mechanical plugs

7/29/2019 Mechanical Plugs

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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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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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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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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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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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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.

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