Dealloying (Dezincification/ Denickelification) | Materials And Corrosion Control

Damage Description

·         Component failure may occur suddenly and unexpectedly because mechanical properties of the dealloyed material are significantly degraded.

Affected Materials/Equipment

Control Methodology

·         Altering the exposure of a dealloyed component conditions or replacing it with a resistant material.

·         Depending on the alloy-environment combination, cathodic protection or barrier coatings may be effective.

·         Limit Zn content in brasses to 16% maximum, if possible
(SAES-L-108).

Monitoring Techniques

·         Dealloying in brasses (i.e., dezincification) is visually evident by a reddish, copper color instead of the yellow brass color.

·         Graphitic corrosion turns cast iron charcoal gray and the material can be cut or gouged with a knife.

·         Metallographic examination may be required to confirm the extent of damage.

·         A significant reduction in hardness may accompany dealloying, although affected areas may be localized.

·         Acoustic techniques (loss of “metallic ring”) and ultrasonic attenuation are applicable, but UT thickness measurements are not.

·         Fitness-for-Service (FFS) analysis of dealloyed components should consider that the dealloyed portion may be brittle and contribute little or no mechanical strength or load bearing capability.

Inspection Frequency

KPIs

·         Number of failures caused by dealloying

Reference Resources (Standards/GIs/BPs)

·         SAES-L-108