We manufacture Solar wate heaters. We use SS 304 2B grade sheet metal (0.5mm thickness) to make inner tanks. Welding of this tank is the most crucial step in our manufacturing process. We are using Resistance Seam welding to make the tanks. Material thickness will be 0.5mm. We do both logitudanal seam and circumfrential seam welding on our machine. We weld the joints by overlapping the sheet ends for logitudal welding. We do leak test for every tank and no leaks were identified so far. Problem starts after the finished product is delivered to the customer and installed.

Major issue is that thease tanks start leaking after installing for hot water purpose. Water will be heated inside these tanks by capturing solar energy. When we open the problamatic tanks, we see that there are small pin holes just beside the welding joint where the sheet overlapping ends. some times on the welding joint aswell. There are absolutely no hole anywhere elese in the tank except beside the welded joints.

We have tried various options such as changing welding parameters (Current, speed, weld and cool time etc) , increasing the sheet overallping area etc. But the problem continues. We are looking for experts to help us as we are clue less.

We then tried manual TIG welding of the tanks and installed at the same place and there are no problems as part of our research. But manual welding is not scalable. What i fee is that it got to do something with the welding process. Our welding machine supplier is also clue less as he says the welding joint is excellent and strenght of the welding also is good.  Point to note is that these tanks will have hot water inside 24hrs with temperate anywhere from 60degree Centigrade to 90Degree centigrade

Hope I get some help/guidance here from this forum. Please let me know incase you need any more data or information from me.

Regards

Ravi