Studying The Use Of Inconel 625 For Crevice Corrosion Resistance
Before going into the potential of certain alloys to resist crevice corrosion, it is necessary to find out what is crevice attack. This kind of attack develops when unlike material come into contact with each other and the second material may be used for connection such as screws or fasteners either made from the same material or different from the first. The second material develops crevice in all those places where there is mud accumulation and oxides along with other solid particles tend to develop precipitates on the surface of the alloy. Corrosion due to crevice occurs by exposing a similar surface to atmosphere or due to the presence of moisture. However, the other surface that I far away from the crevice tends to dry and drain. The phenomenon of crevice and pitting corrosion is similar although various factors can determine the rate of the attack such as the concentration, corrosive conditions and the composition of the alloy.
Various alloys such as Inconel 625 offer high performance when the conditions are severely corrosive such as marine water or high temperature media. Quite naturally, the alloy 625 is one of the prominent alloys to be used for sea water applications due to its resistance towards pitting and crevice corrosion. Moreover, it also has high corrosion-fatigue strength, tensile strength, and can also resist chloride ion stress corrosion cracking. No wonder it is widely used in the wire rope, the propulsion motors, and in the process of sheathing for the communication cables under the sea.
Experimental study with Inconel 625
When an experimental study was conducted to find out the influence of temperature on crevice corrosion initiation for alloy 625 in natural seawater, the following results were achieved. The tests clearly showed that there was a crucial relationship temperature and time that is required for the initiation of crevice corrosion. The potential required to cause crevice corrosion in alloy 625 reduced when the temperatures were increased from ambient to 40 degrees Celsius. Similarly, the crevice initiation potential reduced from 300 mV for ambient seawater temperature to 100 mV for seawater in 40 degrees Celsius. However, the initiation of crevice remained unchanged between 40 and 65 degrees Celsius while the time required to initiate crevice corrosion reduced with an increase in the temperature.
Marine applications and Inconel 625
The nickel-based Inconel 625 alloy is use for fasteners, expansion joints, and shaft seals. Alloy 625 offers excellent resistance to marine conditions although it can be highly expensive for some of the applications even if it offers the benefits of preventing crevice corrosion. No wonder the use of Inconel 625 for crevice corrosion cracking is widely noted.
One of the ways to prevent high cost is to use the alloy as weld overlay on materials that are less expensive and the areas are the shaft surfaces on the way of seals and the crevice regions in the pump casings and pipes. The method of weld overlaying using alloy 625 is commonly used for offshore and seawater applications and the recent demands for materials with high consistency and small life cycle costs is more likely to make this alloy highly usable for marine water applications.