How to Modify Pipework Without Draining the System

HOW TO MODIFY PIPEWORK WITHOUT DRAINING THE SYSTEM

Modifying an active piping system does not always require draining the entire network. In many mechanical, utility, district energy, and industrial systems, live-work methods can be used to create new connections, establish temporary isolation points, replace valves, or support repairs while the larger system remains in operation.

Two of the most common methods are hot tapping and line stopping. Hot tapping creates a new opening or branch connection on an active line. Line stopping uses a temporary plugging device to isolate a selected section after access points have been established. Depending on the project, these methods can be used independently or together.

WHY AVOID DRAINING A PIPING SYSTEM?

A conventional shutdown can involve much more than stopping flow. It may require system isolation, drain-down, product transfer, temporary storage, refill, air removal, water-treatment adjustment, pressure restoration, balancing, restart, recommissioning, and coordination with building operations or production.

For large buildings, district energy networks, industrial plants, data centres, hospitals, commercial facilities, and other critical systems, those activities can create significant operational disruption. Live-system methods can provide another option when the piping and operating conditions are suitable.

METHOD 1: HOT TAPPING

A hot tap is a controlled method of creating a new connection on a live, pressurized piping system. A branch fitting and isolation valve are installed on the existing pipe. A hot tapping machine is mounted to the valve and aligned with the proposed connection.

The valve is opened and the cutter advances through the branch fitting into the active pipe. A circular section of the existing pipe wall is removed and retained by the tapping assembly. This removed section is commonly called the coupon.

Once the cut is complete, the cutter and coupon are retracted through the valve. The valve can then be closed, allowing the tapping machine to be removed while the existing system remains contained.

WHEN IS A HOT TAP USED?

Hot tapping can support system expansion, new branch connections, new equipment connections, future tie-in points, bypass connections, access points for line stopping, valves, and certain instrumentation connections.

METHOD 2: LINE STOPPING

Line stopping is used when a section of active piping must be temporarily isolated. Unlike a hot tap, which creates a connection, a line stop inserts a temporary stopping head or plugging device into the pipe to control flow through a selected section.

The line stopping equipment typically accesses the pipe through fittings and valves installed using hot tapping techniques. Once the stopping head is positioned, the targeted section can be isolated so repair, replacement, or modification work can be completed.

WHEN IS LINE STOPPING USED?

Typical applications include failed valve replacement, repair of a leaking pipe section, replacement of a piping component, controlled isolation for an upgrade, and maintenance where the larger connected system needs to remain operating.

HOW HOT TAPPING AND LINE STOPPING WORK TOGETHER

Hot tapping and line stopping are often part of the same project. A typical sequence is to install the required fittings, perform the hot taps, mount the line stopping equipment, insert the stopping heads, establish temporary isolation, complete the repair or modification, remove the line stops, and return the system to normal operation.

In this arrangement, hot tapping creates the access needed for the line stop. The line stop then creates the temporary isolation required to perform the work.

WHEN IS A BYPASS REQUIRED?

Some systems cannot tolerate an interruption in flow even while a section is temporarily isolated. In these situations, a temporary bypass may be installed. Hot taps can establish the bypass connections before the line stops are inserted, allowing flow to continue around the isolated section.

EXAMPLE: VALVE REPLACEMENT WITHOUT FULL DRAIN-DOWN

A common application for line stopping is replacement of a valve that no longer provides reliable isolation. Without live-system methods, a facility may need to shut down and drain a much larger section of piping. With a properly planned line stop, temporary isolation can be established around the valve so the affected section can be worked on while the wider system remains available.

EXAMPLE: ADDING A NEW CONNECTION WITHOUT SHUTDOWN

If the project only requires a new branch connection, a line stop may not be necessary. A hot tap can create the new opening directly on the active pipe.

WellFab has completed live hot tap work including a 24-inch hot tap on an active pipeline, a 14-inch live hot tap on a glycol storage tank, a 10-inch Tonisco valve solution, two 8-inch cooling hot taps, 6-inch branch connections, a 3-inch turnkey nitrogen hot tap, and PVC hot tapping work.

WHAT INFORMATION IS NEEDED BEFORE LIVE PIPEWORK MODIFICATION?

Useful project information includes existing pipe size, pipe material, wall thickness, operating pressure, operating temperature, system contents, pipe condition, proposed branch size, required isolation length, valve and fitting requirements, working clearance, shutdown limitations, flow-continuity requirements, photographs, drawings, and site access constraints.

For line stopping projects, the required isolation arrangement is especially important because the number and position of stopping points depend on what section must be isolated and whether a bypass is required.

PLANNING THE LIVE WORK

Hot tapping and line stopping should be treated as controlled field operations, not simply as mechanical connections. The work plan should consider system condition, operating parameters, fitting compatibility, valve selection, equipment capacity, clearance, equipment support, cutting sequence, coupon recovery, line-stop placement, bypass requirements, pressure monitoring, restoration, and QA/QC documentation.

HOT TAP OR LINE STOP: WHICH METHOD IS NEEDED?

If the project requires a new connection, hot tapping may be the primary method. If the project requires temporary isolation of an existing section, line stopping may be required. If the project needs both access and isolation, the two methods can be used together. If flow must continue around the isolated section, a bypass may also be required.

OTHER WAYS TO REDUCE SYSTEM DRAIN-DOWN

For certain pipe sizes, materials, fluids, and operating conditions, pipe freezing may also be considered. A controlled freeze creates a temporary ice plug inside the pipe and can provide isolation without installing a permanent fitting. Suitability should be reviewed separately for each application.

WHY LIVE-SYSTEM WORK CAN REDUCE PROJECT DISRUPTION

Avoiding a full drain-down can reduce outage coordination, fluid handling, refill time, air removal, treatment recovery, restart procedures, recommissioning, disruption to connected equipment, and impact on building occupants or operations.

LIVE-SYSTEM SUPPORT FROM WELLFAB

The correct method depends on what the project needs to accomplish. A new branch connection, failed valve, leaking section, system expansion, bypass requirement, or equipment modification can each require a different arrangement.

WellFab supports hot tapping and line stopping projects from initial review through field execution, including connection planning, fitting and valve requirements, equipment selection, live cutting, coupon recovery, temporary isolation, bypass planning, system monitoring, and final restoration.