{"id":6212,"date":"2026-07-01T05:37:27","date_gmt":"2026-07-01T13:37:27","guid":{"rendered":"https:\/\/changyupump.com\/?p=6212"},"modified":"2026-07-01T05:37:28","modified_gmt":"2026-07-01T13:37:28","slug":"chlor-alkali-corrosive-pump","status":"publish","type":"post","link":"https:\/\/changyupump.com\/pt\/blog\/chlor-alkali-corrosive-pump\/","title":{"rendered":"Bomba Corrosiva para Cloro-\u00c1lcali: Transfer\u00eancia de HCl & Soda C\u00e1ustica"},"content":{"rendered":"\n

Quick Answer<\/h2>\n\n\n\n

A chlor-alkali corrosive pump<\/strong> handles the two extremes of the chemical spectrum \u2014 concentrated hydrochloric acid on one side, concentrated sodium hydroxide (caustic soda) on the other \u2014 often within the same production facility. Standard metal pumps fail rapidly in this environment because materials that resist acid (such as stainless steel) are attacked by caustic, and materials that resist caustic (such as certain plastics) may be degraded by acid or solvents. Key selection factors:<\/p>\n\n\n\n

    \n
  1. Material must handle both acid and alkali<\/strong>: Chlor-alkali plants process hydrochloric acid (HCl) at concentrations up to 37%, sodium hydroxide (NaOH) at concentrations up to 50%, plus sodium hypochlorite (NaClO), wet chlorine gas, and high-purity brine. A single material strategy cannot serve all these fluids \u2014 but UHMWPE (ultra-high molecular weight polyethylene) lining is one of the few materials that is chemically inert across this entire range.<\/li>\n\n\n\n
  2. Leak-free design is a safety requirement<\/strong>: Wet chlorine gas, hydrogen, and concentrated HCl are hazardous \u2014 a mechanical seal leak is not a maintenance issue, it is a safety incident. Sealless magnetic drive pumps eliminate the mechanical seal \u2014 the primary leak path in conventional pumps \u2014 providing the highest level of leak protection for hazardous chlor-alkali media.<\/li>\n\n\n\n
  3. Caustic soda crystallizes when it cools<\/strong>: 50% NaOH solution begins to crystallize at approximately 12\u201314\u00b0C. In unheated outdoor installations or during winter shutdowns, caustic crystals can block pump passages, seize mechanical seals, and prevent pump restart. Crystallization protection \u2014 through heating, insulation, or flushing \u2014 is essential for reliable caustic soda pumping.<\/li>\n<\/ol>\n\n\n\n

    Chlor-alkali production is the simultaneous manufacture of chlorine, hydrogen, and sodium hydroxide by electrolysis of brine. The process handles the full chemical spectrum \u2014 from acidic to alkaline, from oxidizing to reducing, from high-purity to slurry. A pump that survives in the hydrochloric acid transfer system may fail catastrophically in the wet chlorine service if the materials were not specified for the specific chemical environment.<\/p>\n\n\n\n

    \"Chlor-Alkali<\/figure>\n\n\n\n

    After reading this guide, you will understand the six critical pumping applications in a chlor-alkali plant, which materials serve which media, how to achieve leak-free operation for hazardous fluids, how to prevent caustic soda crystallization, and how to select the right pump for each chlor-alkali process stream. With over 20 years of pump manufacturing experience, Changyu Pump presents this focused selection guide for chlor-alkali corrosive pump applications.<\/p>\n\n\n\n

    1. What Are the Key Pumping Challenges in Chlor-Alkali Plants?<\/h2>\n\n\n\n

    The chlor-alkali process<\/a> electrolyzes brine to produce chlorine gas, hydrogen gas, and sodium hydroxide<\/a> solution \u2014 plus derivative chemicals including hydrochloric acid and sodium hypochlorite. Each process fluid imposes distinct demands on pump materials and design.<\/p>\n\n\n\n

    Chlor-Alkali Process Fluids<\/h3>\n\n\n\n

    Hydrochloric Acid (HCl):<\/strong>
    Produced by reacting chlorine with hydrogen, hydrochloric acid is pumped at concentrations from dilute to 37% (concentrated). HCl is a strong, reducing acid that attacks most metals, including stainless steel. It releases hydrogen chloride gas, which is corrosive to surrounding equipment and hazardous to personnel. Pumps handling HCl must be constructed of chemically inert materials with zero-leak sealing.<\/p>\n\n\n\n

