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Guide to pipe cutting and removing flanges with a split frame cutter


How split frame cutters are used

Split frame cutters, or ‘clam shell cutters’ as they are often called, are frequently used in the oil, gas, and petrochemical industries for parting, bevelling and counter-boring large diameter pipes. 


The commonest application for split frame cutters is during the construction of oil and gas pipelines. Pipe cutting or bevelling may be needed as preparation for flanges before welding onto a pipe. New flanges can also be damaged in transit, or may not meet the correct specification, in these situations repair is sometimes possible using a flange facing machine, however in some instances the most cost effective solution is often to remove the flange entirely and replace it with a new one).

Aside from pipeline construction, other applications for split frame cutters include maintenance and alterations to an existing pipelines. They can also be used for cutting through casings such as master valves used on oil wellheads.


How split frame cutters work

The machines consists of one stationary and one rotating ring; both of which consist of two halves which are assembled for installation onto continuous pipelines. The machine assembly incorporates the motor housing (which can be powered hydraulically or pneumatically), the pinion gear and the clamping feet used for attaching the machine to the pipeline. The rotating assembly includes the cutting tools which rotate around the axis of the stationary main body.

The feed is determined by a striker wheel and peg trip assembly. The two tool posts normally have different sized tool inserts, one to act as the lead cutter, the second to widen the cut.

You can see an animated demonstration of a split frame machine working in our YouTube video.

split-frame-cutter-mounting-options.pngSuitable materials

The robust machine construction and tooling results in machines capable of cutting and bevelling a wide range of materials, including high performance materials such as ‘Super Duplex’, Carbon Steel, Hastelloy and Incolloy.

Feed rates

As mentioned above, the feed is normally determined by a striking wheel at a rate of 0.05mm per hit. If a faster feed rate is required it is possible to fit up to 4 more pegs to the machine.



How to choose the right split frame cutter

Selecting the right machine for the project is simply based upon the diameter of the pipe to be cut or bevelled. The Mirage range of machines cover pipe diameters from just 2 inches all the way up to 48 inches.

Working in tight spaces

Fortunately, even the largest machines can fit into tight spots, but you should always make sure there is sufficient clearance to allow for the machine and any supporting equipment. One feature which helps is that the motor housings can be mounted either horizontally or vertically to suit the space available.


Typical accessories include extended heavy duty tool slides, front drive adapters allowing the motor to be fixed to the front of the machine and counter-boring attachments that can generate a variety of tapered and/or parallel counter-bores.

What are the major safety considerations?

  • The area surrounding where the machine is to be installed should be surveyed, taking particular note of work space constraints, machine operating clearances and the need for scaffolding to support equipment or workers.
  • The machine should be mounted on a work piece that will not collapse or fall when the machine completes its cut. The work piece should be either small enough to not cause any harm when it falls, or should be supported sufficiently to prevent it from falling when the cut is complete.
  • The operator of the machine should be fully conversant and trained in use of the equipment.
  • When using a split frame cutter, personal protection equipment will be needed including; eye protection, ear protection, hard hats, protective gloves footwear and overalls.
  • Make sure you have a plan for containment of cutting debris and coolant used during operation.

Getting the machine into position

  • Machines exceeding your working safety lifting limits must be lifted using suitable equipment. Large machines are provided with lifting eye bolts in main body of the machine to aid lifting. You should use at least two lifting eye bolts whether you are lifting the machine as a whole or in halves.
  • When lifting the machine in halves always ensure that the ‘stab pins’ are located to prevent the internal gear from falling out. These should remain in place until both halves of the machine are securely fixed in place.
  • It is a good idea to remove the motor & trip assembly before lifting to prevent them being damaged.
  • Select the most suitable range of ‘Jaw Extensions’ to allow the machine to clamp to the outside diameter of the pipe. The largest, useable set of jaws should be selected to allow the machine to be mounted as rigidly as possible.

Using the machines

  • Both tool posts should be advanced manually until they touch the work piece. This is done by turning the striker wheel counter clockwise.
  • Both tool posts are retracted ½ to 1 full turn back by turning the striker wheel clockwise.
  • The machine should be checked to ensure that it spins freely.
  • Turn on the air supply & push the trigger on the motor to start rotating the tool posts.
  • Engage the trip assembly by pulling the lever up. The cutting tools should now start feeding in, towards the work piece.
  • Adjust the pneumatic motor controls to maintain optimum power & torque during the cutting operation. If the machine is struggling to cut through the pipe/work piece then the trip should be disengaged momentarily until the machine has regained speed.
  • It is recommended that some form of cutting fluid or coolant is applied to the work piece during cutting operations

 Is a split frame cutter right for your project? -  Get in touch with us or download our Buyer’s Guide to pipe and casing cutting.

 Disclaimer: The purpose of this blog post is not intended as training but for informational purposes but as an introductory guide to how and why these machines are used. Each Mirage machine delivered to a customer is accompanied by a manual including full operating details.

Free download: Pipe and Casing cutting on-site machining buyer guide

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