In field-welding HT 80 steel heavy plates with E 11016 type electrodes, preheating temperature around 150°C is usually required for preventing weld cracks. This makes it difficult physiologically for workers to do continuous welding works in the tunnel. Fundamental study made so far reveals that undermatching electrodes of lower NTS level than the base plates are effective to lower the preheating temperature required for preventing weld cracks without appreciable decrease in joint strength. In order to improve the environmental conditions mentioned above, therefore, the authors have undertaken to apply the undermatching electrodes to the circumferential welding of the penstocks being under planning.
Weld cracking tests of a HT 80 steel plate, 50 mm thick, were carried out with two types of electrode, AWS E 11016 and JIS D 5816. Susceptibility for root cracking in heat-affected zone of the first-pass welding was studied by the y-groove weld cracking test, and for weld metal cracking in multi-pass welds by H-type restraint test. Conditions of humid absorption in the electrodes selected and joint restraint severity were varied.
Test results obtained are summarized as follows:
(1) In the welded joint of HT 80 steel plates, both root crack along fusion line of the first-pass weld and weld metal crack in multi-pass welds are likely to occur. The undermatching electrodes lower effectively the preheating temperature required for preventing the root crack by around 25°C as compared with the E 11016 type electrode under the same hydrogen level.
(2) The weld metal cracking in multi-pass welds is not affected apparently' by joint restraint intensity.
(3) The undermatching electrode has been found so effective for preventing the weld metal crack in multi-pass welds that the preheating temperature required is lowered by around 75°C as compared with the E 11016 type electrode.
