Forms of Metallic Corrosion
65
Decarburization has also been reported in nickel alloys during heat treatment at 2012°F (1100°C) in hydrogen atmospheres. Damage may also be
caused in other materials as the result of hydrogen reacting at high temperature with foreign elements other than carbon in the matrix. Examples
include the formation of steam in welded steels, copper, nickel, and silver by
reacting with oxygen; and formation of ammonia in molybdenum by reaction with nitrogen. The disintegration of oxygen-containing copper in the
presence of hydrogen is a typical example of hydrogen attack.
3.10.3 Preventive Measures
3.10.3.1 Hydrogen Blistering
Preventive measures for hydrogen blistering include:
1. Material selection. Corrosion-generated hydrogen blistering can be
minimized using metals that are chemically resistant to the environment. Nickel-containing steels, including austenitic stainless steels
and nickel-based alloys, have very low hydrogen diffusion rates and
are often recommended to prevent hydrogen blistering.
On the other hand, rimmed steels contain numerous voids and
are very prone to blistering and flaking. Killed steels show much
less susceptibility. Silicon-killed steels are preferable to aluminumkilled steels. However, all these latter steels are subject to hydrogen
blistering.
2. Removal of poisons. The incidence of hydrogen blistering can be
greatly reduced by removing such hydrogen evolution poisons as
sulfides, arsenic compounds, and phosphorus-containing ions from
the environment. These poisons are very prevalent in petroleum process streams. The basic approach to reduction of corrosion-induced
hydrogen blistering in catalytic cracking units is to reduce the concentration of sulfur and bisulfide ions in water condensate.
3. Control of inclusions in steel. Inclusion-free steels are recommended
because inclusions are responsible for blistering or flaking in steel.
Particularly harmful are elongated inclusions because they induce
lamination. Because hydrogen evolution is reduced at low sulfur or
sulfide levels, the use of low-sulfur, calcium-treated, or argon-blown
steels is recommended. Treatment with synthetic slag or the addition of rare earth metals can favor the formation of less detrimental globular sulfides. On the same basis, hot-rolled steel or annealed
steel is preferable to cold-rolled steel.
4. Use of coatings. Hydrogen blistering on the inside of steel tanks or
containers can be avoided by installing a liner that is resistant to
the medium and impervious to hydrogen penetration. The coatings
65
Decarburization has also been reported in nickel alloys during heat treatment at 2012°F (1100°C) in hydrogen atmospheres. Damage may also be
caused in other materials as the result of hydrogen reacting at high temperature with foreign elements other than carbon in the matrix. Examples
include the formation of steam in welded steels, copper, nickel, and silver by
reacting with oxygen; and formation of ammonia in molybdenum by reaction with nitrogen. The disintegration of oxygen-containing copper in the
presence of hydrogen is a typical example of hydrogen attack.
3.10.3 Preventive Measures
3.10.3.1 Hydrogen Blistering
Preventive measures for hydrogen blistering include:
1. Material selection. Corrosion-generated hydrogen blistering can be
minimized using metals that are chemically resistant to the environment. Nickel-containing steels, including austenitic stainless steels
and nickel-based alloys, have very low hydrogen diffusion rates and
are often recommended to prevent hydrogen blistering.
On the other hand, rimmed steels contain numerous voids and
are very prone to blistering and flaking. Killed steels show much
less susceptibility. Silicon-killed steels are preferable to aluminumkilled steels. However, all these latter steels are subject to hydrogen
blistering.
2. Removal of poisons. The incidence of hydrogen blistering can be
greatly reduced by removing such hydrogen evolution poisons as
sulfides, arsenic compounds, and phosphorus-containing ions from
the environment. These poisons are very prevalent in petroleum process streams. The basic approach to reduction of corrosion-induced
hydrogen blistering in catalytic cracking units is to reduce the concentration of sulfur and bisulfide ions in water condensate.
3. Control of inclusions in steel. Inclusion-free steels are recommended
because inclusions are responsible for blistering or flaking in steel.
Particularly harmful are elongated inclusions because they induce
lamination. Because hydrogen evolution is reduced at low sulfur or
sulfide levels, the use of low-sulfur, calcium-treated, or argon-blown
steels is recommended. Treatment with synthetic slag or the addition of rare earth metals can favor the formation of less detrimental globular sulfides. On the same basis, hot-rolled steel or annealed
steel is preferable to cold-rolled steel.
4. Use of coatings. Hydrogen blistering on the inside of steel tanks or
containers can be avoided by installing a liner that is resistant to
the medium and impervious to hydrogen penetration. The coatings