3. Removal of oxide film and discoloration. This is usually accomplished concurrently with removal of weld
spatter by abrasive cleaning. However, if required, other methods such as chemical treating, grinding and polishing, etc.,
4. Warping of part and excess metal in weld zone. Warpage should be corrected immediately after welding and
prior to heat treatment. In many instances, depending on the alloy, straightening of parts should be accomplished at pre-
heat or postheat temperatures. Excess metal is removed by grinding or polishing or both. Good smooth surface finishes
are necessary to prevent stress risers, etc., which are origination joints for concentrated stress and subsequent failure.
5. Heat treatments for restoration of corrosion resistance, stress relieving and softening is accomplished as
necessary, depending on the alloy involved and intended in-service use. (See Table 2-18 for recommended treatment).
2-176. ELECTRODES FOR ARC WELDING. Electrodes shall be carefully selected in order to govern mechanical and
corrosion resistant properties of welded joints. The analysis of the electrode core material are usually formulated to
compensate for normal losses of certain alloying ingredients that pass through the arc. By controlling electrode analysis
it is possible to obtain a deposit matching the alloy/ strength range of the material being welded. For example, a wire
(electrode) with a 20%chromium content will normally produce a head with a 19% chromium content. In a like manner
additional columbium/columbium plus tantalum compensates for a normal (30-35%) loss of that ingredient during
combining (arc) of electrode with metal being welded.
2-177. The above is not true for all ingredients involved. Nickel and molybdenum are not subject to loss and conversely
titanium is practically all lost through the arc and no compensation can be made. This is the basis for utilizing columbium
bearing electrodes where stabilization against carbide precipitation is required. The carbon content of electrodes for
welding corrosion steels is also held low and carbonaceous type material in the coating is controlled to prevent carbon
pickup in the weld deposit.
2-178. For general data or selection of electrode to parent alloy and for other characteristics see Table 2-18.
Electrode should be properly identified as to grade, type, etc., and stored in a clean dry area.
Store in closed container (original package) when possible/practical to prevent moisture
absorption. When necessary, moisture can be removed by heating to about 200°F. Also,
electrode shall be handled with care to prevent shipping of coating.
2-179. Electrodes shall also be selected in accordance with current (direct current, alternating current) direct current,
etc., and position of welding. For example, electrode classification AWS-E308-16 (AWSASTM) is for use AC or DC in
positions (F) flat, (V) vertical, (OH) overhead and (H) horizontal.
2-180. INERT GAS SHEILDED ARC WELDING. This is a method of arc welding in which the weld zone is protected by
maintaining an inert atmosphere with helium, argon, or a mixture of both. The welding is accomplished using non-
consumable electrodes. Weld deposits made by this method have good physical and corrosion resistant properties and
are clean, smooth, free of flux (flux not normally required) and spatter.
2-181. The use of direct current is suitable for welding all thickness; however, for welding thicknesses less than 0.037"
the use of alternating current will help prevent blow through. Alternating current produces less heat in the metal being
welded because its rapidly changing polarity results in the hottest part of the arc being at the work end only 50% of the
time. Also, because of reduced heating it produces a narrower line of fusion.
2-182. Observance of the following rules will aid in producing welds of desired quality.
a. Grind tungsten electrode joint to approximately 65-70 degrees angle if not previously accomplished.
b. Accomplish welding in still atmosphere, free of wind currents/drafts.
c. Gas cap shall be of proper size and held as close as possible to the work.
d. Do not attempt to strike an arc in molten weld pool.
e. If electrode is accidentally struck or dipped in molten pool regrind to remove contamin2ants.
f. When using filler rod, keep it away from the electrode to avoid touching and contaminating. Hold rod end in gas
envelope at about a 20° angle with the plane of the work. The rod should point down toward the puddle from the
opposite direction of the arc travel. The electrode is normally held at an angle of 65-75 degrees with the work, the slope
being toward the direction of travel.
g. Use gas welding flux, sparingly on underside of weld area when it cannot be protected by inert gas to control
h. Use correct filler rod as specified or as directed by process engineer.
i. Control electrode length; maximum length of electrode protruding beyond end of gas cup should not exceed 1/2