Manufacturing of Welded Rings : Evaluation of Post-Weld Operations

Pipe and ring blanks can be produced in several different ways. Today's focus on environmental effects motivates companies to develop processes that are as efficient as possible in their production. Ringsvets AB is a company that produces pipe and ring blanks from a flat stock by rolling and welding the piece to make it stay in its desired form. The direct benefit of the method is the minimizing of material loss, and it has thereby both environmental and economical advantages. The downside of the method is that the processes involved changes the mechanical behavior of the ring, locally around the weld zone. The focus of this master thesis is the processes and how they affect the material, both microstructure and behavior. The processes involved are; rolling, welding, shaping, brushing, forging, heat treatment, and calibration. The purpose of this work was to elevate the knowledge and understanding of the processes at Ringsvets. The goals were to give a theoretical description of them along with practical test results and explanations of how and why they function in reality. A literature study has been conducted which provided a theoretical basis on how the material reacts on certain processes. Practical examination of samples from current production has been done to get evidence of how well the processes are used, and how well they function, in today's production. Lastly, the main focus of the thesis, an evaluation has been made; do theory and practice correlate, and should anything be changed to correlate better? The results showed that the first operations do not alter the material behavior to an unacceptable extent. Forging, on the other hand, gives the material a very high hardness in the weld zone, and that needs to be corrected. The following heat treatment should compensate for that in a perfect world, but does not in reality. The finished ring shows good properties in general but with places where the heat treatment has failed to correct the uneven behavior