Coating resistance determination

Protection current density and coating resistance are important for the current distribution and for the range of the electrochemical protection. The coating resistance determines, as does the polarization resistance, the polarization parameter (see Sections 2.2.5 and 24.5). For pipelines the protection current density determines the length of the protection range (see Section 24.4.3). 

Coating resistance determined for this section of pipeline... 

Fig. 3-13 Determination of the protection current density and coating resistance of a pipeline (explanation in the text).

The cell current is determined by the coating resistance r and the size of the coated surface S. Neglecting the anode resistance, the cell current from these two quantities is given by [see Eq. (2-43)] ... 

Sometimes the type of coating is determined by special requirements such as abrasion or heat resistance. The coating may have to withstand specific chemicals or solvents. All coatings have to be a compromise of properties. A gain in one may be a loss in another. 

Complex structures such as tank farms, tank bottoms and marine installations have complicated attenuation patterns and it is not feasible to use complex equations to determine the effect. This must be determined by a current drain test or by practical experience. For pipelines the attenuation depends on the linear resistance of the pipe, coating resistance, and to some extent the resistivity of the soil. Connections to foreign structures and the method of termination of the line also affect the attenuation (see Section 10.1). 

Changes in corrosion resistance of the electrolytic tin coatings were determined by the iron-solution-value test and the alloy-tin-couple test (6). Corrosion resistance data for the 43 kg (95 lb), Type MR-TU, No. 25 tinplate are presented in Table VIII. These data show that there is no significant difference in the corrosion resistance of the unirradiated... 

ISO 4665 1998 Rubber, vulcanized and thermoplastic - Resistance to weathering ISO 6179 1998 Rubber, vulcanized or thermoplastic - Rubber sheets and rubber-coated fabrics - Determination of transmission rate of volatile liquids (gravimetric technique)... 

DC techniques Include measurement of DC resistance, determination of polarization behavior, and measurement of polarization resistance. Coating resistance has been correlated with corrosion performance by a number of workers. As svunmarlzed by Leldhelser ( ), the results of several independent investigations suggest that coating resistance below about 10 ohm/cm Is associated with the formation of visible under-film corrosion. Parallel DC resistance measurements on thin film metal substrates have been used to study the deterioration of coated metals the technique successfully detected the effects of water after migration to the coating/metal interface (351. 

ISO 5470-2 Rubber or plastics coated fabrics - Determination of abrasion resistance -Martindal abrader. 

ISO 5470-1 Rubber- or plastic-coated fabrics Determination of abrasion resistance Part 1 Taber abrader... 

For each oven taiperature setting, the residence recruized to produce a "cured" coating was determined. "Cure" was determined by a block resistance test. Ttoo coated board samples exiting frcm the oven were allowed to cool to 66°C and then pressed together face-to-face in a heated press (66°Cl set at a pressure of 80 psi. After 10 minutes, the boards were ranoved from the press and separated frcm one another. The coatings were considered "cured" if no blocking occurred. 

Figure 20 Coating resistance versus time for bare 2024-T3 surfaces exposed to Ce sealed hydrotalcite, a Ce(III) conversion coating, and bare 2024-T3 in the simulated scratch cell. Rc was determined ex situ during immersion in 0.05 M NaCl solution. The plot indicates an elevated resistance to corrosion for the sample exposed to the Ce sealed hydrotalcite coating. (From S. B. Mamidipally, P. Schmutz, R. G. Buchheit. Corrosion, 58, 3, 2001.)...

Tensile stress is used to characterize cohesiveness between particles, or in a certain powder cake, coating resistance in an encapsulated powder. Shear stress refers to the stress component tangential to the plane on which forces act and is mainly used to determine frictional properties (e.g., angle of internal friction) between particles under a pressure load. Furthermore, because individual particles predominantly slide across each other in a shearing action during flow, shear stress measurement allows determination of flow properties. 

Impact resistance of epoxy coatings, as determined by a reverse Gardner impact test, is enhanced by liquid polymer addition independent of functional type. Again, these results are consistent with both unpigmented and pigmented model coatings. Although... 

ISO 5978. 1990. Rubber and plastics coated fabrics—Determination of blocking resistance. 

The effective coating resistance can be determined at any section of the pipehne by applying a cathodic current [53,56]. The temporary current should be interrupted at defined time intervals (40 s with 20 s off). The current-induced difference may be found out at two different locations of the pipehne. Once these differences in pipefine current (7 = Ian 7ofr) and the difference in potential (E=Ean — ofr) are known at two locations, the coating resistance can be estimated by using the expression ... 

The scratch tests are very similar to the nanoindentation tests and can be considered side by side. In both teclmiques, a prime tip is used for the adhesion measurements by dragging across the measuring surface under an increasing load, which results in an indentation. Scratch and indentation tests are suitable for the analyses of the coatings and thin films [100]. Sharp diamond indenters are usually used for the adhesion and scratch resistance determination between the substrate and coating. These techniques can fail for the analyses of hard coatings on soft substrates due to no detectable failures as a result of small critical loads. Therefore,... 

An example of combinatorial screening using a zero-order measurement approach is illustrated in Figure 5.2. Abrasion resistance of organic protective coatings was determined from measurements of scattered light from each coating in a 48-element array. A simple zero-order measurement approach was useful because it provided the required information about... 

The sprayability of a coating is determined by its viscosity at application. The viseosity is a measure of the ability of a material to resist flow and is an important formulation design parameter. Application viscosity is affected by the ambient conditions and by the degree of... 

---