A multi-diameter pipeline pigging solution, designed to run on the pipe centreline. VariPig provides support in all diameters including large diameter pipeline changes

To meet the demands of pigging increasingly complex pipeline systems, there is a drive to provide pipeline pigs with increased flexibility, adaptability, operational repeatability and improved efficiency.

FTL developed the multi-diameter capable VariPig to meet these increased challenges and the modular system now has a proven track record of successful project completion in ‘difficult to pig’ pipelines.

Varipig is the name given to our multi-diameter capable pigging system (Varipig is a patented system).

Typically two suspension arm modules are coupled together or a single offset suspension arm module is created to build a Varipig for a given application. 

The basic suspension system comprises a number of suspension arms connected to a central piston, so that when one wheel arm deflects, the other arms will also deflect. 

A spring loaded piston forces the suspension arms outward. 

The basic principle of operation is that the combined total spring force acting on the pistons is greater than the weight of the pig therefore the pig rides on its true geometrical centreline.

Any pipeline feature causing the pig to deviate from the pipeline centreline is immediately countered by the restoring force thereby restoring centreline running.

Repeated testing and field experience has shown that the Varipig suspension system will run within 0.2% of pipe centreline.

The Varipig suspension system is the key to optimising any pigging operation due to the removal of typical key pig performance inhibitors:

Drive pressure differential

With pre-commissioning, commissioning and even for operational cleaning having a low differential drive pressure is considered as beneficial.

The contribution to total pig friction (differential pressure across the pig) from the wheeled suspension modules is negligible in all pipeline diameters, as it is merely rolling friction from the wheels.

Changes in diameter

The changes in a multi- diameter pipeline require careful analysis when looking into seal design for the diameter changes. 

When operating in the larger diameter pipeline the seal needs to provide an effective seal (e.g. for dewatering) but must then be able to fold down when entering the smaller diameter pipeline without inhibiting performance.

Drive discs can be sized to give the desired benefit for a pigging operation by minimising the need to oversize to compensate for negotiating bends and pipeline features.

Distance to Travel

One of the main objectives when looking at pigging long distances is seal wear both in constant bore and multi diameter pipelines.

The functional discs will have controlled wear due to induced pig rotation by the suspension which in arduous or long operational runs gives optimum performance.

Utilisation and repeatability

The vehicles can be quickly re-configured around the basic Varipig platform to perform multiple roles in a single run.

The same vehicle can be used for different functions as the suspension can be tuned to account for different load carrying requirements.

Previous Experiences

The Varipig system has been shown to provide both a stable centralised rotating platform, to allow optimised seal design/reduce seal wear, as well as requiring a low drive pressure. The Varipig system has been successfully deployed within dual/multi-diameter pipeline systems and over long operational distances. 

  • Oil & Gas
  • New deep water
  • Offshore
  • Long export lines
  • Duel or multi-diameter

VariPig was designed and patented as a direct result of the pipeline pig functional requirements for the Statoil Asgard Pipeline RFO commissioning project in 1998. Early on in the design procedure for VariPig, it became apparent that a revolutionary approach had to be adopted if the functional requirements were to be met, whilst at the same time upholding FTL’s philosophy.

By applying basic hydraulic cylinder design principals, FTL decided that, contrary to previous designs, the support function of the pig should be completely separate from the sealing and drive function. Due to the expected high rate of wear that the sealing discs would have to withstand, the unprecedented step of mounting the whole unit on a self-supporting and self-centering suspension system was adopted.

The major benefit of VariPig is its ability to run on the pipe centreline in multi-diameter pipelines, allowing the VariPig to provide support in all diameters including large diameter pipeline changes. This centreline running reduces the differential pressure required to propel the VariPig, particularly when passing form large to small diameters.

Running on the pipe centreline allows FTL to optimise the seal disc package design for sizing and seal wear with the contact area of the seal being constant around the pipe. This, coupled with VariPig’s support against the pipe being provided by wheel assemblies, consequently reduces the breakaway and steady state friction and therefore reducing the pressure needed to move the VariPig.

VariPig is particularly suitable in low flow pipelines and pipeline commissioning operations where it facilitates the ability to work with low differential pressures.

