Hello Sasa,
E-9015/9016-9018-B9 are the three popular AWS classifications for SMAW welding electrodes which applies for grade -91 steel. E-9018-H4 are the latest developments, however the manufacturers endorsement is essential.
You may find the following article as of interest the use of E-9018-H4 electrodes.:-
E-9015/9016-9018-B9 are the three popular AWS classifications for SMAW welding electrodes which applies for grade -91 steel. E-9018-H4 are the latest developments, however the manufacturers endorsement is essential.
You may find the following article as of interest the use of E-9018-H4 electrodes.:-