PSI - Issue 13

M. Newishy et al. / Procedia Structural Integrity 13 (2018) 353–360 M. Newishy / Structural Integrity Procedia 00 (2018) 000–000

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4.3. SEM and EDS examinations Scanning electron microscope (SEM) examination has been used for in-depth examination of the microstructure of the black and brown sheet materials. Typical austenitic grains with deformation bands (white wavy lines) were observed in Fig. 5. Fig. 6 shows the fine intergranular corrosion cracks initiated from the outer surface in the direction normal to the cold deformations. Shear bands are more visible at the cross-section of the sheets as shown in Fig. 6. Energy dispersive spectroscopy (EDS) spot analysis was carried out on 9 different locations as shown in the Fig. 7. Example of The result of EDS are given in Figs. 8-10. The obtained result shows that the matrix is close to 316 austenitic stainless steel composition; (point 6). Meanwhile, the other point showed compositions away from the composition of 316 stainless steels. Most importantly, the corrosive chloride (Cl) element was detected in many positions (points 1, 2, 3, 4 and 7) which means that Cl is introduced to the metal from the working environment (probably from water) especially at the crack site. The scales from the packing sheets were also analyzed using XRF analysis and the results are given in Table 3. High percentage of Si, Al, S, Ca, Cu, Zn and K were detected in corrosion scales. Cl was also detected in the corrosion scales. This means that the water used was not cleaned enough before starting the operation. 5. Discussion General visual examination of the received segment of packing sheets showed that the corrosion scale covered all the surfaces with many perforated attacks on high stressed location for sheets having black color. Chemical analysis by spark ignition spectroscopy showed conformity of the un-used material with the chemical composition of 316L. Microstructure investigations, SEM images, EDS analysis and hardness measurements indicated the presence of Cl and residual few shear bands related to sheets manufacturing process (cold deformation). deformation on corrosion is related to additional energy. It leads in consequences to decreasing the thermodynamic durability of the material. The occurrence of (CLSCC) depends mainly on three factors: susceptibility of the material, environment and considerable residual stresses.

Fig. 5. SEM microstructure of the corroded black sheet showing austenitic grains with remaining shear bands resulted from deformation.

Table 3. XRF analysis of the deposits on the corroded packing

K

Ca

Ti

V

Elem.

Na

Si

P

S

Cl

%

0.87

6.7 Mn

0.14

3.41

0.4 Cu

3.99

1.28 Mo

0.8 Ba

0.8

Elem.

Cr

Fe

Al

Zn 2.8

Sr

%

3.83

0.44 Mg

25.8

5.43

1

11.09

0.46

0.99

Elem.

Ni

%

28.436

0.7