Mechanized orbital welding has been among the core competences of Bilfinger Engineering & Technologies for more than 25 years. This technology is used wherever extreme precision and special requirements are necessary. There is now an innovative new procedure for the direct welding of mixed seams which had its premiere recently.
The newly-developed welding technology was successfully implemented at the end of 2017 for the modernization of two nuclear power plants in Sweden. The technology in question is known as “high-tech orbital welding”. In addition to the dismantling and reassembly of piping components, pumps and fittings, the operators commissioned Bilfinger with the production of complex mechanical orbital narrow-gap welding. The new procedure was standardized for future applications in the course of the commissioning.
For the orders in Sweden, the welds had to be carried out mechanically, which means that they were done remotely and monitored by a camera. There are not very many companies that are capable of executing projects of this nature because demands in terms of personnel and equipment are enormous. Among other things, specialized qualifications for welding techniques are needed in order to be permitted to weld with certain materials or in certain dimensions. There are also very strict HSE requirements in place. This is on top of tight space conditions on site and the very short timeframe available for the execution of the work. This situation demands special modifications, qualifications and trainings for those involved.
The Bilfinger location in Osterode, Germany, has its own welding centre that is used for training purposes. The spacious hall has 6 mechanized and 16 manual training stations. The facility provides ideal practice conditions for those who have to take tests or who want to gain additional qualifications. The training centre is also used on a regular basis by other Bilfinger units and external companies. In advance of projects, for example, test welds are conducted here. To this end, the new “hightech orbital welding" was developed. All of this is complemented by the facility’s own laboratory where, for example, welding seams can undergo both destructive and non-destructive testing. The German Technical Control Board (TÜV) certifies the suitability of new welding procedures.
Depending on the relevant regulations, various classifications, quality levels and standards are to be observed for welding processes. A number of welding seams were produced and extensively qualified for both nuclear power plants. “There is a more substantial investment need at one of the two plants”, explains Michael Wedemeyer, Project Director in Osterode. There are a lot of modernizations planned at this location in the coming years. “We have the technical capabilities to deal with 'special problems' – and we have a unique selling proposition in the nuclear area”, says Wedemeyer. Mechanical orbital welding could also be used in the pharmaceutical industry.
The advantages of the new technology can be found mainly in the reduced effort needed due to the elimination of puffering – a great deal of time is saved and experience has shown that time is scarce in the inspections of nuclear power plants. When it comes to the execution of maintenance works, every minute counts. Work goes on day and night, in a total of three shifts. “It can get extremely expensive if you can’t get the work done within the given timeframe”, confirms Wedemeyer. “In general, an order like this has a run-up period of at least one and a half years for preparation.”
Once the preparations have been completed, the planned work steps are presented in a model simulation. As part of this so-called mock-up, the customer can make sure of the performance and professional implementation. The customer was more than satisfied with the fast implementation and the quality of the execution.
Orbital welding is a fully-mechanized gas-shielded welding process in which the electric arc is mechanically guided without interruption around pipes. With the procedure that was newly-developed by Bilfinger, mixed seams of stainless (austenite) and unalloyed (ferrite) steel can, for the first time, be mechanically welded without the need for the otherwise necessary secondary step (puffering).