PSI - Issue 68

3

Reza Khadem Hosseini et al. / Procedia Structural Integrity 68 (2025) 409–414 R. K. Hosseini / Structural Integrity Procedia 00 (2025) 000–000

411

Fig. 2. (a) Inner and outer surfaces of tube sample B; (b) inner surface of tube sample A and its stereographic image.

Table 1. Chemical composition of the tube material compared to the ASTM A213 (wt. %)

Elements

C

Mn

Si

Cr

Mo

S

P

Fe

Tube materials

0.15

0.47 0.30- 0.60

0.52 0.25- 1.00

9.10

0.95 0.90- 1.10

0.013 0.025 max.

0.008 0.025 max.

Ball.

ASTM A213 standard

8.00- 10.00

0.15 max.

Ball.

2.3. Macro and Micro-structure Evaluation A macro-etch test was conducted to investigate carburization phenomena in the cross-section of the tubes, while chemical etching was performed to observe microstructural characteristics using light microscopy with 10% and 2% Nital etchants, respectively. As shown in Fig. 3, carburization was observed near both internal and external surfaces in the cross-sections of both samples A and B. The optical micrographs of areas adjacent to the tube's inner wall of samples A and B are presented in Fig. 4a and Fig. 4b, respectively. The microstructural evaluations presented in Fig. 4b indicate that the microstructure of areas close to both tube walls is fully carburized.

Fig. 3. (a) Inner and outer surfaces of tube sample B; (b) inner surface of tube sample A and its stereographic image.

Fig. 4. The optical micrographs of areas adjacent to the tube's inner wall; (a) tube A; (b) tube B.