Properties and long term behaviour of welded joints and claddings in high pressure hydrocracking equipment
The evaluation of metallurgical aspects of both the quality and fracture safety of welded joints and claddings in high temperature heat exchangers of a recently installed petrochemical plant has been carried out in a collaboration between the user and the producer of these components. This work has been motivated by questions about the strictness of the specification and the related long term behaviour on the one hand and about practical feasibility on the other. The paper commences with a comprehensive survey of the technological background of quality requirements and recommendations for production, the point of view being somewhat different from that of producers of welding materials, for instance. The second part describes some features of representative test materials, which were obtained in a pragmatic rather than a systematic way, by normal quality assurance procedures and by fracture mechanics, and medium term simulation of service at a temperature of 450 C. These data are a modest contribution to our knowledge in this field: for the user they should serve as a significant appendix to the quality documentation which could become valuable not only through its effect on service and maintenance practices, but also when long term experience with this equipment is discussed.