Figure 7-42.Butt joints and socket fitting joints.
Butt joints are commonly used between pipes and
between pipes and welded fittings. They are also used
for butt welding of flanges and welding stubs. In making
a butt joint, place two pieces of pipe end to end, align
them, and then weld them. (See fig. 7-42.)
When the wall thickness of the pipe is 3/4 inch or
less, you can use either the single V or single U type of
butt joint; however, when the wall thickness is more than
3/4 inch, only the single U type should be used.
Fillet welds are used for welding slip-on and
threaded flanges to pipe. Depending on the flange and
type of service, fillet welds may be required on both
sides of the flange or in combination with a bevel weld
(fig. 7-43). Fillet welds are also used in welding screw
or socket couplings to pipe, using a single fillet weld
(fig. 7-42). Sometimes flanges require alignment. Fig-
ure 7-44 shows one type of flange square and its use in
vertical and horizontal alignment.
Another form of fillet weld used in pipe fitting is a
seal weld A seal weld is used primarily to obtain tight-
ness and prevent leakage. Seal welds should not be
considered as adding strength to the joint.
Figure 7-43.Flange connections.
Figure 7-44.Flange alignment.
JOINT PREPARATION AND FIT-UP
You must carefully prepare pipe joints for welding
if you want good results. Clean the weld edges or
surfaces of all loose scale, slag, rust, paint, oil, and other
foreign matter. Ensure that the joint surfaces are smooth
and uniform. Remove the slag from flame-cut edges;
however, it is not necessary to remove the temper color.
When you prepare joints for welding, remember
that bevels must be cut accurately. Bevels can be made
by machining, grinding, or using a gas cutting torch. In
fieldwork, the welding operator usually must make the
bevel cuts with a gas torch. When you are beveling, cut
away as little metal as possible to allow for complete
fusion and penetration. Proper beveling reduces the
amount of filler metal required which, in turn, reduces
time and expense. In addition, it also means less strain
in the weld and a better job of design and welding.