Temperature corrosion affected

Most wrought alloys are provided in conditions that have been strengthened by various amounts of cold work or heat treatment. Cold worked tempers are the result of cold rolling or drawing by prescribed amounts of plastic deformation from the annealed condition. Alloys that respond to strengthening by heat treatment are referred to as precipitation or age hardenable. Cold worked conditions can also be thermally treated at relatively low temperatures to affect a slight decrease in strength (stress rehef annealed) to benefit other properties, such as corrosion resistance and formabiUty. 

The controlled deposition of thin adherent films of calcium carbonate is probably the cheapest method of reducing corrosion, but may not always be entirely satisfactory because local variations in pH and temperature will affect the nature and extent of film deposition. 

Caustic cracking (caustic embrittlement) Intergranular corrosion affects both carbon steels and austenitic steels and accelerated by high stress, higher temperatures, and impurities in grain boundaries. 

Although high temperature corrosion can occur in many systems, given the conditions that promote the problem, it is usually in combustion systems that the problem is manifest. ESDU [1992] reviewed corrosion associated with combustion. The nature of the fuel involved, particularly its chemical composition, will affect the potential corrosion. In general given good combustion control, it is usually the impurities in the fuel that give rise to the problem. The impurities are often minerals that were included in the fiael when it was formed or, in the case of waste material, from the constituents of the waste. 

The critical regions in oil-fired furnaces are the evaporator tubes, steam superheater tubes, air heater, and channel. Evaporator tubes are affected by hot gas corrosion from hydrogen sulfide as the temperature exceeds 280°C. Superheater tubes suffer from sulfate/sulfite corrosion induced by molten sulfates above 620"C. Superheater tube holders undergo vanadic corrosion caused by molten vanadate species in the range of 550 C-600 C. Air heaters are subject to low-temperature corrosion from liquid sulfuric acid at 100°C-140°C. Flue gas channels suffer from acid deposits at the dew point (Balajka 1980). 

Resistance to environmental impact (UV, ozone, humidity, temperature, corrosive gases) which affects the life span... 

An incomplete list of material characteristics affecting high-temperature corrosion are ... 

The rate of corrosion is controlled by the rate of dissolved oxygen reaction on the surface, which is controlled by the rate of transport of dissolved oxygen to the surface. Similar mass transfer mechanisms control the rate of transfer of fouling ions to the surface. In a system containing a corrosion inhibitor, the transfer of inhibitor to the surface is also controlled by the same factors. Once the reactants are at the surface, reaction rates are affected by temperature. Temperature also affects the properties of the fluid film in contact with the surface. For example, viscosity typically decreases in the film on the surface of a hot wall, facihtat-ing reactant transfer. It is difficult to generalize about the affect of temperature on corrosion rates in a system treated with corrosion inhibitor. Increased temperature is likely to accelerate the corrosion inhibition reactions as well as the corrosion reaction. The net change in corrosion rate could be either an increase or a decrease, depending upon the effectiveness of the corrosion inhibition treatment. 

The cumulative effect of an anodic ORR (induced by O2 crossover from the cathode to the anode) on cathode carbon catalyst-support loss (C corrosion) under fuel starved and ordinary (e.g. constant current) PEMFC operating eonditions were studied.The effects of C corrosion at constant cmrent are less severe than start-up and fiill H2 partial starvation, but they are large enough to affeet the cell performance after a long-time operation. The design factors of the MEA and operational factors such as humidity and temperature also affect carbon loss. The influence of these parameters is not always simple, and the coupling of these factors was addressed with MEMEPhy s to elucidate the rate of carbon loss under normal PEMFC operation... 

Hydrogen or hydrogen-induced corrosion at ambient temperature can affect carbon and low-alloy steel, and high-strength steel, in many different ways ... 

The inferior performance was manifested in high temperatures necessary to transfer the oxygen to the liquid phase for chemical reaction. The higher-than-desirable temperatures adversely affected reaction selectivity, producing undesirable quantities of non-usable by-products, e.g., carbon dioxide and water. If lower reaction temperatures could be achieved without lowering reactant feed rates, reaction selectivity would change to enhance both the acetic acid and valuable reaction by-product efficiencies. In addition, lower tesiperatures would decrease reactor metal corrosion rates and allow more stable and flexible control of the reaction system. 

Sulfidation is a common high-temperature corrosion-failure mechanism. As the name implies, it is related to the presence of sulfur compounds. When examining this form of damage microscopically, a "front" of sulfidation is often seen to penetrate into the affected alloy. Localized pitting-t5 e attack is also possible. A distinction can be made between sulfidation in gaseous environments and corrosion in the presence of salt deposits on corroding surfaces. Only the former is considered in this section, the latter being discussed in... 

