What Is a Hot Tap?

Quick Answer

A hot tap is the procedure of cutting into a live, pressurized pipeline to create a branch connection without shutting down the pipeline or depressurizing the system. The operation uses a specialized hot tapping machine that drills or cuts through the pipe wall while maintaining containment of the pipeline contents through a valve assembly mounted on a welded fitting.

Hot tapping allows pipeline operators to add branch connections, install bypass lines, install pig launcher/receiver connections, or tie in new pipelines without interrupting product flow or revenue.

Hot Tapping Equipment

Component	Function
Split tee or weldolet	Welded to the pipe; provides the branch connection
Isolation valve	Full-bore gate or ball valve mounted on the fitting
Hot tapping machine	Bolted to the valve; contains the cutter and pressure housing
Pilot drill + cutter	Hole saw or annular cutter that penetrates the pipe wall
Coupon retainer	Holds the cut-out disc (coupon) to prevent it from falling into the pipeline
Pressure housing	Sealed chamber above the valve that contains the cutter during operation

Hot Tap Procedure

Step	Activity
1	Engineering assessment: verify pipe condition, wall thickness, material
2	Weld split tee or weldolet to live pipeline (qualified WPS required)
3	Install isolation valve on the branch
4	Pressure test the welded connection and valve assembly
5	Bolt hot tapping machine onto valve
6	Open valve, advance cutter through the valve into the pipe wall
7	Cut through full pipe wall thickness
8	Retract cutter with coupon, close valve
9	Remove hot tapping machine
10	Connect new branch piping to the valve

Safety and Engineering Requirements

Requirement	Criteria
Minimum wall thickness	Verified by UT (must exceed design minimum + corrosion allowance)
Pipe material	Known specification, weldable (CE < 0.43 preferred)
Pipeline pressure (during tap)	Typically reduced to 80% MAOP or less
Welding on live pipeline	Qualified WPS for in-service welding (API 1104 Appendix B)
Burnthrough risk	Wall thickness must be > 6.4 mm (1/4 in) for safe in-service welding
Hydrogen cracking	Low-hydrogen electrodes (E7018 or E8018) mandatory
Preheat	Per WPS and CE of pipe material
NDT on weld	100% MT or PT on fillet welds after cooling
Flow conditions	Minimum flow maintained to prevent heat buildup

Hot Tap Size Limits

Pipeline Size	Max Hot Tap Branch Size	Notes
NPS 4	NPS 2	Limited by fitting availability
NPS 6-8	NPS 4	Standard practice
NPS 10-16	NPS 8	Common for pipeline tie-ins
NPS 20-36	NPS 12-16	Large-diameter tapping machines
NPS 42-56	NPS 20-24	Specialized equipment required

The branch size is typically limited to 50-75% of the header diameter to maintain structural integrity and avoid excessive stress concentration at the connection.

Standards and Codes

Standard	Scope
API 2201	Safe hot tapping practices in the petroleum industry
API 1104 Appendix B	In-service welding on pipelines
ASME B31.4 / B31.8	Pipeline design (provisions for hot taps)
ASME PCC-2	Repair of pressure equipment (hot tap guidelines)
CSA Z662	Oil and gas pipeline systems (Canadian, includes hot tap provisions)

Pro Tip

The most critical safety consideration for hot tapping is preventing burnthrough during in-service welding. For pipe wall thicknesses below 6.4 mm, the risk of the welding arc melting through the remaining wall is significant, especially on liquid pipelines where the flowing product removes heat from the weld area. For thin-wall pipe, use controlled low heat input, monitor the cooling rate from the flowing product, and consider using full-encirclement fittings (sleeve tees) that do not require fillet welds directly on the pipe wall.

When Hot Tapping Is Not Permitted

• Pipe wall thickness below safe in-service welding limits (< 5 mm)
• Unknown or unweldable pipe material
• Pipe with active corrosion or erosion damage at the tap location
• Lines containing oxygen, chlorine, or unstable chemicals
• Pipeline operating above its safe working pressure
• When the pipeline contents are incompatible with welding heat (explosives, peroxides)

For removing sections of live pipeline without a hot tap, see the cold cut method.

Read the full guide to pipe types