Evolution of the Corrosion Product Film and Its Effect on the Erosion-Corrosion Behavior of Two Commercial 90Cu-10Ni Tubes in Seawater

doi:10.1007/s40195-018-0745-1

Abstract

Abstract:

The composition and structural evolution of the corrosion product film of two commercial 90Cu-10Ni tubes, namely Tube A and Tube B, after being immersed in natural seawater for 1, 3, and 6 months were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy, and its effect on the erosion-corrosion behavior of the tubes was determined through a rotating cylinder electrode system using various electrochemical techniques. For the freshly polished samples used as contrast samples, the flow velocity mainly enhanced the cathodic reaction at low flow velocities while both the anodic and the cathodic reactions were remarkably accelerated at higher flow velocities. The corrosion product films formed on the two commercial 90Cu-10Ni tubes after being immersed in seawater for up to 6 months are of a complex three-layer or multilayer structure. The structural evolution of the films is out of sync for the two tubes. A continuous residual substrate layer depleted of Ni was observed in the inner layer of the films on Tube B after 30, 90, and 180 days’ immersion, while it was observed in the film on Tube A only after 180 days’ immersion. The nature of the inner layer plays a crucial role in the erosion-corrosion resistance of the 90Cu-10Ni tubes at higher flow velocity. The film with a compact and continuous inner layer of Cu₂O doped with Ni²⁺ and Ni³⁺ which bonds firmly with the substrate could survive and even get repaired with the increased flow velocity. The film on Tube B possessing a hollow and discontinuous inner layer composed of the residual substrate was degraded rapidly with increasing rotation speed in spite of its quite good resistance at the stagnant or lower speed conditions.

Key words: Copper-nickel alloy, Seawater immersion, Erosion-corrosion, Corrosion product film, Flow velocity

Okpo O. Ekerenam, Ai-Li Ma, Yu-Gui Zheng, Si-Yu He, Peter C. Okafor. Evolution of the Corrosion Product Film and Its Effect on the Erosion-Corrosion Behavior of Two Commercial 90Cu-10Ni Tubes in Seawater[J]. Acta Metallurgica Sinica (English Letters), 2018, 31(11): 1148-1170.

Figures/Tables 25

Table 1 Chemical composition (wt%) of the two experimental 90Cu-10Ni alloy tubes

Material	Ni	Fe	Mn	C	Pb	S	P	Zn	Cu
Tube A	10.4	1.73	0.68	0.014-0.027	<?0.001	0.004	0.003	<?0.01	Bal.
Tube B	10.4	1.51	0.59	0.009	<?0.001	0.002	0.002	<?0.01	Bal.

Fig. 1 Immersion test in Zhoushan sea area, China

Fig. 2 OCP measurements for Tubes A and B after a 0, b 30, c 90, d 180 day’s immersion in natural seawater

Fig. 3 Potentiodynamic polarization curves for the freshly polished (0 day) Tubes A a and B b, after (i) 0 and (ii) 30 days’ immersion in natural seawater

Fig. 4 Potentiodynamic polarization curves for Tubes A a and B b after (i) 90 and (ii) 180 days’ immersion in natural seawater

Table 2 Corrosion parameters of samples A and B obtained from Figs. 3 and 4

Immersion time (day)	Rotation speed (rpm)	Beta C (V/decade)		E_corr (mV)		I_corr (μA/cm²)		Corrosion rate (mpy)
Immersion time (day)	Rotation speed (rpm)	A	B	A	B	A	B	A	B
0	0	0.213	0.278	-?270.9	-?311.7	206.8	184.5	5.3	4.7
	400	0.183	0.173	-?237.9	-?274.6	265.6	254.9	6.8	6.6
	1300	0.175	0.225	-?248.8	-?253.5	954.1	323.5	24.5	8.3
	2200	0.185	0.159	-?241.4	-?254.3	941.5	511.7	24.2	13.2
30	0	0.284	0.292	-?535.2	-?485.2	73.4	58.5	1.9	1.5
	400	0.275	0.296	-?497.1	-?384.6	55.6	72.3	1.4	1.9
	1300	0.305	0.274	-?373.8	-?349.4	31.5	78.9	0.8	2.9
	2200	0.153	0.202	-?304.4	-?309.4	71.0	83.0	1.8	2.1
90	0	0.340	0.312	-?334.9	-?423.7	91.4	54.9	2.3	1.4
	400	0.279	0.267	-?348.9	-?419.7	58.5	76.1	1.5	2.0
	1300	0.269	0.240	-?367.2	-?362.5	55.7	136.7	1.4	3.5
	2200	0.374	0.240	-?350.5	-?323.8	49.0	128.4	1.3	3.3
180	0	0.282	0.286	-?570.2	-?562.4	112.2	184.2	3.7	4.7
	400	0.236	0.252	-?452.4	-?433.1	144.9	153.8	8.3	4.0
	1300	0.270	0.242	-?322.2	-?300.5	159.1	84.3	4.1	2.2
	2200	0.363	0.237	-?243.8	-?294.9	112.4	126.1	2.9	3.2

