[WRE ADVISOR | BUSINESS]
Exploring the Validity of Rope Discard Criteria
BY MARK FORD, TECHNICAL MANAGER, INTERNATIONAL MARINE CONTRACTORS ASSOCIATION (IMCA) L
ifting and rigging is fundamental to the work of marine contractors the world over, and reason enough for IMCA, the international trade association representing over one thousand companies and organizations engaged in delivering offshore, marine and underwater solutions around the world, to stage the ever popular IMCA Rope Forum. In June, members and guests attended the seventh in the series (held at Schipol Airport, Amsterdam) to discuss “Wire Rope – Validity of Rope Discard Criteria.” Te one-day event was a continuation of previous forums, and focused on the validity of the current rope discard criteria for high value subsea construction ropes, comparing the theory versus reality of what was being performed, highlighting the issues and concerns, and pinpointing the future requirements needed to improve rope assurance. Like earlier events in the series it drew representation from rope manufacturers, rope users, third party assurance suppliers, and academic development institutes. David Cannell of Technip, the Rope Forum Chairman,
welcomed delegates to a packed and informative day that combined presentations and workshops and which saw two scene-setting presentations “Established codes and guidance” by Inger-Lise Tangen of DNV GL; and Steve Cawthorne of Bridon on “How codes are achieved: who sets them, and how they are produced.”
Ten the delegates
got to work, with a short, sharp “Post-It Challenge” where they were asked to consider three questions “Do we discard our ropes too early?”; “What are the main drivers for discard – theoretical/actual?” and “What (if anything) is overly conservative within the current discard criteria?”). Tis produced an interesting range of answers, and plenty of lively discussion. Under the session heading of “Teory of Rope
Decay” Gregor Novak, from IFT, University of Stuttgart presented on “Rope fatigue: bending and tension-tension under twisting” covering a number of studies performed to help develop further the Feyrer formula, the theoretical equation which helped to predict the life of a rope, noting however that the equation was only valid when specific factors were met with adjustment factors required for corrosion, etc. Current testing is ongoing for larger diameter ropes, and tension-tension with twist. Dr Chris Newton of Bridon then spoke on “Corrosion and effective lubrication of wire ropes offshore” – he noted that even when using pressure lubrication methods on multi-strand ropes, you cannot get lubricant penetration “much further than the outer layers.” Te main findings from the Bridon study to improve subsea deep water construction rope life were that blocking compounds (lubricants and polymers) have a greater influence on long term corrosion performance than wire coatings such as zinc and galfan. He also highlighted that “if you are messing with lubricants, you are messing with the environment” highlighting that regional legislation has a very important role to play. Te third presentation in this session was by Maurizio
Meleddu of Redaelli on wire material changes during the life of the rope, especially related to temperature effects. Robin Van Nieuwkerk of Huisman set the scene for
the “Equipment Design Requirements” session looking at issues and experience for high value subsea construction ropes, including key factors such as “design of equipment for purpose;” the essential nature of condition-based maintenance for wire ropes which brings cost saving, and increases both up-time (“unplanned downtime can be very expensive” and safety. A 40-minute workshop followed enabling delegates to discuss:
• Can we base discard criteria purely on condition monitoring / regular inspection? What else do we need to know?
WIRE ROPE EXCHANGE SEPTEMBER-OCTOBER 2016 75
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