It is appropriate that SFA-5.1 is the first
specification in Section II, Part C. Among the first classifications developed
were those for carbon steel electrodes, which are widely used for welding plain
carbon steel in B&PV Code applications. Electrodes in this specification
are used mainly for shielded metal arc welding (SMAW) of base metals grouped as
P-Number 1 in QW/QB-422 of Section IX.
Covered electrodes are classified in SFA-5.1 mainly
by strength and usability. Below illustrates a typical electrode classification
for this specification. The letter “E” at the beginning of the classification
stands for electrode; the first two numbers that follow—either a 60 or
70—designate the minimum required tensile strength in KSI (1,000 psi), and the
third number designates welding position usability. For example, the “1” in
E6010 indicates that the electrode is usable in all positions (flat, horizontal,
vertical, and overhead). The third number is then taken together with the
fourth number (i.e., 10 in E6010) to designate the type of current and the type
of electrode covering.
Sometimes, optional supplemental designators are
used to further identify electrodes that meet certain addition requirements.
The “–1” designator in E7024-1 means that the electrode meets impact
requirements at a lower temperature than that required for the classification.
Low-hydrogen electrodes can also be given the optional designator “R,” such as
in E7018R, to indicate that the electrodes meet low-moisture-absorption (i.e.,
moisture-resistant) requirements. Even more optional supplemental designators
can be included for moisture or hydrogen testing. If the designator HZ” follows
the four-digit classification, the electrode will meet the requirements for an
average diffusible hydrogen content of not more than “Z” ml/100 g of deposited
metal when tested in the as-received or conditioned state. Therefore, an
E7018-1H4 electrode produces a minimum 70 KSI tensile strength weld deposit
70), has a low-hydrogen coating for alternating current (ac) or
SFA-5.1:
TYPICAL SMAW CARBON STEEL ELECTRODE CLASSIFICATION
E
– 7018
E
–
Electrode
70
– Tensile Strength (70 Ksi)
1
–
Position (All)
8
–
Covering and Current
Direct current (dc) welding in all positions (18),
has improved fracture toughness (–1), and meets a maximum of 4 ml/100 mg of
diffusible hydrogen (H4).
Covered electrodes are composed of a covering and a
carbon steel core wire. Flux, minimal alloying, and iron powder (in some
classifications) are used to make the covering. The core wire is usually carbon
steel that has a chemical composition different from that of the weld deposit.
Low-hydrogen electrodes (E7015, E7016, E7018, E7018M, E7028, and E7048) have
low-moisture (i.e., low-hydrogen) mineral coverings. The E60XX electrodes have
cellulose, Titania, or similar coverings that are not low in hydrogen. Both
types of electrodes are acceptable for welding carbon steels for which hardenability
is not a concern. Under certain conditions, hydrogen can lead to cracking in
either the heat affected zone or the weld deposit in hardenable steels. One
source of hydrogen is the moisture in the electrode coverings, for which reason
low-hydrogen electrodes should be selected for steels susceptible to
hydrogen-induced cracking.
Electrodes classified in this specification are
manufactured to meet moisture limits based on the type of covering and strength
of the weld metal. Therefore, proper storage, treatment, and handling of
electrodes are all necessary. Packaging normally provides some degree of
moisture protection during storage. After the electrodes are removed from the
packaging, low-hydrogen electrodes are normally stored in heated containers in
accordance with the Manufacturer’s recommendations. Unlike the low hydrogen electrodes
in this specification, cellulose coverings for E6010 and E6011 electrodes need
moisture levels of 3 – 7% for their proper operation. Heated storage is not
recommended and drying these electrodes may adversely affect their operation.
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