    Sodium Hydroxide (NaOH \/ Caustic Soda):<\/strong>
    Produced at the cathode of the electrolysis cell, caustic soda is concentrated from approximately 32% to 50% through evaporation. Concentrated NaOH is a strong alkali that attacks aluminum, zinc, and certain stainless steel grades through caustic stress corrosion cracking at elevated temperatures. It also crystallizes at moderate temperatures \u2014 50% NaOH begins to crystallize at approximately 12\u201314\u00b0C, and 32% NaOH below approximately 0\u00b0C.<\/p>\n\n\n\n

    Sodium Hypochlorite (NaClO \/ Bleach):<\/strong>
    Produced by reacting chlorine with sodium hydroxide, sodium hypochlorite is a powerful oxidizing agent. The combination of chloride ions and active chlorine creates a uniquely aggressive environment that attacks standard stainless steel grades \u2014 including 316L and duplex \u2014 through the synergistic mechanism of chlorine oxidation and chloride pitting. Titanium and fluoroplastic-lined pumps are the standard materials for this service.<\/p>\n\n\n\n

    Wet Chlorine Gas:<\/strong>
    Chlorine gas leaving the electrolysis cell is saturated with water vapor, creating wet chlorine \u2014 a mixture of chlorine gas, hydrochloric acid, and hypochlorous acid. This environment is extremely corrosive to metals and requires non-metallic or fully lined pump construction. Sealless magnetic drive pumps are specified for this service because any leakage of wet chlorine gas is a serious safety hazard.<\/p>\n\n\n\n

    High-Purity Brine (NaCl):<\/strong>
    The electrolysis feed is a near-saturated sodium chloride solution that must meet strict purity standards to prevent membrane fouling. Pumps handling brine must resist chloride corrosion and must not leach metal ions or other contaminants into the solution. UHMWPE and fluoroplastic-lined pumps provide both the chemical resistance and the purity required.<\/p>\n\n\n\n

    Demineralized \/ Pure Water:<\/strong>
    High-purity water is used throughout the chlor-alkali process for brine preparation, membrane washing, and product dilution. Pumps must be constructed of materials that do not leach ions \u2014 stainless steel (316L) is the standard material, with polished surfaces for high-purity applications.<\/p>\n\n\n\n

    Chlor-Alkali Media Characteristics Summary<\/h3>\n\n\n\n
    Process Fluid<\/th>Concentration<\/th>pH Range<\/th>Temperature<\/th>Corrosion Mechanism<\/th>Key Material Requirement<\/th><\/tr><\/thead>
    Hydrochloric acid (HCl)<\/td>Up to 37%<\/td>< 1<\/td>20\u201350\u00b0C<\/td>Strong acid attack on metals<\/td>Chemically inert lining<\/td><\/tr>
    Caustic soda (NaOH)<\/td>32\u201350%<\/td>> 13<\/td>30\u201390\u00b0C<\/td>Caustic SCC; crystallization<\/td>Alkali-resistant; anti-crystallization<\/td><\/tr>
    Sodium hypochlorite (NaClO)<\/td>5\u201315% available Cl<\/td>11\u201313<\/td>20\u201330\u00b0C<\/td>Oxidation + chloride pitting<\/td>Titanium or fluoroplastic-lined<\/td><\/tr>
    Wet chlorine gas<\/td>Saturated Cl\u2082 + H\u2082O<\/td>< 1<\/td>20\u201340\u00b0C<\/td>Acid + oxidizing<\/td>Non-metallic; zero-leak<\/td><\/tr>
    High-purity brine (NaCl)<\/td>Near-saturated<\/td>7\u20139<\/td>40\u201380\u00b0C<\/td>Chloride pitting<\/td>Non-contaminating<\/td><\/tr>
    Pure water<\/td>\u2014<\/td>7<\/td>20\u201340\u00b0C<\/td>\u2014<\/td>Non-leaching (316L SS)<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

    2. Why Is UHMWPE Lining Ideal for Chlor-Alkali Pumps?<\/h2>\n\n\n\n

    UHMWPE (ultra-high molecular weight polyethylene) is one of the few materials that can handle the full chemical spectrum encountered in chlor-alkali production while providing superior abrasion resistance at a moderate cost.<\/p>\n\n\n\n

    The Three-Dimensional Protection of UHMWPE<\/h3>\n\n\n\n

    Universal Chemical Resistance in Chlor-Alkali Service:<\/strong>
    UHMWPE is chemically inert to hydrochloric acid (all concentrations), sodium hydroxide (all concentrations), sodium hypochlorite, wet chlorine, and high-purity brine. No other single pump material provides this breadth of compatibility. Stainless steel \u2014 including 316L and duplex grades \u2014 is attacked by HCl and NaClO. Titanium is attacked by HCl. Natural rubber is attacked by NaClO and wet chlorine. UHMWPE is unaffected by all of them.<\/p>\n\n\n\n

