The sea load is getting heavier and heavier, and the submarine elevator has been getting deeper. Julian Champkin investigated the hazards and development.
Lifts in offshore oil and gas are generally much heavier than lifts on land. Even normal-sized offshore lifts are dangerous. Unknown complex factors abound on land; and the consequences of failures can be more extreme, more difficult (and more costly) to remedy-and more dangerous to life.
People would think that the deeper the ground, the more dangerous the environment. Felix Nyberg, Gunnebo's global product manager, said this is not necessarily the case.
"Corrosion is an obvious hazard; but in fact, deeper water contains less dissolved oxygen, so it is less corrosive to chains, shackles and other parts. Close to the surface, especially in the splash zone, is the most corrosive Severe places. Not only there is more oxygen, but the wave action can wash away any protective layer of corrosion products that have formed, and these corrosion products can serve as a barrier to further seawater action. "Protective coatings are a defensive measure. The other is to add zinc flakes or coatings as a sacrificial anode; it corrodes more easily than the surrounding steel, thereby protecting the load-bearing parts. However, the price of safety is always being vigilant; both paint and sacrificial anodes need to be checked frequently to ensure they are in good condition.
Salt water corrosion is just one of the hazards of seabed lifting. The other is hydrogen embrittlement, also known as hydrogen-induced cracking. Hydrogen diffuses to the steel surface, especially through microcracks and roughness and stress points. It penetrates into the steel and may cause brittle damage-complete, accidental, and extremely dangerous in hooks or lifting chains at sea. Nyberg said the key is to ensure that the selected materials are suitable for the environment. In particular, you need to check the hardness of the steel-or rather, the lack of hardness. Hard steel fails in brittle mode-that is, suddenly and without warning. On the other hand, softer steels are ductile: they stretch and deform before failure, so careful and frequent inspections will reveal the need for replacement before an accident occurs. Check that the HRc (Rockwell) hardness value is the index here: For offshore conditions, steel with HRc lower than 39 should be used.
The crane vessel moves up and down with the waves; the dynamic load that this creates may be many times the actual weight of the load-or, if the vessel suddenly sinks, the dynamic load may even become negative. These loads must then be taken into account when calculating safe workloads. You should not even rely on the SWL of the ropes, hooks and shackles specified. Repeated loading close to the SWL value will cause metal fatigue, which in turn will cause sudden failure and shorten the safety life. Only when frequent loading is limited to 80% or less of SWL, the service life of the component will not be affected.
Nyberg's summary recommendation is to choose the right materials and check the components frequently. Crane manufacturer William Hackett made similar recommendations and actually published an industry report on the subject in October 2020. Its importance is reflected in its title, which begins with "Technical Guidelines on the Effects of Hydrogen Embrittlement on the Materials Used in Upper and Subsea Lifts", but continues to read "Helps to minimize the risk to human life... ...."
The report has been peer-reviewed by multiple organizations and authorities to help minimize the risk of hydrogen embrittlement (HE) and stress-induced corrosion cracking (SICC) in marine and subsea operations.
“Hydrogen is known for causing the notorious and unpredictable structural integrity problems, so new guidelines and solutions are needed,” said Dr. Emilio Martínez-Pañeda, an assistant professor at Imperial College London and a world-recognized hydrogen embrittlement expert. Who doesn’t Participate directly in the findings of the report. He pointed out that although the scientific community has made great progress in using simulation tools to predict the behavior of components exposed to hydrogen, challenges remain.
"The entire industry is very concerned about the impact of HE and SICC on the chains and links used in crane and lift products in the offshore environment," said Ben Burgess, director of William Hackett. "Based on our own experience of how our products operate at sea, combined with the manufacturing expertise of chain manufacturer McKinnon Chain and the detailed technical analysis results of industry partners, we have determined that when the hardness of the material exceeds 39-40 HRC, the risk of HE SICC will increase as the hardness value increases," he continued, echoing Gunnebo's Nyberg point of view. The available hydrogen, the materials used, and the stresses imposed on the components are all contributing factors to hydrogen embrittlement (see Figure 1).
"The problem with HE is not limited to one type of offshore activity," Burgess said. "Examples include the failure of the G10 welded chain sling in a container fleet in Norway. In the United States, a multinational oil company had to withdraw some lifting equipment and immediately introduced an inspection system before any future crane work.
"Meeting specific international standards should not be regarded as a guarantee that specific equipment is suitable for the marine environment," he said. "The specific environmental and performance considerations of equipment used at sea need to be a key part of the material specification and selection process.