  • True centreline running.
  • Typically within 0.2% of pipeline centreline.
  • Utility pigs operate below centreline & have a tendency to nose dive
  • Utility pig discs have to support & seal.
  • Varipig has low differential drive pressure by separation of support & sealing function.
  • Varipig runs on wheels.
  • Utility pig sealing discs large percentage oversize, disc has to support & seal.
  • Varipig reduced drive pressure, can be a major cost saving in long distance & deepwater pipelines
  • Varipig typical straight line drive pressure 0.2 - 0.3 Bar
  • Low friction - Rolling friction of wheels
  • Varipig design of the suspension arms induces controlled pig rotation.
  • Ensures even & consistent sealing disc wear.
  • Utility pigs do not usually have this feature & when combined with the required larger volume of Polyurethane wear can bean issue
  • Varipig has a true multi-diameter capability.
  • With Varipig diameter changes >100% are possible.
  • Other dual / multi-diameter pigs are available but they generally utilise Polyurethane or independent type suspensions.
  • Not as flexible or able to accommodate such large diameter changes.
  • Varipig provides high efficiency & repeatable performance.
  • Experience & results has demonstrated that Varipig will outperform standard utility pigs.
  • Previous dual diameter long distance >700Km dewatering operation Varipig was recorded as being 10 times more efficient that previous dewatering operations using standard pigs.
  • Operator stated that Varipig had provided the most efficient dewatering operation they had ever completed.
  • Varipig should be considered as a reusable asset which following simple infield maintenance movement can then be redeployed.
  • Varipig is adaptable & can be reconfigured for different functions, operational cleaning, dewatering, tow module, etc.
  • Utility pigs are generally single use specific duty & are none adaptable, reduce number of required pigs, cost saving.
  • Varipig can cover several pipeline diameters.
  • Typically standard utility pigs will only cover a single pipeline diameter, reduce number of required pigs, cost saving.

To prove the operational performance of wheel assemblies with regard to operational parameters, FTL has designed purpose made test rigs.

The FTL test rigs simulate the dynamic loads that a wheel would encounter inside a pipeline. When the test drum has rotated, the equivalent of a 12 metre pipe spool, a PLC controlled weld bead can be introduced into the path of the loaded wheel assembly.

Wheel assembly loading is controlled by calibrated compression springs, which are set to replicate the mean load exerted on the wheels by the VariPig system, simulating true wheel loading conditions when installed on the VariPig vehicle.

  • Dual diameter pipelines.
  • Multi diameter pipelines.
  • Complex features – wye pieces, full bore offtakes, bends.
  • Long distance pipelines
  • Keep drive pressure low.
  • Need high efficiency dewatering.
  • Need high efficiency operational cleaning.
  • Operate many different diameter pipelines, Varipig could allow reduced pig fleet.
  • Progressive cleaning.
  • Require pig to fulfil a number of duties.
  • Regular operational cleaning required – reusable asset.
  • Tow module for inspection technologies.

Q - Is VariPig capable of running in multi diameter pipelines?
A - Yes, we have recently run VariPig in a pipeline with a 75% differential in pipeline diameters

Q - Can Varipig run with low drive pressures?
A - Due to the optimised seal disc design and centreline running break away and steady state friction values are very low allowing VariPig to be propelled by low drive pressure

Q - Can VariPig operate in pipelines featuring Tight Bends, Tee’s and Wye’s?
A - Varipig can accommodate all these features especially tight bends

Q - Does VariPig exhibit low disc wear?
A - Due to the optimised seal disc package, rotation in running and good centreline running capability seal disc wear is very low

Q - Is VariPig redeploy able and adaptable to carry other features?
A - VariPig is both redeploy able, and adaptable and can in fact be reconfigured, it is the ultimate customised bespoke pigging solution

FTL employs a full time in-house engineering design team equipped with the latest 3D modelling CAD software. This enables FTL to fully evaluate the suspension geometry prior to manufacture.

FTL has an unrivalled knowledge to offer its customers in solving complex multi-diameter pipeline pigging problems and offer Design and Feasibility studies for problematic projects.

Technical Paper Multi-diameter Pigging in Challenging Applications Technical Paper

"I have known some of the sales and design engineers for 25 years or more. Their level of expertise has been maintained & the help and assistance when we are looking at sealing arrangements is invaluable and prompt. We use FTL products for all our pump assembly sealing requirements for both rotary and dynamic applications associated with oil lubrication and water hydraulics. I have no hesitation in recommending FTL to our customers and contacts when the occasion arises, and there is always good feedback. They have excellent customer facing engineers with a dedication to making sure the customer gets a product that will work - particularly with respect to heavy industry in the UK."

Technical Engineer from a global leader in plunger pump systems