Hot Tapping & Pressurized Pipe Work

Hot tapping means making a connection to a pipe, tank or vessel that is still in service, by welding a fitting onto it and cutting a hole through the wall while the contents stay inside. It saves shutdown time, but it is one of the highest-risk jobs in refineries, gas, chemical and utility systems. A burn-through, leak or ignition can cause a fire or explosion. It must be done to an engineered procedure by qualified people.

• Pipefitters & Welders
• Pipeline & Gas Utility Crews
• Refinery & Plant Maintenance
• Engineers
• Safety Managers

How hot tapping works

1. A branch fitting or full-encirclement saddle is welded or bolted onto the live pipe or vessel.
2. A valve is attached to the fitting, and a hot tapping machine is mounted on the valve.
3. A cutter drills through the pipe wall inside the fitting, and a coupon (the metal disc cut out) is retained and withdrawn. The valve is then closed behind the cutter.
4. The machine is removed, and the new branch connection is tied in to the system.

Related methods include line stopping and freezing to isolate sections. Industry guidance on hot tapping includes API 2201, Safe Hot Tapping Practices in the Petroleum and Petrochemical Industries, and gas utilities follow their own procedures and pipeline safety rules. See ASME Boiler & Pressure Vessel Code and Process Safety Management.

Why it's dangerous

• Burn-through: heat from welding on a pipe with flowing contents can thin the wall or overheat the pipe wall, allowing the contents to blow through. Thin or corroded walls are especially at risk.
• Ignition of flammable contents in the pipe or by a leak, from welding sparks and heat. See Hot Work Permits.
• Decomposition or reaction: some materials (such as acetylene, ethylene oxide, hydrogen peroxide, oxygen-rich lines and unstable or reactive chemicals) can decompose or explode when heated, so they must not be hot tapped.
• Hydrogen cracking and weld failure from rapid cooling of the weld by flowing fluid.
• Release of toxic or hot material, such as hydrogen sulfide, steam and hot oil, when the pipe is cut. See Hydrogen Sulfide.
• Tool and machine failures as the cutter breaks through, the pipe vibrates or the machine slips.
• High pressure releasing when seals fail. See Hydraulic Hazards for related energy hazards.

Before you hot tap: engineering and procedures

• Decide if hot tapping is appropriate. Consider alternatives such as shutting down and purging. Don't hot tap on the wrong contents or conditions, such as lines with oxygen, acetylene, ethylene oxide or other prohibited materials, or if the wall is too thin.
• Have a written hot tap procedure reviewed by an engineer, covering pipe or vessel material, wall thickness and condition (ultrasonic thickness tests), operating pressure and temperature, flow, contents, welding procedure, fitting design, machine setup, and emergency steps.
• Use a welding procedure and welders qualified for the hot tap, following codes such as ASME Section IX and API 1104 or company rules. See AWS Welding Codes.
• Control flow, pressure and temperature at safe levels for the weld and the cut, as the procedure says. Maintain the pipe contents' flow rate to carry away heat but not so high that it cools the weld too quickly.
• Use a management of change review when hot tapping is a new activity or changes a system. See Management of Change (MOC).
• Get an engineered hot work and hot tap permit signed by the right people, as the site requires. See Hot Work Permits and Permit to Work.

During the work

• Hold a pre-job meeting to review roles, hazards, communication, emergency shutdown and rescue steps. Everyone must know how to stop the job.
• Test the atmosphere around the work with a gas detector before and during the job, and keep ignition sources controlled. See Flammable Gas Detection.
• Use fire watches, fire extinguishers and, if needed, hose lines or firefighting standby. See Emergency Action Plans.
• Wear flame-resistant clothing, face shield, gloves and other PPE suited to the contents, plus respirators if toxic gas is possible. See Flame-Resistant Clothing.
• Keep only essential people in the area, and set up barricades and exclusion zones. Plan escape routes. Don't allow extra work in the area.
• Monitor the weld and the pipe, and stop if there are leaks, unusual heat, noises, smoke or pressure changes. Follow the cutting and withdrawal steps exactly, and pressure test the fitting before cutting if the procedure requires it.
• Keep an emergency plan ready for leaks and fires, with shutdown valves, communication and rescue. Practice it.

Hot tapping checklist

• Hot tapping is appropriate for the contents, pressure and pipe wall condition
• A written, engineered procedure and a qualified welding procedure are in place
• The hot work and hot tap permit is signed and an MOC review is done if needed
• Gas monitoring, fire watch, extinguishers and FR PPE are in place
• The crew had a pre-job meeting and knows the emergency shutdown plan

Last updated: October 5, 2026