"Put this in context, an 8-level main link, when properly heat-treated, will provide toughness, tensile strength, and impact absorption capacity, and will do so at the level of hardness, enabling the steel in the product to be able to Withstand extreme conditions when used in a marine environment."
According to the report, the key areas surrounding HE include causal factors and best practices. The correct choice of materials is essential. Operators need to ensure that despite commercial pressures, products used in the offshore environment are fully suitable for their intended use, and that environmental conditions, mechanical stress, and material sensitivity have been strictly evaluated.
"Managing the risks of HE and SICC requires a change in mindset," Burgess said. "The development of higher grade steel should be treated with caution. If the material and its use at sea are not properly understood, the end result will increase operational risk."
The company is known for its patented Quad Pawl system's subsea SSL5 lever hoist, which we have previously introduced on these pages (see the April 2020 hoist). Its design and extensive corrosion protection make it capable of multiple immersion, and it has been independently verified by DNV. William Hackett has taken further measures to help minimize the risk of HE and extend the service life of its main link by introducing Zinc-Tough. This is an innovation that applies a zinc layer to products that can significantly reduce corrosion. speed. Compared with other coating processes such as galvanizing and electroplating, it prolongs the service life of the product and reduces the risk of HE. To date, William Hackett has delivered more than 550,000 main links. "We are very proud of the track record of providing HA links for Shell, BP, ExxonMobil and all other major offshore operators," Burgess said. "So far, we have not had a suspected case of HE, which reinforces the quality method we use in the product manufacturing process."
Irizar Forge is a fourth-generation family-owned company located in Lazkao, Basque Country, which specializes in but not limited to the development of large forged lifting components for the offshore market. Here, material quality is everything. Sales manager Oier Sarasola said that the advantage of forged products over cast products is the strength of the finished product.
In the casting, the metal particles are arranged randomly; the molten metal is poured into the mold, cooled, and then it is over. In the forging process, hot (but in a solid rather than molten state) metal is hammered and beaten into shape. "This percussion and percussion makes the steel grains thinner and more string-like, and-importantly-aligns them within the work," Sarasola said. "They follow the flow of the work, and they all point in the same direction to provide a finer and more uniform structure. This is the reason for the extra power."
However, forging is not an easy process, especially in large-size machining that Irizar is good at. It requires large equipment and highly skilled workers. This will affect cost accounting. "However, even if the purchase price is more expensive, the market should consider that forging is a stronger and safer option, with lower maintenance costs and longer service life compared to casting or other technologies," he said. Sarasola added: “The hook has very few failures and is malleable rather than brittle, so a lot of warnings are given.”
Irizar Forge has always focused on large size and large capacity. “A few years ago, we checked the largest capacity cranes and found that they were all offshore,” said Maria Lasa Irizar, the company’s director. (Her great-grandfather founded the company in 1923.) "So, we developed this business in particular; it has become our niche market," she added.
"We have standard designs, but most of our business is customized according to customers' individual requirements," Sarasola said. "The shape is a smooth curve, so the sling can work safely and effectively over a long service life." Other Irizar products include diving hooks suitable for ROV recovery. "The challenge of subsea lifting is that the product must be operated by a non-manual remote control vehicle; therefore, the latch and accessories are designed in stainless steel to avoid corrosion. The handle is also made of stainless steel to make it easier to operate on the deck. The hook is completely forged One piece, so no weld may be a weak point."
Irizar recently delivered a 1,000-ton SWL hook set for heavy lifting vessels, and it can provide a higher capacity, and the hook is also 1,500-ton SWL. These are indeed impressive forgings.
Hooks and fasteners are not the only components of subsea lifting; wires, chains or ropes also need attention. One trend in land-based lifting is to replace steel wire ropes with synthetic materials. The same trend is also evident at sea. Compared with steel, synthetic rope has many advantages: it does not corrode, has similar strength dimensions to steel wire, and is extremely light during rigging and is easy to handle on deck. The density of the rope is close to the density of water, which means that regardless of the working depth, the fiber rope has no effect on the overall payload weight. For steel wires or chains, the deeper the operation, it is important to consider the weight of the wire and the effective load at the depth. The weight ratio. Nyberg said: "This means that on a very deep or very deep submarine lift, the load carried by the crane uses the same fiber." "For the wire rope, at the deepest point, the hoist carries the huge weight of the wire rope and the load itself. "The difference is quite big: a 4,000-meter 88 mm fiber rope weighs about 20 tons, while a wire rope of the same length weighs more than 200 tons. A 150-ton SWL crane equipped with a fiber rope crane can lift loads at a depth of 3,000 m, which requires a 250-ton SWL wire rope crane to lift the same payload.
