TPT March 2023


Efficient and economical preparation and cutting for external pipe weld seams

The weld seam preparation machines manufactured by Graebener were the first of their kind. About 150 of these machines are dedicated to the milling of weld seam preparations for circumferential and longitudinal welds on cylindrical and conical components with diameters of up to 15m and wall thicknesses of up to 200mm. In the last few years, more than two dozen circumferential seam milling machines and half as many longitudinal seam milling machines have been sold to the wind offshore industry. In the meantime, all well-known manufacturers of foundation structures for wind turbines in the onshore and offshore sector use milling machines from Gräebener. The offshore market is experiencing a sustained boom and is providing Gräebener with high demand. Wind power is to be used for green energy in more and more parts of the world. The machine manufacturer has already responded to a new market developing in the US with its own subsidiary in Texas, where a transportable circular seam milling machine is available as a demonstration unit. New wind farms are also being built off the coast of Japan. Here, a manufacturer of monopiles wants to carry out the complete assembly process outdoors rather than in a hall. To meet this requirement, Gräebener is developing machines that are also suitable for outdoor use. The monopiles for wind towers are always assembled from several individual cylindrical and conical steel rings, the so called pipe shells. Typical dimensions for such a pipe shell are a diameter of 13m and maximum lengths of 4m. With wall thicknesses of 120mm, this results in an individual weight of up to 150 tons per pipe shell. After bending, the pipe shells are first welded longitudinally from the inside and then from the outside. This is followed by the assembly of up to six sections into one section. Three to four of these assembled sections form the so called monopile. A monopile has a total of approximately 192m longitudinal and 940m circumferential welds and a total weight of up to 2,500 tons.

GRAEBENER ® developed its first milling machines for the preparation of weld seams on pressure vessels in the 1980s, initially only for use in its own large diameter pipe mill. In co-operation with Ingersoll Werkzeuge GmbH, the machines became products for the world market, which today are in great demand especially for the construction of offshore wind towers and their foundation structures. Gräebener can look back on a company history of more than 100 years. When the company was founded in 1921, the family business began with pipe and apparatus construction. Until 1955, the focus was on the production of heavy iron and sheet metal structures including steel and vessel construction. Subsequently, a large pipe mill was built and established in Netphen-Werthenbach in the Siegerland region, which was then sold to Indonesia at the end of the 1990s. Since then, Gräbener has concentrated entirely on mechanical and plant engineering. The company, which currently employs around 80 people, focuses on the development and design of hydraulics, mechanics and automation as well as on the assembly and commissioning of plants and retrofits. The necessary machine components, such as steel structures as well as all other parts, are purchased from suppliers mainly in the regional area. Therefore, Gräebener sees itself as a “virtual factory”, as it does not operate its own facilities for component production. The past is nevertheless present at the company headquarters. On the one hand, production still takes place in the historic halls. On the other hand, the experience built up here over decades and the constant improvements form the basis for the company’s current business success. The construction of the company’s own circular and longitudinal seam milling machines was started in the mid-1980s out of a serious problem. The pipes manufactured in Werthenbach were becoming thicker and thicker and were increasingly causing transport problems. The pipes, which were up to 70m long and weighed up to 70 tons, therefore had to be finally welded together on the construction sites. The idea of a mobile

milling machine was born, with the help of which the weld seam preparation on the pipes could be carried out on site. For the milling machines, Gräebener worked together with INGERSOLL from day one. For machining the tubes, milling heads were jointly developed for circular and longitudinal seam milling, but also for other fields of application, such as weld seam preparation on sheet metal and profiles. At the beginning, they had to contend with considerable difficulties, as Dieter Kapp, managing director of Graebener, said: “The first milling heads only lasted a few days and our gearboxes were damaged just as quickly, as there was no experience for this new machining method.” But Graebener and INGERSOLL stuck to the concept and pursued further development of the machines and milling tools over the years. A few years after the first milling machines for internal use, the machines became durable, powerful, process reliable and thus competitive. McDermott in Scotland and SIF from the Netherlands, at that time two market leaders for thick-walled pipes, vessels and apparatus, were the first two customers for Graebener. Today, SIF is a leading manufacturer of foundation structures for offshore wind turbines.

Gräbener Maschinentechnik GmbH & Co KG


MARCH 2023

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