Fig. 5 Bode and Nyquist plots of freshly polished (0 day) of Tubes A a and B b

Fig. 6 Bode and Nyquist plots of Tubes A a and B b after 30 days’ immersion in natural seawater

Fig. 7 Bode and Nyquist plots of Tubes A a and B b after 90 days’ immersion in natural seawater

Fig. 8 Bode and Nyquist plots of Tubes A a and B b after 180 days’ immersion in natural seawater

Fig. 9 Equivalent circuits used for fitting the impedance spectra of the three alloy specimens after 0, 30, 90, and 180 days’ immersion in natural seawater. Equivalent circuit a for freshly polished samples (0 day) and equivalent circuit b for the filmed samples after 30, 90, and 180 days’ immersion in natural seawater

Table 3 Circuit parameters for sample A after 0, 30, 90, and 180 days’ immersion in natural seawater

Immersion time (day)	Rotating speed (rpm)	R_s (Ω cm²)	R_ct (kΩ cm²)	C_dl (μF cm^-2)	n ₁	R_fp (kΩ cm²)	C_fp (μF cm^-2)	n ₂	W (Ω^-1 S^-1/2)	R_fb (kΩ cm²)	C_fb (μF cm^-2)	n ₃	R_p (kΩ cm²)
0	0	16	0.389	42.1	0.74	1.16	0.03	0.98	0.004				1.55
	400	40.3	0.904	78.1	0.7	0.06	2730	1	0.055				0.96
	1300	18.8	0.008	22.1	0.86	0.67	30.2	0.53	0.371				0.68
	2200	22.7	0.531	280.9	0.82	0.01	82.3	0.02	0.915				0.54
30	0	42.6	0.177	9.6	0.82	0.47	18.97	0.7		6.16	36.71	0.25	6.81
	400	50.9	0.016	0.13	1	5.87	23.62	0.55		2.21	210.4	0.64	8.09
	1300	35.9	0.015	0.9	0.97	2.99	45.84	0.51		1.11	2850	0.88	4.11
	2200	66.4	0.095	2.41	0.95	0.16	4.95	0.92		0.81	45.3	0.58	1.06
90	0	54.3	1.051	31.23	0.55	1.45	2.83	0.99		1.78	0.02	0.84	4.28
	400	22	0.027	0.51	1	0.08	3.95	0.79		2.72	32.81	0.54	2.82
	1300	20.2	0.01	1	0.91	0.05	12.22	0.41		3.22	27.66	0.54	3.28
	2200	55.4	0.023	0.62	0.93	3.02	20.31	0.52		2.8	0.19	0.78	5.84
180	0	20.8	0.011	2.89	1	2.13	51.28	0.6		0.87	165.7	0.22	3.01
	400	21.3	0.016	1.93	0.99	1.98	42.81	0.55		0.01	875.7	0.89	2.01
	1300	21	0.018	2.11	0.97	0.87	74.26	0.52		0.85	3.07	0.37	1.74
	2200	44.4	0.04	2.03	0.9	0.45	31.58	0.6		0.44	24.61	0.74	0.93

Table 4 Circuit parameters for sample B after 0, 30, 90, and 180 days’ immersion in natural seawater

