In AWS A5.1, the electrodes listed include both low hydrogen and non-low hydrogen electrodes. In AWS D1.1-96, Group I steels may be welded with non-low hydrogen electrodes. This would include A36 steel. For Group II steels and higher, low hydrogen electrodes are required. These steels would include A572 grade 50. That means for welding on steels with minimum specified yield strengths exceeding 50 ksi, all electrodes should be of the low hydrogen type with specific coatings that are designed to be extremely low in moisture. Water, or H2O, will break down into its components hydrogen and oxygen under the intensity of the arc. This hydrogen can then enter into the weld deposit and may lead to unacceptable weld heat affected zone cracking under certain conditions. Low hydrogen electrodes have coatings comprised of materials that are very low in hydrogen. The low hydrogen electrodes that fit into the A5.1 classification include E7015, E7016, E7018, and E7028.
SI
NO.
|
Electrode
Classification
|
Properties
|
1.
|
E7015
|
Operate on DC only
|
2.
|
E7016
|
Operate on either AC or DC
|
3.
|
E7018
|
Operate on AC or DC and include approximately 25% iron powder in their coatings; this increases the rate at which metal may be deposited
|
4.
|
E7028
|
Contains approximately 50% iron powder in the coating, enabling it to deposit metal at even higher rates. However, this electrode is suitable for flat and horizontal welding only.
|
For most structural steel fabrication today, low hydrogen electrodes are prescribed to offer additional assurance against hydrogen induced cracking. When low hydrogen electrodes are used, the required levels of pre heat are actually lower, offering additional economic advantages to the contractor.
All the low hydrogen electrodes listed in AWS A5.1 have minimum specified notch toughnesses of at least 20 ft. lb. at 0°F. There are electrode classifications that have no notch toughness requirements (such as E6012, E6013, E6014, E7024) but these are not low hydrogen electrodes. Although there is no direct correlation between the low hydrogen nature of various electrodes and notch toughness requirements, in the case of SMAW electrodes in A5.1, the low hydrogen electrodes all have minimum notch toughness requirements.