    Anti-Adhesion Surface for Caustic Crystallization Control:<\/strong>
    UHMWPE has an extremely low surface energy, which means that caustic soda crystals do not adhere strongly to the pump internal surfaces. While UHMWPE cannot prevent caustic from crystallizing when temperatures drop below the saturation point, it does prevent crystals from building up and blocking flow passages. When the pump is restarted and the caustic warms up, crystals that have formed on UHMWPE surfaces are easily flushed away \u2014 unlike on metal surfaces, where crystal layers bond firmly and resist removal.<\/p>\n\n\n\n

    Non-Contaminating for High-Purity Brine Service:<\/strong>
    UHMWPE contains no plasticizers, stabilizers, or additives that can leach into the pumped fluid. For high-purity brine service, where metal ion contamination can foul expensive ion-exchange membranes, UHMWPE-lined pumps provide the chemical inertness and purity that the process demands.<\/p>\n\n\n\n

    UHMWPE vs Alternative Materials for Chlor-Alkali Service<\/h3>\n\n\n\n
    Material<\/th>HCl Resistance<\/th>NaOH Resistance<\/th>NaClO Resistance<\/th>Wet Cl\u2082 Resistance<\/th>Brine Compatibility<\/th>Temperature Limit<\/th>Relative Cost<\/th><\/tr><\/thead>
    UHMWPE Lined<\/td>Excellent \u2014 all concentrations<\/td>Excellent \u2014 all concentrations<\/td>Excellent<\/td>Excellent<\/td>Excellent \u2014 non-contaminating<\/td>90\u00b0C<\/td>Medium<\/td><\/tr>
    316L Stainless Steel<\/td>Poor \u2014 rapid corrosion<\/td>Good (caustic SCC risk above 60\u00b0C)<\/td>Poor \u2014 pitting<\/td>Poor<\/td>Good (trace metal leaching risk)<\/td>165\u00b0C+<\/td>Medium<\/td><\/tr>
    FEP\/PFA Lined<\/td>Excellent<\/td>Excellent<\/td>Excellent<\/td>Excellent<\/td>Excellent \u2014 non-contaminating<\/td>120\u2013160\u00b0C<\/td>Medium-High<\/td><\/tr>
    Titanium Grade 2<\/td>Poor \u2014 attacked by HCl<\/td>Excellent<\/td>Excellent<\/td>Acceptable at ambient temperature and low flow; limited at elevated temperatures and high velocities<\/td>Excellent<\/td>~80\u00b0C<\/td>High<\/td><\/tr>
    Natural Rubber Lined<\/td>Good (limited temperature)<\/td>Good<\/td>Poor \u2014 oxidation<\/td>Poor \u2014 oxidation<\/td>Good<\/td>70\u00b0C<\/td>Low-Medium<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

    UHMWPE occupies the optimal intersection for chlor-alkali service: it handles HCl, NaOH, NaClO, and brine \u2014 the four most common process fluids \u2014 without the cost premium of fluoropolymer linings or the HCl sensitivity of titanium.<\/p>\n\n\n\n

    Engineers at Changyu Pump recommend:<\/strong> For chlor-alkali plants, UHMWPE-lined pumps are the preferred material for HCl transfer, caustic soda circulation, brine handling, and NaClO service \u2014 covering the majority of chlor-alkali pump applications. For wet chlorine gas, hydrogen, and other hazardous gas-handling applications, upgrade to a sealless magnetic drive pump for zero-leak safety.<\/p>\n\n\n\n

    3. How to Select Materials for Chlor-Alkali Corrosive Pumps?<\/h2>\n\n\n\n

    Material selection for chlor-alkali pumps must be media-specific. A pump material that handles HCl perfectly will fail in NaClO. A material that handles NaOH perfectly will fail in HCl. Understanding these boundaries is the foundation of reliable pump specification.<\/p>\n\n\n\n

