Precision Filter Material Selection – The Impact of Chloride Ions

In applications involving water containing chlorine, the chlorine resistance of the precision filter housing material directly determines the service life, operational safety, and stability of the filtrate quality. Due to differences in chemical structure and composition, different materials show significantly different performance when exposed to chlorine, especially in its active forms such as hypochlorite and chloride ions.

Precision filter housings are mainly divided into metallic and non-metallic materials. Metallic housings are primarily made of stainless steel, while non-metallic housings are typically UPVC (unplasticized polyvinyl chloride) and FRT (fiberglass reinforced plastic).

Figure 1: Position of the precision filter in an RO system

Comparison of Chlorine Resistance Among Mainstream Materials

Chloride-induced corrosion of metals primarily occurs by destroying the passive film, triggering electrochemical corrosion in the form of pitting, crevice corrosion, or stress corrosion.

• 304 stainless steel contains no molybdenum.

  316 and 316L stainless steel both contain 2–3% molybdenum, which significantly enhances the stability of the passive film, particularly in chloride-containing environments. Molybdenum effectively suppresses the initiation and growth of pitting corrosion and increases the pitting potential.

• 316L is the low-carbon version of 316 stainless steel (≤0.03%), making it more suitable for welding with more stable chlorine resistance in welded areas.

• 2205 duplex stainless steel contains higher levels of chromium, nickel, and molybdenum, providing significantly greater resistance to chloride corrosion. At room temperature, it can withstand chloride concentrations exceeding 10,000 mg/L.

The following table shows the typical chloride corrosion resistance range of common metallic materials:

Non-metallic Materials

In most corrosive environments, non-metallic materials offer superior corrosion resistance compared to metals for two main reasons:

1.High chemical stability – Their molecules are mainly composed of high-bond-energy covalent or ionic bonds, making them less likely to react with corrosive media.

2.No electrochemical corrosion – As electrical insulators, they cannot form an electron conduction path, eliminating the galvanic effect that causes continuous oxidation and dissolution in metals.

Among non-metallic materials, the most common are UPVC and FRT, and under normal conditions, the difference between them is minimal; both are virtually unaffected by chloride ions.

Figure 2: Precision filter with UPVC housing

Figure 3: Precision filter with fiberglass housing

Whether for standard filtration or extreme operating conditions, the choice of precision filter housing material should be tailored to the application. Selecting the right material ensures the precision filter delivers its full value.

At Hebei UMEK, we always put customer needs first, combining material characteristics with application requirements to provide a full range of services from material selection to equipment manufacturing. We ensure customers don’t waste money on unnecessarily expensive materials while never compromising safety by using unsuitable ones.

With 28 years of industry experience, UMEK knows that a good filter is not about being the most expensive, but about being the most suitable—and that’s exactly what we help you achieve.

Contact Information:
Tel: +86 19331305749
Email: sales@cnumek.com / sales@amandawatertech.com
Website: www.amandawatertech.com / www.cnumek.com