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Flange Cracking and Leakage

Background:

Cracks were observed on AISI 304 stainless steel flange during NDT inspection near the welded region associated with a leakage. A failure analysis was conducted to identify the failure mechanism(s) and assess causes.

Figure 1: Visual Inspection of As-Received Flange Samples Depicting Cracks

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Figure 2: Optical Micrographs Revealing Intergranular Attack Along the Grain Boundaries

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Figure 3: Typical Intergranular Failure Observed in Scanning Electron Microscopy

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Summary: 

This flange failure was associated with intergranular stress corrosion cracking (IGSCC) attack under caustic environment. Often times during welding operation due to thermal exposure these type of stainless steels are subjected to sensitization temperatures in the heat affected zone. This can lead to deleterious precipitation of Cr-carbides along the grain boundaries that makes the material susceptible to intergranular corrosion and/or stress corrosion attack.


Take Away: 

Thermal exposure during operation, faulty heat treatment, welding etc. can cause microstructural degradation of stainless steels making them susceptible to localized corrosion attack.



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