Effect of long-time postweld heat treatments on the mechanical properties of a carbon-manganese pressure vessel steel: Fid-Bau Portal

Effect of long-time postweld heat treatments on the mechanical properties of a carbon-manganese pressure vessel steel

Pimenta, G. / Bastian, F.

Postweld heat treatment is a common practice among building codes for welded steel structures and equipment to reduce the high as-welded residual stress level, improve the fracture toughness, and increase the critical size of acceptable defects. There are many discrepancies among international codes for storage spheres, pressure vessels, and welded structure components about parameters such as duration and temperature for postweld heat treatments. Furthermore, the codes frequently omit the top number of thermal cycles, which the structure may support to maintain the mechanical properties and toughness in an acceptable level, keeping the physical integrity of the equipment. The present work analyzes the effect of duration of the postweld heat treatments on the mechanical properties and fracture toughness of a carbon-manganese steel of specification ASTM A-516 G 70, which frequently is used to build spheres and pressure vessels in the petrochemical industry. The regions corresponding to the base metal (BM) and heat-affected zone (HAZ) were studied. Through the results obtained from the tensile tests, hardness measurements, Charpy V-notch impact and crack-tip opening displacement (CTOD) testing, and microstructural characterization, it is concluded that the mechanical properties and fracture toughness were reduced by increasing the time of the postweld heat treatment. The degradation of the original properties of the steel is attributed to the changes that occurred in the microstructure. With the welding procedure used, it was verified that the fracture resistance of the HAZ was higher than that of the BM.