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Fuel Nozzle Clip Failures

Numerous fuel nozzle clips from RVs and marine applications were found to be failing unexpectedly. 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.

Overall view of fuel nozzle clips.
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.

Shoulder of fuel nozzle clips.
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.

Surface pitting of failed fuel clip.
Photograph C Surface pitting on failed fuel clip.

Close-up examination revealed superficial corrosion around the fracture and on the clip surface. The corroded surface near the fracture is shown in Photograph D.

Close-up view of surface corrosion on fuel nozzle clip.
Photograph D Close-up view of surface corrosion on failed fuel 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.

Fuel nozzle clip with corrosion near the clip fracture.
Photograph E Failed fuel nozzle clip with corrosion near the clip fracture.

The clip fracture surface is shown in Photograph F.

Close-up view of nozzle clip fracture surface.
Photograph F Close-up view of nozzle clip fracture surface.

The fracture surface appeared 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.

Grainy fracture surface of failed stainless steel.
Photograph G Grainy fracture surface of failed stainless steel nozzle clip.

SEM examination revealed, even at low magnification, the intergranular fracture pattern shown in Photograph H.

Close-up view of nozzle clip fracture surface.
Photograph H Fracture surface indicates intergranular fracture.

A close-up view, at a magnification of 500x, is shown in Photograph I.

Close-up view of nozzle clip fracture surface.
Photograph I 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.

SEM showing fracture of polished metallographic specimen.
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).

Close-up view of nozzle clip fracture surface.
Figure 1 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 therefore were rendered sensitive to intergranular stress corrosion cracking.

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J.E.I. Metallurgical, Inc.

5514 Harbor Town
Dallas, Texas 75287

Phone: (972) 934-0493
Fax: (469) 737-3938
Email: r.c.jerner@metallurgist.com

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