Pipeline Hot Tap Installation
05.20
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:
·
Tapping fittings like Weldolet®,
Reinforced Branch or Split Tee. Split Tees often to be used as branch and main
pipe has the same diameters.
·
Isolation valve like Gate or
Ball valve.
·
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.
·
Design: ASME B31.1, B31.3, ASME
B31.4 & B31.8, ASME Sec. VIII Div.1 & 2
·
Fabrication: ASME Sec. VIII
Div.1
·
Welding: ASME Sec. IX
·
NDT: ASME Sec. V
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
·
A hot tap shall not be
considered a routine procedure, but shall be used only when there is no
practical alternative.
·
Hot Taps shall be installed by
trained and experienced crews.
·
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.
·
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.
·
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).
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. For hot taps, new 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.
Sumber:
http://www.wermac.org/specials/hottap.html
0 komentar