The Corrosion Problem in Vacuum Salt Production
Since the 1950s, vacuum salt production plants have been emerging, and from the 1970s onwards the corrosion and dripping problems faced by salt production equipment became increasingly serious, especially the corrosion caused by chloride ions. Most of the main equipment was originally made of carbon steel, but the service life was short: carbon steel tubes in heat exchangers generally lasted no more than one year, and some perforated within a few months. Copper extended the life to about two to three years, but the equipment then required replacement at high cost and disrupted production. The salt slurry pipelines suffered worst of all, with the lower part of carbon steel pipe corroding into a honeycomb of holes within half a month, requiring replacement many times per year.
Why Titanium Solves the Problem
Titanium's resistance to chloride attack is the property that matters in vacuum salt production. The metal forms a stable, self-healing oxide film that resists pitting, crevice corrosion and stress corrosion in hot chloride solutions. On-site hanging tests in actual salt production conditions confirmed that titanium's corrosion resistance is very significant under real operating conditions, and because titanium does not release metal ions into the brine, it completely solved the two technical problems that limited salt quality: corrosion products contaminating the salt and the frequent loss of production equipment. The adoption of titanium has been described as a new revolution in material selection for vacuum salt production.
Titanium in the Heating Chamber
The heating chamber is the most critical equipment in vacuum salt production, and titanium is mainly used in its heat exchangers and heat exchanger tubes. The tubes are typically 9 meters long with wall thicknesses between 0.8 and 1.5 mm. Because titanium resists corrosion, it does not suffer corrosion perforation or pipe clogging, and its smooth, clean surface prevents the salt scale buildup that plagued carbon steel surfaces. Under the same heat transfer performance, the titanium heating chamber has the advantages of lighter weight and smaller volume compared with a steel tube heating chamber, reducing the structural load of the plant.
Titanium in the Brine Preheater
The brine preheater is another important process equipment in salt production. Titanium has strong corrosion resistance in sodium chloride solutions below 100 degrees Celsius, so using titanium for the tube bundles and heads of the brine preheater effectively avoids the corrosion of the sodium chloride solution on the preheater parts, ensuring normal equipment operation. The same benefit applies to the salt slurry handling systems, where titanium's resistance eliminates the frequent leak repairs and replacements required by carbon steel and stainless steel.
Economic Impact
The economics of titanium in the salt industry are driven by life-cycle cost rather than first cost. Although titanium equipment costs more initially than carbon steel, the elimination of repeated replacement, leak repair, production stoppage and salt quality losses quickly repays the difference. For the plant, the longer service life and reduced maintenance translate into higher availability and lower operating cost, which is why titanium is now the standard material for the critical chloride-exposed equipment of vacuum salt production.
FAQ
Q: Why does salt production equipment corrode?
A: Hot chloride brine attacks carbon steel and even stainless steel, causing rapid pitting and perforation.
Q: What property of titanium suits the salt industry?
A: Its stable, self-healing oxide film resists pitting, crevice and stress corrosion in hot chloride solutions.
Q: How long do titanium heat exchanger tubes last in salt plants?
A: Far longer than carbon steel, which perforates within a year; titanium resists corrosion perforation and clogging.
Q: Why does titanium improve salt quality?
A: It does not release corrosion products into the brine, so the salt is not contaminated by metal compounds.
Q: Is titanium economical for salt plants?
A: Yes, on a life-cycle basis: the elimination of replacement, repair and stoppage costs repays the higher first cost.
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