FEATURE | OFFSHORE AND SUBSEA


Marine corrosion is worst above the waterline in the splash zone.


upthrust until the load is fully submerged. To reduce load peaks on the payload or on the equipment, particularly in this zone, Huisman has a Load Peak Shaving system. This significantly limits the impact forces while lowering payloads through the splash zone and during subsea operations without the need of additional equipment in the rigging.


CORROSION Offshore is a harsh environment, even in calm weather. Salt water, sea air, waves and wind form an extreme environment, and normal steel, good for many years of use inland, will corrode extremely quickly in marine applications. For which reason, special coatings, special steels and protective techniques such as sacrificial anodes are de rigeur at sea. Even simple hand hoists and winches


need to be marinised. Dutch company Gebuwin are specialists in hoists and winches, for many applications, but the maritime and offshore industry is its largest market. Gebuwin has therefore developed hand winches especially for this industry. All parts of the marine winch that are exposed to the weather are made of stainless steel 316, which is the highest corrosion- resistance grade. The winch has a worm gear transmission to increase safety when hoisting, pulling or tensioning heavy loads. The transmission is enclosed with an IP54 rating against particle and water ingress. It is also possible to apply a marine coating to the winches For example, its 3,000kg worm gear


hand winch in addition to the stainless steel construction has three layers of C5M paint – C5M, whose technical


26 | April 2025 | www.hoistmagazine.com


classification is Very High Corrosivity, Marine is the standard for very high protection in coast and sea environments. The winch is ATEX certified and can be driven pneumatically or electrically as well as by hand, and 500kg and 1,500kg versions are also available. Corrosion, of course, affects onshore equipment also, but steel in marine environments is subject to a type of attack and consequent failure that is much more frequent, and much more severe, offshore than on. Hydrogen embrittlement is a phenomenon that was until very recently not well understood. Ben Burgess, director at chain and hoist specialists William Hackett, produced a peer-reviewed report on the topic just a few years ago, which is still a standard reference. For hydrogen embrittlement to take place, he says, three elements are required: first, a source of hydrogen – such as the hydrochloric acid that is a product of corrosion; second, material susceptibility – harder and lighter steels, such as increasingly used at sea, are more susceptible than low-strength ones; and, thirdly, mechanical stress. The mechanical stress, says Burgess,


typically comes not from the strains of conventional lifting but from dynamic loading, which as we have seen, is an offshore phenomenon. Those stresses open up micro-scale gaps in the grain structure of the steel. Hydrogen migrates into those cracks. There it creates internal pressure, which tends to push the steel apart. This can lead to catastrophic failures. Unlike weakening of machinery directly caused by macroscopic cracks, hydrogen embrittlement is near impossible to observe and to predict, says Burgess. This, of course, makes it highly dangerous. As we have seen, harder steels are


more susceptible than softer ones. This is a consequence of their tighter grain structures, which allow more scope for hydrogen to penetrate between the grains. Preventative measures recommended by the William Hackett report therefore include maximum hardness quotas on steel for chains used in the offshore industry, as well as the application of corrosion-resistant finishes to all chain types. Both these measures make it more difficult for hydrogen to enter the structures in the first place. Another relevant factor is that


Norwegian government regulations, the


Norsok Standards that are a requirement for North Sea and other operations, dictate that marine lifting slings should be made from chain rather than wire. They forbid any mechanical fixings, meaning the normal method of cutting chain and using connectors is not permitted. Chain slings, therefore, stay attached semi- permanently to the load and are left open to the hostile marine environment where hydrogen embrittlement can occur. William Hackett has therefore developed


its Zinc Tough Technology coating, which satisfies all Norsok requirements and all but eliminates the risk of salt water ingress and hydrogen embrittlement. With its manufacturing partner


Mckinnon Chain in South Africa, it produces fully welded chain sling assemblies from its Marine Grade 8 lifting chain. Manufactured specifically to be suitable for working in extreme environments, the chain undergoes a specific heat treatment process that controls the alloy steel to give it a maximum hardness of 38HRC. The chain is fully treated with the Zinc Tough technology, while the assemblies are DNV type approved. The company holds stocks of common sizes, but most assemblies are made to order. The chains have a range of diameters


from 7-32mm. All sizes are proof tested at manufacture to 2.5 times the given working load limit and are fully compliant to EN818 material requirements. The manufacturing process of the Marine Grade 8 chain gives improves toughness and ductility in extreme conditions with increased resistance to hydrogen embrittlement and stress induced corrosion cracking. It is possible that in all the above we may


have given the impression that offshore lifting is an order of magnitude more difficult than standard onshore operations, with hazards and factors all of its own. If we have, we may not be that far wrong.


Hydrogen embrittlement can be catastrophic. (Credit: William Hackett)


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79