Corrosion in phosphoric acid

Phosphoric acid is a kind of reducing inorganic acid, also called non-oxidizing acid. Its corrosiveness to the material depends on the type of phosphoric acid. Phosphoric acid and wet-process phosphoric acid are two types of phosphoric acid currently used in industrial applications. The former is pure phosphoric acid without reagents for reagent-grade phosphoric acid and the latter is phosphoric acid with large amounts of impurities (F−, CI−, SO42−, SiO2). Mainly used in phosphate fertilizer production. For the corrosion of village materials, the former is inferior to the latter. In the pure phosphoric acid corrosion conditions, super austenitic stainless steel is usually used. The impurity content of wet dust phosphoric acid exacerbates its corrosive destructiveness. The materials used are transitions to iron-nickel-based and nickel-based corrosion-resistant alloys. Test results in factories and laboratories show that except for purification at high temperatures >200°C with nitrogen. In the phosphoric acid, the corrosion resistance of B-2 alloy was the best. The test results of other test conditions showed that the nickel-base and iron-nickel-based corrosion resistant alloys with high chromium content supplemented with molybdenum alloys are the most suitable for corrosion resistance to phosphoric acid. Structural materials. The corrosion resistance of some typical corrosion resistant alloys in various phosphors is shown in the table.

Corrosion rates of several alloys in wet-process phosphoric acid

medium

material

corrosion rate g﹒(m²﹒h)⁻¹

70% H₃PO₄+4% H₂SO₄+0.5%F⁻+60X10⁻⁶CI⁻+0.6%Fe³⁺    Temperature: 90ºC           Time:one day + one day + three days

Sanicro-28

0.12

2RK65

0.8

Capenter 20Cb-3

6.2

Incoloy 825

6.7

Hastelloy G

0.54

Hastelloy C

0.52

 

Corrosion of nickel-based and iron-nickel based corrosion resistant alloys in pure phosphoric acid (280ºC), purged with nitrogen prior to testing)

material corrosion rate mm﹒a⁻¹
108% H₃PO₄ 112% H₃PO₄
G-30 9.4 32.5
G-3 7.9 24.4
625 4.6 14.9
C-22 2.6 3.9
C-276 1.4 1.8
B-2 0.23 0.05

 

Corrosion of various alloys in reagent grade H₃PO₄ and wet H₃PO₄

material

corrosion rate mm﹒a⁻¹

reagent 75% H₃PO₄,115ºC

wet method:75% H₃PO,54%P₂O₅,115ºC mineral resources A/B

TP316

0.38

29/1.7

825 alloy

none

14/0.64

C-276

0.38

1.9/0.71

C-22

0.3

0.84/0.28

625 alloy

0.3

0.91/0.3

600 alloy

0.13

0.5/0.18

G-30 alloy

0.13

0.46/0.15

 

Corrosion test results of some corrosion resistant alloys in a wet H₃PO₄ evaporator

Medium condition Material corrosion rate mm﹒a⁻¹
53%H₃PO₄,1%~2%H₂SO₄,1%~1.5% Fluoride,120ºC,time 42 days 20cb-3 0.12
Hastelloy  C 0.13
alloy825 0.16
alloy317 0.26
monel400 0.64
TP316 1.1
inconel600 >33,sample disappear
hastelloy  B >33,sample disappear

 

Corrosion resistance of some nickel-based and iron-nickel-based alloys in wet-process phosphoric acid

Medium condition

temperature ºC

corrosion average rate/ mm﹒a⁻¹

G-30

625

G-3

Sanicro-28

C-22

C-276

28%P₂O₅ + 2000×10⁻⁶CI⁻

85

0.025

0.038

0.023

0.775

/

42%P₂O₅ + 2000×10⁻⁶CI⁻

85

0.023

0.033

0.275

3.025

/

44%P₂O₅ + 0.5%HF

116

0.4

1.5

/

/

/

52%P₂O₅ + 2000×10⁻⁶CI⁻

116

0.098

0.3

0.275

1.2

/

52%P₂O₅ + 2000×10⁻⁶CI⁻

149

0.7

1.975

1.6

6.2

/

54%P₂O₅ + 2000×10⁻⁶CI⁻

116

0.2

0.4

0.4

1.375

/

54%P₂O₅ + 2000×10⁻⁶CI⁻

116

0.175

0.4

0.4

2.3

/

38%P₂O₅ + 2000×10⁻⁶CI⁻

85

/

0.05

/

/

<0.03

0.3

38%P₂O₅ + 0.5%HF

85

/

0.21

/

/

0.18

1.1

 

Corrosion resistance of Alloy 31 and G-35 alloys in phosphoric acid again illustrates the applicability of high Cr-containing nickel-based corrosion-resistant alloys and iron-nickel-based corrosion-resistant alloys in various phosphoric acids.

Corrosion of Alloy 31 in Wet Process Phosphoric Acid Production Medium

Medium condition temperature ºC corrosion rate/ mm﹒a⁻¹
alloy31 Sanicro-28
52%P₂O₅+4.5%H₂SO₄+0.9%H₂sSiF₆+1.5%Fe₂O₃+400×10⁻⁶CI⁻ 80 0.02 0.0075
120 0.78 /
52%P₂O₅ 116 0.08 1.2
30%P₂O₅+2.4%H₂SO₄+2.3%H₂sSiF₆+1%Fe₂O₃+1000×10⁻⁶CI⁻ 80 0.015 /
54%P₂O₅+1000×10⁻⁶CI⁻ 120 2.04 2.3
100 1.3 /

 

Alloy 33 Corrosiveness in Phosphoric Acid

Phosphoric acid concentration %

temperature ºC

corrosion rate/ mm﹒a⁻¹

alloy33

G-30 alloy

Sanicro-28

Inconel 690

85

100

0.2

0.3

0.2

1.25

154

1.075

1.33

1.4

/

 

Corrosion resistance of nickel-based and iron-nickel based corrosion resistant alloys in pure H₃PO₄

 H₃PO₄ concentration %

temperature ºC

corrosion average rate/ mm﹒a⁻¹

G-35

625

C-2000

G-30

C-276

50

boiling

0.01

0.02

0.03

0.01

0.18

60

boiling

0.01

0.16

0.08

0.14

0.28

70

boiling

0.11

0.89

0.15

0.35

0.13

80

boiling

0.42

4.9

0.4

0.61

0.31


Post time: Mar-21-2018
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