66
Fundamentals of Corrosion
may be organic, inorganic, or metallic. A rubber lining on steel, or
the cladding of steel with austenitic stainless steel or nickel, are
approaches that have been used.
5. Use of inhibitors. Inhibitors can minimize corrosion-generated hydrogen blistering because the cathodic reduction of hydrogen ions is
also retarded. However, inhibitors must be used in closed-circuit
systems in order to be economical.
6. Improvements in design. Careful consideration must be given before
modifications in design can improve the performance. For example,
external support pads should not be continuously welded to the
vessel itself, if blistering is expected, in order to prevent hydrogen
entrapment at the interface
7. Proper heat-treating procedure. The decreased solubility of hydrogen
in bcc structural steel compared to the fee structure leads to flaking
and fish-eye formation in steels when they are cooled in hydrogen
atmospheres from high temperatures (above 2012°F [1100°C]). The
damage is aggravated if the cooling is rapid because this results in
hydrogen-sensitive martensitic microstructure. A reduced cooling
rate inhibits the formation of martensite and also allows hydrogen to
be slowly released from the steel, there by eliminating the damage.
3.10.3.2 Hydrogen Embrittlement
Preventive measures against hydrogen embrittlement include:
1. Material selection. The susceptibility of steel to hydrogen embrittlement increases with the tensile strength of the material. The threshold
tensile strength is 1000 MPa, which can be lower in acidic environments. The most aggressive environment in promoting hydrogen entry is wet hydrogen sulfide. Common metals and alloys are
graded according to strength level and/or heat treatment in terms of
their resistance to hydrogen-induced cracking. The steels are generally restricted to a maximum hardness of 22 HRC (35 HRC for other
alloys).
2. Heat treatment. For the same stress level, the susceptibility to hydrogen embrittlement of steels depends on their microstructure.
Untempered martensite is the most susceptible phase. Quenched
and tempered microstructures are more resistant than normalized
and tempered. Accordingly, the heat treatment procedure may be
selected.
The removal of hydrogen in steels can be carried out by heat treatment at temperatures up to 392°F (200°C), a process known as baking.
In the absence of irreversible damage inside the material, a baking
Fundamentals of Corrosion
may be organic, inorganic, or metallic. A rubber lining on steel, or
the cladding of steel with austenitic stainless steel or nickel, are
approaches that have been used.
5. Use of inhibitors. Inhibitors can minimize corrosion-generated hydrogen blistering because the cathodic reduction of hydrogen ions is
also retarded. However, inhibitors must be used in closed-circuit
systems in order to be economical.
6. Improvements in design. Careful consideration must be given before
modifications in design can improve the performance. For example,
external support pads should not be continuously welded to the
vessel itself, if blistering is expected, in order to prevent hydrogen
entrapment at the interface
7. Proper heat-treating procedure. The decreased solubility of hydrogen
in bcc structural steel compared to the fee structure leads to flaking
and fish-eye formation in steels when they are cooled in hydrogen
atmospheres from high temperatures (above 2012°F [1100°C]). The
damage is aggravated if the cooling is rapid because this results in
hydrogen-sensitive martensitic microstructure. A reduced cooling
rate inhibits the formation of martensite and also allows hydrogen to
be slowly released from the steel, there by eliminating the damage.
3.10.3.2 Hydrogen Embrittlement
Preventive measures against hydrogen embrittlement include:
1. Material selection. The susceptibility of steel to hydrogen embrittlement increases with the tensile strength of the material. The threshold
tensile strength is 1000 MPa, which can be lower in acidic environments. The most aggressive environment in promoting hydrogen entry is wet hydrogen sulfide. Common metals and alloys are
graded according to strength level and/or heat treatment in terms of
their resistance to hydrogen-induced cracking. The steels are generally restricted to a maximum hardness of 22 HRC (35 HRC for other
alloys).
2. Heat treatment. For the same stress level, the susceptibility to hydrogen embrittlement of steels depends on their microstructure.
Untempered martensite is the most susceptible phase. Quenched
and tempered microstructures are more resistant than normalized
and tempered. Accordingly, the heat treatment procedure may be
selected.
The removal of hydrogen in steels can be carried out by heat treatment at temperatures up to 392°F (200°C), a process known as baking.
In the absence of irreversible damage inside the material, a baking