In pipe welding, it is a normal practice to make root pass by using TIG process. Because of some production factors, joining of pipes is divided into two processes; root pass with TIG while the filling and capping is done by shield metal arc (SMAW).
Sometimes in welding of certain materials, inert gas purge is applied during root pass in order to support solidification of molten weld, giving desirable metallurgical, corrosion and mechanical properties. Purge of inert gas at specific flow rate, is applied as backing of weld. This practice is popular in welding of stainless steel and duplex stainless steel family.
The above picture shows complete TIG weld on pipe joint. In case of above mentioned variation in production process, fill and cap passes can be done by SMAW process. For this a wide range of consumables are available for joining of several materials, which can be used in both arc welding processes. The consumables have almost the same composition as that material to be joined.
The color on weld portion in the above picture is named as post weld color. These colors define the level of mechanical properties of weld, HAZ (heat affected zone) and base metal.
Comments
In last it should be better to discuss the comparison of both arc welding processes. TIG produces more clean and sound welds without slag handling, as compared to SMAW. On the other hand TIG is slower and cannot be helpful in those applications where high production rate is required.
