Effect of pitting corrosion on the mechanical properties of 316 grade stainless steel

Effect of pitting corrosion on the mechanical properties of 316 grade stainless steel

Materials Today: Proceedings xxx (xxxx) xxx Contents lists available at ScienceDirect Materials Today: Proceedings journal homepage: www.elsevier.co...

1MB Sizes 0 Downloads 54 Views

Materials Today: Proceedings xxx (xxxx) xxx

Contents lists available at ScienceDirect

Materials Today: Proceedings journal homepage: www.elsevier.com/locate/matpr

Effect of pitting corrosion on the mechanical properties of 316 grade stainless steel Kiran Lakkam ⇑, Shirish M.Kerur, Anilkumar Shirahatti Department of Mechanical Engineering, Jain College of Engineering, Belagavi, India

a r t i c l e

i n f o

Article history: Received 1 August 2019 Received in revised form 25 November 2019 Accepted 27 November 2019 Available online xxxx Keywords: Stainless steel 316 Pitting corrosion Mechanical properties pH value Ferric chloride solution

a b s t r a c t Stainless steel, due to its high corrosion resistance finds exhaustive industrial and architectural applications. This resistance to corrosion in stainless steel can be attributed to the presence of about 18% of Chromium. Chromium forms a shining, thin passive film that protects the surface from the external corrosive environment. By increasing chromium and nickel contents, this type of steel becomes increasingly resistant to pitting corrosion. However, higher concentrations of these alloying elements results in lower carbon solubility and carbide segregation. The main objective of accelerated corrosion testing is to simulate the field environment under laboratory conditions. To see the actual effect of corrosion on stainless steel it takes a few years. Therefore, the controlling factors for accelerated corrosion test are similar to those in the field tests. Ó 2019 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of the scientific committee of the First International Conference on Recent Advances in Materials and Manufacturing 2019.

1. Introduction Pitting corrosion is one of the most widespread and a devious form of localized corrosion of passive metals and it commonly occurs in a range of aggressive environments [17]; Lee et al., 2011). This type of corrosion is generally restricted to a small area of the metal surface and it can cause the structure to fail by perforation or by generating stress corrosion cracks (Tian et al., 2014). Pitting corrosion is normallyseen in austenitic steel exposed to aqueous media containing chloride ions. The most aggressive ion is chloride in Pitting corrosion and has always been considered one of the major operational problems in power plants and anion found in many natural and industrial environments including seawater. Field performance testing in a relevant environment is the most reliable form of evaluating pitting resistance of steel but it can take many years to produce useful performance data. Therefore, laboratory tests, which simulate natural exposure in an accelerated manner consistent with the field performance, are required to produce data in months rather than years [4]. The main objective of accelerated corrosion testing is to simulate the field environment under laboratory conditions and therefore, the controlling factors for accelerated corrosion test are similar to ⇑ Corresponding author.

those in the field tests. Research shows the common factors contributing to the initiation and propagation of pitting corrosion are:  Localized chemical or mechanical damage to the protective oxide film  Factors that can cause breakdown of a passive film, such as acidity, low dissolved oxygen concentrations and high chloride concentrations; these are likely to turn a protective oxide film less stable, and thereby initiate pit.  Localized damage to, or poor application of, protective coating  Presence of non-uniformities in the metal structure of the component such as non-metallic inclusions. Pitting corrosion can produce pits with their mouth open (uncovered) or covered with a semi-permeable membrane of corrosion products. Pits can be of various shapes. Fig. 1 shows the common pit shapes divided in two groups namely: trough pits (upper) and sideway pits (lower): Pitting cavities may fill with corrosion products and form caps over the pit cavities, sometimes creating nodules or tubercles. While the shapes of the pits vary widely, as observed in Fig. 1, they are usually roughly saucer-shaped, conical, or hemispherical for steel and many associated alloys. Zaya et al. studied pitting theory and stages of pit development; the schematic of different stages for the development of an individ-

E-mail address: [email protected] (K. Lakkam). https://doi.org/10.1016/j.matpr.2019.11.293 2214-7853/Ó 2019 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of the scientific committee of the First International Conference on Recent Advances in Materials and Manufacturing 2019.

