PSI - Issue 3

M.A. Beltrán et al. / Procedia Structural Integrity 3 (2017) 57–67 Author name / Structural Integrity P o edi 00 (2017) 000–000

65

9

L C Fig 9. Fracture surfaces of CVN specimens oriented in the L and C directions of API-5L X46 steel.

3.8 Coefficient of relative variation From the mechanical tests results, it was observed that the behavior of the analyzed material moves away from the isotropy, since the value of its mechanical properties depends on the direction in which they are measured. This condition is mainly attributed to the microstructural characteristics of the material, however, there is no parameter that relates the anisotropic mechanical behavior to the microstructural characteristics. Therefore, the variation of the microstructural and mechanical properties between the C and L directions were assessed by a comparison parameter designated as the coefficient of relative variation “r rv ”, which enable to correlate the influence of the microstructural properties on the mechanical anisotropic behavior of the API-5L. This parameter was obtained using the values in the L direction as the base parameter to divide the C values. Hence if the r rv value is equal to 1, the mechanical property possesses an isotropic behavior, on the other hand, if the r rv ≠1 there is an anisotropic behavior. The r rv results are shown in the Table 7.

Table 7. The r rv coefficient values for the L and C directions within the API-5L X46 steel.

C L

  rv c r

Property

(Unit less)

YS

1.25 1.05 1.13 1.11 1.31 0.71 1.75

UTS

C v

K IC-CV % RA

A i

(101) oriented planes

Consistent with the r rv coefficient values, the anisotropy on the fracture resistance properties (C v , K IC-CV ) and tensile strength properties (YS, UTS) are directly related to the content of grains oriented in the {101} planes. Thus, the higher content of grains oriented in the planes {101} the better the fracture resistance will be. On the other hand, the microstructural banding (Ai) shows an inverse relationship by reducing the pipeline steel fracture resistance (C V , K IC CV ). Hence, the higher banding degree the lower C V energy and K IC-CV values. Conclusions According to the obtained results, the API-5L X46 pipe-line steel showed an anisotropic behavior, getting a larger fracture resistance in the C crack propagation direction than the L direction, which variation is about the 18%. Also the tensile strength properties shows the same behavior, with larger values of YS and UTS in the C oriented specimens than the L oriented specimens. The variation of the microstructural and mechanical properties between the C and L