Copper alloys distillation plant

An ammonia-rich gas stream was once accidentally charged to a gas plant. Shortly thereafter, leaks appeared in many of the tubes of the distillation towers reflux condensers. The admiralty tubes (a copper alloy in the condensers) were cracked by the ammonia environment. Admiralty may also experience stress-corrosion cracking when exposed to concentrated amines. 

The protective film continues to become more protective with time, as indicated by corrosion rate measures made over several years. Studies in quiet seawater show that the time span approaches 4 years before the decrease in corrosion rate becomes negligible. In flowing water, the corrosion rate was found to decrease continually over at least a 14-year period, the effect being similar for both 90-10 and 70-30 alloys. The normal corrosion product film is thin, adherent, and durable. Once fully formed and reasonably mature, the film on copper-nickel alloys will withstand considerable excursions in water velocity, pollution, and other conditions normally adverse to the good performance of copper alloy tubing. Copper-nickel alloys remain resistant to corrosion in deaerated seawater at low pH, as has been experienced in numerous distillation-type desalination plants. ... 

IMaterials and Scaling Issues. Two aspects of the basically simple desalination process require special attention. One is the high corrosivity of seawater, especially pronounced in the higher temperature distillation processes, which requires the use of corrosion-resistant, and therefore expensive, materials. Typical materials in use are copper—nickel alloys, stainless steel, titanium, and, at lower temperatures, fiber-reinforced polymers and special concrete compositions (39). It is noteworthy that in quest of a lower initial cost, the use of inadequate materials of constmction in many locations combined with poor operation by virtually untrained hands led to rapid deterioration and failure of plants long before their estimated design life. Adequate experience suggests by now how to avoid such failures. The other aspect is scale formation (40,41), discussed in mote detail below. 

The corrosive action of dilute hydrochloric acid at the temperatures encountered in distillation equipment cannot be satisfactorily withstood by any common materials. However, the copper-base alloys have been widely used for hydrochloric acid and brine corrosion. Although conditions are not the same in all plants, the use of copper-base alloy tubes for condensers and water-cooled exchangers appears to be increasing. One refiner has been using the following kinds of tubes ... 

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