Please cite this article as: K. Lakkam, S. M.Kerur and A. Shirahatti, Effect of pitting corrosion on the mechanical properties of 316 grade stainless steel, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.11.293

2

K. Lakkam et al. / Materials Today: Proceedings xxx (xxxx) xxx

Fig. 1. Common pit shapes [23].

pits appears to be unpredictable. This form of localized corrosion can lead to accelerated failure of structural components by perforation or by acting as an initiation site of cracking. Fig. 3 shows an SEM image of the deep pits on a metal surface. As the oxygen content in the sea water is higher at the surface water, there will be higher electrode potential of the metal in the sea. Hence there will be faster corrosion rate of the metal. But when stainless steel is oxidized, the surface forms a thin layer of oxide film to protect the metal and prevents further corrosion, that is, to maintain a passive state [27,28].

2. Objectives of this research

Fig. 2. Various stages of pitting corrosion process [24].

ual pit can be seen in the Fig. 2. They distinguished various stages of the pitting corrosion process and divided them into four stages. Stage 0 represents an un-attacked metallic surface which is completely covered with the passive films. Stage 1 involves the rupture of the passive layer; the substrate is still protected except for a small patch in contact with the electrolyte. The dimension of the small patch in stage 1 can be smaller or comparable to the thickness of the passive film. Subsequently, the dissolution of the substrate begins. Stage 2 is reached when the conditions for pit growth are met and re-passivation cannot occur anymore i.e. the pit begins to grow. Therefore, in stage 3 the dissolution of the substrate begins to grow and the pit becomes about 1 to 10 which can be seen under optical microscope. Pits have a shape of hemisphere or of a polyhedron by stage 3. At the final stage 4 the pits can be seen with the naked eye. The pit can have an irregular shape if partially covered around the mouth with solid corrosion products. Many researchers, as Evens and Bannister in 1931, and later Richardson in 1973, claim that local weak spots or defects are always present in the passive films. Therefore stage 0 never exists and, immediately after immersion in a corrosive solution, the process starts at stage 1, where the metal and solution are in contact. The induction period only corresponds to the rate time necessary for the corrosion to be well developed and detectable. Additionally, the corrosive attack is highly localised and the precise location of

The present work employs the ASTM G48-11 [12] standard to evaluate the extent of pitting corrosion damage on 316 stainless steel specimen. During the experimental procedure, several challenges were encountered, including the limited information available on experimental factors and response variables such as the pH, chemical properties of the ferric chloride and its proper concentration, orientation of the specimens, and time of exposure, all of which control the pitting process. Empirical knowledge, gained through experimentation is presented in this paper to

Fig.3. Deep pits on a metal surface [17].

Please cite this article as: K. Lakkam, S. M.Kerur and A. Shirahatti, Effect of pitting corrosion on the mechanical properties of 316 grade stainless steel, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.11.293

3

K. Lakkam et al. / Materials Today: Proceedings xxx (xxxx) xxx

The specimen are prepared as per [10] standards for conducting tensile test as shown if Fig. 4 and [11] standard is used for impact test as shown in Fig. 5. Fig. 4 shows a rectangular cross section tensile test specimen. The width at the gripper end is maintained to 10 mm, with its length as 30 mm. The gauge length is 25 mm. suitable fillet radius were provided when there was a sudden change in the cross section to reduce the stress. Fig. 5 shows the specimen used to test the impact strength. Charpy impact test is conducted where the angle of swing of the hammer is 140°. The notch was kept facing away from the hammer. The specimen is kept in the form of simply supported beam.

address these challenges. We have attempted to achieve the following objectives:  To carry out accelerated pitting corrosion on stainless steel grade 316 by immersing the specimen in a corrosive solution for varying time periods i.e. 24 h, 48 h, 72 h and 96 h  To study the effect of corrosion on the mechanical properties of the specimen. Focus was on the main mechanical properties viz. Tensile strength, Impact strength and Hardness.  To evaluate the loss of mass in the specimen after corrosion.  To Study the pH of ferric chloride solution.

