抄録
A heat exchanger for vaporizing liquefied natural gas (LNG) is made of Al alloy tubes and the way of protecting the tubes from corrosion by sea-water is to form a sacrifical anode layer by thermal-spray coating of Al-2 mass% Zn on Al alloy tubes. But in some cases, damage is found in the lower part of heat exchangers which are exposed to low temperature and flowing sea-water.
In order to understand the corrosion behavior of coated Al-Zn alloy in this environment, the influence of temperature and rotating speed on the polarization behavior was examined by a rotating disk method simulating the flowing sea-water.
In the case of low temperature and high rotating speed, the limiting current density of oxygen diffusion increased on the cathodic polarization curve. The corrosion reaction on the coated Al-Zn alloy is controlled by the cathodic reaction. Therefore, the corrosion rate increased in this case.
With the addition of suspended solids, the corrosion potential on the coated Al-Zn alloy shifted to the less noble direction, indicating the removed of passive-film on the coated Al-Zn alloy.
Therefore, it is concluded that the corrosion damage in this environment is caused by a kind of erosion-corrosion and is accelerated with the addition of suspended solids, such as crushed shell.
