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The continuous development of the centreline multidiameter suspension system (CMSS). Designed and built by FTL Technology at their premises in Leeds.

The benefits of a true centreline running multidiameter pipeline pig

Centreline running
In repeated testing it has been found that a CMSS suspension will run within 0.2% of centre line ( 1.0-2.0mm in a 42" flow line). This performance is maintained even when negotiating pipeline features such as small diameter bends. "Nose Diving", due to the weight of the pig, when running horizontally, can be a problem, in long dry pipeline runs. The force generated by the suspension system is such that it is greater than the weight of the pig unit. By fitting a pair of CMSS modules a stable horizontal platform can be obtained.

Low delta P drive pressure
CMSS runs on centreline giving a benefit to the pig manufacturer and the operator in that the oversize on the diameter of the drive discs, (previously made generously oversize in diameter to compensate for wear in long dry gas pipeline runs) is now reduced.

As there is less material in contact with the pipeline wall during the pigs journey the friction generated between drive disc and pipe wall is now much reduced. Test conducted in the Statoil's K lab show that a drive pressure differential of approximately 0,5bar was sufficient to move the unit smoothly along the pipe.

Even wear of drive discs
The added bonus of even wear on drive discs is shown in operation. By offsetting the longitudinal axis of the suspension arms by a small amount the pig assembly is encouraged to rotate. This gives two benefits:

• the drive disks are worn evenly
• each wheel experiences an amount of zero load bearing when at top dead centre

Ability to traverse dual diameter vertical "Y" pieces
CMSS runs at or near centre. Because all suspension arms are interconnected, the suspension can maintain its pipe diameter geometry with only two of the eight arms in touch with the pipe wall. This feature offers an additional benefit to operators in that should off-takes not be fully barred then there is little fear of losing a wheel and suspension arm as is the case on some independently sprung system where the suspension arms are not connected together.

Wheel assembly tested for operational performance on weld bead simulation
To prove the operational performance of the wheel assembly (tyre/hub/bearings/stub shaft/seals/lubricants) with regard to load, distance and durability/bond integrity of the tyre material a purpose built testing facility has been developed by FTL Technology.The insides of pipelines are normally in good condition. However, there is one regular surface defect caused by the weld bead.

The FTL test rig simulates the inside of the gas pipe line. But after the wheel has run for 12 metres length a 6mm high (worst case) weld bead can be introduced into the path of the loaded wheel assembly. Wheel assembly loading is affected by calibrated compression springs which are set to simulate the mean load exerted on the wheels of the CMSS system when mounted on the vehicle for which the wheel assembly is intended.

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Further Information
For further information relating to any of the above products, please contact Tony Snowdon on 0113 252 1061 or e-mail tonys@ftltech.co.uk