    Chlor-Alkali Material Selection Matrix<\/h3>\n\n\n\n
    Process Fluid<\/th>Recommended Pump Material<\/th>Alternative (Budget)<\/th>Alternative (Premium)<\/th>Seal Recommendation<\/th><\/tr><\/thead>
    Hydrochloric acid (HCl) \u2014 all concentrations<\/td>UHMWPE lined<\/td>PP (polypropylene) \u2014 limited temperature<\/td>FEP\/PFA lined<\/td>Double mechanical seal, PTFE secondary seals<\/td><\/tr>
    Caustic soda (NaOH) \u2014 32\u201350%<\/td>UHMWPE lined<\/td>316L SS (up to 60\u00b0C, with SCC monitoring)<\/td>FEP\/PFA lined<\/td>Double mechanical seal; heated seal flush for outdoor installations<\/td><\/tr>
    Sodium hypochlorite (NaClO)<\/td>UHMWPE lined or FEP\/PFA lined<\/td>\u2014<\/td>Titanium Grade 2<\/td>Double mechanical seal, PTFE secondary seals<\/td><\/tr>
    Wet chlorine gas<\/td>FEP\/PFA lined magnetic drive<\/td>\u2014<\/td>\u2014<\/td>Sealless magnetic drive (required)<\/td><\/tr>
    High-purity brine (NaCl)<\/td>UHMWPE lined<\/td>316L SS (with passivation, for less critical purity)<\/td>FEP\/PFA lined<\/td>Standard mechanical seal<\/td><\/tr>
    Pure water<\/td>316L stainless steel<\/td>\u2014<\/td>\u2014<\/td>Standard mechanical seal<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

    The HCl Challenge: Why Most Metals Fail<\/h3>\n\n\n\n

    Hydrochloric acid attacks metals through a well-documented mechanism: the chloride ion penetrates the passive oxide layer on stainless steel, initiating localized electrochemical corrosion of the metal substrate. Unlike sulfuric acid, which can form a protective passive layer on carbon steel, HCl does not form a stable protective film on any common engineering metal. Even high-nickel alloys that resist sulfuric acid \u2014 such as Hastelloy C-276 \u2014 have limited HCl resistance at higher concentrations and temperatures.<\/p>\n\n\n\n

    For HCl service, the material strategy is clear: common engineering metals such as carbon steel and standard stainless steels are not suitable for continuous HCl contact. Non-metallic materials \u2014 UHMWPE, PP, PVDF, PTFE\/PFA \u2014 provide the necessary chemical inertness. UHMWPE is the preferred choice for HCl concentrations up to 37% at temperatures up to 90\u00b0C, as it combines chemical inertness with excellent abrasion resistance and moderate cost. For service above 90\u00b0C, PVDF or fluoropolymer linings are more appropriate.<\/p>\n\n\n\n

    The NaOH Challenge: Caustic Stress Corrosion Cracking<\/h3>\n\n\n\n

    Concentrated sodium hydroxide attacks metals through a different mechanism than acids. While the general corrosion rate of stainless steel in NaOH is relatively low, the combination of tensile stress (from pump pressure and thermal expansion), elevated temperature, and high caustic concentration can cause caustic stress corrosion cracking (SCC). This failure mode is particularly dangerous because it occurs without visible general corrosion \u2014 a pump that looks intact can fail suddenly through crack propagation.<\/p>\n\n\n\n

    316L stainless steel is generally acceptable for NaOH service up to approximately 60\u00b0C and 50% concentration, provided that residual stresses from welding and machining have been properly relieved through post-weld heat treatment. Above 60\u00b0C or for concentrations above 50%, the risk of caustic SCC increases significantly, and UHMWPE-lined or fluoroplastic-lined pumps are preferred.<\/p>\n\n\n\n

    Engineers at Changyu Pump recommend:<\/strong> For all HCl service, use non-metallic or lined pumps exclusively \u2014 metals are not suitable for continuous HCl contact. For NaOH service below 60\u00b0C, 316L stainless steel is acceptable with proper stress relief; for higher temperatures or where SCC risk is a concern, UHMWPE-lined pumps provide complete immunity to caustic attack. For NaClO service, use UHMWPE-lined, FEP\/PFA-lined, or titanium pumps \u2014 never standard stainless steel.<\/p>\n\n\n\n

    \"Self-Priming-Pump\"<\/figure>\n\n\n\n

    4. How to Achieve Leak-Free Pumping for Hazardous Chlor-Alkali Media?<\/h2>\n\n\n\n

    Wet chlorine gas, hydrogen, and concentrated HCl are hazardous fluids where any leakage is unacceptable. Standard mechanical seals \u2014 even double mechanical seals \u2014 have a finite leak rate and require regular maintenance. For these services, sealless magnetic drive pumps provide the definitive leak-free solution.<\/p>\n\n\n\n

    Why Magnetic Drive Pumps Eliminate Seal Leakage<\/h3>\n\n\n\n

    A magnetic drive pump<\/a> transfers motor torque to the impeller through a sealed containment shell using magnetic coupling. There is no shaft penetrating the pump casing \u2014 and therefore no dynamic mechanical seal to leak. The pumped fluid is completely contained within a static sealing system.<\/p>\n\n\n\n

    This design provides three critical advantages for chlor-alkali hazardous media service:<\/p>\n\n\n\n