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7/29/2019 Mechanical Plugs
1/6
Procedure for Use of High Pressure Mechanical Plugs on Piping in
Hydrocarbon Service
Allowed Uses Of Plugs
1. High pressure mechanical plugs may be used for isolation and purging of piping in utility and
hydrocarbon services at distribution terminals. High pressure mechanical plugs are also allowed in
hydro-test procedures.
2. High pressure mechanical plugs may not be used as the sole barrier between the process (eg. liquid
hydrocarbons contained in a tank) and the work. The installation of blinds/block plates is
mandatory.
3. High pressure mechanical plugs may be used to hydro-test new piping or tie-in welds only when the
test media is either glycol or water.
4. The use of any type of plug is not allowed in any pneumatic pressure test.
Types Of Plugs
1. High Pressure Mechanical Plugs
High pressure mechanical plugs are designed to withstand a given pressure and temperature. Ensure
the manufacturer of the plug will certify the plug for use within the stated pressure and temperature
ranges.
One style of high pressure mechanical plug has a design feature (serrated teeth) which mechanically
prevents the plug from moving after it has been installed in the pipe.
Note: High pressure mechanical plugs allow for the safe isolation of piping where flange blind
locations are remote from the work area, and it is not possible to completely gas free the piping.
Use of this procedure requires the development of a specific work procedure and the approval
of the Terminal Superintendent and Distribution Engineer.
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Procedure for Use of High Pressure Mechanical Plugs on Piping in
Hydrocarbon Service
1. High Pressure Mechanical Plugs (contd)
These plugs can also be used in hydro-test procedures because they are designed to withstand full
hydro-test differential pressure across the plug. This style of plug is also direction dependent. That
is, the serrations hold in one direction only. The plug must be installed in one direction for welding,
then removed and reversed for the hydro-test. Plugs meeting the above description are also known
as engineered plugs, hydro-test plugs or by various brand names such as Thaxton or Proline.
Bi-directional High Pressure Mechanical Plugs are available from some manufacturers. These plugs
can be used without having to change their orientation.
Another type of high pressure mechanical plug is a double plug design which maintains a positive
pressure between two adjacent plugs. Car-Ber plugs are of this type. This style of plug can
contain the positive barrier pressure but it is not capable of withstanding a large differential pressure
across the plug. Car-Ber plugs should not typically be used for hydro-testing.
The user of a high pressure mechanical plug must have in his possession the plug manufacturers data
sheet verifying design temperature and pressure.
2. Low Pressure Plugs
Note: Low pressure plugs are not to be used for piping that has been in hydrocarbon service.
Low pressure plugs (also known as plumbers plugs) typically consist of a rubber donut that is
compressed between two steel plates. When compressed, the donut expands to seal against the
pipe. The friction created by the rubber-to-pipe contact holds the plug in place.
The only approved application of Low Pressure Plugs would be in utility, sewer, sanitation systems.
3. Special Plugging Operations
There are a variety of special plugging operations offered by contractors. These include, but are not
limited to the use of mechanical plugs as positive pressure barriers, freeze plugs, mud plugs, ice
plugs, and Stopple plugs. None of these special plugging operations are covered in this
procedure. Use of these special plugging operations requires the completion of a Plant Change
form, critical task analysis and Head Office Distribution Specialist approval.
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Procedure for Use of High Pressure Mechanical Plugs on Piping in
Hydrocarbon Service
Instructions For Using Plugs
Action Information1. Planning and Documentation
Proper planning is required to use a high
pressure mechanical plug prior to performing
hot work.
Identify the service of the piping to be isolated
and define the limits of equipment to be
isolated or purged. Identify the location of all
plugs to be installed.
Select the appropriate plug.
Review the need for special procedures.
Write specific procedures for the job (written
procedure must identify isolation/blinding
points, venting and drain locations, test hole
and cold cut locations.
Consider distillate flush in gasoline piping
systems to reduce LELs prior to blinding.
2. Select The High Pressure Mechanical Plug The design pressure of the selected plug must
be at least 110% of the hydro-test pressure.
Ensure that the seal material of the plug is
compatible with the product or test media in
the pipeline.
Consider the direction of hydro-test pressure
against the plug and ensure that the plug is
installed as designed to withstand maximum
pressure forces.
Inspect and verify that the plug is properly
positioned in the piping.
High pressure mechanical plugs typically have a
chain or other restraining device. How this
device will be secured must be considered
when selecting the plug.
3. Approvals Use of any high pressure mechanical plug in
hydrocarbon service requires the completion ofa Plant Change form and the approval of the
Terminal Superintendent and the Distribution
Engineer.
