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Wellhead valve repair using a hot tapping machine


Following our recent infographic blog post coveringAPI gate valves, this time we take a look at the VHT range of valve hot tapping machines, which are designed for oil and gas high pressure maintenance operations, such as drilling through seized slab gate valves.

The VHT range comprises of 5 high pressure hot tapping machines, each adapted to operate with the extended stroke required for reaching through a wellhead Christmas tree assembly. 

Another way in which they differ from conventional hot tapping machines is that the cutter sizes used are normally smaller and not much greater than the spindle diameter, which can be 1”, 1.5”, or 3” diameter.

Features of the VHT valve hot tapping range

  • High torque transfer with smooth power delivery
  • Geared mechanical depth display
  • Helical geared drive
  • Counter display shows depth of travel in mm.
  • Constant seal & pressure monitoring
  • Feed dump valve protects against mechanical damage, eliminating the possibility of the machine continuing to feed whilst the cutter is in a stalled position
Technical details of the VHT hot tapping range
  •  5 machines with varying stroke from 38” to 160”
  •  Pressure capacity of 5000 and 10,000 p.s.i
  • Can withstand temperatures of 110°C (option available for 120°C)
  • Spindle RPM from 5 to 40
  •  Power output: 5hp (3.73kw)
  •  Spindle diameters: 1”, 1.5” and 3”
  • Manual Feed rate 3mm per revolution
  • Auto feed rate 0 -20mm per minute

With an isolation valve installed, the procedure is as follows:
  • Install the VHT machine and flange adaptor, always carry out this process with the valve shut. Ensure the cutter and the pilot does not interfere with valve operation. Tighten the bolts keeping the flanges parallel. 
  • Install the bleeder valve and the pressure gauge.
  •  If you need to monitor the seal pressure integrity, gauges can be installed into the pressure seal ports. If no monitoring is required, then the blanking plugs should be left inserted. A hydrostatic seal can be installed by pumping grease between the seals.
Pressure Testing
  • Using the bleeder valve, a pressure test of the of the VHT machine, fitting, valve and flange adaptor is performed, to confirm there are no leaks and the system is safe to operate.
  • Once a successful pressure test has been performed the bleeder valve is closed.
  • Using the hand wheel, the boring bar is extended close to the component to be cut.
  • Next, the cutter rotation is started. Checking the flow rate will indicate any problems occurring with the cutter rotation. The system is aided by an internally balanced system, enabling a smooth cutting operation under high pressure.
  • The auto feed is engaged and the feed motor started. Once the cutter has penetrated the pipe, the gauge should show the pressure that is contained in the system.
  • After the required cutting has finished, the bleeder valve can be opened to purge the pressure from the machine. (When doing this, the operator should make sure this is piped away from the working area).

After use

Due to the highly corrosive nature of some Hot Tapping substances it is important that the VHT Pressure Cylinder is flushed if the time between tapping operations exceeds 12 hours. This helps to prevent corrosion of the driveshaft assembly and to prolong the working life of the machine.

Download the Hot Tapping Buyers Guide, or if you would like to speak to our technical team you can get in touch here.

 Download the Mirage Machines Hot Tapping and Line Stopping Buyers Guide

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