Tables at a glance

Table 1

Table 2

Table 3

Table 4

Figures at a glance

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Table 1

Potential E0	-0.020 V vs open circuit potential
Potential E1	0.020 V vs open circuit potential
Step height	0.100 mV
Scan rate	0.166 mV/s
Step time	0.602 s
Number of points	401

Table 1: Polarization parameters

Table 2

Sample	% C	% P	% S	% Mn	% Si	% Cu
Annealed	0.2	0.03	0.031	1.16	0.06	0.054
Non- annealed	0.2	0.02	0.028	0.88	0.02	0.05
API5L2000	0.18-0.23	0.03 max	0.031 max.	1.40	-	-

Table 2: Chemical analysis results (% W)

Table 3

Sample/features	% vol. inclusions	% vol. ferrite	% vol. pearlite	ASTM grain size	Vickers hardness
Annealed base metal	0.45	76	24	10	187
Annealed ERW seam	0.61	68	32	11	190
Non-annealed base metal	0.62	73	27	8	214
Non-annealed ERW seam	0.80	62	38	11.5	242

Table 3: Quantitative microstructure features of samples

Table 4

	Sour solution pH = 5	Acid solution pH = 3
Zone	CR [mp/y]	CR [mp/y]
Annealed base metal	23.20	36.26
Annealed ERW seam	28.15	40.10
Non-annealed base metal	23.90	29.45
Non-annealed ERW seam	30.45	34.16

Table 4: Electrochemical parameters applied in the PR tests

FIGURE 1

Figure 1: ERW pipe failed in service due to selective corrosion at the seam weld

FIGURE 2

Figure 2: Diagram of the of the sample section

FIGURE 3

Figure 3: Princeton EG and G applied research digital potentiostatic. (a) Gases system. (b) Cell used. (c) Computer system

FIGURE 4

Figure 4: Non-annealed pipe microstructure, etched with 3% Nital [26, 27]. (a) Base metal; (b) Welded area; (c) HAZ

FIGURE 5

Figure 5: Annealed pipe microstructure, optical microscope [27]. (a) Base metal; (b) Internal surface; (c) ERW seam

FIGURE 6

Figure 6: Internal surface microstructure of the non-annealed pipe. (a) Before corrosion test; (b) After corrosion test (c) Corrosion product

FIGURE 7

Figure 7: Sample wall microstructure at the ERW seam after the SPP electrochemical test.

FIGURE 8

Figure 8: Current trend during 3.3 h SPP electrochemical test, corrosion test solution pH = 3

FIGURE 9

Figure 9: Current trend during 3.3 h SPP electrochemical test, corrosion test solution pH = 5