Pipes and Fittings

The need to add new customer service branch pipes to existing main gas or
water utility pipelines has long been recognized. The safest method is to
isolate the section of main pipeline, depressurize, purge, cut a hole,
clean out, and permanently attach a tee adapter to which the branch pipe
can be attached while the pipeline is depressurized. However, to reduce
service interruptions to existing customers connected to the main
pipeline, hot tapping tools have been developed for metallic pipelines
that can drill or cut into the main pipeline while still in service under
gas or water pressure.

Prior art for hot-tapping a main plastic pipeline
involves attaching a pipe saddle fitting to the main pipeline and then
attaching an appropriate tubular adapter having a flange, or some type of
mechanical joint outlet connector, to the pipe saddle fitting. Finally, a
short length of branch pipe is connected to the tubular adapter, and a
hole is drilled in the main pipeline for fluid communication with the
branch pipe. A tapping tool, which includes a compression seal butted
against the open end of the branch pipe, a drill mounted on a shaft
extending through the compression seal and the pipe saddle, and means to
advance/retract the drill bit from outside the fitting, is then used to
drill the hole in the main pipeline. After the hole is drilled, the drill
bit is retracted toward the compression seal within the now pressurized
length of branch pipe. If a full flow valve is not included in the branch
pipe, a squeeze off tool is used to seal the branch pipe near the pipe
adaptor, before removal of the tapping tool. After attaching the remainder
of the branch pipe to the tapped section, the full flow valve is opened,
or the squeezed section of the branch pipe is rerounded. Use of hot
tapping tools has become so common, especially in water distribution, that
the manufacturers of the tools have developed dimensional standards for
hot tap tools offered for sale.

Several problems, however, are inherent in the prior art techniques for
using the standard hot-tap tool on plastic pipelines. The use of the
hot-tap tool requires extensive evacuation/back filling for buri
d
pipelines, such that restricted access may prevent installation of the hot
tap tool in some locations.

Another problem is that commercially available plastic pipe saddle fittings
and plastic tubular adapters having flange or mechanical joint outlet
connections are of lengthy and bulky construction. Accordingly, when an
available plastic tubular adapter is fused to an available plastic pipe
saddle fitting, the passageway of the resulting assembly, through which
the drill bit of the tapping tool must pass, is too long to allow use of
many commonly sized tapping tools.

Other problems arise because commercially available plastic pipe saddle
fittings lack sufficient mass, especially in the base section of the
saddle, to overcome the weakening effects of a hole cut in the main
pipeline. Once the hole in the main pipe has been cut and the coupon
removed, the lack of sufficient mass in the base of the saddle fitting
also results in inadequate contact surface for fusion to the main pipe.
Accordingly, the lack of contact surface and/or reinforcing mass in the
plastic saddle, result in failure of the fitting to provide a pressure
rating equal to that of the main host pipe.