Immersion time (day)	Rotating speed (rpm)	R_s (Ω cm²)	R_ct (kΩ cm²)	C_dl (μF cm^-2)	n ₁	R_fp (kΩ cm²)	C_fp (μF cm^-2)	n ₂	W (Ω^-1 S^-1/2)	R_fb (kΩ cm²)	C_fb (μF cm^-2)	n ₃	R_p (kΩ cm²)
0	0	21.8	0.011	6.42	1	1.961	70.55	0.69	0.004				1.97
	400	37.2	0.838	85.84	0.65	1	2004	0.31	0.88				1.84
	1300	25.9	0.35	31.33	0.81	0.796	53.99	0.45	0.462				1.15
	2200	26	0.401	39.49	0.76	0.137	2620	0.4	0.447				0.54
30	0	21.9	0.031	3.62	0.86	2.035	10.45	0.7		4.212	29.59	0.34	6.28
	400	34	0.015	3.71	1	2.678	18.12	0.61		1.793	26.44	0.6	4.49
	1300	23.9	0.053	5.59	0.86	1.261	37.28	0.58		2.478	62.83	0.01	3.79
	2200	44.7	0.128	4.55	0.8	1.896	24.23	0.55		0.164	170.7	0.12	2.19
90	0	31.2	0.024	10.51	1	6.023	14.11	0.57		3.541	943	0.66	9.59
	400	26.7	0.025	1.2	0.9	4.703	31.67	0.52		4.75	2195	1	9.48
	1300	17.3	0.192	16.18	0.74	0.829	29.71	0.55		0.069	487.2	0.98	1.09
	2200	26	0.216	9.07	0.77	0.001	12.69	0.83		1.057	49.47	0.3	1.27
180	0	23.9	0.011	2.05	1	2.373	17.1	0.75		1.22	108.8	0.59	3.6
	400	23.2	0.018	1.06	1	0.782	18.1	0.66		2.948	47.44	0.53	3.75
	1300	25.1	0.005	2.91	0.95	0.017	268.7	0.39		1.213	83.67	0.59	1.23
	2200	49.7	0.042	3.61	0.85	0.891	43.94	0.59		0.173	2788	1	1.11

Fig. 10 Variation of Rp obtained from the EIS fitting with the immersion time in natural seawater and with increasing rotation speeds [0 rpm (A), 400 rpm (B), 1300 rpm (C), 2200 rpm (D)] used in the erosion-corrosion test

Fig. 11 Cross-sectional morphologies (backscattered electron images) of the corrosion product films formed on Tubes A a, c, e and B b, d, f after 30 days a, b, 90 days c, d, 180 days’ e, f immersion in natural seawater

Fig. 12 EDS line scan analysis of the corrosion product films formed Tube A a, c, e and Tube B b, d, f after 30 days a, b, 90 days c, d, 180 days’ e, f immersion in natural seawater. The light blue dash line marked within each subfigure is where the EDS line scan was carried out

Fig. 13 XRD patterns of the corrosion product formed on the surface of the 90Cu-10Ni Tubes A a and B b, respectively, after 30, 90, and 180 days’ immersion in natural seawater

Fig. 14 XPS depth profiles of elements sputtered at the original surface (i) and at the slope (ii) between the exposed alloy substrate and the original surface formed by the scrapping process of the corrosion product film on Tubes A a and B b, respectively, after 30 days’ immersion in natural seawater

Fig. 15 XPS depth profiles of the elements sputtered at the original surface (i) and at the slope (ii) between the exposed alloy substrate and the original surface formed by the scrapping process of the corrosion product film on Tubes A a and B b, respectively, after 90 days’ immersion in natural seawater

Fig. 16 XPS depth profiles of the elements sputtered at the original surface (i) and at the slope (ii) between the exposed alloy substrate and the original surface formed by the scrapping process of the corrosion product film on Tubes A a and B b, respectively, after 180 days’ immersion in natural seawater

Fig. 17 XPS spectra of Ni 2p sputtered for 300 s from (i) the original surface of the corrosion product and (ii) the slope between the exposed alloy substrate and the original surface after scrapping process of corrosion product film on Tubes A a and B b after 30 days’ immersion in natural seawater

Fig. 18 XPS spectra of Ni 2p sputtered for 300 s from (i) the original surface of the corrosion product and (ii) the slope between the exposed alloy substrate and the original surface after scrapping process of corrosion product film on Tubes A a and B b after 90 days’ immersion in natural seawater

Fig. 19 XPS spectra of Ni 2p sputtered for 300 s from (i) the original surface of the corrosion product and (ii) the slope between the exposed alloy substrate and the original surface after scrapping process of corrosion product film on Tubes A a and B b after 180 days’ immersion in natural seawater

Fig. 20 An ideal schematic mechanism of the corrosion process of the freshly polished samples in 3.5 wt% NaCl solution at the stagnant condition and at different rotation speeds

Fig. 21 Schematic diagrams of the structural changes of the corrosion product films formed on Tubes A a, c, e and B b, d, f after 30 days a, b, 90 days c, d, 180 days’ e, f immersion in natural seawater

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