High efficient welding of water wall panel steels
Water walls are gas-tight components fabricated from seamless tubes of approximately 22 m in length, 52 mm in diameter and 6.3 mm wall thickness which are connected to web plates of around 15 mm in width and 6 mm in thickness by fillet welds in PB position. These panels are pre-fabricated in the workshop commonly using submerged arc welding process. First tube twins, quads, etc. are welded from one side using multiple welding head equipment. Subsequently the panel is reversed and the backside is welded. Once the maximum width of the welding machine is achieved a manual SAW tractor is commonly used to join the water wall panels. To reach the full length of the water wall panel the tube to tube connections are welded by tungsten inert gas welding process. It is economically and technically not fea-sible to apply a postweld heat treatment for these components during workshop fabrication due to the large dimensions of the water wall panel and during on-site erection due to the high thermal stresses which will be introduced by a local post-weld heat treatment.
Although solid wires are predominantly used for the fabrication of water wall panels by submerged arc welding process some fabricators benefit from the advantage of a seamless metal cored wire. In comparison to the solid wire the wetting behavior, bead appearance and slag detachability is improved. All together, these advantages allow increasing the travel speed up to 1.5 m/min which is 20 % faster compared to solid wire application. The heat input is decreased as a consequence of the higher travel speed at constant amper-age which can minimize residual welding stresses as well as distortion of the water wall panel. This leads to a reduction of extensive straightening work, thus increasing the produc-tivity of the fabricator.
For the fabrication of grade 1 (16Mo3) water wall panels voestalpine Böhler Welding successfully qualified a welding procedure specification for submerged arc welding using Union MV Mo S / UV 305 seamless metal cored wire flux combination together with our customers and approved by the notified body (TÜV). Travel speed of 1.45 m/min has been realized using 2.0 mm wire for tandem DC/DC welding. Hardness level of less then 225 HV10 in the weld metal and heat affected zone has been achieved without preheating and post weld heat treatment. The require-ments for the fabrication of water wall panels according to EN 12952-5 and VdTÜVMerkblatt Dampfkessel 451-68/1 have been approved
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Story from Dr. Ronny Krein – Global Application Engineering