Coating damage

The evaluation of At/ values together with off potentials are aids in deciding whether coating damage should be repaired. In addition, by comparison with previous results, intensive measurements indicate whether new coating defects have arisen. These could be the result of external foreign forces on the pipeline. 

All reported incidents. Includes all reports of anchor, cable or trawl contact and also severe concrete coating damage. 

In many cases there will be a need to test metal-coated specimens, e.g. galvanised steel, tin-plated copper, nickel-plated zinc, etc. It will then be necessary to test specimens in the completely coated condition and also with the coating damaged so that the basis metal is exposed. The latter condition will provide the conditions for galvanic action between the coating and the basis metal. With sheet specimens this condition is most readily achieved by leaving cut edges exposed to the test environment. 

Special measures to reduce coating damage during handling, transport or erection and measures for maintenance of incomplete systems stored in the open. 

For these reasons, EIS has been explored as an alternative proof test for evaluation of conversion coatings. In these tests, conversion coated surfaces are exposed to an aggressive electrolyte for some period of time during which coating damage will accumulate. An impedance spectrum is collected and evaluated using a suitable equivalent circuit model and complex nonlinear last-squares fitting. 

Figure 3 Comparison between different coating damages in the over...

The influence of coating damage on the ICCP cathodic protection effect... 

Table 1 Shipboard coating damage extent and position.

Parameters that are important to achieve reproducible results include the condition of fibre coating (damage, contamination by high molecular weight semi-volatiles), sampling temperature, sampling time (if non-equilibrium... 

Double-hulled tankers are in use over the single-hulled variety in coastal waters. The space between the inner and outer hulls of the tankers is often used for ballast water, and the coating damage occurs here and hence corrosion. Greater corrosion damage in oil tanks because of the thermos effect has been observed. In double-hulled tankers the temperature is 46-55 °C, which leads to a higher corrosion rate. 

Double-hulled tankers are designed to have a ship inside a ship to reduce the risk of sinking of the ship and loss of cargo. The space between the inner and outer hulls is often used for ballast water to balance the tanks. These areas often have coating damage followed by corrosion because of the conditions in the tanks. These are difficult to inspect, and corrosion occurs because of the thermos effect. 

Another problem is the repair and rehabilitation of the pipeline coatings. In case the pipeline is damaged due to some mechanical failure or due to corrosion attack, or many old pipelines result in coating damage, repair of the coating is of prime importance. Again, there are several coatings used... 

Any of the standard welding methods can, with care, be used for joining aluminum-coated steel, spot and seam welding being especially desirable since these keep coating damage to a minimum. However, care should be taken to avoid conditions where brittle intermetaUics can form with resulting embrittlement of weld zones. 

Coating damage during fuel manufacture, resulting in heavy metal contamination on coating surfaces and in the fuel body matrix. 

Distribution of internal stresses in organotin coatings is defined by formation of two phase boundaries, i.e. gas-liquid (polymer, as highviscous liquid), liquid-solid body (Fig.I). In this model the internal stresses are presented as balls with dimensions proportional to stress value and arrows show direction of forces. The coating damage starts from the surface and boundary layers. 

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