Technology
A monopile for a modern offshore turbine is a steel tube more than ten metres across, over a hundred metres long and weighing well over a thousand tonnes. Making one is a plate rolling and welding business, and the yards able to do it at that size are few enough to count.
In one sentence
Offshore wind foundation fabrication is the rolling, welding and coating of the steel structures that fix a turbine to the seabed — monopiles with their transition pieces in shallower water, welded tubular jackets in deeper water — produced in quayside yards and moved by sea.
A monopile is made by rolling heavy plate into cylindrical cans, welding them together along circumferential seams, testing every weld, coating the structure inside and out, and fitting the secondary steel a technician needs to work on it: boat landing, ladders, internal platforms and the tubes the cable enters through. It is the same process as a wind tower on a much larger scale, and several tower fabricators have moved into it for that reason.
Jackets are a different product from the same industry. A lattice of tubular members welded at shaped nodes, a jacket suits deeper water and harder seabeds, uses less steel per unit of stiffness and far more welding hours per tonne. Yards therefore price and schedule the two quite differently, and a yard set up for monopile throughput does not simply switch to jackets.
Each can is rolled from a single plate, so the mill's maximum width and thickness sets the diameter and wall a yard can produce. As turbines grew, monopile diameters went past what much of the plate base and much of the rolling and handling equipment was built for, and every step up has stranded some capacity that was competitive at the previous size.
Output is measured in welded metres, not in tonnes of steel bought. Circumferential seams are laid down by submerged-arc machines and every one is inspected, while jacket nodes are largely manual work by certified welders. Both are limited by qualified people, which is why a yard's capacity responds to hiring and training rather than to order intake.
A finished monopile cannot travel by road at all. It leaves on a barge or is loaded straight onto the installation vessel at the quay, so a fabrication plant needs deep water, a load-bearing quay and space to lay structures down. Adding capacity means building all of that, which is why announced expansions turn into delivered steel years later.
2 of these are marked as a chokepoint: a handful of qualified suppliers, a multi-year lead time, or a single geography.
Wide, thick plate in the grades that survive decades of reversing load is the bill of materials, and it comes from a small number of mills.
Production must sit on deep water with a load-bearing quay, so capacity is a construction project rather than a shift pattern.
Welding qualification and non-destructive testing of every seam set the throughput, and both take years of training to expand.
A structure this size leaves the yard by sea and is upended by a vessel, so fabrication schedules are written around vessel availability.
Installation vesselsA foundation is certified against fatigue rules by a classification society before it is installed, and the design case is decades of reversing load rather than peak strength.
What each company supplies at this step, and — where a public figure exists — its share of this specific market — with what that share measures, the period it covers and who published it. Some rows also show the company’s own reported revenue for the segment covering this step, which is a different thing: it says how much this business matters to that company, not how much of the market it holds. Not a ranking and not a recommendation.
Rolls and welds the largest monopiles from a single quayside plant in the Netherlands.
Manufactures monopiles and transition pieces from plants in Germany, the United Kingdom and Asia.
Fabricates offshore foundations, transition pieces and substation structures in Denmark alongside its onshore tower plants.
Rolls monopiles and towers at a deep-water yard in northern Spain.
Fabricates transition pieces and jacket structures in Belgium as part of Eiffage.
Fabricates monopiles and jackets alongside onshore towers.
Manufactures offshore foundation structures at volume and exports them.
Whether the monopile plants announced in Europe and the United States reach production.
Whether plate mills add the width and thickness the largest diameters need.
Whether jacket demand grows as fixed-bottom projects move into deeper water.
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