3.1. Procedure for pitting corrosion (ASTM G48)

3. Experimental studies

 600 ml of ferric chloride test solution was poured in a 1000 ml test beaker. Provide a solution volume of at least 5 ml/cm2(30 ml/in.2) more than of specific surface area. Transfer the test beaker to a constant temperature bath and allow the test solution to come to the equilibrium temperature of interest. Recommended temperatures for evaluation are 22 ± 2 °C and 50 ± 2 °C.  The specimen is placed in a glass cradle and immersed in the test solution after it has reached the desired temperature. Maintain test solution temperature throughout the test.  Cover the test vessel with a watch glass. Specimen is kept in the solution for 24 h, 48 h, 72 h, and 96 h.

Grade 316 is the standard ‘‘18/8” stainless steel; it is the most versatile and most widely used stainless steel, available in a wider range of products, forms and finishes than any other. It has excellent forming and welding characteristics. Grade 316 is readily roll formed into a variety of components for applications in the industrial, architectural, and transportation fields. Grade 316 also has supreme welding characteristics. Post-weld annealing is not required when welding thin sections. The composition of 316 grade stainless steel used for the present work is tabulated in Table 1 and the mechanical properties 316 stainless steel are tabulated in Table 2.

Table 1 Composition of 316 stainless steel. Grade 316

Min Max

C

Mn

Si

P

S

Cr

Mo

Ni

N

– 0.08

– 2.0

– 0.75

– 0.045

– 0.030

16 18

2.00 3.00

10.0 14

– 0.10

Table 2 Mechanical properties of 316 stainless steel. Grade

Tensile Strength (MPa) min.

Yield Strength 0.2% Proof (MPa) min.

Elongation (% in 50 mm) min.

Rockwell Hardness (HR B) max.

316

515

205

40

95

Fig. 4. Schematic diagram of the stainless steel test specimen for tensile testing. (ASTM E8/E8M-13a).

Fig. 5. Stainless steel specimen for impact testing [11].

Please cite this article as: K. Lakkam, S. M.Kerur and A. Shirahatti, Effect of pitting corrosion on the mechanical properties of 316 grade stainless steel, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.11.293

4

K. Lakkam et al. / Materials Today: Proceedings xxx (xxxx) xxx

Fig. 6. Experimental setup for pitting test [25].

4. Results and discussion Impact test was conducted on two specimens each for varying times of corrosion to obtain the average value. Table 3 shows the average impact strength for specimen with different corrosion times. These values are graphically represented in Fig. 8. The tensile test results are tabulated in Table 4 and represented graphically in Fig. 9. It can be easily concluded from Fig. 8 that corrosion treatment has a positive effect on the impact strength. This is mainly because corrosion essentially is a surface or subsurface phenomenon. During this, the internal grain structure modifies itself to resist corrosion thereby increasing its impact strength. Keeping the specimen in a corrosive environment for 72 h resulted the maximum impact strength. Size parameters like pit depth and pit density i.e. measured in terms of pits per square inch or millimetre, can easily influence the mechanical properties of the material (David and Hoeppner). Plate thickness does not have significant impact because pitting corrosion essentially occurs at the surface. Material hardness varies with intensity of corrosion since it is a surface property. pH of solution used for testing also influences the rate of corrosion. Further, it is observed that as the exposure time increases the pH level of solution decreases Tables 5–7. Specimen without corrosion treatment exhibited better tensile strength than specimen with corrosion treatment (24 h, 48 h and 92 h respectively). However, specimen with 72-hour corrosion treatment showed a higher tensile strength amongst the entire specimen. A SEM analysis of the entire specimen can give a clear understanding as to the reason behind this phenomenon.

