WHAT IS HOT TAP AND WHY IS IT MADE?
Hot Taps or Hot Tapping is
the ability to safely tie into a pressurized system, by drilling or cutting,
while it is on stream and under pressure.
Typical connections consist:
o
Tapping
fittings like Weldolet®, Reinforced Branch or Split Tee. Split Tee often to be
used as branch and main pipe has the same diameter
o
Isolation
Valve like gate or Ball Valve.
o
Hot tapping
machine which includes the cutter, and housing.
Mechanical fittings may be
used for making hot taps on pipelines and mains provided they are designed for
the operating pressure of the pipeline or main, and are suitable for the
purpose.
There are many reasons to
made a Hot Tap. While is preferred to install nozzles during a turnaround,
installing a nozzle with equipment in operation is sometimes advantageous,
especially if it averts a costly shut down.
REMARKS BEFORE MADE A HOT TAP
o
A hot tap
shall not be considered a routine procedure, but shall be used only when there
is no practical alternative.
o
Hot Taps
shall be installed by trained and experienced crews.
o
It should be
noted that hot tapping of sour gas lines presents special health and
metallurgical concerns and shall be done only to written operating company
approved plans.
o
For each
hottap shall be ensured that the pipe that is drilled or sawed has sufficient
wall thickness, which can be measured with ultrasonic thickness gauges. The
existing pipe wall thickness (actual) needs to be at least equal to the
required thickness for pressure plus a reasonable thickness allowance for
welding. If the actual thickness is barely more than that required for
pressure, then loss of containment at the weld pool is a risk.
o
Welding on
in-service pipelines requires weld procedure development and qualification, as
well as a highly trained workforce to ensure integrity of welds when pipelines
are operating at full pressure and under full flow conditions.
HOT TAP SETUP
For a hot tap, there are
three key components necessary to safely drill into a pipe; the fitting, the
Valve, and the hot tap machine. The fitting is attached to the pipe, mostly by
welding.
In many cases, the fitting
is a Weldolet® where a flange is welded, or a split tee with a flanged outlet
(see image above).
Onto this fitting, a Valve
is attached, and the hot tap machine is attached to the Valve (see images on
the right). For hot taps, new Stud Bolts, gaskets and a new Valve should always
be used when that components will become part of the permanent facilities and
equipment.
The fitting/Valve
combination, is attached to the pipe, and is normally pressure tested. The
pressure test is very important, so as to make sure that there are no
structural problems with the fitting, and so that there are no leaks in the
welds.
The hot tap cutter, is a
specialized type of hole saw, with a pilot bit in the middle, mounted inside of
a hot tap adapter housing.
The hot tap cutter is
attached to a cutter holder, with the pilot bit, and is attached to the working
end of the hot tap machine, so that it fits into the inside of the tapping
adapter.
The tapping adapter will
contain the pressure of the pipe system, while the pipe is being cut, it houses
the cutter, and cutter holder, and bolts to the Valve.
HOT TAP OPERATION
The Hot Tap is made in one
continuous process, the machine is started, and the cut continues, until the
cutter passes through the pipe wall, resulting in the removal of a section of
pipe, known as the “coupon”.
The coupon is normally
retained on one or more u-wires, which are attached to the pilot bit. Once the
cutter has cut through the pipe, the hot tap machine is stopped, the cutter is retracted
into the hot tap adapter, and the Valve is closed.
Pressure is bled off from
the inside of the Tapping Adapter, so that the hot tap machine can be removed
from the line. The machine is removed from the line, and the new service is
established.
HOT TAP COUPON
The Coupon, is the section
of pipe that is removed, to establish service. It is very highly desirable to
“retain” the coupon, and remove it from the pipe, and in the vast majority of
hot taps, this is the case.
Please note, short of not
performing the hot tap, there is no way to absolutely guarantee that the coupon
will not be “dropped”.
Coupon retention is mostly
the “job” of the u-wires. These are wires which run through the pilot bit, and
are cut and bent, so that they can fold back against the bit, into a relief
area milled into the bit, and then fold out, when the pilot bit has cut through
the pipe.
In almost all cases,
multiple u-wires are used, to act as insurance against losing the coupon.
LINE STOPPING
Line Stops, sometimes called
Stopples (Stopple® is a trademark of TD Williamson Company) start with a hot
tap, but are intended to stop the flow in the pipe.
Line Stops are of necessity,
somewhat more complicated than normal hot taps, but they start out in much the
same way. A fitting is attached to the pipe, a hot tap is performed as
previously detailed. Once the hot tap has been completed, the Valve is closed,
then another machine, known as a line stop actuator is installed on the pipe.
The line stop actuator is
used to insert a plugging head into the pipe, the most common type being a
pivot head mechanism. Line stops are used to replace Valves, fittings and other
equipment. Once the job is done, pressure is equalized, and the line stop head
is removed.
The Line Stop Fitting has a
specially modified flange, which includes a special plug, that allows for
removal of the Valve. There are several different designs for these flanges,
but they all work pretty much the same, the plug is inserted into the flange
through the Valve, it is securely locked in place, with the result that the
pressure can be bled off of the housing and Valve, the Valve can then be
removed, and the flange blinded off.
LINE STOP SETUP
The Line Stop Setup includes
the hot tap machine, plus an additional piece of equipment, a line stop
actuator. The Line Stop Actuator can be either mechanical (screw type), or
hydraulic, it is used, to place the line stop head into the line, therefore
stopping the flow in the line.
The Line Stop Actuator is
bolted to a Line Stop Housing, which has to be long enough to include the line
stop head (pivot head, or folding head), so that the Line Stop Actuator, and
Housing, can be bolted to the line stop Valve.
Line stops often utilize
special Valves, called Sandwich Valves. Line Stops are normally performed
through rental Valves, owned by the service company who performs the work, once
the work is completed, the fitting will remain on the pipe, but the Valve and
all other equipment is removed.
LINE STOP OPERATION
A Line Stop starts out the
same way as does a Hot Tap, but a larger cutter is used,.
The larger hole in the pipe,
allows the line stop head to fit into the pipe. Once the cut is made, the Valve
is closed the hot tap machine is removed from the line, and a line stop
actuator is bolted into place.
New gaskets are always to be
used for every setup, but “used” studs and nuts are often used, because this
operation is a temporary operation, the Valve, machine, and actuator are
removed at the end of the job.
New studs, nuts, and gaskets
should be used on the final completion, when a blind flange is installed
outside of the completion plug. The line stop actuator is operated, to push the
plugging head (line stop head), down, into the pipe, the common pivot head,
will pivot in the direction of the flow, and form a stop, thus stopping the
flow in the pipe.
COMPLETION PLUG
In order to remove the Valve
used for line stop operations, a completion plug is set into the line stop
fitting flange (Completion Flange).
There are several different
types of completion flange/plug sets, but they all operate in basically the
same manner, the completion plug and flange are manufactured, so as to allow
the flange, to accept and lock into place, a completion plug.
This completion plug is set
below the Valve, once set, pressure above the plug can be bled off, and the
Valve can then be removed.
Once the plug has been
properly positioned, it is locked into place with the lock ring segments, this
prevents plug movement, with the o-ring becoming the primary seal.
Several different types of
completion plugs have been developed with metal to metal seals, in addition to
the o-ring seal.
No comments:
Post a Comment