Prevention of Weld Crack in HT80 Heavy Plates with Undermatching Electrodes and its Application to Fabricating Penstock

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In field-welding HT80 steel heavy plates with E11016 type electrodes, preheating temperature around 150℃ is usually required for preventing weld cracks. In order to improve the environmental conditions, the authors have undertaken to apply undermatching electrodes to the circumferential welding of the penstocks being under planning. Weld cracking tests of an HT80 steel plate, 50mm thick, are carried out with two types of electrodes, AWS E 11016 and JIS D 5816. Susceptibility for root cracking in heat-affected zone of the first-pass welding is studied by the y-groove weld cracking test, and for weld metal cracking in multi-pass welds by the H-type restraint test. Test results obtained are summarized as follows : (1) In the welded joint of HT80 steel plates, both root crack and weld metal crack are likely to occur. An undermatching electrode lowers effectively the preheating temperature required for preventing the root crack by around 25℃. (2) The weld metal cracking in multi-pass weld is not affected apparently by joint restraint intensity. (3) An undermatching electrode is so effective for preventing the weld metal crack in multi-pass welds that the preheating temperature required is lowered by around 75℃.
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