(a) Container for conducting Corrosion experiment Fig. 7a. Container for conducting Corrosion experiment.

5. Conclusion

(b) Chemicals used for Corrosion experiment Fig. 7b. Chemicals used for Corrosion experiment.

 Remove the specimen, rinse with water and scrub with a nylon bristle brush under running water to remove corrosion products, dip in acetone or methanol, and air-dry.  Weigh each specimen to an accuracy of 0.001 g or better and reserve for examination Figs. 6, 7a and 7b show the schematic representation of the set up used to conduct the corrosion experiment.

Increase in time duration of corrosion, results in increase of impact strength of stainless steel grade 316. This may be attributed to the compaction of microstructure in the presence of a corrosive environment. The microstructure rearranges itself to resist the attack from corrosion ions. The tensile strength after immersing the specimen in the corrosive bath reduces. However, it is observed that for 24 h, 48 h the tensile strength keeps on increasing, reaches a maximum at 72 h and later reduces at 96 h of immersion. The trend can be further assessed by keeping the specimen for 120 h. There is a marginal reduction in the hardness of specimen with respect to the increase in the time of immersion. Hardness being

Table 3 Impact test results for stainless steel grade 316. Sample No.

Normal

24 h

48 h

72 h

96 h

01 02 Average in J/mm2

1.6125 1.6538 1.6331

1.9873 1.8125 1.8999

2.2692 2.200 2.2346

2.4625 2.0519 2.2572

2.1428 2.1375 2.1401

Please cite this article as: K. Lakkam, S. M.Kerur and A. Shirahatti, Effect of pitting corrosion on the mechanical properties of 316 grade stainless steel, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.11.293

5

K. Lakkam et al. / Materials Today: Proceedings xxx (xxxx) xxx

Impact strength (J/mm2)

2.5 2

Normal

1.5

24 hours 48 hours

1

72 hours 0.5

96 hours

0 Normal

24hours

48hours

72hours

96hours

Fig. 8. Graphical representation of impact strength values for stainless steel grade 316.

Table 4 Tensile test results for stainless steel grade 316. Sample No.

Normal

24 h

48 h

72 h

96 h

01 02 Average in MPa

977.7 975.8 976.7

708.3 672.2 690.2

738.8 726.3 732.6

802.5 736.1 769.3

751.3 746.9 749.1

Tensile strength (MPa)

1200 1000 Normal

800

24 hours

600

48 hours

400

72 hours

200

96 hours

0 Normal 24 hours

48 hours

72 hours 96 hours

Fig. 9. Graphical representation of tensile strength values for stainless steel grade 316.

Table 5 Weight loss in the specimen for varying corrosion times. Tensile specimens

Impact specimens

Duration in Hours

Before corrosion (grams)

After corrosion (grams)

Weight loss in grams

Before corrosion (grams)

After corrosion (grams)

Weight loss in grams

24 24 24 Average

84.65 83.74 81.20 83.19

80.08 78.92 76.21 78.64

4.57 4.82 4.99 4.79

42.79 42.83 41.45 42.34

41.43 41.61 40.19 41.07

1.36 0.22 1.26 0.94

48 48 48 Average

83.28 80.51 81.86 81.88

78.58 74.88 76.52 76.66

4.70 5.63 5.34 5.22

42.54 43.02 42.82 42.79

41.23 41.79 41.57 41.53

1.31 1.23 1.25 1.26

72 72 72 Average

92.28 84.77 84.15 87.06

86.92 79.33 79.26 81.83

5.36 5.44 4.89 5.23

43.01 43.08 42.64 42.91

41.48 41.89 41.47 41.61

1.53 1.19 1.17 1.29

96 96 96 Average

87.19 82.40 82.49 84.02

78.72 76.38 75.68 76.76

8.47 6.02 6.81 7.1

42.57 42.86 42.83 42.75

41.07 40.57 40.87 40.83

1.50 2.30 1.97 1.92

Normal Normal Normal Average

92.60 82.54 83.50 86.21

– – –

– – –

42.93 43.14 42.80 42.95

– – –

– – –

Please cite this article as: K. Lakkam, S. M.Kerur and A. Shirahatti, Effect of pitting corrosion on the mechanical properties of 316 grade stainless steel, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.11.293

