Experimental investigation of anisotropy in API X65 steel pipe using Charpy fracture energy

To use higher capacities in Iran's energy transmission systems, API standardized pipes made of API X65 steel have been utilized (made of thermo-mechanically controlled rolling process, TMCR steels). The TMCR inherently increases the anisotropic properties of steel coils and plates used for pipe manufacturing. In addition, the production of helical welded pipe involves steps that can lead to different mechanical properties in different directions. The aim of the present study is to measure the orientation dependence of the Charpy fracture energy. Therefore, the effect of changing the angle of specimens relative to the rolling direction and also the effect of changing the notch orientation (three notch A, B and C in total) on the fracture energy in API X65 steel has been experimentally determined. The maximum change in the average Charpy fracture energy at different angles relative to the rolling direction is a maximum of 13% (in notch B), but the largest change in the average Charpy fracture energy between different notches is a maximum of 12.2% (at an angle of 0 °). As a result, the effect of changing the angle of the specimen relative to the rolling direction is greater than the effect of changing the notch orientation on the Charpy fracture energy. Also, at an angle of 67.5 degrees to the direction of rolling (equivalent to the diagonal direction (D-D)), the most fracture energy for all notches was obtained. To quantitatively compare the fracture energy changes in different notches, an index called anisotropy index has been presented.