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Hot tapping in subsea environments: overview and considerations

Posted by Alan Hillier on Jun 21, 2016 11:00:00 AM


    

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Above: The Mirage CHT1000-SSSW subsea hot tapping machine 

Hot tapping challenges

Although the hot tapping has process has been carried out routinely by pipeline engineers for many decades, each project presents different obstacles to be overcome such as:

  • Location of pipeline – surface or subsea.
  • Pipeline size, wall thickness and materials vary.
  • Pipeline is under pressure, safety and containment of product essential.
  • Pipeline product, flow and pressures vary.
  • Variations in project scope – basic hot tap branch, angle, horizontal, temporary and permanent bypass, tank taps, valve recovery through isolation and completion.
  • Cut size can vary from ½” through to 60” diameter.
  • Pipeline stresses when designing the fitting – weldolet, split tee or bolted, tapping or line stop.

Subsea hot tapping: additional difficulties

In addition to the above, hot tapping in subsea situations adds further difficulties to an already complicated process:

  • The industry drive to ROV deployable solutions.
  • The pipeline is usually under higher pressure.
  • Pipeline size, wall thickness and materials vary, along with external condition and coatings including; Asphalt enamel, Concrete weight coating, Fusion bonded epoxy and 3 layer polypropylene.
  • Pipeline location – associated handling tools and installing the fitting – mechanical or use of hyperbaric welding

Hot tapping machine improvements

Hot tapping machine design has not fundamentally changed since the 1950’s, with just minor improvements made to a configuration that worked. However, pipeline materials, product and pressures have evolved requiring a different approach that enables;

  • Higher pressure capability – hot tap and wellhead drilling capability
  • Internally pressure balanced to combat increased the cutting forces seen at higher pressures
  • Improvement in the cutting process and time taken to complete the process through product design, this in turn improves the reliability of the cut

Each of the above has influenced the development of Mirage’s subsea hot tapping equipment; including the new CHT1000-SSSW subsea hot tapping machine, which has been designed to hot tap into live pipelines to a depth of 300m sub-sea. The machine has a working pressure capacity of 5000 psi and can hot tap from 3 – 12”.

Features of the CHT1000-SSSW subsea hot tapping machine include:

  • Helical geared high torque drive
  • Drive as close to cutter as possible to optimise cutting performance
  • Internally pressure balanced system for high working pressures
  • Auto variable feed gearbox and motor to suit pipeline material
  • Geared mechanical depth display
  • Constant seal & pressure monitoring

To find out more about this new machine please get in touch.

Isolating subsea pipeline

As with surface hot tapping, the pipeline should be isolated before any cutting commences and the process in subsea environments is very different.“Piggable” tools provide pipeline pressure isolation, allowing repairs, maintenance or modification of a pressurized pipeline in a safe, convenient and cost effective manner.

These tools offer a remotely operated (through-ground, through-wall communication), solution, allowing hydrotesting/maintenance/repair of the pipeline without purging or de-pressurizing.

The benefits include:

  • Configurable with single or Double Block and bleed capability.
  • No pipeline excavation required.
  • Remotely operated with advanced through wall communications.
  • No fitting, valve or welding required.
  • Fail safe seal set and pressure monitoring.

Operation of subsea isolation tool

A typical tool has three main components: the control module, seal module and pig module. These are used for single isolation or combined to provide double block and bleed isolation and remotely operated via a control station.

The process

  • Tool is launched through a pig into position
  • Tool is designed to be easily piggable and work with 1.5D bends and tracked at long range using ELF signal technology
  • The seals are then set remotely using wedges under a set of grips that actuate radially against the pipe wall
  • The packer is then actuated causing the seal to expand the seal engages with the pipe and creates a pressure barrier
  • Once set greater differential pressure further contracts the tool which intensifies the set and seal pressure

Download the Subsea Case Study Pack

Topics: Subsea, hot tapping

   

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