Figure 7-45.Angle iron jig.
Align the piping before welding and maintain it in
alignment during the welding operation. The maximum
alignment tolerance is 20 percent of the pipe thickness.
To ensure proper initial alignment, you should use
clamps or jigs as holding devices. Apiece of angle iron
makes a good jig for a small-diameter pipe (fig. 7-45),
while a section of channel or I-beam is more suitable for
larger diameter pipe.
When welding material solidly, you may use tack
welds to hold it in place temporarily. Tack welding is
one of the most important steps in pipe welding or any
other type of welding. The number of tack welds re-
quired depends upon the diameter of the pipe. For
1/2-inch pipe, you need two tacks; place them directly
opposite each other. As a rule, four tacks are adequate
for standard size of pipe. The size of a tack weld is
determined by the wall thickness of the pipe. Be sure
that a tack weld is not more than twice the pipe thickness
in length or two thirds of the pipe thickness in depth.
Tack welds should be the same quality as the final weld.
Ensure that the tack welds have good fusion and are
thoroughly cleaned before proceeding with the weld.
In addition to tack welds, spacers sometimes are
required to maintain proper joint alignment. Spacers are
accurately machined pieces of metal that conform to the
dimensions of the joint design used. Spacers are some-
times referred to as chill rings or backing rings, and they
serve a number of purposes. They provide a means for
maintaining the specified root opening, provide a con-
venient location for tack welds, and aid in the pipe
alignment. In addition, spacers can prevent weld spatter
and the formation of slag or icicles inside the pipe.
Select the electrode that is best suited for the posi-
tion and type of welding to be done. For the root pass of
a multilayer weld, you need an electrode large enough,
yet not exceeding 3/16 inch, that ensures complete
fusion and penetration without undercutting and slag
Make certain the welding current is within the range
recommended by the manufacturers of the welding
machines and electrodes.
Do not assign a welder to a job under any of the
following conditions listed below unless the welder and
the work area are properly protected:
c When the atmospheric temperature is less than
l When the surfaces are wet
l When rain or snow is falling, or moisture is
condensing on the weld surfaces
l During periods of high wind
At temperatures between 0°F and 32°F, heat the
weld area within 3 inches of the joint with a torch to a
temperature warm to the hand before beginning to weld.
The Seabee welder can greatly extend the life of
construction equipment by the use of wearfacing proce-
dures. Wearfacing is the process of applying a layer of
special composition metal onto the surface of another
type of metal for the purpose of reducing wear. The
selection of a wearfacing alloy for application is based
on the ability of the alloy to withstand impact or abra-
sion. Impact refers to a blow or series of blows to a
surface that results in fracture or gradual deterioration.
Abrasion is the grinding action that results when one
surface slides, rolls, or rubs against another. Under
high-compressive loads, this action can result in goug-
Alloys that are abrasion resistant are poor in with-
standing impact. Conversely, those that withstand im-
pact well are poor in resisting abrasion; however, there
are many alloys whose wearfacing properties fall be-
tween the two extremes. These alloys offer some pro-
tection against abrasion and withstand impact well.
Before you wear-face a workpiece, all dirt, oil, rust,
grease, and other foreign matter must be removed. If you
do not, your finished product will be porous and subject
to spalling. You also need a solid foundation; therefore,
repair all cracks and remove any metal that is fatigued
or rolled over.