Scientific paper ID 776 : 2013/2

The quality of a welded joint in expansion tank of the water cooling system of a photovoltaic installation is identified. A lot of flaws are found after analyzing the macro- and micro structure, and the chemical content of the welded joint. The incorrectly followed mode of welding with high linear energy has resulted in high residual welding stresses, overheating of the metal and continued detention at high temperature. Thus the corrosion resistance of the metal in the heat affected zone (HAZ) decreases and this is the most likely reason for corrosion and cracking.