Environmental Engineering Reference
In-Depth Information
Figure 8.16
Radiograph of a forged shafting showing the presence of internal hydro-
gen flakes [19].
there had been a relatively rapid cool from forging temperatures. These factors
contributed to the formation of shatter cracks or flakes in this steel with normal
hydrogen conent.
The failure of several aircraft components due to hydrogen embrittlement has
been reported [20]. These include landing gear cylinders, main landing gear pivot
pins, and main landing gear drag link bolt made of 4340 steel. These components
were either chromium- or cadmium-plated and hydrogen pickup during the plat-
ing operation was considered to be the cause of embrittlement. The failure also
occurred in a propeller retaining ring having the composition Fe-0.5C-2.5Ni-
0.75Cr. The component had been heat-treated to a strength of 1379 MPa and a
bright electroplated cadmium coating had been applied.
Failure by HSC has been reported [21] in AISI 4137 steel bolts having a
hardness of 42 HRC. Figure 8.17 shows the multiple, branched cracking originat-
ing from the thread roots. Although the service temperature was too high (400
C)
for hydrogen embrittlement, its occurrence was attributed to corrosion caused by
acidic chlorides from a leaking polymer solution at ambient temperatures during
the extended shutdown periods. The corrosive environment contained trace hy-
drogen chloride, acetic acid vapors, and calcium chloride, and the bolt surfaces
°
