Although 316 stainless steel pipes are usually used in marine environments, the corrosion resistance of the steel and seawater is limited and can not be resistant to corrosion in all states. Which is more susceptible to local corrosion, mainly crack corrosion and point corrosion. So this limits the scope of application of 316 stainless steel tubes in marine environments.
Factors that can affect the corrosion resistance of 316 stainless steel pipes in seawater are water quality, flow rate, temperature, oxygen content and cathodic protection. Of course, there are other factors, but the relationship is not, it is not within the scope of this article.
The quality of sea water
Marine water quality is mainly affected by the geographical and tide, which chloride content will be different. Even in slightly salty seawater, the chloride content is higher than the amount of water that poses a corrosion threat to crack corrosion.
Intermittent exposure to seawater, such as tidal areas, 316 stainless steel pipe corrosion risk will be small, perhaps because the steel surface by the water level changes occur when the effective erosion of the impact.
But once the chloride is concentrated in a humid and rainy environment, the risk of corrosion increases after evaporation of seawater in the splash zone.
Do not let seawater contact stainless steel when it is not necessary. For example, the cross section of the 316 horizontal pipe that deals with seawater will only be subject to corrosive damage in the short term.
Free drainage surfaces and avoiding cross tube movement are important for the successful use of 316 steel in areas of contact with seawater. If the piping system uses seawater for hydrostatic testing, it must be drained and rinsed immediately after the test, otherwise it will corrode 316 stainless steel pipe.
Sea water flow
The higher the flow rate of seawater is a better condition (usually greater than 1m / s). While the slow flow of water is likely to lead to biological pollution, and then lead to crack corrosion. So be sure to avoid seawater stagnation.
Increasing the flow rate of seawater will reduce the risk of corrosion, so it is very appropriate to use 316 stainless steel tubing in areas such as pumps, such as pumps.
Sea water temperature
With the increase in water temperature, stainless steel crack corrosion is also more likely to produce, so stainless steel is best not to contact hot sea water.
Stress corrosion cracking is usually not considered at the operating temperature of 316 stainless steel tubes, because however, higher temperatures may cause cracking and pitting.
Oxygen content in seawater
Oxygen can help stainless steel to maintain self-passivation, but oxygenated seawater is more corrosive. In very low oxygen content, as in about 200 meters deep in the sea, the erosion is very small, which will reduce the pitting rate of stainless steel.
Cathodic protection in seawater
Cathodic protection is used in electrical engineering and is obtained by contact with less inert metals including carbon steel and aluminum. Direct contact with these metals, at the expense of other metals on the basis of help to improve the 316 stainless steel tube corrosion resistance. While it is beneficial to stainless steel, it should also be considered that the combined durability of products involved in this combination may be diminished.
Source: China 316 Stainless Steel Pipes Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)