However, there is a disadvantage: synthetic materials are more elastic than steel. Synthetic rope stretches under load, so it is stretched when it is wound on the drum winch under tension during lifting operations. It is not recommended to store stretched ropes under high tension; the energy contained can be dangerous, the winding is uneven, and frictional heat is generated when the rope is loose.
Parkburn Precision Handling Systems, a Scottish company based in Hamilton, has developed a solution to solve this problem. Its patented deep-water winch relieves the tension of the synthetic rope when it is wound. It consists of two independent reels that intersect each other: each reel has 16 "fingers" that are interlaced with the fingers of the other reel to provide a rope support surface. The rollers are offset from each other around the center of rotation to form a natural spiral and a slightly elliptical cable path through the machine. This creates a unique tensioning/untensioning profile that distributes the work evenly on the rope as it passes through the machine. After coming out of the deep water winch, the rope can be stored under low tension. Each drum has its own motor and gearbox, provided by Dana SAC. The equipment can also be used for cranes: the 150-ton variant of the Parkburn deepwater winch is located at the heart of MacGregor’s FibreTrac 1500 marine crane.
Another maritime trend is the ever-increasing size and weight of lifts. The upper part of the drilling platform is now standard built as larger modules for transportation and lifting into place, rather than being built at sea. An important part of this type of lift is the hanger beam, and the professional Modulift has just built their largest beam ever. It can lift an astonishing 2,000t with a span of 33m. The feat of the hook project was delivered to the Dutch company Safe Lifting Europe for offshore operations. This is not the first record-breaking beam it provides for safe lifting. The earlier 20m span 1,500t beam designed for the same client was also a record-breaker for Modulift at the time. "We work in a market that shows unlimited potential in terms of capacity," said Jacques Vroegop, European Safety Lifting Technology Director.
"We may talk about heavier lifts becoming commonplace. Currently, we are working with cranes that can provide up to 1,000 tons of lifting capacity, but we are in a very dynamic industry." "Although processing these recent orders is very demanding. People are satisfied, but we are not surprised,” said Sarah Spivey, Managing Director of Modulift. "We realized the potential of the super-heavy market early on-the middle market remains quiet. I don't want this to be our long-term highest capacity beam. We have engineering capabilities of up to 5,000 tons and will continue to push the boundaries." Modulift is already in Consider upgrading the upcoming project with the customer to 3000 tons.
The increase in size also affects crane vessels. Fred. Olsen Windjammer is responsible for the installation of the wind farm, and its Brave Tern and Bold Tern are specially built heavy professional crane vessels designed to lift themselves from the seabed when the tower and rotor are hoisted in place. They also transport the tower and rotor from the loading port to the installation site on the deck. Bold Tern is currently building the world's largest offshore wind farm, Hornsea One on the coast of Yorkshire. This project is the first project with a capacity of more than 1GW; it will power more than one million homes. Its sister ship is currently building the new Yunlin Wind Farm in Taiwan, but will soon be upgraded to include the tallest crane on the market in its superstructure. When the project is completed in February 2022, she will be one of the few ships that can install the foundation and tower of the next generation of wind turbines. The tower of this turbine is 138m high to the nacelle, and the rotor is 220m above sea level. The brave tern, when raised with her four legs, the main hook can reach 238m and the secondary arm can reach 256m.
Her new unique crane will be a 1,600 ton LEC 65500 ring-leg crane from Weimar. It will be installed on the rear port side leg of Brave Tern; the lambda-shaped boom is very stiff, reducing cutting-edge movement; the compact size of the crane combined with its low dead weight and 1600-meter high lifting capacity makes it unique, suitable for wind turbines The installation-which requires a long boom and lightweight crane design-and the installation foundation-requires a short boom and a strong crane structure. The crane adopts full electric drive, lower power consumption, higher reliability, and the machine is more environmentally friendly. Fred CEO Alexandra Koefoed said: "This unique crane has been enhanced with key updates and more extreme booms. Olsen Windmill. "Despite the increased weight of the crane, the increased outreach capacity of the new crane allows us to Load wind turbine components in a more flexible way to maintain or exceed the payload we carry for our customers. As the weight and size of wind turbine components continue to increase, this is a considerable life extension for ships. "
For lifting engineers, life on the waves will obviously continue to provide more and more opportunities.
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