In recent years, various types of stainless steel materials have been used more and more in the marine environment. Most of the stainless steel materials are used well in the marine environment, but the sensitivity to stress corrosion cracking is different for different brands. Let's talk about common marine equipment that uses stainless steel as a manufacturing material.
Bulk container: stainless steel has been used as a bulk bag container in freight transportation to load liquefied natural gas (LNG), chemicals, beverages, etc. 304L stainless steel is used for the container of LNG in freight transportation. Its purpose is not to resist corrosion but to consider the mechanical properties at low temperature.
For containers of marine chemicals, the purpose of using stainless steel is mainly to consider its corrosion resistance, which is different from the storage and transportation of terrestrial chemicals. If the vessel is a general non-scheduled freighter, the container carrying the chemicals can also carry anything from acetic acid, bad pulp to xylene. Type 316L stainless steel is generally used for valves, freight pumps, pipes, heating coils and the vessel itself. The container can be composed of integral stainless steel or made of carbon steel clad with a layer of 0.06~0.08in (1.5-2.0mm) stainless steel plate. Before use, the sheet must be carefully inspected for defects and thoroughly cleaned and passivated.
Experiments have shown that passenger vessels containing chemicals are allowed to be flushed with sea water, but must then be flushed with fresh water very quickly. As with any stainless steel heating device in the vessel, it should not be activated until the chloride has been completely flushed out to prevent stress corrosion cracking. Chemical containers should not be designed to hold sea water because doing so would create a risk of crevice corrosion. If it is specified in the design plan that it must be used to hold seawater, then a cathodic protection system must be considered to control the development of crevice corrosion. In this case, stainless steel vessels can create calcareous deposits that are difficult to remove, which is a concern.
Heat Exchanger: Austenitic stainless steel pipes have been widely used in condensers of forced water circulation systems and steam condensers in power plants, and copper alloy materials are not suitable for the water inlet of the latter due to high pollution. A more popular good material is Type 316 stainless steel. In coastal and harbour areas, large amounts of foreign agglomerates and silt entering the condenser pipes are particularly prone to serious obstructions that must be eliminated. A reasonable measure is to use rubber balls to circulate through the pipe, because the rubber balls can squeeze and clean the pipe wall. When the flow speed of seawater is about 1m/S, it can prevent the marine organic debris from being sucked in, thereby protecting the condenser pipeline from pitting corrosion. Unlike other non-ferrous alloys, the pipeline using stainless steel as the condenser is not limited by the maximum flow rate, but it is related to the economic effect of the entire pump device.