CEMP-E
TI 809-26
1 March 2000
APPENDIX C
WELDING PROCESSES
1. SHIELDED METAL ARC WELDING (SMAW).
a. Process Principles. The Shielded Metal Arc Welding (SMAW) process is commonly known as
"stick" welding, and is performed as "manual" welding. An electric arc is produced between the tip of the
electrode and the base metal, melting both. The molten weld pool, and completed weld, is a mixture of
base metal and electrode materials.
(1) The core of the electrode is steel. The coating is of various materials designed to provide arc
stability, shield the molten weld puddle from atmospheric gases, flux the molten puddle of impurities,
deoxidize the molten weld puddle, and cover the solidifying weld to improve bead profile. Some coatings
contain metallic powders, adding specific alloys to the weld composition.
(2) SMAW may be operated using either DC (direct current) or AC (alternating current) polarity.
Generally, DC is used for smaller diameter electrodes, typically those with a diameter of less than 4.8
mm (3/16 in.). To eliminate undesirable arc blow conditions, larger electrodes are typically operated
using AC. Electrodes used on AC must be designed specifically to operate in this mode, where the
current changes direction 120 times per second on 60 Hertz power. AC electrodes may also operate
using either DCEN (DC Electrode Negative, DC-, also called "straight" polarity) or DCEP (DC Electrode
Positive, DC+, also called "reverse" polarity), and in some cases, either DC polarity.
b. Filler Metal Designation, Specification and Certification. Filler metal specification AWS A5.1
provides the requirements for carbon steel covered electrodes used with SMAW. AWS A5.5 similarly
covers the low-alloy steel electrodes for SMAW.
(1) Generally, when welding on structural steels with a minimum specified yield strength equal to or
exceeding 485 MPa (50 ksi), SMAW electrodes should be of the low hydrogen type. See AWS D1.1
Table 3.1 lists specific steels and grades where the use of low hydrogen electrodes is required for the
prequalification of SMAW Welding Procedure Specifications (WPSs). Table 3.1 also provides the
strength of electrode required for these steels to provide the "matching" strength for the base metal.
Group I steels, including A36 steel, may be welded with non-low hydrogen electrodes. For Group II
steels, including A572 grade 50, and higher strength groups, low hydrogen electrodes are required. For
most structural steel fabrication today, low hydrogen electrodes are prescribed to offer additional
assurance against hydrogen induced cracking.
(2) Low hydrogen electrodes have coatings of inorganic materials that are very low in hydrogen,
and are designed to be extremely low in moisture. Water (H2O) will break down into its components,
hydrogen and oxygen, under the arc. This hydrogen can then enter into the weld deposit and may lead to
unacceptable weld and heat affected zone cracking under certain conditions.
(3) The term "low hydrogen" was initially used to separate those SMAW electrodes capable of
depositing weld metal with low levels of diffusible hydrogen from non-low hydrogen electrodes such as
E6010 and E6012 that contain, by design, coating moisture levels of 2 to 4%. For prequalified WPSs,
AWS D1.1 Table 3.2 provides one series of minimum preheat and interpass temperatures for "non-low
hydrogen electrodes", and another series of values for SMAW with low hydrogen electrodes and all
FCAW, SAW and GMAW. This implies a similarity in expected maximum levels of diffusible hydrogen.
C-1
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