The influence of soluble salts content on the performance of an epoxy coating system via accelerated corrosion tests

Zimmermann, Camila Aparecida; Koslowski, Luciano André Deitos; Araújo, Maria Inês Siqueira; Silveira, Marcia Luciane Lange

doi:10.1590/S1517-707620200002.1048

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Articles • Matéria (Rio J.) 25 (2) • 2020 • https://doi.org/10.1590/S1517-707620200002.1048 copy

The influence of soluble salts content on the performance of an epoxy coating system via accelerated corrosion tests

Authorship SCIMAGO INSTITUTIONS RANKINGS

ABSTRACT

It is generally accepted that surpassing a threshold value of water-soluble salts at the substrate/coating interface can impart premature failure in painted structures. The Coatings industry has an identified need in defining a maximum allowable soluble salts content, however, a variety of threshold values are found in published data. Based on that, this work aims at evaluate the effect on epoxy coating performance of three different ranges of soluble salts content taking into account the maximum allowable values specified by NORSOK M-501 and IMO PSPC MSC.215, two important standards of naval and offshore sectors.

Blast-cleaned carbon steel specimens contaminated with sodium chloride solutions diluted in methanol ranging 20, 50 and 100 mg/m² NaCl were painted with two epoxy-amine paint coats. Samples were evaluated by cathodic disbondment, water immersion at 40 ºC, pull-off adhesion strength and cyclic corrosion tests.

Larger blisters and loss of adhesion were observed as the soluble salts content at the interface increased. Although, it was not possible to find a critical level of soluble salts even considering data about similar coating systems. A safe soluble salt content must be chosen based on tests that closer reproduce service and environmental conditions to which a painted structure will be exposed.

Keywords
Carbon steel; Corrosion; Soluble Salts Content; Epoxy; Paint

CONDITION	SPECIMEN SIZE (mm)	AREA (m²)	TARGET VALUE (mg/m² NaCl)	NaCl SOLUTION (g/L)	APPLIED VOLUME ON THE SURFACE FOR CONTAMINATION (mL)
A	100 x 150	0.01500	16	0.300	0.8
A	75 x 150	0.01125	16	0.300	0.6
B	100 x 150	0.01500	40	0.750	0.8
B	75 x 150	0.01125	40	0.750	0.6
C	100 x 150	0.01500	100	1.875	0.8
C	75 x 150	0.01125	100	1875	0.6

TEST	STANDARD PROCEDURE FOR TESTING	ESTIMATED LENGTH OF TIME (h)	DIMENSIONS OF SPECIMENS (mm)	NUMBER OF SPECIMENS PER CONDITION
Pull-off adhesion	ISO 2812-2 [³²32 ISO - INTERNATIONAL STANDARD ORGANIZATION. “ISO 2812-2: Paints and varnishes - Determination of resistance to liquids -- Part 2: Water immersion method”. Switzerland, 2007.]	24	100 x 150 x 3	1
Cathodic disbondment by impressed current	ISO 4624 [³³33 ISO - INTERNATIONAL STANDARD ORGANIZATION. “ISO 4624: Paints and Varnishes – Pull off test for adhesion”. Switzerland, 2002.]	720	100 x 150 x 3	3
Immersion in deionized water at 40° C	ASTM G-8 [³⁴34 ASTM - AMERICAN SOCIETY FOR TESTING AND MATERIALS. “ASTM G-8: Test Methods for Cathodic Disbonding of Pipeline Coatings”. West Conshohocken, United States of America 1996.]	3000	100 x 150 x 3	3
Cyclic corrosion	ISO 20340 [³⁵35 ISO - INTERNATIONAL STANDARD ORGANIZATION. “ISO 20340: Performance requirements for protective paint systems for offshore and related structures”, Switzerland, 2009.]	4200	75 x 150 x 3	3

DEGREE	RUSTED AREA (%)
Ri 0	0
Ri 1	0.05
Ri 2	0.5
Ri 3	1
Ri 4	8
Ri 5	40 a 50

GRADE	QUANTITY	GRADE	SIZE
0	None	S0	Not visible under x 10 magnification
1	Very few	S1	Only visible under magnification up to x 10
2	Few	S2	Just visible with normal corrected vision
3	Moderate	S3	Clearly visible with normal corrected vision (up to 0.5mm)
4	Considerable	S4	0.5 to 5 mm
5	Dense	S5	Larger than 5 mm

CONDITION	TARGET OF SOLUBLE SALTS CONTENT (mg/m² NaCl)	SOLUBLE SALTS CONTENT AVERAGE (mg/m² NaCl)
A	Up to 20	13.4 ± 0.8
B	From 21 up to 50	48.4 ± 0.8
C	From 51 up to 100	96.2 ± 8.1

