OFFSHORE AND SUBSEA LIFTING | APPLICATION REPORT


R Irizar’s forging technology gives stronger grain structure…


ExxonMobil, and every other major offshore operator,” says Burgess. “We have not had one suspected case of HE to-date, which reinforces the quality approach we take in how our products are manufactured.” Irizar Forge, a fourth-generation family company based in Lazkao in the Basque country, has developed a speciality in large-size forged lifting components for, but not limited to, the offshore market. Here again, quality of material is everything. The advantages of forged over cast products is in the strength of the finished product, says sales manager Oier Sarasola. In a cast item the grains of metal are


randomly arranged; the molten metal is poured into its mould, cools down, and that’s an end of it. In forging, the red-hot (but solid, not molten) metal is hammered and beaten into shape. “This hammering and beating makes the grains of steel finer and more string-like, and also – importantly - aligns them inside the piece,” says Sarasola. “They follow the flow of the piece, all pointing in the same direction to give a finer, more uniform structure. This is what imparts the added strength.” Forging is not, though, an easy process


to carry out, especially at the huge sizes in which Irizar specialises. It calls for big equipment and highly skilled workers. That affects costings. “But, even if the purchase price is more expensive, the market should take into account that forging is the stronger and safer option, there are fewer maintenance costs and a longer lifespan than with cast or other technologies”, he says. “Hook failure is minimal and is ductile


P Irizar Forge produce large components 32 | May 2021 | www.hoistmagazine.com


rather than brittle, so plenty of warning is given,” adds Sarasola. Irizar Forge has always specialised in


large size and capacity. “A few years ago, we looked at the largest-capacity cranes, and found they are all offshore,” says Maria Lasa Irizar, director of the company. (Her great-grandfather founded the firm in 1923.) “So, we have especially developed that side of the business; it has become something of a niche for us,” she adds. “We have standard designs, but most


of our business is custom-made to clients’ individual requirements,” says Sarasola. “Shapes are smooth curves so that slings can work safely and efficiently on them over long lifetimes.” Other Irizar products include submersible hooks that are friendly for ROV recovery. “The challenge in subsea lifting is that products must be operated by non-human remotely controlled vehicles;


so latches and fittings are designed accordingly, in stainless steel to avoid corrosion. Handles, also in stainless steel, are added for easier handling on deck. Hooks are fully forged in one single piece, so there are no welds which can be points of weakness.” Irizar recently delivered a 1000t SWL hook block for a heavy lift vessel, and can deliver even higher capacities, with hooks of 1500t SWL as well. These are truly impressive forgings. Hooks and fastening are not the only components of undersea lifting; the wire, chain or rope needs attention also. A trend in onshore lifting is replacement of wire rope by synthetic. The same trend is visible offshore. Synthetic rope offers a number of advantages over steel: it does not corrode, has similar strength size as steel wire and is extremely light and easy to handle on deck during the rigging process. The density of the rope is close to the density of water, which means that irrespective of the depth of operations the fibre rope has no impact on the overall payload weight, whereas with wire or chain, the deeper the operations it is important to consider the self-weight of the wire to the weight of the payload at depth. “That means that on a deep or very deep subsea lift, the load carried by the lifting machinery remains constant using fibre,” says Nyberg. “With a wire rope, at the deepest level the hoist is carrying the huge weight of wire rope as well as the load itself.” The difference is considerable: 4,000 metres of 88mm fibre rope weighs approximately 20 tonnes, compared to over 200 tonnes for the equivalent length of steel rope. A 150t SWL crane with fibre rope crane can lift loads at depths of 3,000 m that would


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