TPT March 2009

I ndustry N ews

Expert forum on narrow gap welding

Polysoude, France, played host to an expert forum on narrow gap welding from 5-7 November 2008. The successful event welcomed around one hundred experts from France, Germany, Austria, Switzerland, Russia, Hungary and the Czech Republic. The event involved two different sessions in both the French and German languages. A number of high profile speakers gave presentations targeted at welding experts from the high-purity industries, including food, pharmaceuticals, chemicals, semi- conductor technology, aerospace and the onshore/offshore industry. The power plant construction sector is currently booming worldwide, with 700 degree power plants the focus of attention. For plant construction this means using more pressure-resistant, thick-walled pipes made from high temperature steels such as P91 and its successor P92 (X10 CrMoVNb 9-1, WKN 1.4903), conforming to the ASTM standard (American Society for Testing Materials). The key quality features of this new steel grade are the values for high creep rupture strength that also apply without restriction as the benchmark for every weld seam on these pipes. In particular, the forum on narrow gap welding addressed this area of automated welding technology. Before the start of the conference programme, delegates were given a tour of the factory where P91 pipes (Ø 620mm and 180mm wall thickness) were joined using a narrow gap torch in the TIG orbital welding process using a hot wire additive. The joined seams offer 100 per cent

penetration, are x-ray proof, and meet the highest requirements for metallurgic and mechanical quality values. Following the tour, the host and Polysoude’s CEO, Mr Hans-Peter Mariner, offered an in-depth insight into the latest developments in narrow gap welding. This presentation highlighted that with wall thicknesses of over 60mmm, welding time is shortened by a factor of five to ten in comparison to conventional TIG processes with a traditional V seam. The welding characteristics of the parent material are the decisive factor in the application of the narrow gap process. Technical advances in equipment technology such as automatic centring, HF-free ignition, seam preparation and optimised gas protection further increase the application limits. The geometry and gap width of the weld groove are based on the mechanical properties of the materials being joined, with the shrinkage characteristics of the seam being particularly important. Another key part of the programme was a presentation on the three different narrow gap-welding techniques. The first involves a single pass weld per layer and torch or workpiece revolution. The second is dual pass welding next to one another, when the seam preparation or positioning exceed the required narrow tolerances of a few tenths of a millimetre for one stringer bead per layer. TIG narrow gap welding with a shuttle- motion electrode is ideal with very large wall thicknesses of 150-200mm. This is particularly the case if the necessary

boundary conditions – such as accuracy of the seam preparation, handling of the shrinkage process and torch design – cannot easily be ensured for joining using one stringer bead per layer. The second day of the forum began with an in-depth presentation on ‘Applications, solutions – implemented projects’. During the past financial year, in the area of boiler construction for power plants, Polysoude has fitted more than 30 made-to-measure circumferential seam welding systems for automated TIG welding and several hundred orbital welding systems for custom applications. Following a comprehensive question and answer session, the perfected, mechanised welding process was demonstrated on a rotating part. To conclude the expert forum, the turnkey solutions offered by Polysoude for joining rotors were on display for participants. A narrow gap welding system for manufacturing turbine rotors of up to 300 tonnes was set up in the factory hall. Polysoude will hold a new conference session for experts in narrow gap welding in the English language, at the end of March.  In practice – setting of a narrow gap torch on a P91 pipe (620mm diameter and 180mm wall thickness)

 The expert forum for narrow gap welding – specialists all over Europe were interested in this technology for the field of energy production and boiler manufacture

Polysoude – France Fax : +33 240 681 188

Email : info@polysoude.com Website : www.polysoude.com

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M arch 2009

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