The prediction of risk of welding defects at the procedure stage using computer knowledge based systems.

The purpose of this research was to develop a methodology to evaluate the likelihood of defective welds as a procedure proposal is entered into a computerised database system. The approach developed was assessed for hydrogen induced cold cracking (HICC) since this defect is a major problem in welding technology. An expert system was used to implement the methodology. The information for the expert system knowledge base was partly gathered from previous work in this area. The technique necessary to analyze and incorporate knowledge was organized in a structured form including the major area to be attacked. The final system was implemented using an expert system shell. The global task of analyzing a welding procedure was broken-down into three different stages. A welding procedure specification comprised the first stage. In the second stage, an interface between the expert system software and a database was implemented. Having proved the feasibility and advantages of integrating the expert system shell with a relational database the remainder of the work was devoted to the development of a strategy for operating the expert system and in particular dealing with uncertainty. Detailed validation of the knowledge base and the system as a whole were confined to a single defect type in the belief that the modularity of the system would allow extension to other defect types and the strategies developed in the present work should it be applicable. Results have shown that the system performs well in the specified area. Validation trials using simulated welding conditions generated by the expert system have shown a very good correlation with practical results for different classes of steels. The integration between approved welding procedure records and procedure qualification records could be the basis for a complete welding database management. Practical application of this system could be extended for educational purpose and training facilities.