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Procedure for Use of High Pressure Mechanical Plugs on Piping in
Hydrocarbon Service
Execution of a High Pressure Mechanical Plug Operation
The safe execution of a high pressure mechanical plug operation depends on the proper use of plugsand the execution of any special procedures. The following steps are required to properly execute a
high pressure mechanical plug operation:
Action Information
1. Inspect plugs prior to use Ensure that seal material is compatible with process
fluids. Obtain manufacturers specifications, inspection
procedures and operating procedures and review them
prior to commencing the operation.
2. Conduct pre-job safety meeting with
contractor and operating staff
Outline specific safety issues pertinent to the job.
Inspect the area where work will be performed. All
contractor personnel must be familiar with Shells Work-
site Health and Safety Rules and sign the
acknowledgement form. A safe evacuation route must
be mapped out and posted. Complete the Terminal safe
Work Permit form. Develop step by step job
procedures, review them in detail, and initial.
3. Isolate the piping system Close tank valve, any upstream valves, load rack valves
and any isolation valves as appropriate. Use double
lockout procedure for all valves and pumps that require
isolation.
4. Drain product from the piping Drain as much product as possible from the line.
Contractor to use a respirator during this procedure.
Vacuum trucks and drain pans are to be properly
bonded during draining procedure. Vacuum truck to be
vented down wind and away from the work area. Refer
to the Distribution Safe Work Practice For The Use of
Vacuum Trucks.
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Procedure for Use of High Pressure Mechanical Plugs on Piping in
Hydrocarbon Service
Action Information
1. Install blinds at isolation locations Steam cleaning the piping is an acceptable procedure to
remove hydrocarbon liquids and vapours.
For pipelines in gasoline service, flushing the pipeline
with diesel is an acceptable procedure to reduce
flammable vapours.
2. Install vent piping Ensure that a high point vent is used to vent the pipeline.
Vent piping to be located away from the work area.
3. Drill test hole in top of pipe Use an air drill to drill a small hole in the top of the
pipeline. The hole is used as a vapour test port near the
cold cutting location. Vapour must be less than 20%
LEL. (For vapour concentrations > 20% LEL,
additional ventilation is required; before cold work can
be initiated.)
Note: If a high point vent or low point drain is available
at the work area, the test hole can be eliminated.
4. Cold cut the pipe Cold cut the piping at two locations. Ensure there is
enough room in the cut-out section to allow the plugs to
be inserted.
5. Install the high pressure mechanical plug Clean the interior wall surface of the pipe to ensure a
good seal between the plug and the pipe. Ensure that
the plug is properly installed (i.e., at least 300 mm from
the proposed welded joint)
6. Gas test plug seal area Use a gas detector to sniff the inside of the pipe around
the sealing surface of the plug to ensure that positive
isolation has been achieved.
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Procedure for Use of High Pressure Mechanical Plugs on Piping in
Hydrocarbon Service
Action Information
1. Vent the contained piping area between
the high pressure mechanical plugs andthe isolation point
Vent the plug downwind to a remote location at least 10
metres away from the hot work location. Alternatively,the plug vent can be capped and the other end of the
pipeline can be used to vent.
2. Perform hot work (welding) Ensure that the work area is suitable for welding. An
area free of combustible material with a radius of 15 m is
recommended. Weld new flanges on the pipeline.
Constant hydrocarbon vapour monitoring must be
performed throughout the welding procedure.
Contractor to monitor wind direction and vapour levels
throughout the welding operation.
To avoid contact between the welding rod and the vent
pipe, install insulating material around the vent pipe.
Provide fire fighting equipment in the direct vicinity of the
welding operation (minimum of 2 20 lb Class BC fire
extinguishers)
Ensure that the area directly in front of the open pipe is
clear. Equipment and personnel should not be placed in
line with the end of the pipe.
3. Hydro-test the flange Once the weld area has completely cooled, perform
hydro-test on the new flange. The high pressure
mechanical plug must be chained to prevent loosing the
plug into the pipe during the hydro-test.
4. Plug removal and spool installation Following completion of the work and any testing
required, remove the plug from the piping as per the
manufacturers instructions.
Install spool piece in piping.
5. Re-commissioning the system. Write a re-commissioning procedure for the system.
Remove all lockouts (i.e., blinds, chains, locks, etc.).
Close all drains and control the closure of all high point
vents according to the pipeline filling procedure. Install
bull plugs in drains and vents. Flood/refill the piping to
remove all air from the system.