This document recommends specific suggestions to be followed when using a vented pipe seal plug. This includes plug vendors, steps for installation of the plugs, and a suggested checklist to be followed prior to authorizing work behind a vented pipe seal plug.


Vented Pipe Seal Plug is a mechanical plug used to seal a pipe opening that contains a vent pipe through the center of the plug to prevent pressure build-up behind the plug.

Vented pipe seal plugs that are rated for high pressure, are designed to fit inside the open end of a pipeline to form a vapor tight seal.

Vented high pressure pipe seal plugs can be used to perform hot work downstream of a single block valve (the vented plug provides a second block and bleed), but all other options for equipment isolation should be exhausted.

The recommended seal plug is a vented pipe seal plug with metal grippers which is rated for the design pressure of the line in which it will be installed. The following are two examples of seal plugs which should be used:

  1. T.D. Williamson - Wedge-Lock Pipe Plug
  2. Expansion Seal Technologies - Grip Tight High Pressure Test Plug

Note: Plugs with wing nuts are not allowed as the amount of torque applied cannot be measured.

Plumber’s plugs and other pipeline plugs that are not rated for pressure are not recommended for use.

Vented pipe seal plugs are provided with a vent pipe through the center of the plug. The vent is intended to prevent any build-up of pressure on the plug. Alternatively, a pipeline bleed point located between the isolation valve and the plug may be used to prevent pressure build-up behind the plug.

A non-vented seal plug may be used when the pipe’s last bleed point is between the isolation valve and end of the pipe.

No valve should be installed between the vented pipe seal plug vent connection and the end of the extended piping or the connected hose.

Preparation for Installation of The Seal Plug

  • Remove all pressure from the line to be worked on.
  • Thoroughly clean oil/chemical and scale from the internal surfaces of the pipe where the vented pipe seal plug will be installed.
  • Check rubber seals as follows:
    • Remove any oil/chemical or scale deposits
    • Check for cuts
    • Check for burned areas
  • If welding is to be performed on the open end of the pipe, insert the vented pipe seal plug in the pipe sufficiently (per the manufacturer’s requirements) to preclude damaging the rubber seal by flame impingement or conducted heat.
  • Maintenance personnel should have written installation procedures from the seal plugs' vendor in hand in the field for plug installation.
  • Install vented pipe seal plug per vendor installation procedures.
  • When the vented pipe seal plug is firmly seated, connect the piping or hose to the seal vent connection.
  • Alternatively, a bleed point located between the vented pipe seal plug and the isolation valve may also be used to prevent build-up of pressure on the plug.
  • Check the vent piping or hose to ensure that it is unobstructed and clear. Check the hose to be sure that there are no low points, no coiling, and that the hose discharges below the plug to prevent any liquid build-up that can cause back pressure on the plug.
  • Ensure that the pipe plug spindle (center vent pipe) is always kept parallel with the pipe.
  • Place the end of the vent piping or hose at least 50 feet downwind of the work area.

Recommended Procedure for Hot Work Using Vented Pipe Seal Plug

  • In preparation for Hot Work that is utilizing a vented pipe seal plug, the area authority and the maintenance supervisor must verify and sign off hazards checklist as recommended below. The Checklist should be attached to the work permit for the hot work.
  • Minimize the time the plug is used to reduce exposure to plug-related hazards. The plug should not be left installed at the end of the shift (leaves an open-ended pipe). The work should continue until completion so that a blind flange or other positive isolation device can be installed.
  • The welding machine or other sources of ignition should not be located within 50 feet of the seal vent outlet or any other vent in the connected pipe.
  • Maintenance should request a Hot Work Permit from the area's authority.  An explosimeter test should be taken around the seal of the plug and around the vent coming off the line.
  • Ensure that the weld has sufficient time to cool before attempting to remove the vented pipe seal plug from the pipeline.
  • Remove vented pipe seal plug.

Vented Pipe Seal Plugs Checklist

Note: Where application of a plug requires cutting of an existing line, Line ID should be calculated prior to cutting the line to install the plug.

  • Is plug seal material compatible with line service and temperature?
  • Is pipe OD cleaned of scale or residue?
  • Is plug in good mechanical condition? Check for damage to the metal parts. Check rubber seat for physical damage, oil or scale deposits.
  • Is a copy of the plug manufacturer’s operating instructions and installation instructions at the task location and have they been reviewed and understood by those who will be performing the work?
  • Consider the possibility of the plug coming loose or leaking. Where will the plug and the material behind the plug go? Consider body position of workers if plug comes loose.
  • Discuss if the plug only holds pressure in one direction. Ensure that grippers are installed in the correct direction.
  • How will the plug be tested throughout the time it is being used to ensure it has not loosened? To ensure that it is not leaking vapor or liquid?
  • Is the hose or pipe used to vent the pipeline plug at least 50 feet downwind of the work location? Check hose for low points, coiling, kinks, hose discharge point below plug elevation. Ensure hose is protected from possible damage from welding or grinding operations.
  • Does the use of the plug result in energy (pressure, hot liquids or gases) being stored behind the plug? If yes, how will we minimize the risk? How will the plug be safely removed at the end of the work?
  • Consider the ergonomics of the work area. Will the workers be able to perform the necessary work without inadvertently bumping or possibly loosening the plug? Is the hose or vent piping out of the way so that it will not be bumped?
  • Has all of the above information and the work plan been communicated to the mechanics who will be performing the work?
  • How are plug, line, temporary piping, welding machine, and other equipment grounded to ensure no spark occurs?
  • Does the plan comply with all applicable sections of Company Safety Manual? If not, has an authorized Safety Manual Exception been obtained?