rigged for that purpose. The unheated portion forms
the heel (outside) of the bend, while the wrinkle is
formed at the throat (inside) of the bend due to
It should be understood that the pipe should not be
bent through very large angles (12 degrees being
considered the maximum for one wrinkle) to avoid the
danger of the pipe buckling. The procedure in making
a large bend is to make several wrinkles, one at a time.
If, for example, you want to produce a bend of
90 degrees, a minimum of eight separate wrinkles
could be made. Figure 13-65 shows a 90-degree bend
made with ten separate wrinkles. The formula to
determine the number of wrinkles is to divide the
degrees per wrinkle required into the degrees of the
Figure 3-65.90-degree bend made with ten separate
Wrinkle bending has been successful on pipe of
more than 20 inches in diameter. Experience has
shown that, for 7-inch-diameter pipe and over, more
complete and even heating is accomplished using two
welding torches, rather than one. In any event, the
heating procedure is the same-the torch or torches
being used to heat a strip approximately two thirds of
the circumference of the pipe (fig. 3-66). The heated
strip need not be very wide (2 to 3 inches, or 5.08 to
7.62 cm, is usually sufficient) since the bend will only
be through 12 degrees at most. The heated portion, as
we have noted, is the part which will compress to
become the inside of the bend. The portion which is
not heated directly will form the outside of the bend.
The technique most often used to bend the pipe,
once it has been heated, is simple and straightforward.
The pipe is merely lifted up by hand (or by tackle),
while the other end is held firmly in position.
Figure 3-66.Part of pipe heated before wrinkle bending.