The corrosion rate is controlled by time of wetness, temperature and the electrolyte composition. Atmospheric corrosion is most predominant of all the other forms of corrosion. The importance of atmospheric corrosion is exemplified by the fact that the cost of protection against atmospheric corrosion is about 50% of the total cost of all other corrosion measures. No other form of corrosion affects the materials and equipment harder than atmospheric corrosion. Its devastating range extends firom small... 

H2S can cause corrosion of stainless steels such as 316 and 410 stainless in the form of sulfide stress cracking. (Other factors, such as pH, chloride concentration, and temperature also affect the potential for steel cracking.) Copper alloys corrode rapidly in H2S service. An industry value that has been developed is NACE MR-01, 2003, from the National Association of Corrosion Engineers. In the gas phase, a stream is sour if the H2S partial pressure exceeds 0.05 psia. If a single phase hquid is in equilibrium with a gas phase, where the gas phase H2S partial pressure exceeds 0.05 psia, then that hquid is also considered to be sour. If the liquid is not in equihbrium with the gas phase, then the liquid is considered sour, if this bubble point gas phase H2S partial pressure exceeds 0.05 psia. The presence of water is not required for a gas and/or hquid to be considered to be sour, nor is there a minimum pressure to avoid designating a gas or hquid as sour. 

Where a differential of temperature could affect the corrosivity of the enviroiuneut or cause adverse stresses in materials, provision for adjustment of the temperature of the transported hquid should be made. 

A key concept of this principle is that the temperature gradient affects the extent of phenomena seen in slag corrosion. In a very steep temperature gradient, very little penetration of slag is seen, with corrosion reactions more or less restricted to the immediate slag and refractory interface. Mobility of fresh slag (reactant) to... 

It is found that the hot face temperature primarily affects the rate of corrosion reactions. If the hot face temperature is held just below the point that the products of corrosion become liquid (melt), corrosion will be very slow or nonexistent. Most authorities believe that if the hot face is maintained at no more than 20°C above this melting temperature (called a lowest eutectic temperature), reasonable corrosion rates will be observed. However, when the hot face temperature is more than 20°C above the eutectic, corrosion is rapid. 

Tortorelli P F and Natesan K (1998), Critical Factors Affecting the High-Temperature Corrosion Performance of Iron Aluminides, Mater Sci Eng, A258, 115-125. 

Many factors can affect high temperature corrosion processes in the petrochemical industry. Current investigations therefore aim to find the potential influences of some major factors on the corrosion processes and rates, such as temperature, velocity of flow and vacuum on high temperature naphthenic acid corrosion, and temperature and active sulfur content on high temperature sulfidation. 

The most direct effect of defects on tire properties of a material usually derive from altered ionic conductivity and diffusion properties. So-called superionic conductors materials which have an ionic conductivity comparable to that of molten salts. This h conductivity is due to the presence of defects, which can be introduced thermally or the presence of impurities. Diffusion affects important processes such as corrosion z catalysis. The specific heat capacity is also affected near the melting temperature the h capacity of a defective material is higher than for the equivalent ideal crystal. This refle the fact that the creation of defects is enthalpically unfavourable but is more than comp sated for by the increase in entropy, so leading to an overall decrease in the free energy... 

HCl gas reacts with metal oxides to form chlorides, oxychlorides, and water. Therefore, all the steel equipment should be pickled to remove the oxide scales before it is put in service. Because oxidi2ing agents in the HCl gas such as oxygen or chlorine significantly affect the corrosion rate, it is essential that the operating temperature of the steel equipment be kept below the temperature (316°C) at which ferric chloride is vapori2ed from the metal surface. 

The following variables can affect wall friction values of a bulk soHd. (/) Pressure as the pressure acting normal to the wall increases, the coefficient of sliding friction often decreases. (2) Moisture content as moisture increases, many bulk soHds become more frictional. (3) Particle size and shape typically, fine materials are somewhat more frictional than coarse materials. Angular particles tend to dig into a wall surface, thereby creating more friction. (4) Temperature for many materials, higher temperatures cause particles to become more frictional. (5) Time of storage at rest if allowed to remain in contact with a wall surface, many soHds experience an increase in friction between the particles and the wall surface. (6) Wall surface smoother wall surfaces are typically less frictional. Corrosion of the surface obviously can affect the abiUty of the material to sHde on it. 

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