Weld Deposit Hydrogen Levels

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As mentioned above, no definition exists for a “low hydrogen weld deposit.” The word “low” is an imprecise description. The preferred method of controlling the level of hydrogen in a weld deposit is to use the optional hydrogen designators as defined by the American Welding Society. These designators are in the form of a suffix on the electrode classification (e.g., H8, H4, and H2). The filler metal manufacturer may choose to add the hydrogen designator to the electrode classification if the filler metal meets the diffusible hydrogen requirements in the applicable AWS A5.x filler metal specification.

Following are examples of the designator requirements: To avoid hydrogen induced cracking, the hydrogen level in the material must be held to a certain maximum level. This level is a function of the microstructure susceptibility, constraint (or restraint), and residual stresses.

Microstructure susceptibility to hydrogen induced cracking often increases with increasing steel strength. Therefore, for higher strength steels lower levels of hydrogen are required. To simply state “use low hydrogen” is not enough. For example, “low” for a 50 ksi steel may not be “low” for a 100ksi steel. Rather than require that “only low hydrogen electrodes can be used,” engineers and fabricators are should use statements such as, “only electrodes or electrode-flux combinations capable of depositing weld metal with a maximum diffusible hydrogen content of 8 mL/100g (H8) are permitted.”

by R. Scott Funderburk

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