawn through a series of dies which elongated it to form a pipe. This method
was inefficient because it was difficult to drill the hole in the center. This
resulted in an uneven pipe with one side being thicker than the other. In 1888,
an improved method was awarded a patent. In this process the solid billed was
cast around a fireproof brick core. When it was cooled, the brick was removed
leaving a hole in the middle. Since then new roller techniques have replaced
these methods.
Design
There are two types of steel
pipe, one is seamless and another has a single welded seam along its length.
Both have different uses. Seamless tubes are typically more light weight, and
have thinner walls. They are used for bicycles and transporting liquids. Seamed
tubes are heavier and more rigid. The have a better consistency and are typically
straighter. They are used for things such as gas transportation, electrical
conduit and plumbing. Typically, they are used in instances when the pipe is
not put under a high degree of stress.
Certain pipe characteristics
can be controlled during production. For example, the diameter of the pipe is
often modified depending how it will be used. The diameter can range from tiny
pipes used to make hypodermic needles, to large pipes used to transport gas
throughout a city. The wall thickness of the pipe can also be controlled. Often
the type of steel will also have an impact on pipe's the strength and
flexibility. Other controllable characteristics include length, coating
material, and end finish.
Raw Materials
The primary raw material in
pipe production is steel. Steel is made up of primarily iron. Other metals that
may be present in the alloy include aluminum,
manganese, titanium, tungsten, vanadium, and zirconium. Some finishing
materials are sometimes used during production.
Seamless pipe is
manufactured using a process that heats and molds a solid billet into a
cylindrical shape and then rolls it until it is stretched and hollowed. Since
the hollowed center is irregularly shaped, a bullet-shaped piercer point is
pushed through the middle of the billet as it is being rolled.
used if the pipe is coated.
Typically, a light amount of oil is applied to steel pipes at the end of the
production line. This helps protect the pipe. While it is not actually a part
of the finished product, sulfuric acid is used in one manufacturing step to
clean the pipe.
The Manufacturing Process
Steel pipes are made by two
different processes. The overall production method for both processes involves
three steps. First, raw steel is converted into a more workable form. Next, the
pipe is formed on a continuous or semicontinuous production line. Finally, the
pipe is cut and modified to meet the customer's needs.
Ingot production
1. Molten steel is made by melting iron ore and coke
(a carbon-rich substance that results when coal is heated in the absence of
air) in a furnace, then removing most of the carbon by blasting oxygen into the
liquid. The molten steel is then poured into large, thick-walled iron molds,
where it cools into ingots.
2. In order to form flat products such as plates and
sheets, or long products such as bars and rods, ingots are shaped between large
rollers under enormous pressure.
Producing blooms and
slabs
3. To produce a bloom, the ingot is passed through
a pair of grooved steel rollers that are stacked. These types of rollers are
called "two-high mills." In some cases, three rollers are used. The
rollers are mounted so that their grooves coincide, and they move in opposite
directions. This action causes the steel to be squeezed and stretched into
thinner, longer pieces. When the rollers are reversed by the human operator,
the steel is pulled back through making it thinner and longer. This process is
repeated until the steel achieves the desired shape. During this process,
machines called manipulators flip the steel so that each side is processed
evenly.
4. Ingots may also be rolled into slabs in a process
that is similar to the bloom making process. The steel is passed through a pair
of stacked rollers which stretch it. However, there are also rollers mounted on
the side to control the width of the slabs. When the steel acquires the desired
shape, the uneven ends are cut off and the slabs or blooms are cut into shorter
pieces.
Further processing
5. Blooms are typically processed further before
they are made into pipes. Blooms are converted into billets by putting them
through more rolling devices which make them longer and more narrow. The
billets are cut by devices known as flying shears. These are a pair of
synchronized shears that race along with the moving billet and cut it. This
allows efficient cuts without stopping the manufacturing process. These billets
are stacked and will eventually become seamless pipe.
6. Slabs are also reworked. To make them malleable,
they are first heated to 2,200° F (1,204° C). This causes an oxide coating to form
on the surface of the slab. This coating is broken off with a scale breaker and
high pressure water spray. The slabs are then sent through a series of rollers
on a hot mill and made into thin narrow strips of steel called skelp. This mill
can be as long as a half mile. As the slabs pass through the rollers, they
become thinner and longer. In the course of about three minutes a single slab
can be converted from a 6 in (15.2 cm) thick piece of steel to a thin steel
ribbon that can be a quarter mile long.
7. After stretching, the steel is pickled. This
process involves running it through a series of tanks that contain sulfuric
acid to clean the metal. To finish, it is rinsed with cold and hot water, dried
and then rolled up on large spools and packaged for transport to a pipe making
facility.
Pipe making
8. Both skelp and billets are used to make pipes.
Skelp is made into welded pipe. It is first placed on an unwinding machine. As
the spool of steel is unwound, it is heated. The steel is then passed through a
series of grooved rollers. As it passes by, the rollers cause the edges of the
skelp to curl together. This forms an unwelded pipe.
9. The steel next passes by welding electrodes.
These devices seal the two ends of the pipe together. The welded seam is then
passed through a high pressure roller which helps create a tight weld. The pipe
is then cut to a desired length and stacked for further processing. Welded
steel pipe is a continuous process and depending on the size of the pipe, it
can be made as fast as 1,100 ft (335.3 m) per minute.
10. When seamless pipe is needed, square billets are
used for production. They are heated and molded to form a cylinder shape, also
called a round. The round is then put in a furnace where it is heated
white-hot. The heated round is then rolled with great pressure. This high
pressure rolling causes the billet to stretch out and a hole to form in the
center. Since this hole is irregularly shaped, a bullet shaped piercer point is
pushed through the middle of the billet as it is being rolled. After the
piercing stage, the pipe may still be of irregular thickness and shape. To
correct this it is passed through another series of rolling mills.
Final processing
11. After either type of pipe is made, they may be
put through a straightening machine. They may also be fitted with joints so two
or more pieces of pipe can be connected. The most common type of joint for
pipes with smaller diameters is threading—tight grooves that are cut into the
end of the pipe. The pipes are also sent through a measuring machine. This
information along with other quality control data is automatically stenciled on
the pipe. The pipe is then sprayed with a light coating of protective oil. Most
pipe is typically treated to prevent it from rusting. This is done by galvanizing it or
giving it a coating of zinc. Depending on the use of the pipe, other paints or
coatings may be used.
Quality Control
A variety of measures are
taken to ensure that the finished steel pipe meets specifications. For example,
x-ray gauges are used to regulate the thickness of the steel. The gauges work
by utilizing two x rays. One ray is directed at a steel of known thickness. The
other is directed at the passing steel on the production line. If there is any
variance between the two rays, the gauge will automatically trigger a resizing
of the rollers to compensate.
Pipes are also inspected for
defects at the end of the process. One method of testing a pipe is by using a
special machine. This machine fills the pipe with water and then increases the
pressure to see if it holds. Defective pipes are return
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