Investigation of Stress Corrosion Cracking of Austenitic, Duplex and Super Duplex Stainless Steels under Drop Evaporation Test using Synthetic Seawater

Pereira, Henrique Boschetti; Panossian, Zehbour; Baptista, Ilson Palmieri; Azevedo, Cesar Roberto de Farias

doi:10.1590/1980-5373-MR-2018-0211

Henrique Boschetti Pereira ^**e-mail: henriquenono@yahoo.com.br

Instituto de Pesquisas Tecnológicas do Estado de São Paulo, Laboratório de Corrosão e Proteção, São Paulo, SP, Brasil

http://orcid.org/0000-0001-5415-6586

Zehbour Panossian

Instituto de Pesquisas Tecnológicas do Estado de São Paulo, Laboratório de Corrosão e Proteção, São Paulo, SP, Brasil

Ilson Palmieri Baptista

Centro de Pesquisa da Petrobrás, CENPES, Rio de Janeiro, RJ, Brasil

Cesar Roberto de Farias Azevedo

Departamento de Engenharia Metalúrgica e de Materiais, Escola Politécnica, Universidade de São Paulo, São Paulo, SP, Brasil

http://orcid.org/0000-0002-0813-6231

*e-mail: henriquenono@yahoo.com.br

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Figure 1
SCC mechanism: tensile decohesion of the atomic bounds due to the presence of adsorbed ions in the crystal lattice ahead of the crack tip⁴4 Raja VS, Shoji T, eds. Stress Corrosion Cracking - Theory and Practice. Sawston: Woodhead Publishing; 2011..

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Figure 2
SCC mechanism: cracking propagation of the crack tip due to the surface mobility induced by corrosive environment⁴4 Raja VS, Shoji T, eds. Stress Corrosion Cracking - Theory and Practice. Sawston: Woodhead Publishing; 2011.^,²⁵25 Galvele JR. Surface mobility mechanism of stress-corrosion cracking. Corrosion Science. 1993;35(1-4):419-434..

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Figure 3
SCC mechanism: formation of a brittle surface film at the crack tip²⁸28 Ricker RE, Fink JL, Escalante E. Evidence of film-induced cleavage by electrodeposited rhodium. Corrosion Deformations Interactions. In: Magnin T, Gras JM, eds. Corrosion Deformations Interactions. Les Ulis: Editions de Physique (EDP Sciences); 1993..

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Figure 4
SCC mechanism in FCC metals: hydrogen induced plasticity, promoting denser dislocation pile-up and higher stress field, causing the nucleation and brittle propagation of secondary cracks from the obstacle towards the tip of the primary crack. The stress field will also activate the slip system of the adjacent grain, repeating the process of nucleation and brittle propagation of secondary cracks⁴4 Raja VS, Shoji T, eds. Stress Corrosion Cracking - Theory and Practice. Sawston: Woodhead Publishing; 2011..

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Figure 5
Microstructure of the investigated SSs: (a) UNS S31603 ASS; (b) UNS S32205 DSS; (c) UNS S32750 SDSS. Optical microscope. Electrolytic etching: oxalic acid for ASS and KOH for DSS and ASS.

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Figure 6
Schematic representation of the apparatus for mechanical loading (four-point bending) of the specimen and their geometrical parameters³⁷37 ASTM International. ASTM G39-99 - Standard Practice for Preparation and Use of Bent-Beam Stress-Corrosion Test. West Conshohocken: ASTM International; 2011..

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Figure 7
General aspect of the salt deposit formed on the surface of all specimens after DET at 110 ºC for 500 h.

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Figure 8
Visual inspections of specimens tested at 110 ºC for 500 hours after the cleaning. (a) UNS S31603 ASS tested at 50 % of the yield stress (139 MPa); (b) UNS S32205 DSS tested at 100 % of the yield stress (473 MPa); and (c) UNS S32750 SDSS tested at 100 % of the yield stress (589 MPa). Visual inspection.

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Figure 9
Metallographic examination of the crack propagation, cross section after DET at 110 °C. (a) UNS S31603 ASS tested at 50 % of the yield stress (139 MPa); (b) UNS S32205 DSS tested at 100 % of the yield stress (473 MPa); (c) UNS S32750 SDSS tested at 100 % of the yield stress (589 MPa). Optical microscope.

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Figure 10
Propagation of the SCC along the microstructure after DET at 110 °C. (a) UNS S31603 ASS tested at 100 % of the yield stress (278 MPa); (b) UNS S32205 DSS tested at 100 % of the yield stress (473 MPa); (c) UNS S32750 SDSS tested at 100 % of the yield stress (589 MPa). Optical microscope.

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Figure 11
Microfractographic examination of the exposed surface of the cracks after DET at 110 °C. (a) UNS S31603 ASS tested at 100 % of the yield stress (278 MPa); (b) UNS S32205 DSS tested at 100 % of the yield stress (473 MPa); (c) UNS S32750 SDSS tested at 100 % of the yield stress (589 MPa). SEM.

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Figure 12
Microestrutural characterization below the exposed SCC surface after DET at 110 °C. (a) UNS S31603 ASS tested at 100 % of the yield stress (278 MPa); (b) UNS S32205 DSS tested at 100 % of the yield stress (473 MPa); (c) UNS S32750 SDSS tested at 100 % of the yield stress (589 MPa). FIB.

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Figure 13
Scheme of the salt deposit formed on all the DETed specimens tested at 110 ºC for 500 h. The SCCs were nucleated under the salt deposit, approximately 22 mm away from the center of the dripping region, by crevice corrosion⁴¹41 Pereira HB, Azevedo CRF. Can the drop evaporation test evaluate the stress corrosion cracking susceptibility of the welded joints of duplex and super duplex stainless steels? Engineering Failure Analysis. 2019. In Press..