CONDITION	DFT (µm)	PULL-OFF STRENGTH
CONDITION	DFT (µm)	DOLLY 01	DOLLY 02	DOLLY 03
A	290 – 305	5.68 MPa 98.2% C/Y, 1.8% Y/Z	5.26 MPa 100% C/Y	5.17 MPa 0.4% B/C; 99.6% C/Y
B	285 – 305	10.66 MPa 100% C/Y	9.05 MPa 100% C/Y	9.69 MPa 100% C/Y
C	245 – 300	8.65 MPa 100% C/Y	8.81 MPa 0.2% A/B; 0.5% B/C; 99.3% C/Y	7.49 MPa 100% C/Y

CONDITION	DFT (µm)	RUSTING DEGREE	ECD (mm)	PULL-OFF STRENGTHAFTER TEST
A	310 – 355	Ri 0	10.1	9.4 MPa 100% C/Y
	265 – 330	Ri 0	11.3	8.00 MPa 100% C/Y
	270 – 330	Ri 0	5.7	11.09 MPa 100% C/Y
B	285 – 310	Ri 0	13.0	6.19 MPa 33.2% A/B; 66.8% C/Y
	295 – 325	Ri 0	12.7	5.14 MPa 91.1% A/B; 8.9% C/Y
	300 – 330	Ri 0	13.7	5.59 MPa 16.0% A/B; 84.0% C/Y
C	300 – 340	Ri 0	Total disbondment	3.59 MPa 100% A/B
	295 – 355	Ri 0	Total disbondment	4.94 MPa 100% A/B
	305 – 340	Ri 0	Total disbondment	5.06 MPa 100% A/B

CONDITION	DFT (µm)	RUSTING DEGREE	BLISTERING DEGREE
A	295 – 320	Ri 0	4 (S3)
	300 – 330	Ri 0	4 (S3)
	280 – 340	Ri 0	4 (S3)
B	275 – 310	Ri 0	3 (S5)
	285 – 320	Ri 0	3 (S5)
	295 – 340	Ri 0	3 (S5)
C	295 – 335	Ri 0	3 (S5)
	255 – 305	Ri 0	4 (S5)
	290 – 330	Ri 0	3 (S5)

CONDITION	DFT (µm)	RUSTING DEGREE	CORROSION AROUND THE SCRIBE (mm)	PULL-OFF STRENGTHAFTER TEST
A	268 – 321	Ri 0	11.83	9.84 MPa 100% C/Y
	255 – 323	Ri 0	11.65	9.64 MPa 100% C/Y
	278 – 307	Ri 0	15.53	9.24 MPa 100% C/Y
B	291 – 310	Ri 0	15.15	6.75 MPa 100% C/Y
	293 – 317	Ri 0	13.83	7.15 MPa 100% C/Y
	291 – 333	Ri 0	14.49	8.60 MPa 100% C/Y
C	298 – 355	Ri 0	16.03	6.60 MPa 36.5% A/B; 63.5% C/Y
	301 – 360	Ri 0	12.38	6.21 MPa 22.8% A/B; 77.2% C/Y
	299 – 340	Ri 0	35	68 MPa 21.6% A/B; 78.4% C/Y

Laboratório de Hidrogênio, Coppe - Universidade Federal do Rio de Janeiro, em cooperação com a Associação Brasileira do Hidrogênio, ABH2 Av. Moniz Aragão, 207, 21941-594, Rio de Janeiro, RJ, Brasil, Tel: +55 (21) 3938-8791 - Rio de Janeiro - RJ - Brazil
E-mail: revmateria@gmail.com

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[1] Autor Responsável: Camila Aparecida Zimmermann

SUBSTRATE	Steel hot rolled, ASTM A36-08 (Usiminas)
SURFACE PREPARATION	Abrasive blast-cleaned at Sa 2 ½ [²⁵25 ISO - INTERNATIONAL STANDARD ORGANIZATION. “ISO 8501-1: Preparation of steel substrates before application of paints and related products - visual assessment of surface cleanliness -- part 1: rust grades and preparation grades of uncoated steel substrates after overall removal of previous coatings”. Switzerland, 2007.]
ROUGHNESS PROFILE (µm)	Between 50 and 80
MANUFACTURER	Weg Tintas LTDA. (Guaramirim, Brazil)
FIRST COAT	Primer-top coat epoxy amine two pack Grey N 6.5
NOMINAL DRY FILM THICKNESS – NDFT (µm)	150
SECOND COAT	Primer-top coat epoxy amine two pack White N 9
NOMINAL DRY FILM THICKNESS – NDFT (µm)	150