Hydrogen chloride corrosion

Hydrogen chloride released dissolves in water during condensation in the crude oil distillation column overhead or in the condenser, which cause corrosion of materials at these locations. The action of hydrochloric acid is favored and accelerated by the presence of hydrogen sulfide which results in the decomposition of sulfur-containing hydrocarbons this forces the refiner to inject a basic material like ammonia at the point where water condenses in the atmospheric distillation column. 

Gaseous Hydrogen Chloride. Cast Hon (qv), mild steel, and steel alloys are resistant to attack by dry, pure HCl at ambient conditions and can be used at temperatures up to the dissociation temperature of HCl. The corrosion rate at 300°C is reported to be 0.25 cm/yr and no ignition point has been found for mild steel at 760°C, at which temperature HCl is dissociated to the extent of 0.2%. 

Nickel-based aUoys have superior corrosion resistance to Hon-based aUoys. The only aUoys recommended for hot hydrochloric acid use are Ni—Mo aUoys containing 60—70% Ni and 25—33% Mo. Chlorimet (63 Ni, 32 Mo, 3 Fe) and HasteUoy (60 Ni, 28 Mo, 6 Fe) are found to be stable at aU acid concentrations in the absence of aH and Hon chlorides. Electroless nickel, a Ni—P aUoy containing 2—10% P, shows exceUent resistance to hot hydrogen chloride (71). The corrosion resistance increases with phosphoms content. This coating can be deposited on cast Hon, wrought Hon, mild steel, stainless steels, brass, bron2e, and aluminum (qv). 

The furnace is constmcted with a steel shell lined with high temperature refractory (see Refractories). Refractory type and thickness are deterrnined by the particular need. Where combustion products include corrosive gases such as sulfur dioxide or hydrogen chloride, furnace shell temperatures are maintained above about 150—180°C to prevent condensation and corrosion on the inside carbon steel surfaces. Where corrosive gases are not present, insulation is sized to maintain a shell temperature below 60°C to protect personnel. 

Because phosgene reacts with water, great care must be taken to prevent contamination with traces of water since this could lead to the development of pressure by hydrogen chloride and carbon dioxide. Wet phosgene is very corrosive therefore phosgene should never be stored with any quantity of water (4). 

Health nd Safety Factors. Thionyl chloride is a reactive acid chloride which can cause severe bums to the skin and eyes and acute respiratory tract injury upon vapor inhalation. The hydrolysis products, ie, hydrogen chloride and sulfur dioxide, are beheved to be the primary irritants. Depending on the extent of inhalation exposure, symptoms can range from coughing to pulmonary edema (182). The LC q (rat, inhalation) is 500 ppm (1 h), the DOT label is Corrosive, Poison, and the OSHA PEL is 1 ppm (183). The safety aspects of lithium batteries (qv) containing thionyl chloride have been reviewed (184,185). 

Compound (1) decomposes to form dichloroacetyl chloride, which in the presence of water decomposes to dichloroacetic acid and hydrochloric acid (HCl) with consequent increases in the corrosive action of the solvent on metal surfaces. Compound (2) decomposes to yield phosgene, carbon monoxide, and hydrogen chloride with an increase in the corrosive action on metal surfaces. 

Since the formation of the chlorohydrin is accompanied by the production of an equimolar quantity of hydrogen chloride [7647-01 -OJ, the reaction solution is strongly acidic and corrosive. The first chlorohydrin reaction towers were built of stoneware or of mild steel and lined with mbber and ceramic tiles. More recently corrosion-resistant reinforced plastics have been used with good results, but operating pressures must be maintained at or near atmospheric. 

Chemical Reactivity - Reactivity with Water Forms hydrogen chloride (hydrochloric acid). Reaction not very vigorous in cold water Reactivity with Common Materials Slow corrosion of metals Stability During Transport Stable Neutralizing Agents for Acids and Caustics Flush with and rinse with sodium bicarbonate or lime solution Polymerization Not pertinent Inhibitor of Polymerization Not pertinent. 

Severe Severely corrosive, severely abrasive or severely plugging (e.g., wet hydrogen chloride, coal slurry, heavies, uninhibited monomer). 

Tubesheets form the end barriers to separate the shell-side and tube-side fluids. Most exchangers use single plates for tubesheets. However, for hazardous or corrosive materials such as chlorine, hydrogen chloride, sulfur dioxide, etc., where the intermixing due to leakage from shell- to tube-... 

This is of more significance in corrosive or polymer-forming services than in clean hydrocarbon or air applications. For example in hydrogen chloride and chlorine service using cylinders with either (a) cast iron liners or (b) carbon piston rings, a speed of around 600 ft per min is acceptable. 

Other acid gases such as hydrogen chloride and oxides of nitrogen produce similar corrosion problems. The corrosion effects produced by acid condensate are amplified by the motion of the gas stream (typically 20-53 m/s) and erosion effects due to entrained solids and impingement at bends, damper plates, reheaters, etc. 

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