Metallurgical Technologies, Inc.
Case Study: Analysis of a leaking diesel engine manifold
A pressure tested diesel engine manifold exhibiting a pinhole defect was analyzed to determine the cause of the flaw. A red arrow points to the port where leak testing revealed an internal breach in the water jacket. The manifold was dissected to expose the leak defect. Transverse cuts were made on each side of the port and the outer 1/3 of the manifold toward the port opening was cut off in the axial direction.
The exposed inside surface of the manifold exhibited a pinhole as presented in this close-up view. The pinhole diameter measures approximately 0.09-in. on this surface.
A close-up view of a small cross-section through the pinhole reveals two significant voids. The voids are lined with oxides or possibly sand from the casting operation. An arrow points to the pinhole observed in the inner manifold surface.
The surface inside one of the voids was examined at high magnification using a scanning electron microscope (SEM) to determine whether the void was a corrosion pit or a casting defect. The surface is smoothly contoured and exhibits evidence of dendritic solidification structures indicative of a casting void.
The microstructure was examined at high magnification in a cross-section through the edge of one of the voids using an optical microscope. Additional smaller voids are noted. The void edges are rounded (smooth) and dendritic penetrations are noted. Dendritic penetrations at the arrow are provided at a higher magnification in the following image.
The dendritic penetrations along the edge of the void are indicative of a casting defect.
CONCLUSIONS:
Results indicate that the pinhole was a result of a significant casting void in the cast aluminum manifold. Two casting voids approximately 0.180 - 0.275-in diameter were found in the water jacket surface at the pinhole location. The voids encompassed approximately 90 - 95% of the wall thickness. The premature manifold leak is a result of a significant casting defect. The insurance company that requested this study was able to collect on the manufacturers warranty.
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