2-162. The co-efficient of thermal expansion of the nickel (high) alloys is about the same as the carbon steels and
consequently warpage and stress resulting from heating will be approximately the same. Also the same joint designs
used for carbon steels are used to weld the high-nickel alloys.
2-163. After welds are completed it is important that all flux or slag be removed especially if the assembly/part is to be
used in a high temperature application. The flux becomes progressively more corrosive in the molten state which will
occur if part is installed in a heated area which reaches or exceeds the wetting temperature of the flux. The flux used
should be clean; flux used with corrosion resisting stainless and other carbon or low alloy steels should not be mixed with
that to be used for welding nickel, monel or inconel. If intermixed fluxes are used, welds with low mechanical or unsound
properties may occur as a result of contaminants transferred through the flux into the weld joint.
2-164. GAS WELDING NICKEL AND HIGH NICKEL ALLOYS. Generally oxyacetylene welding may be used in the
fabrication of parts in which high-nickel alloys are used. However welding of some grades such as Inconel is not
recommended because of refactory oxides formed during welding.
2-165. The welding flame recommended for oxyacetylene welding high-nickel alloys is slightly reducing (carburizing). A
soft flame is preferable to a heavy flame like that which will result from use of too small a tip. During welding the end of
the filler rod should be in the protective atmosphere of the flame envelope to prevent oxidation of the heated rod. In
addition the tip of the inner cone of the flame should contact the pool of molten metal in order to obtain concentrated
heat and to prevent oxidation.
2-166. SHIELDED METAL ARC WELDING NICKEL AND HIGH NICKEL ALLOYS. The same general practices in
layout joint design, jigging and welding techniques for welding steel are followed in shielded metal arc welding nickel and
high-nickel alloys. Nickel and monel can be usually welded in all positions, however, inconel should be positioned for
down hand welding when possible.
2-167. For data concerning general welding characteristic of Nickel Chromium Iron Alloy, See Table 2-19.
2-168. ARC WELDING.
2-169. When arc welding the 18-8 (300 series)corrosion resisting alloys and chromium nickel iron alloy, current should
be adjusted to the amperage, which will just produce sufficient heat for adequate fusion. A basic rule for starting is to set
amperage at 10% less than would be required for the same thickness of carbon steel. The reason for reducing amperage
is that stainless melts at a lower temperature and has higher electrical resistance than carbon steel. Also, holding
amperage at the minimum required for good fusion, is an important means of reducing effects of excessive heat build-
2-170. Due to the many variables in welding machines, arc characteristics, inaccuracy of voltmeters and ammeters,
differences in individual welders ability and type of weld joint exact currents will not be recommended. The values cited
in Table 2-16 are being provided as a guide in starting and adjusting welding current.
2-171. The corrosion resisting and nickel chromium iron alloy are generally welded with reverse polarity. The electrode
tip is positive and the work negative, which results in faster heating and melting of the electrode. Concurrently, because
of the fast heating and melting of electrode, temperate buildup in the base metal is held to a minimum. Thin sheet may,
however, be welded with straight polarity to prevent blow through, if required. Preferred method for welding thin sheet
unless otherwise specified is the inert gas shielded arc. This method will be explained in further details in paragraph 2-
2-172. JOINT DESIGNS AND PREPARATION FOR ARC WELDING. Generally flat butt/square edges are satisfactory
for welding of corrosion resisting and nickel chromium iron alloy up to about 0.125 inch thick. Thickness from 3/16" to
1/2" are usually prepared with a single V beveled edges with 300 bevel on a side and a 1/16" root opening and throat.
For thicknesses over 1/2" a double V with 300 bevel on both sides and a 1/8" gap and throat. The use of the double V
beveled edge with thicknesses over 1/2" will provide accessibility for the electrode that is necessary for obtaining
penetration and uniform wall fusion. Also, this type of joint can be utilized in such a manner as to reduce deformation
(wrapping) caused by shrinkage inherent in the single V joint design.