Gases, aqueous corrosion

CHEMICAL PROPERTIES Flammable gas volatile corrosive to carbon steel slowly oxidizes to formic acid react violently with strong oxidizers FP (133°F) AT (300°C for gas, 430°C for aqueous solutions) LFL (7.0%) UFL (73%). 

Bhattacharyya, S., Hill, V. L., Humphreys, B. A., and Hamel, F. B., "Aqueous Corrosion in Coal Gasification Pilot Plants," Anerican Gas Association, Ninth S3mthetic Pipe Gas Symposium, Chicago, Illinois,... 

The more common classification scheme is to divide the corrosive media into their state of aggregation, that is to subdivide into corrosion by solids, liquids and gases. While solid state corrosion is rarely dealt with, we have vast amount on literature on hot gas corrosion. The case of corrosion by liquids is commonly further subdivided into more specific cases, such as aqueous corrosion (e.g. acids and water), corrosion by glasses, metal melts and salt melts. The last case is for historic reasons known in the form of a rather misleading expression hot corrosion. A special case, which spans from the liquid into the gaseous state is given by the corrosion in hot water systems hydrothermal corrosion. 

STM has been used to study adsorption on surfaces as it relates to corrosion phenomena [6, 7]. Sulfiir is a well known corrosion agent and is often found in air (SO2, FI2S) and in aqueous solution as dissolved anions ( HSO7) or dissolved gas (FI2S). By studying the interaction of sulfur with surfaces, insights can be gained into... 

Although many problems still remain to be overcome to make the process practical (not the least of which is the question of the corrosive nature of aqueous HBr and the minimization of formation of any higher brominated methanes), the selective conversion of methane to methyl alcohol without going through syn-gas has promise. Furthermore, the process could be operated in relatively low-capital-demand-ing plants (in contrast to syn-gas production) and in practically any location, making transportation of natural gas from less accessible locations in the form of convenient liquid methyl alcohol possible. 

A Hquid-phase variation of the direct hydration was developed by Tokuyama Soda (78). The disadvantages of the gas-phase processes are largely avoided by employing a weakly acidic aqueous catalyst solution of a siHcotungstate (82). Preheated propylene, water, and recycled aqueous catalyst solution are pressurized and fed into a reaction chamber where they react in the Hquid state at 270°C and 20.3 MPa (200 atm) and form aqueous isopropyl alcohol. Propylene conversions of 60—70% per pass are obtained, and selectivity to isopropyl alcohol is 98—99 mol % of converted propylene. The catalyst is recycled and requites Htde replenishment compared to other processes. Corrosion and environmental problems are also minimized because the catalyst is a weak acid and because the system is completely closed. On account of the low gas recycle ratio, regular commercial propylene of 95% purity can be used as feedstock. 

Chemical Reactivity - Reactivity with Water Reacts slowly to form flammable hydrogen gas, which can accumulate in closed area Reactivity with Common Materials Corrosive to natural rubber, some synthetic rubbers, some greases and some lubricants Stability During Transport Stable Neutralizing Agents for Acids and Caustics Flush with 3% aqueous ammonia solution, then with water. Methyl alcohol may also be used Polymerization Not pertinent Inhibitor of Polymerization Not pertinent. 

Table 1.29 tabulates most known examples of erosion corrosion problems occuring in aqueous systems. Historically, erosion corrosion first became a problem with the copper alloy (70%Cu 29%Zn l%Sn) condensers of naval shipsErosion corrosion of copper alloys has been an ongoing problem since then. The other major problem areas are (a) power plants where steels are exposed to water or water/steam mixtures in the temperature range 90°-280°C (b) the oil and gas industry where steels are exposed to various liquid, gas, and sometimes solids combinations containing carbon dioxide. 

---