TPT November 2012

Technology News

Hire wire welding of boiler tubing

tube bundle inside the surrounding boiler shell; steam produced inside the tube bundle is used to power steam turbine generators for electricity production. The boiler erection operations can be divided into three main parts:

FOR boiler manufacturing in the energy industry, increased efficiency and lower emission levels are increasingly important. Overall life cycle costs have to be reduced, which is only possible by the use of advanced materials such as P92 and T92, which guarantee high temperature strength with reasonable resistance to oxidation. This concerns every new plant, as well as the modernisation of existing plants. For boiler tubing, only mechanised TIG hot wire welding can be considered for these newmaterials as a compromise between quality and productivity. During the prefabrication process of boiler tubing for power plants an important number of welds have to be carried out in the workshop. Special attention should be paid to the features of the weld lathe at the beginning of the assembly line. Here, different concepts and types are presented and discussed. During energy production in fossil fuel- fired power plants, various types of fuel areburned insidea combustion chamber. The released heat is conducted to the

centred and rotated at the desired travel speed to carry out the weld. The proper welding operation is performed by means of the welding torch, which remains in a fixed position. The welded tubes are taken out of the welding lathe and, after testing of the welds and an in some cases necessary heat treatment, they are assembled using corresponding bends and form pieces. A significant number of welds have to be realised, either manually, or by means of orbital welding. The production time of these pre-assembled units can be considerably influenced by the number of welding machines and staff available to execute this work. In the second method of prefabrication, many pipes are welded together. The final length corresponds to the total length of the pre-assembled unit, which can be up to 100m. Several bending operations are then carried out to transform the pre-assembled unit to its final shape. This type of prefabrication requires virtually all welds to be carried out by the welding lathe or tube welder at the beginning of the assembly line. The total production time of each pre-assembled unit is influenced strongly by the capacity of this machine. Due to the importance of these straight tube welders their design has been continuously improved and adapted to the specific needs of production. With the increase in efficiency of power plants, higher service temperatures became necessary and new heat- resistant materials had to be developed, making welding operations more and more delicate.

making available the appropriate pipes with matching dimensions, made of the requested material, corresponding to the specified quality level, shipped at the desired date; prefabrication work such as cutting, joining and bending of the pipes in the workshop; and final boiler assembly with the prefabricated parts on site. Pipes available on the market are generally of fixed lengths, which depend on production methods and transport limitations. During prefabrication, the pipes are welded together to get appropriate lengths for the pre-assembled units. These are shipped to the site where they are used to construct the boiler.

Use of “straight tube welder” in boiler manufacturing

The prefabrication can be organised in two different ways, which results in different structures concerning the production line and the required equipment. The first prefabrication technique consists of welding several pipes together (depending on the length of the delivered pipes, for example two or three sections); the final shape of the pre-assembled unit is arrived at by joining them with bends. This prefabrication tech- nique requires a welding machine for the joining of the tubes at the beginning of the production line. At this stage of operation the workpieces are still rotationally sym- metrical, so the welds are carried out usually on rotating tubes with the torch at a fixed position. On the commonly implemented welding lathe the tubes are clamped,

Polysoude SAS – France Email: info@polysoude.com Website: www.polysoude.com

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N ovember 2012