Tulsa daily world. [volume] (Tulsa, Indian Territory [Okla.]) 1905-1919, 1918-11-08
"IronIng Onl" mrircd" PING.


steel which has been subjected 30
repeated shocks Will break easily.
and the fracture show a crystalline
appearance, due to repeated stresses
which occur therein. What
happens is that ~ the steel iI repeat
rdly strest. either hy bending. pu''iry
or twisting, II becomes fitlgIrd. This
fatigue ~ probably merely the frsi
stages OF an infinite number ~ small
cracks or tears IN the body ~ ia"
steel, and these tears naturally tend
to occur along Ia" faces ~ the cryS-
tails OF the material, At first Of mi
croscoplC Dimensions thWt do not
materially weaken the metal As they
spread they greatly weaken tho
metal which eventually parts along
the crystal faces, and tn" character
istlc fracture. which IL referred to rs
crystnlllZations, occurs
"Heforc this state Of fatigue con
tinucs sufficiently to weaken the
metal materially. or. in other words.
II It IL taken In time. II can be partly
arrested hy heating the material 20
welding heat Hut tho mere heat
ing, while II tcnds To stop the cracks
from spreading the while II may to-
arrange the CRYSTALS 50 that some uf
the cracks are partly duseN, is Of lit
tie value unless 10 TX done carly. and,
In fact, before much NJ this tearing
away W the metal occurs A badly
fatigued pipe can not he restored tu
its original strength by merely heat
ing It.
The Harden process not only
heats the pipe, hut also involves the
application of longitudinal pressure.
In the first place, during heating tho
pipe has heavy spring pressure on its
ends, VI that there Is a constant pres
sure OF about 1900 pounds on 1t I'm
the direction Of its length As the
pipe IL heated to a carefully rCgu-
lated temperature this pressure tends
to squeeze the pipe together and TO
repair any small cracks.
"In the process electricity is used
as the heating medium and, while
somewhat expensive, IL necessary for
reasons which will he later pointed
out The first great advantage or
the electric method IL that each Joint
can be heated separately and the
heat carefully controlled. In prar-
tlse II requires something over -
minutes in which to heat siN-inch
pipe 20 fcet long, and during tn"
heating the operator IL able at al
times tn observe the pipe, which
rests on flat surface and is Gov
cred with u light asbestos hood. Nv
heating II electrically and slowly tho
IOint is very evenly heated through
out its length and has "A chance to
expand slowly, AS soon az the pipe
reaches n desired temperature the
heating operating is shut off Instant
~. As during the heating operation
tho current actually flows through
the pipe and the heat IL generated in
tho body Of the pipe this heat Is
evenly generated throughout the
body OF the metal. and as all IN"
losses are on the outer and inner sur
faces It follows that these surfaces
are the cooler. Considering the pipe
AS a platc. 1t will hc seen that the
surfaces OF the plate are cooler than
the interior. II IL highly prohahl"
that this unequal heating through
the thickness ot the material causes
a working which helps To weld NE
cracks and arrest tho fatiCuc II is
not this feature which makes tho
process "A success. however, but the
electromagnetic action which Is tax
ing place simultaneously
II Is easy 10 calculate that the steel
Of the pipe is saturated with mdGnc-
tism. II is. further, easy ~ calculate
that the force eNertcd, which Is In
effect "A squeezing Of the pipe to
gether. y in excess of 800 pounds per
square inch. In other words, the
magnetic pull In the body of the ma
tcrial IL at least 900 pounds per
square inch. Under this enormous
pressure any cracks are 'ironCd out
and tho material Of the pipe re-
welded over the cracks, Moreover.
as the pipe Is treated on alternating
current. this magnetic pull is applied
and released from so to 100 times
second As tho pipe is under this
pressure, which is working con-
stantly for from 10 to 20 minutes, II
Is not surprising that after being
cooled It fails to show, any evidence
OF fatigue. Literary Digest,