Corrosion from autoclaves

Y. Daigo, Y. Watanabe, K. Sue, Effect of chromium ion from autoclave material on corrosion behavior of nickel-based alloys in supercritical water. Corrosion 63 (12) (2007) 277-284. 

A feature of corrosion studies which has been stressed recently (2) is the complete failure of laboratory tests on their own to predict how reliable operation of some nuclear steam generators can be maintained. At least a part of this problem is likely to arise from different redox and/or pH conditions imposed by the solution in autoclave tests and in plant conditions and many low level contaminants could be involved. In view of what has been said earlier concerning the role of Mo(VI) in stagnant water it is clear that some data, at least on the thermodynamics of aqueous Mo species, should be sought at high temperatures. 

The following procedure serves to produce a slow, controlled and steady gas flow through the burner nozzle into the reaction cell Two additional cylindrical feed autoclaves from a non-corrosive high strength steel alloy, each with 80 cm internal volume and inlets at both ends are used. Both contain stainless steel bellows of 30 cm capacity, connected with one of the inlets. The bellows can be filled with methane, oxygen or any other gas to pressures of 2000 bar, provided that the space outside the bellows is filled through the second inlets with water and brought to the same pressure. These water-filled spaces of the feed autoclaves can be connected with the interior of the reaction cell, when this is filled with the... 

Figure 3. Experimental arrangements for studying glass corrosion. Conditions (a,b) ASTM, T = 121°C-autoclave, t = I h (c) IAEA, T = 25°C, t = variable (d) ISO, T = variable, t = variable (e) Soxhlet, T 100°C, t = variable and (f) T = 25-95°C, t = variable. (Reproduced, with permission, from Ref. 1. Copyright 1980, North-Holland Publishing Co.)...

For high pressure and/or high temperature syntheses, reactions were carried out in autoclave bombs fabricated from Monel and provided with thick copper gaskets, capable of withstanding 500 atmospheres pressure at 600 C. These bombs were used with nickel liners to minimize corrosion and to facilitate handling the solid products in the drybox. 

Fig. 3 Crevice and pitting corrosion of a stainless steel autoclave head. Note the crevice corrosion underneath the bolts (now removed) and in the gap between the two parts that are still assembled, and the pitting corrosion on the free surface. This corrosion was probably caused by chloride derived from thermal insulation. (View this art in color at www. dekker.com.)...

Another method is also employed to prevent loss of the contents of the reactor. A safety valve, placed after the rupture disc, is set to open about 50 psi below the bursting point of the frangible disc. Thus, a rupture of the diaphragm is.sure to be followed by the op ng of the relief valve which has been protected from the corrosive vapors of the autoclave. It is usually feasible to complete the run and then replace the disc and overhaul the safety valve. 

This approach was first accomplished by Ziegler in his early work when nickel was introduced with titanium, either purposely or through autoclave corrosion as part of the investigation of the Aufbau reaction. The nickel dimerized ethylene to butene, while the titanium incorporated it at low levels yielding poly ethylenes with low levels of ethyl branches. We have been told that this work appears in early notebooks from the Ziegler laboratory, but we have been unable to find a reference in the open literature. 

They also found that combined surface treatment with H2C1O4, HF, and H3PO4 improved the corrosion resistance of the magnets in both the water and autoclave environments. They thought that this improvement comes from (a) the removal of nucleation sites for corrosion by chromic acid, and (b) the formation of a protective film at the smface by chromate conversion. 

Precipitation from solution under hydrothermal conditions has been widely used for the synthesis of fine crystalline particles of various oxides [178-180]. The process involves heating reactants, such as metal salts, oxide, hydroxide, or even metal powder, in the form of solution or suspension, at certain temperatures. Water is the most widely used solvent. In this case, the precipitation temperatures are set between the boiling and critical points of water, i.e., 100-374 °C, while the pressures are up to 22.1 MPa, which is the vapor pressure of water at the critical point. Due to the presence of high pressures, hardened steel autoclaves are usually used to carry out hydrothermal reactions. The autoclaves have inner surfaces of which are lined with a plastic, such as Teflon, to prevent corrosion of the vessels. Similar to chemical precipitation method, hydrothermal synthesis also offers almost unlimited flexibility in combination of types and concentrations of starting reactants, additives, pH levels, temperatures, time durations, and so on. 

Approximately 90% of the chlorine is removed in gaseous form. Because of the extreme corrosiveness prevailing in the reactor, this vessel, which is in fact an agitated autoclave, has to be fabricated from titanium and lined with acid-resistant brick. 

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