When working on a decommissioning project in the oil, gas and energy sectors, sooner or later you’ll be faced with the challenge of cutting through large scale tubular items such as casings, platform legs or piles.
So how can this be done? and what equipment is available?
The two obvious contenders are portable band saws and portable diamond wire saws. Both types are robust enough to carry out offshore heavy duty cutting tasks - but to make your selection you'll need to understand the key differences between these two powerful on-site machines.
Let’s take a look at both options:
PORTABLE BAND SAWS
These are heavy duty and bigger versions of the saws that you may have seen in carpentry workshops – these are in a portable format and are primarily designed for cutting metals. Mirage offers three sizes of machine; the BS924 for cutting diameters up to 24”, the BS1636 for up to 36” and the BS3248 for up to 48” diameter.
Subsea or Topside?
Mirage Portable Band Saws are mostly used for topside cold cutting applications, however they can also can be used for occasional subsea use such as severing wellheads.
Band Saws are secured into position using a swing clamp which is operated manually.
Performance Under Load
No matter how powerful and durable the band saw blades are, they'll only cut effectively without any compressive force on them. So if your intention is to cut through a vertical pile or casing, you’ll need to support it from above - taking the load off the blade as the cut progresses. A useful machine tool for creating lift holes to do this is the Mirage double drill unit.
Compared with diamond wire saws, the need to replace the looped band saw blades is much less frequent. This means the band saw is a good choice of machine on projects where retrieving a saw to change a diamond wire rope would result in long periods of inactive cutting time. (e.g when cutting subsea).
The portable band saw range covers diameters from 9” all the way up to 48”. The capacity of each machine is as follows;
DIAMOND WIRE SAWS
As with the band saw range, Mirage Diamond Wire Saws use a pulley system that incorporates a hydraulically powered main drive wheel. Instead of using a metal looped blade with teeth, the cutting is carried out using a looped steel rope with very small diamonds attached to the outside surface.
Subsea or Topside?
Mirage Diamond Wire Saws are designed for underwater use, however they can also be used topside with a coolant, (but not considered to be a cold cutting method).
When it comes to securing the saw onto the workpiece, diamond wire saws have the edge over band saws – all thanks to their two remotely operated hydraulic clamping jaws which are controlled from the ROV hydraulics, or up on deck using a hydraulic control panel.
Performance Under Load
This is another the area in which the diamond wire saw is the clear winner. With the wire rope being covered in diamonds around its diameter it is capable of resisting compressive forces and cutting in all directions simultaneously
Replacing Diamond Wire Rope
If you are going to make many cuts in a subsea environment, the diamond wire rope should be more or less considered as ‘consumable’. You’ll need replacement ropes with you on location, and should allocate time in your project to retrieve the saw for replacement. The process of adding a new rope is pretty straightforward, the time consuming part is retrieving the machine from near the sea bed.
At Mirage we’re often asked how many cuts can be made with a single rope and the answer is ‘it depends’. The type of materials to be cut and how the saw will be used will impact upon the life of each rope. As an example, during this demanding pipeline removal project a total of 22 cuts were made, with each rope averaging 4 cuts through the 12” diameter super duplex pipe.
You may have seen the diamond rope cutting method used in quarries for cutting large marble blocks and other rocks. So obviously the potential is there for a purpose designed machine to cut through huge diameters in difficult environments. Mirage has taken this technology and applied it to a portable, robust machine that’s easy to install in difficult environments. The resulting product range comprises of the following sizes;
Manipulator Diamond Wire Saws
In addition to the four Diamond Wire saw models described above, Mirage also manufactures two different sized ‘Manipulator Saws’. These are smaller and simpler versions of the standard diamond wire saws - but without the clamping mechanism. This format makes them quicker to deploy on small cutting jobs up to 15” in diameter, with one example application being the cutting of mooring chains.
Summary: Portable Band Saw and Portable Diamond Wire Saw - At a Glance Comparison