Copper alloys should not be used for welding stainless steel components
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Stainless steel components should not be welded using copper alloys. Example: A small plate-and-frame 316 stainless steel heat exchanger became damaged after 6 to 12 months of use. This heat exchanger uses steam (862 kPa, 121°C) to heat tap water (from room temperature to 75°C). It was suspected that the flow rate was too high; therefore, two heat exchangers were installed in parallel to reduce the flow rate, but the damage did not stop. The final reason has been found. It turns out that the heat exchangers were joined by copper welding. During welding, liquid copper penetrates along the grain boundaries, causing grain boundary corrosion, increasing local stress, and leading to fatigue cracks. Analysis: This example shows us that stainless steel components should not be brazed using copper alloys (or copper-containing silver alloys).
In this example, welding stainless steel components with copper led to grain boundary corrosion and fatigue cracks. Copper diffuses into the grain boundaries of stainless steel at high temperatures, resulting in a decrease in the material’s corrosion resistance. The potential difference between stainless steel and copper alloys can also induce galvanic corrosion. Therefore, in order to maintain the corrosion resistance and mechanical strength of stainless steel, copper alloy welding should not be used. The correct approach is to use welding materials that match the composition of the stainless steel. .
This doesn’t clarify the following: 1. Whether the welding method is fusion welding or brazing; 2. What welding materials are used. The simple conclusion provided is hard to understand. . At a quick glance, it seems that stainless steel cannot be welded using copper materials