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51312-01502-The corrosion resistance of duplex stainless steel grades in sulfuric acid

Product Number: 51312-01502-SG
ISBN: 01502 2012 CP
Author: Carolina Canderyd
Publication Date: 2012
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Sulfuric acid is one the most common chemicals used and handled within the process industries. Applications range from leaching through polymer production to food and pharmaceuticals manufacture. The range of concentrations extends from the very dilute to the viscous oil-like concentrated acid and this results in a range of corrosion issues. From a corrosion point of view sulfuric acid can be reducing at low concentrations and oxidizing at high concentrations which clearly presents challenges to the materials specifier. The corrosion resistance varies with concentration and temperature with its most aggressive condition at the mid-range concentrations. In this paper the performance of a number of stainless steel grades in sulfuric acid have been thoroughly investigated in a series of laboratory tests including evaluation of parameters such as the effect of impurities oxygen level and flow rate. The addition of impurities can change the behavior of the material for example chlorides can drastically increase the corrosion rate while iron sulfate can decrease it. Oxygen is needed to maintain the passive layer and its absence can lead to loss of passivity. Results show that the measured corrosion rates are strongly influenced by actual test procedure employed and the different stainless steels cannot be properly compared unless the tests have been carried out with a rigorous control of the methodology. Different parameter such as activation of specimens and type of activation is discussed. Using a test method which includes activation of the specimens is shown to give more conservative results. In most applications this is most relevant since the results from a non-activating technique are only applicable when the stainless steel maintains full passivity not when the surface may suffer mechanical damage. The presence of free oxygen or its avoidance by purging with nitrogen is also a critical factor. Electrochemical measurements and accelerated immersion tests are compared with long term immersion tests and their relevance is discussed. The conclusion is that stainless steels can be for handling sulfuric acid with certain limitations and some restrictions in concentration and temperature will be presented for different duplex stainless steels.
Sulfuric acid is one the most common chemicals used and handled within the process industries. Applications range from leaching through polymer production to food and pharmaceuticals manufacture. The range of concentrations extends from the very dilute to the viscous oil-like concentrated acid and this results in a range of corrosion issues. From a corrosion point of view sulfuric acid can be reducing at low concentrations and oxidizing at high concentrations which clearly presents challenges to the materials specifier. The corrosion resistance varies with concentration and temperature with its most aggressive condition at the mid-range concentrations. In this paper the performance of a number of stainless steel grades in sulfuric acid have been thoroughly investigated in a series of laboratory tests including evaluation of parameters such as the effect of impurities oxygen level and flow rate. The addition of impurities can change the behavior of the material for example chlorides can drastically increase the corrosion rate while iron sulfate can decrease it. Oxygen is needed to maintain the passive layer and its absence can lead to loss of passivity. Results show that the measured corrosion rates are strongly influenced by actual test procedure employed and the different stainless steels cannot be properly compared unless the tests have been carried out with a rigorous control of the methodology. Different parameter such as activation of specimens and type of activation is discussed. Using a test method which includes activation of the specimens is shown to give more conservative results. In most applications this is most relevant since the results from a non-activating technique are only applicable when the stainless steel maintains full passivity not when the surface may suffer mechanical damage. The presence of free oxygen or its avoidance by purging with nitrogen is also a critical factor. Electrochemical measurements and accelerated immersion tests are compared with long term immersion tests and their relevance is discussed. The conclusion is that stainless steels can be for handling sulfuric acid with certain limitations and some restrictions in concentration and temperature will be presented for different duplex stainless steels.
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