Resistivity in seawater

Aluminum and silicon bronzes are very popular in the process industries because they combine good strength with corrosion resistance. Copper-beryllium alloys offer the greatest strength and excellent corrosion resistance in seawater and are resistant to stress-corrosion cracking in hydrogen sulfide. 

A protective film may be physically removed at still greater velocities by high shear stresses. In fact, some Cu alloys have good corrosion resistance in seawater that is attributed to the formation of a protective oxychloride film. It has been theorized that high fluid velocities produce shear stresses that alter or... 

The corrosion rate of a totally immersed copper sample in seawater is about 0.02-0.07 mm/yr and at half-tide the rate is 0.02-0.1 mm/yr. In this respect the corrosion resistance of copper is 2-5 times greater than mild steel under total immersion conditions and even greater under half-tide conditions. The copper loses its corrosion resistance in seawater of velocities greater than 1 m/s and the rate of dissolution is such that toxic copper species produced are beneficial in that they are used in marine antifouling agents. 

These alloys have an hep crystal structure known as alpha phase. The beta-transus temperature of CP titanium alloys is -910 15 °C (1670 27 °F), depending on the oxygen content (Ref 1). These alloys are not strengthened by heat treatment, like some other titanium alloys. They also have excellent corrosion resistance in seawater and marine environments. 

Alloy C-22 and Alloy 59 were developed for applications where resistance to corrosion under highly oxidizing conditions is required. The high chromium content in these alloys, 22% and 23% for C-22 and 59, respectively, imparts excellent corrosion resistance of these alloys to nitric acid [23]. In addition, these alloys have been found to have superior crevice corrosion resistance in seawater [24]. 

Stainless steels are susceptible to localized corrosion in quiet seawater but maintain good corrosion resistance in seawater flow conditions due to the increased oxygen supply, which promotes passivity of these alloys. Biofouling is also minimized in high velocity conditions, and this in turn minimizes the number of sites for crevice or poultice attack... 

The very good corrosion resistance in seawater and the fact that titanium metal is non-magnetic has naturally interested designers of submarines. 

Nickel-alloyed cast iron with content levels of 1-3% nickel is often used in pump casings, water chambers and other castings used in contact with seawater. The addition of nickel increases the strength and reduces the porosity of the casting, but has practically no influence on the corrosion resistance in seawater. 

The silicon cast alloys with content levels of about 15% silicon show good resistance in seawater. Their corrosion rates are around 0.05-0.01 mm/a (2.0-0.4 mpy). They are also used as anodes for cathodic corrosion protection with external current with a material consumption level of 0.4—0.9 (kg/A a). 

In the ferritic chromium steels, the resistance to pitting and crevice corrosion depends on the pitting resistance equivalent PRE = % Cr -r 3.3 x % Mo. Steels with a pitting resistance equivalent of 32 are sufficiently resistant in seawater under normal conditions. Under critical conditions for crevice corrosion, materials with a pitting resistance equivalent of 35 are required [99]. 

The effect of sigma phase precipitation at 800 °C on the corrosion resistance in seawater of a high-alloyed duplex stainless steel... 

Chromium. It is usuaUy added to Al-Mg alloy and Al-Mg-Zn alloys in amounts of 0.1-0.3%. It has a beneficial influence on pitting resistance in seawater. 

Seawater covering 70% of the earth s surface has been offering unlimited material benefits to b) Chloride Ions mankind ever since the dawn of history. The ocean floor is a full hydrospace for minerals, fuel, food and energy. Seawater is, however, knovm to be quite corrosive and increased exploitation and exploring activities require materials resistant to seawater corrosion. Due to its corrosivity, corrosion resistance in seawater is taken as an index of corrosion tendency of materials. A material... 

Which of the following category of brasses would show the best corrosion resistance in seawater ... 

Protective film formation. The good corrosion resistance in seawater offered by copper-nickel alloys results from the formation of a protective oxide film on the metal surface. The film forms naturally and quickly, changing the alloy s initial exposure to seawater. In clean seawater, the film is predominantly cuprous oxide, with the protective value enhanced by the presence of nickel and iron. Cuprous hydroxy-chloride and cupric oxide are often also present. ... 

Water environments can also have a variety of compositions and corrosion characteristics. Freshwater normally contains dissolved oxygen as well as minerals, several of which account for hardness. Seawater contains approximately 3.5% salt (predominantly sodium chloride), as well as some minerals and organic matter. Seawater is generally more corrosive than freshwater, frequently producing pitting and crevice corrosion. Cast iron, steel, aluminum, copper, brass, and some stainless steels are generally suitable for freshwater use, whereas titanium, brass, some bronzes, copper-nickel alloys, and nickel-chromium-molybdenum alloys are highly corrosion resistant in seawater. 

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