Hot Tap Inspection Considerations
By Vincent A. Carucci
Careful inspection is essential to achieving a successful hot tap. This
inspection includes the pipe or equipment being hot tapped, the hot tap
equipment, and the hot tap itself. Inspection guidelines are highlighted
below and may be used to develop site and application specific inspection
- Examine the pipe or equipment in the immediate area of a proposed
hot tap using UT to check for thin areas and laminations, MT or PT to
check for surface defects, and UT if hydrogen attack is suspected.
- If pitting, cracking, or fissuring may be present, check the
material by radiography, UT, dye penetrant, or other appropriate
- 100% radiograph any longitudinal weld seams that will be welded
over or covered by the hot tap components.
- If other forms of degradation could have occurred that would
significantly affect material properties, then determine its extent
and confirm that the material condition is safe.
- Inspect components prior to installation, and confirm that they
are the proper material, size, rating, etc.
- Inspect the welding electrodes for correct material and condition,
and review the welding procedure.
- Review any precautions to be followed before or during welding and
- Confirm that the correct location has been selected for the hot
- Perform a high-pressure seat leakage test on the hot tap valve no
more than 24 hours before the hot tap. The allowable leakage should be
zero. This is a critical step since if the valve leaks after the hot
tap cut is made, the hot tap machine cannot be removed without taking
the system out of service.
- Inspect the welded assembly for compliance with specified flange
alignment tolerances and clearances.
- Confirm that the hot tap valve and machine are suitable for the
service conditions. Witness the pressure tests of the valve and
- After welding the nozzle and before adding any reinforcement,
visually and 100% PT or MT inspect the completed nozzle-to-pipe (or
equipment) and nozzle-to-flange welds.
- Witness the pressure test of the nozzle assembly.
- Measure the weld hardness if required for particular materials
(e.g., 1-1/4 Cr-1/2 Mo), and confirm that it is acceptable.
- Visually, and PT or MT inspect the reinforcing pad welds. Witness
the reinforcing pad leak test.
- Verify alignment of the hot tap assembly at each step of the
attachment procedure. This includes the nozzle, valve, and hot tap
- Inspect the coupon after it is removed to evaluate the extent of
header internal corrosion and verify wall thickness. This is useful
information to help plan future inspection needs and intervals for the
system based on the amount of corrosion that has occurred.