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Pipe material can be a very volatile
subject. It has
been a stumbling block to the use of pipe bursting technologies
with some utilities around the country. Many of these
utilities are so invested in certain pipe materials that it
is almost impossible for them to consider other piping materials. While
there is a high level of familiarity with the application of
HDPE pipe in pipe bursting, there is still considerable interest,
in other pipe material options, by owners, engineers and contractors.
Various pipe manufacturers are working
diligently with pipe bursting equipment developers and manufacturers to find
real world ways to adapt their pipe products to pipe bursting
installations. It takes the extensive experience of these
parties to find suitable ways to install what is best described
as sectional, gasketed pipe in the pipe bursting process. There
are many factors to consider in what is necessary for these
pipe materials to work in pipe bursting applications.
Pipe Bursting Overview
With the recent introduction of new hydraulically powered
static pipe bursting system, contractors now have the ability
to split and replace ductile iron, steel and lined pipes, as
well as pipes with ductile iron and steel repairs.
During the static bursting process,
specially designed bladed rollers are pulled through an existing
line by a hydraulically powered bursting unit. As the bladed rollers are pulled
through, they split the host pipe. An expander attached
to the rollers forces the fragmented pipe into the surrounding
soil while simultaneously pulling in the new pipe.
The bladed roller configuration
is an essential part of static bursting success for steel
and ductile iron pipe materials. The
specially designed bladed rollers actually split the host pipe
instead of ripping or tearing it. This is a clean process
and prevents potential damage to the product pipe.
The old pipe must be fractured or
split, the remaining fragments compacted into the surrounding
backfill, and the new pipe pulled/pushed in before the temporary
annular space, created by the pipe bursting tool, begins
to collapse and get a firm grip on the new pipe. Once
the soil has a firm grip on the pipe, it is very difficult
if not all but impossible to continue to move the column
of new pipe forward.
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Product Pipe Options
HDPE for Sewer and Water, MDPE for Natural Gas
The industry
is very knowledgeable about this pipe material and pipe bursting
installations. Fusion welded joints help to make this type
of pipe into a one-piece pipe section to whatever length is
required for a pipe bursting reach. For
example, a section to be replaced is 500 feet long; a string
of PE pipe will be welded together into a string slightly longer
than 500 feet and will be laid down in alignment with the launching
pit. This method represents at least 95% of all pipe
bursting installations. This procedure always requires
adequate lay-down area. Fusion welding this type of pipe
during the pipe bursting process is very time-consuming and
generally not performed in the field. Because of years
of field experience a number of ways to connect PE pipe to
the pipe bursting tooling have been developed. They are
generally all reliable with various advantages to the methods.
Both pneumatic and static pipe bursting systems can be used
for this type of pipe.
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Fusion Welded PVC
The water and sewer industry are just
beginning to see this relatively new type of PVC pipe. It
is butt fusion welded, similar to PE, and offers a PVC pipe
that is suitable for many pipe bursting applications. Although
the pipe is somewhat stiffer, thus requiring longer launching
pits. 5:1 ratio (Length to Depth), the fusion procedures for
welding this type of pipe must be adhered to very precisely. Experience
has shown that the typical scratching on the outside diameter
(OD) of the pipe is within the manufacturers allowances. This
type of pipe cannot withstand the heavy hammering action of
a pneumatic pipe bursting system. Because the pipe is
stiffer than HDPE for example, it must be installed with a
static pipe bursting system so as not to fracture the pipe’s
connection to the pipe bursting tooling.
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Restrained Joint Ductile Iron Pipe
This is another new
application for a type of pipe that has been on the scene for
a very long time. The bell and
spigot restrained joint configuration requires that the pipe
be pulled backwards (spigot end first). This allows each
consecutive bell joint to act like an additional pipe bursting
expander. Only a static pipe bursting system should be
used for this type of pipe. The pipe is assembled one
joint at a time in the launching pit and pulled one joint at
a time. The joints are made up quite quickly, usually in just
a couple of minutes.
The advantage of this cartridge
loading approach is there is no need for a pipe staging area. The new replacement
pipe can be unloaded, as needed, from a truck and at the end
of the day there is no pipe left on site. This process
requires the pipe bursting system to start and stop repeatedly.
Each joint is made-up in the launch pit, pulled in and then
stopped while the next section of pipe is lowered into
the launch pit and assembled to the previous joint.
Loose polyethylene encasement of
the ductile iron pipe is not done, as the wrap will be severely
damaged by the old pipes fragments during the installation. A
pushing jack may be used to help the column forward during
difficult bursting operations.
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C-900 PVC pipe with a restrained joint utilizes a spline and
groove assembly that is very strong. This pipe is assembled
and pulled much the same as restrained joint ductile iron
pipe. Only static pipe bursting systems should be used
due to the stiffness of the pipe. The connection of
the PVC pipe to the bursting head consists of an adapter
using the pipe and a steel pulling head of the same configuration
as the pipe joint. A cartridge loading method can be
used. However, this type of pipe appears to be flexible
enough to join together before a pipe burst and insert through
the launch pit with minimum bending.
This type of pipe has a very low profile joint and was developed
primarily for pipe jacking type installations. When pipe
bursting with non-restrained joint pipe it is normal to place
the static bursting system pulling rods through the length
of each new pipe section and connect to a backup clamp that
essentially helps to push the column of pipe from the backside. This
insures that the non-restrained pipe joints stay in compression
thus staying together. The internal lining of the new
pipe must be protected from the rods or cable used to pull
the pipe. In many situations, the rods are sheathed inside
small diameter plastic pipe. This helps prevent any rubbing
damage to the lining.
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This particular pipe product is much the
same as other
non-restrained pipe types. Because this is a clay pipe, special care
will be necessary to keep the column in good alignment. These
pipe sections come with a layer of compressive material at
the joints to help equalize the jacking pressures against the
end of each section. Clay pipe is quite heavy and you
would expect to see some sort of pushing jack in use along
with the static pipe bursting system. This type of pipe
is installed using the cartridge loading method.
Welded steel
is installed by pulling with static pipe bursting systems. The
pipe is by definition flexible. So
it can be welded together and then pulled in similar to PE
pipe. The reality is that this pipe is not really that flexible
and probably will need to be welded together as each joint
goes in.
The specified pipe and specific pipe bursting equipment
should have a proven history similar with the intended application
and service environment, as well as data that reflects third-party
testing, to substantiate suitability of the pipe by physical
property and chemical resistance claims of the manufacturer. The
pipe bursting equipment system(s) to be used should be proven
to be capable of the required pipe replacement.
The structural condition of the
existing pipe also needs to be
evaluated and point repairs
identified. CCTV is a
very useful tool in identifying many pipe defects. Recent
CCTV tapes and logs should be included as part of the plans
and specifications for projects. Multiple pipe bursting
systems and replacement pipes may be evaluated and subsequently
specified. Since all systems are not alike, pipe
and pipe bursting system capabilities must be evaluated to
determine the proper selection for the project under consideration.
There are other types of restrained
joint and non-restrained joint pipe that can be installed
with similar methods. Consulting
with well-qualified pipe bursting consultants and knowledgeable
equipment manufacturers can help to make these applications
possible.
Collins Orton
Product Specialist, TT Technologies, Aurora, Ill
WESTT,
Summer 2006 |
