Monitoring wire ropes for safe lifting

Magnetic Rope Testing (MRT) plays a vital role in improving rigging and lifting safety in the offshore energy sector, says Ben Dobbs, Head of Technical Services at LEEA (Lifting Equipment Engineers Association).

Wherever you look, the Covid-19 pandemic has given rise to new ways of doing things. While restrictions imposed to counter the virus caused massive disruption, in most instances lifting has continued throughout the Coronavirus outbreak and carries on as we await a post vaccination return to normal life. Maintenance and thorough examination of equipment therefore also continues.

LEEA (Lifting Equipment Engineers Association) has been working with other stakeholders and the Health & Safety Executive (HSE) on the revision of the HSE’s guidance document to thorough examinations during the Covid-19 outbreak. It can be found at https://www.hse.gov.uk/news/work-equipment-coronavirus.htm, where other related content that will be helpful for operational continuity can also be found. If you have any further questions or require additional support then please do not hesitate to contact us at technicaladvice@leeaint.com

Regular inspection on the structure of a crane, its sheaves, the jib and the slew mechanism are just some of the areas of focus for maintenance programmes carried out in by offshore energy operators. Wire ropes should also be a key part of the programme, yet too often this element is overlooked. Without proper maintenance and inspection of the crane rope, there is a risk of internal degradation that can lead to the wire rope giving way completely with catastrophic results. 

Many operations still rely only on visual inspection of wire ropes. However, plant engineers need to be made aware of the existence of Magnetic Rope Testing (MRT) and the crucial role it can play in maintenance – particularly on high integrity cranes that are being used intensively throughout their working life. MRT gives a view into the heart of a wire rope used on cranes in order to detect any deterioration that might have occurred in service. It gives plant engineers the ability to predict the life expectancy of the rope, allowing them to plan replacement in a just-in-time manner, without the need for bulky wire rope to be hogging storeroom space.

This technology for the non-destructive examination of wire rope has been around since the mid-1950s. The method involves passing the rope through a permanent magnet. This sets up an electromotive force, which is picked up with electronic sensors that can detect any breaks in the rope or any corrosion that occurs throughout the section of the rope, which is known as Loss of Metallic Area (LMA). There are different MRT equipment manufacturers but the method is the same with each one, giving clear visibility of any broken wires, voids and corrosion.

Examining the core of a rope without MRT requires a special tool to open the rope’s strands. But this still only gives visibility of a small percentage of the rope’s length. On multi-strand crane ropes, the core is never revealed because the multiple layers can’t be opened up due to the underlying layers being laid in the opposite direction to the outer strands.

The first MRT machines comprised components of a considerable size – the recorder and oscilloscope almost filled an entire room.  So in the past MRT was not always possible for maintenance of wire ropes installed on cranes. However, advances in technology have made MRT eminently portable – it can even become a fixture of the crane itself in some cases, allowing the rope to be constantly monitored as it is used. An MRT unit today can send a signal directly to a manager’s computer screen to give a visual representation of how the wire rope is deteriorating over time.

The technology has been incorporated into ISO 4309 Cranes – Wire ropes – Care and maintenance, inspection and discard as a method of examination of in-service cranes ropes, but only as a supplement to visual examination. MRT is, however, a vital tool for safety and maintenance systems and has become crucial for routine monitoring of ropes in offshore applications, where minimising costly downtime is particularly critical. A rope that outwardly looks perfectly OK can drop a load because its core is completely and utterly degraded through fatigue failure. This failure would be detected quickly through MRT, preventing the risk of accident. The technology is discussed within a guide on the condition monitoring of wire ropes in offshore installations published by the International Marine Contractors Association (IMCA), which itself is starting to drive greater awareness for using the technology in other sectors.

For high integrity cranes, particularly those used offshore, wire rope manufactures will use MRT to produce a ‘baseline’ as a ‘birth certificate’ for a length of wire rope. So when it enters service, the engineer knows precisely what that rope is like at the outset and can then accurately monitor any deterioration throughout its service life. When the rope gets to the point of rejection criteria, managers can plan in the change without fear of rope failure, maximising uptime in busy operations.

When it comes to the provision of lifting equipment maintenance and repair services it is always prudent to seek out the ‘gold standard’. In addition to offering expertise on MRT and condition monitoring of wire ropes, LEEA members are structured to provide specialised repair and maintenance as well as the inspection function, as separate parts of a one stop shop, in compliance with HSE guidelines.
For further information, please contact LEEA: mail@leeaint.com or visit www.leeaint.com

Read the latest issue of the OGV Energy magazine HERE.