Corrosions in HF acid

HF acid is a reductive inorganic acid widely used in chemical processing. The industrially applicable HF acid concentration ranges from 30% to 70% HF aqueous solution and anhydrous HF. Although chemically classified, HF acid is a weak acid relative to hydrochloric acid and sulfuric acid, but its corrosiveness is extremely strong. In many nickel-base and iron-nickel-based corrosion-resistant alloys, Monel 400 with 30% Cu performs the best. Prominently, it has excellent corrosion resistance in all concentrations of HF acid at 120 degrees Celsius. In addition to Monel alloys, Ni-Cr-Mo corrosion resistant alloys with high Mo content containing Cu also have good resistance to boiling HF acid corrosion.

Corrosion of some corrosion resistant alloys in dilute HF

Grade

The corrosion rate (mm/a)

2% HF

5% HF

70deg celsius

boiling

70deg celsius

boiling

C-276

0.24

0.076

0.25

0.1

C-22

0.23

0.94

0.34

0.84

625

0.5

0.51

0.4

0.51

C-4

0.43

0.51

0.38

0.51

200

0.51

0.51

0.46

0.51

600

0.51

0.51

0.23

0.51

B-2

0.51

0.51

0.38

0.51

G-3

0.51

0.51

0.5

0.51

G-30

0.25

0.51

0.76

0.51

The dissolution of the oxidizing medium in the HF acid solution increases the corrosion of the alloy in the medium. The results of the Monel 400 and C-276 alloys show that Monel 400 has a PMS in a high temperature 95°C concentration = <0.5% HF solution. Cracks, this crack susceptibility has nothing to do with the presence or absence of oxygen, such cracks did not appear in the liquid phase. The 16Cr-16Mo corrosion-resistant nickel alloy containing a small amount of copper has a tendency of uniform stress corrosion cracking in 40% HF acid boiling liquid. However, as long as the conditions of use are controlled, both alloys exhibit suitable corrosion resistance. The results of a factory test in an HF-containing process medium show that Monel 400 alloy has the best corrosion resistance in various HF acid media.

Effect of Oxygen on the Corrosion of Monel 400 in HF Acid Solution

oxygen content in cleaned gas X10⁻⁶

The corrosion rate (mm/a)

boiling 121deg Celsius,38%HF

boiling 108deg Celsius,38%HF

Liquid phase

gaseous phase

Liquid phase

gaseous phase

less 5

0.24

0.17

0.28

0.076

less 500

0.43

0.3

0.56

0.1

1500

0.79

1.24

0.7

0.61

2500

0.74

0.46

0.69

0.23

3500

0.86

1.37

0.86

0.74

4700

1.3

2.7

1.1

2.1

10000

1.2

0.64

1.2

1.9

Influence of Air Infiltration on Corrosion of C-276 and Monel 400 Alloys in 70% HF

Grade

The corrosion rate (mm/a)

Throught nitrogen

C-276

0.008

0.94

Monel 400

0.013

0.58


Post time: Mar-19-2018
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