Experiment 3 Corrosion Rate - Weight Loss Nurul Husna

CHM578/674

Experiment 3:

2020

Corrosion Rate (Weight Loss Method)

Name: Nurul Husna binti Ibrahim

ID: 2018226626

(20 marks) Group: AS2224M1

(Refer Lab manual Exp. 3 CHM674 prior to answering the following Post-Lab Questions) Objectives a) To study the corrosion of steel in two different acid solutions. b) To study the corrosion resistant efficiency of steel alloy (ie: stainless steel).

Background: Steel will corrode when exposed to acid solutions. Electrochemical reactions involved for steel in two different acids are as follows: Anodic reaction: Fe → Fe2+ + 2e Eo = -0.44 V Cathodic Reaction: NO3- + 4H+ + 3e ↔ NO + 2H2O Eo = +0.96 V 2+ SO4 + 4H + 2e ↔ SO2 + 2H2O Eo = +0.17 V The simplest, and longest-established method of estimating corrosion losses in plant and equipment is weight loss analysis. A weighed sample (coupon) of the metal or alloy under consideration is introduced into the process, and later removed after a reasonable time interval. The coupon is then cleaned of all corrosion product and is reweighed. The weight loss is converted to a corrosion rate (CR) as follows:

Density: steel = 7.86 g/cm3 , Stainless Steel = 7.0 g/cm3 , Exposed Area : 2 x 2 x 2 = 8 cm2, K–factor (corrosion rate in mm/yr) = 8.76 x 104

Procedure: All metal specimens (steel and stainless steel) must be in the same size. All the metal specimens were polished with emery paper to remove all dusts and impurities and then rinsed with alcohol. 12 vials or containers were labeled as S1(a)- (c), S2(a) – (c), SS1(a) – (c) and SS2(a) – (c). All the metal specimens were weighed prior to immersion in acidic solution using a 4decimal analytical balance. Each of the specimen was put into the right labelled container containing the right acidic solution as in the report table. All samples were taken out after 1 hour; and dried before re-weighing.

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CHM578/674

2020

The corrosion resistance efficiency of stainless steel is calculated using the following equation: Corrosion Protection/Resistance Efficiency (η%) Results

= CR steel - CR stainless steel x 100 CR steel

(4 marks)

1. Immersion of Steel in 1M H2SO4 for 1 hour Metal specimen S1(a) S1(b) S1(c) Observation: surface.

Weight before Weight after immersion (g) immersion (g) 3.0570 3.0250 3.0621 3.0301 3.0562 3.0254 All solutions turned to cloudy with a lot of bubbles

Average weight loss (WL):

Weight loss (g) 0.0320 0.0320 0.0308 formed on the steel

0.0320+0.0320+0.0308 =0.0316 g 3

2. Immersion of Steel in 1M HNO3 for 1 hour Metal specimen

Weight before Weight after Weight loss (g) immersion (g) immersion (g) S 2(a) 3.0560 2.8592 0.1968 S 2(b) 3.0630 2.8707 0.1923 S 2(c) 3.0521 2.8668 0.1853 Observation : All solutions turned to green-black solution, a lot of bubbles evolved. Average weight loss (WL):

0.1968+0.1923+0.1853 =0.1915 g 3

3. Immersion of Stainless Steel in 1M H2SO4 for 1 hour Metal specimen

Weight before Weight after Weight loss (g) immersion (g) immersion (g) SS 1(a) 3.0156 3.0155 0.0001 SS 1(b) 3.0293 3.0290 0.0003 SS 1(c) 3.0179 3.0170 0.0009 Observation: No changes in the solution and on the surface of specimen. Average weight loss (WL):

0.0001+ 0.0003+0.0009 =0.4333 ×10−3 g 3

4. Immersion of Stainless Steel in 1M HNO3 for 1 hour Metal specimen SS 2(a)

Weight before immersion (g) 2.9980

Weight after immersion (g) 2.9978 2

Weight loss (g) 2×10-4

CHM578/674

2020

SS 2(b) 3.0188 3.0178 1×10-3 SS 2(c) 3.0298 3.0290 8×10-4 Observation: No changes in the solution and on the surface of specimen. Average weight loss (WL):

( 2× 10−4 ) + ( 1× 10−3 ) +(8 ×10−4 )

Post- Laboratory Questions

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=6.6667× 10−4 g

(16 marks) :

1. Calculate the corrosion rate of steel and stainless steel in both acids for 1 hour. Exposed Area : 8 cm2 Corrosion rate (mm/yr) of steel in 1M H2SO4:

Corrosion rate=

¿

¿

Weight loss ( g ) × K Alloy Density ¿ ¿

0.0316 g × 8.76 ×1 04 7.86 g × 8 cm2 ×1 hr 3 cm 44.02 mm yr Corrosion rate (mm/yr) of steel in 1M HNO3:

Corrosion rate=

¿

¿

Weight loss ( g ) × K Alloy Density ¿ ¿

0.1915 g ×8.76 ×1 0 4 7.86 g × 8 cm2 ×1 hr 3 cm 266.78 mm yr Corrosion rate (mm/yr) of stainless steel in 1M H2SO4:

Corrosion rate=

¿

Weight loss ( g ) × K Alloy Density ¿ ¿

0.0004 g × 8.76 ×1 04 7. 0 g × 8 cm2 ×1 hr 3 cm 3

CHM578/674

¿

2020

0.63 mm yr

Corrosion rate (mm/yr) of stainless steel in 1M HNO3:

Corrosion rate=

¿

¿

Weight loss ( g ) × K Alloy Density ¿ ¿

0.0007 g × 8.76× 1 04 7.0 g × 8 cm2 ×1 hr 3 cm 1.095mm yr

2. Why corrosion rate of steel is higher in nitric acid than in sulfuric acid? -

The corrosion rate for steel in nitric acid is higher than in sulfuric acid because any additional chlorides or fluorides in nitric acid may increase the corrosion rate by pitting in the steel.

3. Why corrosion rate of stainless steel is lower than of steel? -

Stainless steel will not corrode as fast as the corrosion rate for steel because stainless steel is less corrosiv because of their better composition and physical properties because stainless steel is made up of alloy that have a better resistant

4. Calculate the corrosion resistance efficiency of the alloy (ie: stainless steel) in nitric acid. Answer:

CR steel−CR stainless ×100 CR steel 266.78−1.095 Corrosion Resistance Efficiency= × 100 % 266.78 ¿ 99.59 % Corrosion Resistance Efficiency ( % )=

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