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Figure 14
(a) Scheme showing the relative position of the cathodic (dripping zone) and the anodic reactions (under the salt deposit); (b) Temperature distribution along the upper surface of the specimen at 110 ºC. The temperature in the center of the dripping region is roughly 10 ºC lower than the testing temperature. Points located at -25 mm and + 25 mm represent the usual SCC nucleation sites⁴¹41 Pereira HB, Azevedo CRF. Can the drop evaporation test evaluate the stress corrosion cracking susceptibility of the welded joints of duplex and super duplex stainless steels? Engineering Failure Analysis. 2019. In Press..

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Table 1
General properties of UNS S31603, UNS S32205 and UNS S32760 stainless steels⁵5 Granta Design. CES Edupack 2017: General information, Database level 3. Oxford: Granta Design; 2017..

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Table 2
Chemical composition of UNS S31603 ASS, UNS S32205 DSS and UNS S32750 DSS ^* * Sulphur contents are not show in the table, but they were in accordance with the requirements of ASTM A24035. .

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Table 3
Mechanical properties of UNS S31603 ASS, UNS S32205 DSS and UNS S32750 SDSS at room temperature and the values of maximum tensile stress used for DET for conditions (a) and (b).

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Table 4
Saline concentration of synthetic sea water according to ASTM D1141³⁸38 ASTM International. ASTM D1193-06 - Standard Specification for Reagent Water. West Conshohocken: ASTM International; 2006.^-³⁹39 ASTM International. ASTM D1141-98e1 - Standard Practice for the Preparation of Substitute Ocean Water. West Conshohocken: ASTM International; 1999..

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(1)

Property	UNS S31603	UNS S32205	UNS S32760
Property	ASS	DSS	SDSS
Price (R$/kg)	18.5 to 21.4	20.6 to 22.4	29.4 to 31.8
Elastic modulus (GPa)	190.0 to 205.0	195.0 to 205.0	190.0 to 200.0
Yield strength (MPa)	170.0 to 310.0	460.0 to 510.0	515.0 to 565.0
Fracture toughness (MPa.m^(1/2))	53 to 72	144 to 195	150 to 195
Sea water corrosion resistance	Good	Good	Excellent
Pitting resistance equivalent number (PREN)	22.6 to 27.9	30.5 to 37.0	37.9 to 45.7
Pitting and crevice corrosion (µm)	Medium (20 to 30)	High (30 to 40)	Very high (> 40)
CO₂ footprint (kg/kg)	5.3 to 5.9	4.4 to 4.9	5.1 to 5.6

Steel	C	Si	Mn	P	Cr	Ni	Mo
UNS S31603 (ASS)	0.019 ± 0.001	0.44 ± 0.02	1.34 ± 0.01	0.035 ± 0.002	17.1 ± 0.1	10.1 ± 0.1	2.16 ± 0.01
ASTM A240 ³⁵35 ASTM International. ASTM A240-04 - Standard Specification for Chromium and Chromium-Nickel Stainless Steel Plate, Sheet, and Strip for Pressure Vessels and for General Applications. West Conshohocken: ASTM International; 2004. UNS S31603	< 0.03	< 0.75	< 2.00	< 0.045	16.0 to 18.0	10.0 to 14.0	2.0 to 3.0
UNS S32205 (DSS)	0.017 ± 0.002	0.38 ± 0.01	1.44 ± 0.02	0.026 ± 0.002	22.3 ± 0.3	5.79 ± 0.07	3.08 ± 0.03
ASTM A240 ³⁵35 ASTM International. ASTM A240-04 - Standard Specification for Chromium and Chromium-Nickel Stainless Steel Plate, Sheet, and Strip for Pressure Vessels and for General Applications. West Conshohocken: ASTM International; 2004. UNS S32205	< 0.03	< 1.0	< 2.0	< 0.030	22.0 to 23.0	4.5 to 6.5	3.0 to 5.0
UNS S32750 (SDSS)	0.015 ± 0.001	0.38 ± 0.02	1.44 ± 0.05	0.029 ± 0.002	24.9 ± 0.2	6.92 ± 0.06	3.76 ± 0.04
ASTM A240 ³⁵35 ASTM International. ASTM A240-04 - Standard Specification for Chromium and Chromium-Nickel Stainless Steel Plate, Sheet, and Strip for Pressure Vessels and for General Applications. West Conshohocken: ASTM International; 2004. UNS S32750	< 0.03	< 0.8	< 1.2	< 0.035	24.0 to 26.0	6.0 to 8.0	3.0 to 5.0

Property	ASS	ASTM A240	DSS	ASTM A240	SDSS	ASTM A240
Yield strength (MPa)	278 ± 2	> 170	473 ± 3	> 450	589 ± 3	> 550
Ultimate tensile stress (MPa)	629 ± 4	> 485	749 ± 4	> 655	877 ± 4	> 795
Elongation (%)	51 ± 1	> 40	35 ± 1	> 25	37 ± 1	> 15
DET, condition (a): 50% of the yield stress (MPa)	139	-	236	-	295	-
DET, condition (b): 100% of the yield stress (MPa)	278	-	473	-	589	-

Compounds	Concentration (g/L)
NaCl	24.53
MgCl₂	5.20
Na₂SO₄	4.09
CaCl₂	1.16
KCl	0.695
NaHCO₃	0.201
KBr	0.101
H₃BO₃	0.027
SrCl₂	0.025
NaF	0.003

[1] *e-mail: henriquenono@yahoo.com.br

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Investigation of Stress Corrosion Cracking of Austenitic, Duplex and Super Duplex Stainless Steels under Drop Evaporation Test using Synthetic Seawater

Abstract