Fracture toughness evaluation of 1.4841 bolt subjected to simultaneous effects of creep and hydrogen embrittlement phenomena using small punch test: A case study in a superheater of a petrochemical unit.

Petrochemical components, especially superheater internal parts, work under very harsh conditions and in destructive environments, such as proximity to the high temperature caused by the fire, surrounded by corrosive gases, effects of hydrogen released by burning gas or incomplete burning. All these factors along with loading factors and other destructive phenomena such as creep at high temperatures directly affect the mechanical behavior of components. In other words, because of these conditions, the components will have different mechanical behavior compared to the non-operated components. In the present research, a case study was conducted on the failed bolts supporting long U-shaped tubes (approximately 17.85 m in length) contain saturated vapor and superheated steam. Previous studies indicated that these bolts are subjected to creep phenomenon and hydrogen embrittlement. A small punch test was used to determine the mechanical properties (i.e., ultimate strength and fracture toughness) of the failed bolts. Moreover, Finite Element (FE) simulation was performed for non-operated bolts made of Stainless Steel 1.4841 (SS 1.4841) and the model validation process was performed using the comparison technique between simulation and laboratory results. Furthermore, the FE model was developed for future research. The results showed that in the studied conditions, the ultimate strength and fracture toughness of SS 1.4841 bolts reduced by 33% and 65%, respectively, compared to the raw situation.