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How to remove subsea piles, strings or members from below the mud line

Posted by Alan Hillier on Feb 23, 2016 8:27:00 AM


    

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The decommissioning of subsea oil and gas installations presents many difficult challenges, each needing to be overcome safely, within budget and without causing harm to the environment.

One example of these problems is the removal of piles or ‘strings’, which may have been used for structural purposes, or as the drill string within a wellhead for transporting the oil from beneath the sea bed.

A product which makes this achievable is a ‘single string cutter’. This particular product is designed for cutting through cylindrical walls made from a ‘single’ material.

This tool is capable of severing a single string of casing, conductor or pile using efficient cutting technology, so let’s take a look at how it works and understand the benefits of using this machine.

How single string cutters work

Unlike other cutting machines such as band saws and diamond wire saws, a single string cutter is designed to fit inside the shaft needing to be severed. A cutter attached to a spindle cuts through the wall thickness and then follows a path around the diameter of the shaft, returning to the starting position to complete the cut.

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Step by step process

  • The machine is lowered from above the surface until it is positioned at the required depth.
  • The machine is secured using the integrated clamping jaws.
  • A mapping roller is rotated to verify the internal size/condition of the pile.
  • The cutter’s spindle is rotated and radial out feed is engaged.
  • The out feed hits the pre-set stop, then rotation for the cut path is engaged.
  • Wedges are deployed into the cut at pre-set intervals, to eliminate the risk of the cutter being trapped.
  • Using the verification software provided, pressure readings show the status of operations including; clamping, feed, follower cutter, wedge system and completion of the cut.
  • When rotation is complete the clamping jaws are released and the machine is retrieved.
  • The severed pile can now be lifted and removed.

 

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Above: Readings show the status of clamping, feed, follower cutter, wedge system and completion of the cut.

 

The benefits of using the SSC2448 Single String Cutter

  • Fast and effective mechanical cold cutting, with feed rates 1” per minute (based on 1 ½” wall thickness.
  • Minimal deck space is needed allowing the machine to be deployed from the back of a small cost-effective vessel.
  • Comprehensive cut monitoring and verification system verifies the blade position, cut depth and final severance.
  • Guaranteed mechanical circular cut path
  • Automated cut wedging system for cut width retention (maintains stability and prevents blade from seizing under load).
  • The machine features out of round compensation.

Single String Cutter: Technical Details

technical_details.pngThe SSC2448 single string cutter is available for rental, and can also be provided with a Mirage machinist and an optional hydraulic power pack. It is purpose designed to cut through single material walls of varying materials. For cutting through more complex composite items there are a wide range suitable decommissioning tools available for rental or purchase.

 If you need any advice for a machining project please click here to email us. You are also welcome to download our Downloading our Decommissioning Tools Buyer’s Guide in pdf format.

Download Decommissioning Buyer's Guide

Topics: Subsea, platform decommissioning

   

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