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Fuel
Nozzle Clip Failures
Fuel nozzle clips from RVs and marine applications
were found to be failing. The failures all had a
characteristic brittle fracture appearance and
visibly indicated no plastic deformation. A sample
of the failed fuel clips is shown in Photograph A.
Photograph A:
Overall view of failed fuel nozzle clips.
Failures of the fuel clips were also found to occur
in the clip shoulder as shown in Photograph B.
Photograph B:
Shoulder failure
of fuel nozzle clips.
These 17-7 PH stainless steel
clips were also observed to exhibit surface pitting
as shown in Photograph C.
Photograph C: Surface
pitting on failed fuel clip.
Closeup examination revealed superficial corrosion
around the fracture and on the clip surface. The
corroded surface near the fracture is shown in
Photograph D.
Photograph D:
Close up
view of surface corrosion on failed fuel nozzle
clip.
An overall view of the fractured
clip in Photograph E illustrating corrosion on the
surface of the failed nozzle clip near the fracture
surface.
Photograph E: Failed
fuel nozzle clip with corrosion near the clip
fracture.
The clip fracture surface is shown in Photograph F.
Photograph F:
Close up view of nozzle clip fracture surface.
It was clearly evident that the fracture surface was
grainy and exhibited no evidence of ductile
fracture. The fracture surface of all of the
clips examined also exhibited a grainy, non-ductile
fracture as shown in Photograph G.
Photograph G: Grainy
fracture surface of failed stainless steel.
SEM examination revealed, even at low magnification,
the intergranular fracture pattern shown in
Photograph H.
Photograph H:
Scanning
electron micrograph of failed nozzle clip. Fracture
surface indicates intergranular fracture.
A close up view, at a
magnification of 500x, is shown in Photograph I.
Photograph I:
Close up
(mag 500x) view of intergranular fracture on failed
nozzle clip.
Metallographic polishing of one
of the clips was conducted and the resulting
polished surface is shown in Photograph J.
Photograph J:
Scanning
electron micrograph (mag 300x)
showing intergranular fracture of polished
metallographic specimen.
Energy dispersive spectroscopy
revealed, as shown in Figure 1, a very large
concentration of chlorine (Cl).
Figure 1:
Close up
(mag 500x) view of intergranular fracture on failed
nozzle clip.
As a result of this investigation
it was determined that the 17-7 PH stainless steel
nozzle clips had been improperly heat treated and
were rendered sensitive to intergranular stress
corrosion cracking.
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