Hot Tap Installation Considerations
By Vincent A. Carucci
Detailed procedures must be used for the fabrication and installation of
hot taps. The following highlights several items that must be considered
when developing site-specific procedures.
- All welders and welding procedures must be qualified to meet all
applicable ASME B31.3 requirements for piping systems, ASME Section
VIII requirements for pressure vessels, and API-653 requirements for
aboveground atmospheric storage tanks.
- Use full penetration welds for the hot tap nozzle.
- Ensure that weld metal does not project past the nozzle inside
diameter. Otherwise, this could impede removal of the coupon.
- Do not weld over known thin areas, material with laminations, or
in areas where temporary repairs have been made which may be adversely
affected by the hot tap welding and cutting.
- Carbon steel welds made at temperatures below 40°F (4°C) may
require special preheat and welding procedures to prevent moisture,
high weld metal temperature quench rates, and potential weld cracking.
Alloy steel welds may require specific minimum preheat temperatures.
- For double welded joints, perform MT or PT inspection of the back
side of the root pass before backwelding.
- Specify appropriate welding electrode type and size, amperage,
weld sequencing, and preheat.
- Protect the welding area from strong winds, blowing dirt, snow, or
- Consider doing a practice session on a full size “mock up” in
certain situations (e.g., when appropriate flow rates and welding
procedures must be established).
- Consider weld overlaying the surface prior to attaching a nozzle
to pipe that is fabricated from plate that is 3/4 in. (19 mm) or
heavier to prevent lamellar tearing of the header pipe.
- Proper attachment and alignment of the hot tap fitting to the pipe
is vital to achieving a successful hot tap. Otherwise, the cutter may
damage the pipe wall.
- Full encirclement fittings require special care during nozzle
installation. The fit should be checked before installation, and care
should be taken to ensure that the matched ends are correctly
- For bolted fittings, thoroughly clean all contact surfaces and
grind off any high spots to leave a smooth surface for attaching the
Use of the above requirements, in conjunction with site and