Forms of Metallic Corrosion
67
treatment can restore the mechanical properties almost to normal
levels.
Hydrogen can be removed from titanium, zirconium, and their
alloys by annealing in vacuum.
3. Alloying additions. The susceptibility of steels can be reduced by alloying with strong hydride-forming elements such as titanium, molybdenum, and vanadium. The concentration of the alloying element
is a factor. For example, molybdenum up to about 0.75% reduces
susceptibility of AISI 4130 steel to sulfide stress cracking. Beyond
this concentration, a tempering treatment at and above 932°F (500°C)
leads to the precipitation of Mo 2 C and the resistance to sulfide stress
cracking decreases.
4. Proper plating conditions and coatings. Hydrogen pick-up can be controlled during plating operations by proper regulation of the bath
composition and plating current; hydriding of titanium can be minimized by anodizing or thermal oxidizing treatments to increase the
thickness of the protective film. Very-high-strength steels should not
be subjected to cadmium plating or hot dip galvanizing
5. Use of inhibitors. Pickling operations are a source of hydrogen pickup by steel. Reducing corrosion of the base metal by the addition of
inhibitors can largely decrease hydrogen pick-up.
6. Proper welding practice. Hydrogen embrittlement problems resulting from welding can be controlled by employing recommended
welding procedures, which include proper cleaning and degreasing
procedures for prepared weld joints, the use of dry electrodes, and the
maintenance of dry conditions during welding. Also recommended
is the use of an appropriate preheat before welding and a postweld
heat treatment. To minimize hydrogen pickup of titanium, zirconium, and their alloys during welding, inert gas shielding should be
employed.
7. Oxygen addition. The embrittlement of steel in gaseous environments
can be inhibited by adding 0.4 to 0.7 vol.% oxygen. However, such
additions are not effective in preventing cracking in hydrogen sulfide gas.
3.10.3.3 Hydrogen Attack
Preventive measures against hydrogen attack include:
1. Use of Nelson curves. The operating limits of various steels in hightemperature, high-pressure hydrogen service can be determined
from the Nelson curves. These curves have been developed from
data resulting from long-term refinery experience. The curves are
67
treatment can restore the mechanical properties almost to normal
levels.
Hydrogen can be removed from titanium, zirconium, and their
alloys by annealing in vacuum.
3. Alloying additions. The susceptibility of steels can be reduced by alloying with strong hydride-forming elements such as titanium, molybdenum, and vanadium. The concentration of the alloying element
is a factor. For example, molybdenum up to about 0.75% reduces
susceptibility of AISI 4130 steel to sulfide stress cracking. Beyond
this concentration, a tempering treatment at and above 932°F (500°C)
leads to the precipitation of Mo 2 C and the resistance to sulfide stress
cracking decreases.
4. Proper plating conditions and coatings. Hydrogen pick-up can be controlled during plating operations by proper regulation of the bath
composition and plating current; hydriding of titanium can be minimized by anodizing or thermal oxidizing treatments to increase the
thickness of the protective film. Very-high-strength steels should not
be subjected to cadmium plating or hot dip galvanizing
5. Use of inhibitors. Pickling operations are a source of hydrogen pickup by steel. Reducing corrosion of the base metal by the addition of
inhibitors can largely decrease hydrogen pick-up.
6. Proper welding practice. Hydrogen embrittlement problems resulting from welding can be controlled by employing recommended
welding procedures, which include proper cleaning and degreasing
procedures for prepared weld joints, the use of dry electrodes, and the
maintenance of dry conditions during welding. Also recommended
is the use of an appropriate preheat before welding and a postweld
heat treatment. To minimize hydrogen pickup of titanium, zirconium, and their alloys during welding, inert gas shielding should be
employed.
7. Oxygen addition. The embrittlement of steel in gaseous environments
can be inhibited by adding 0.4 to 0.7 vol.% oxygen. However, such
additions are not effective in preventing cracking in hydrogen sulfide gas.
3.10.3.3 Hydrogen Attack
Preventive measures against hydrogen attack include:
1. Use of Nelson curves. The operating limits of various steels in hightemperature, high-pressure hydrogen service can be determined
from the Nelson curves. These curves have been developed from
data resulting from long-term refinery experience. The curves are