6

K. Lakkam et al. / Materials Today: Proceedings xxx (xxxx) xxx

Table 6 Brinell Hardness values after testing of stainless steel 316. Sample No.

Normal

24 h

48 h

72 h

96 h

01 02 Average

129.7 128.5 129.1

128.2 130.5 129.3

128 129.2 128.6

129.0 128. 128.6

126.5 126.2 126.3

Table 7 Variation in pH value with respect to time of immersion.

[24] P.G.R. Zaya, Evaluation of Theories for the Initial Stages of Pitting Corrosion, McMaster University, McMaster, 1984. [25] Jyoti Bhandari et al. ‘‘Accelerated pitting corrosion test of 304 stainless steel using ASTM G48; Experimental investigation and concomitant challenges” Journal of Loss Prevention in the Process Industries, 2017. [27] M. Doddamani, M. Mathapati, M.R. Ramesh, Plasma sprayed Cr3C2-NiCr/fly ash cenosphere coating: cyclic oxidation behavior at elevated temperature, Mater. Res. Express 5 (12) (2018) 126404. [28] M. Mathapati, M. Doddamani, Cyclic oxidation behavior of plasma sprayed NiCrAlY/WC-Co/cenosphere coating, AIP Conference Proceedings 1943 (2018).

Further reading

Grade

Normal

24 h

48 h

72 h

96 h

316

1.02

1.56

1.44

1.66

1.5

a surface property, cannot be directly evaluated at the pits that are formed. At other surface, corrosive environment is found to have a less effect on hardness. There is a substantial decrease in the pH value of the solution as the time of immersion increases. This is due to the reaction occurring between the solution and the specimen. CRediT authorship contribution statement Kiran Lakkam: Methodology, Formal analysis, Investigation, Data curation, Writing - original draft, , Visualization. Shirish M. Kerur: Conceptualization, Validation, Resources, Writing - review & editing, Supervision, Project administration. Anilkumar Shirahatti: Conceptualization, Validation, Resources, Writing - review & editing, Supervision, Project administration. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. References [4] D. Ward, Correlation of accelerated corrosion testing with natural exposure after 6 years in a coastal environment, Corrosion NACE Int. (2008). [10] ASTM E18, ASTM E8/E8M-13a International, ‘‘West Conshohocken United States for hardness test and tensile test”. PA 19428-2959. 100 Barr Harbor Drive, PO Box C700. [11] ASTM E2248-15, ASTM, ‘‘Test Method for Impact Testing of MiniaturizedCharpy V-Notch Specimens”. International, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959. United States. [12] ASTM G48 ‘‘Standard Test Method for Pitting and Crevice Corrosion Resistance of Stainless Steels and Related Alloys by Use of the Ferric Chloride Solution Methods E and F”, February 1, 2002. [17] J. Bhandari, F. Khan, R. Abbassi, V. Garaniya, R. Ojeda, Modelling of pitting corrosion in marine and offshore steel structures-a technical review, J. Loss Prev. Process Ind. 37 (2015) 39e62. [23] ASTM G46 ‘‘Standard Guide for Examination and Evaluation of Pitting Corrosion1”, Designation: G 46 – 94 (Reapproved 2005).

