On the extension of CP models to address cathodic protection under a delaminated coating
Cathodic protection models for pipeline and other metallic structures developed to address the presence of coating flaws or holidays do not account explicitly for the presence of a delaminated region surrounding a holiday. The potential drop in the delaminated region was obtained by solving the coupled, non-linear, partial differential, governing equations that describe transport and electrochemical reactions within the delaminated region. The results were used to develop an analytic expression for the potential drop across the delaminated region as a function of delaminated region length and the resistivity of the bulk environment exterior to the holiday. Expressions developed using this approach can be utilized by existing cathodic protection models to deliver improved potential distributions along protected metallic surfaces. The simulations were used to test the commonly employed assumption that transport by diffusion can be neglected in the delaminated region. The influence of diffusion on current was shown to be significant.
Study of cathodic protection shielding under coating disbondment on pipelines
Abstract In this work, the cathodic protection (CP) shielding behavior of pipeline coatings, i.e., high density polyethylene (HDPE) and fusion bonded epoxy (FBE), was investigated. While the HDPE is a CP-shielding coating, the FBE is permeable to CP. The structure of HDPE does not change upon CP permeating test, and water molecules are not absorbed into the coating. Conversely, there are obvious changes of the functional groups in FBE. Water uptakes into the coating occur continuously with time. The CP permeation through FBE coating is time dependent. A more negative CP potential level enhances the CP permeation.
Microstructure of the solder-casting zone in bridges of dental gold alloys.
The composition and structure were studied in the cast and in the solder of bridges which had failed clinically. Both materials were gold alloys but with different contents of Pt, Ag and Zn. The metallographic investigation revealed defects mostly in the solder, situated in the subsurface layer. SEM studied of the fracture surface revealed large porosites and a structure of dense parallel lines--striations--, indicating that the material had failed from fatigue. The materials in the fractured bridges were identified by micro-probe measurements. It was stated that cast material and solder material used together, were of different composition.