4. Forms of Corrosion

4.7 Hydrogen Blistering [2/3]

Hydrogen Damage

Metals and alloys may be damaged by hydrogen blistering, hydrogen embrittlement and high temperature hydrogen attack. A classification of the three damages is shown in Table 4.2 below. Often there is a great deal of confusion in the three phenomena. Each of the above phenomena is presented below.

Table 4.2: Classification of Hydrogen Damages

No. Type of Attack

Environments

 Source of Atomic Hydrogen Type of Metal Deterioration

Method of Prevention
1. Hydrogen attack

Temperature > 230°C. H2 Pressure >7 kg/cm2.

 Equilibrium dissociation of H2 molecules: 

H2 2H°

 Decarburization and fissuring: possibly methane blisters. Serious loss of strength. Use of adequately resistant alloys.
2. Hydrogen blistering (Hydrogen-induced crack, HIC)

Temperature 100°C in presence of moisture and usually H2S. Promoted by cyanides

Generated by corrosion:

H+ + e H

 

 Blisters when defects are shallow from the surface. Cracks parallel to the surface, when defects are deep. Protective linings.

Use of adequate materials (anti-HIC steel).

Chemical treatment of corrosive medium with water, polysulfides or inhibitors

3.

Hydrogen embrittlement

 

 High strength steel in environments same as above Same as above Severe loss of ductility at low strain rates and delayed fracture Same as hydrogen blistering
Nearly atmospheric temperature by rapid cooling of high strength equipment operating at conditions same as in hydrogen attack. Same as hydrogen attack Severe loss of ductility at low strain rates and hydrogen assisted crack growth Use of adequate materials.

Hydrogen degassing.