[1] N.J. Laycock, D.P. Krouse, S.C. Hendy, D.E. Williams, Computer simulation of pitting corrosion of stainless steels, Electrochem. Soc. Interface 23 (2014) 65– 71. [2] R.B. Ribeiro, J. Silva, L. Hein, M. Pereira, E. Corodo, N. Matias, Morphology characterization of pitting corrosion on sensitized Austenitic Stainless Steel by Digital Image Analysis, ISRN Corrosion (2013). [3] J. Bhandari, F. Khan, R. Abbassi, V. Garaniya, R. Ojeda, Reliability assessment of offshore asset under pitting corrosion using Bayesian network, Corrosion NACE Int. 35 (2016) 399–406. [5] I. Chaves, R. Melchers, Long term localized corrosion of marine steel pilling welds, Corrosion Eng. Sci. Technol. 48 (2013) 469–474. [6] S. Caines, F. Khan, J. Shirokoff, W. Qiu, Experimental design to study corrosion under insulation in harsh marine environments, J. Loss Prev. Process Ind. 33 (2012) 39–51. [7] M.T. Woldemedhin, R.G. Kelly, Evaluation of maximum pit size model on stainless steel under atmospheric conditions, ECSV Trans. 58 (2014) 41–50. [8] E. Otero, A. Pardo, M. Utrilla, E. S_aenz, F. Perez, Influence of microstructure in the corrosion resistance of AISI type 304L and type 316L sintered stainless steels exposed to ferric chloride solution, Mater. Charat. 35 (1995) 145–151. [9] V. Zatkaliková, M. Bulovina, V. Škorik, L. Petreková, Pitting corrosion AISI 316 steel with polished surface, Mater. Eng. 17 (2010) 135–147. [13] A.U. Malik, S. Ahmad, I. Andijani, S. Al-Fouzan, Corrosion behavior of steels in Gulf seawater environment, Desalination 123 (1999) 205e213. [14] T.H. Abood. The Influence of Various Parameters on Pitting Corrosion of 316l and 202 Stainless Steel. Department of Chemical Engineering of the University of Technology. University of Technology, 2008. [15] Z. Szklarska-Smialowska. Pitting corrosion of metals. Natl. Assoc. Corros. Eng. Tang, X., Cheng, Y., 2011. Quantitative characterization by microelectrochemical measurements of the synergism of hydrogen, stress and dissolution on near neutral pH stress corrosion cracking of pipelines. Corros. Sci. 53, 2927e2933, 1986. [16] X. Tang, Y.F. Cheng. Quantitative characterization by micro-electrochemical measurements of the synergism of hydrogen, stress and dissolution on nearneutral pH stress corrosion cracking of pipelines Corrosion Science 53 9 2011 2927 2933 DOI: 10.1016/j.corsci.2011.05.032 https://linkinghub.elsevier.com/ retrieve/pii/S0010938X1100254X. [18] R. Melchers, Effect of temperature on the marine immersion corrosion of carbon steels, Corrosion 58 (2002) 768e782. [19] W. Maureen, V.A.A. Lisa, V.W. Lorenzo, Corrosion-Related Accidents in Petroleum Refineries: Lessons Learned from Accidents in EU and OECD Countries, Publications Office of the European Union, 2013. [20] L.T. Popoola, A.S. Grema, G.K. Latinwo, B. Gutti, A.S. Balogun, Corrosion problems during oil and gas production and its mitigation, Int. J. Ind. Chem. 4 (2013) 35. [21] G. Frankel, Pitting corrosion of metals a review of the critical factors, J. Electrochem. Soc. 145 (1998) 2186–2198. [22] R. Abdel-Ghany, S. Saad-Eldeen, H. Leheta, The effect of pitting corrosion on the strength capacity of steel offshore structures, in: ASME 2008 27th International Conference on Offshore Mechanics and Arctic Engineering, American Society of Mechanical Engineers, 2008, pp. 801–805. [26] David W. Hoeppner ‘‘Pitting corrosion:morphology and characterization” RTOAG-AVT-140.

Please cite this article as: K. Lakkam, S. M.Kerur and A. Shirahatti, Effect of pitting corrosion on the mechanical properties of 316 grade stainless steel, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.11.293