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Casting Defect in a Hastalloy Tube

An alloy tube was used to mix sulfuric acid with water.  During pressure testing the tube was found to be leaking.  RSIME was requested to ascertain the cause of leakage.

Procedure:

  • The tube was visually inspected, photo-documented both internally and externally, and then cross-sectioned through the area where the leak was observed. Figure 1 (below) shows a cross-section of the tube indicating porosity.
  • After sectioning with a water-cooled saw, the cross-sectioned surface was polished to inspect flaws found in the tube wall.
  • The cross-section was also photographed using a Scanning Electron Microscope (SEM) to provide improved depth of field photographs (See Figure 2 below).

Conclusion:

The interior surface of the tube did not reveal any evidence of attack from corrosion. The tube had a manufacturing defect in the form of casting porosity and was causing the leakage. There was no evidence that the sulfuric acid had any deleterious effect on the integrity of the tube.

 

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Figure 1 - Cross-section of tube indicating porosity in the tube wall.


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Figure 2 - SEM photograph of porosity in the tube wall.