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Unique wire-free lock for compression tube fittings outclasses traditional solution

11th November 2015

Installs in a fraction of the time of a wire lock and is suitable for new or retrofit applications

A unique wire-free device for locking the nuts of two-ferrule compression fittings on instrumentation tubing is now available from the Instrumentation Products Division of Parker Hannifin – the global leader in motion and control technologies. Dubbed WireFree, the patented safety device is constructed almost entirely from 6Mo austenitic stainless steel for enhanced corrosion resistance. It has been developed at the request of a major supplier of instrumentation to the offshore oil and gas industry, which sought a better alternative to wire locking compression tube fittings on deepwater 'Christmas tree' fluid flow assemblies.

Parker’s two-ferrule compression fittings have been used successfully for subsea instrumentation applications for more than 40 years and there is ample field data to show that they provide reliable long-term performance – making locking devices unnecessary. However, as energy companies strive to recover oil and gas from ever deeper offshore locations, the cost of retrieving subsea equipment for routine maintenance, repair or overhaul continues to escalate. In response, some OEMs are starting to fit wire locks to instrumentation tube compression fittings for deep sea applications, primarily to indicate that the fitting is secure and has not been tampered with or undergone any mechanical change since installation. This approach suffers from a number of disadvantages, not the least of which is that wire lock fittings are expensive to install.

Wire locking is a technique that is widely used in the aerospace industry to guard against components such as securing bolts and nuts on tube fittings working loose during service. It involves the use of pre-drilled parts – which cannot easily be retrofitted – and is only suitable for some types of fittings. The wire that is used is normally stainless steel, which is sharp and difficult to manipulate. And in the case of wire-locked compression tube fittings, it is important that the wire is not tensioned in such a way that it could cause the nut to rotate slightly and potentially compromise connection integrity. Correctly installing wire locking consequently demands skill and is time consuming – it can take anywhere between five and 15 minutes per component, depending on accessibility. On a typical subsea Christmas tree containing several hundred instrumentation tube compression fittings this can easily account for tens of hours of extra assembly time.

Parker’s new WireFree locking device is designed as a ‘fit-and-forget’ solution that overcomes all the disadvantages of wire locking. It can be fitted to standard compression fittings on new or existing systems very easily and quickly, without requiring any modification, realignment or disassembly of components. The device is also ideal for replacing existing wire locks during routine MRO (maintenance, repair and overhaul) operations – installers merely need to remove the wire before fitting the new unit.

Available in straight, elbow, tee and cross type configurations, the locking device is initially being offered in a range of sizes for use with tube fittings from 1/4 to 3/4 inch (6 to 20 mm). Parker intends developing other sizes to suit market requirements.

The WireFree locking device is fabricated entirely from corrosion resistant materials to ensure a long, maintenance-free service life and is based on an open form of construction that minimises crevices. It essentially comprises one or more flexible clamp arms with rigid load spreading support plates, depending on configuration, and is supplied pre-assembled as a single-piece part to simplify installation. The support plates incorporate self-retaining M4 socket head cap screws and use Spiralock self-locking thread technology to prevent them working loose under vibration. Both the flexible and rigid components are made from 6Mo stainless steel, while the securing screws are 316 stainless steel.

Parker’s WireFree device for compression fittings can typically be installed in under two minutes – a fraction of the time that it takes to wire lock components. To fully lock a standard 90 degree elbow fitting, for example, the installer simply places the flexible clamp arm around the two compression nuts, inserts a single cap screw through one of the support plates and tightens it to the recommended torque. The device creates a locking force that is about five times greater than wire, without any risk of incorrect tensioning compromising long term connection integrity. It also provides an anti-tamper function, with secure locking clearly indicated by the close proximity of the support plates.

Parker believes that its new WireFree locking device offers an ideal solution for OEMs seeking a more reliable and cost-effective alternative to wire locking instrumentation tube compression fittings on deep sea equipment. The devices are also likely to prove popular for topside equipment such as compressors and hydraulic power units.

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