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Application Guide

Valves for Chlor-Alkali Plants

Chlor-alkali plants produce chlorine, caustic soda (NaOH), and hydrogen from the electrolysis of brine — three process streams that each require completely incompatible valve materials. Wet chlorine gas attacks almost every common metal; HCl attacks stainless steel; caustic soda attacks aluminium and some plastics. Vajra Industrial Solutions has deep expertise in chlor-alkali valve selection: PVDF-lined or titanium valves for chlorine, Hastelloy C-276 or rubber-lined valves for HCl, and SS316L or Alloy 20 for caustic service.

ASME B16.34ISO 9001:2015API 609 (Butterfly)EN 12756 (Valve Stuffing Boxes)ATEX / IECEx (Chlorine Zone 1)Chlorine Institute Pamphlet 6
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Recommended Valve Types for Chlor-Alkali Plants

PVDF-Lined Butterfly Valve

PN 10 / PN 16

Why: Wet chlorine gas isolation — PVDF lining (or solid PVDF body) is uniquely resistant to wet Cl₂; titanium disc for highest corrosion resistance

Materials: WCB or SS316 shell; PVDF lining; titanium disc; FKM seat for Cl₂ service

Standards: API 609, Chlorine Institute Pamphlet 6, ATEX Zone 1

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Hastelloy C-276 Ball Valve

Class 150 / 300

Why: Hydrochloric acid (all concentrations, up to 100°C) — only Hastelloy C-276 and titanium resist HCl above 10% concentration

Materials: Hastelloy C-276 (UNS N10276) body, ball, and stem; PTFE seats

Standards: ASME B16.34, API 607 (fire-safe HCl service)

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SS316L Diaphragm Valve

PN 10 / PN 16

Why: Caustic soda (NaOH 30–50%) process and transfer — SS316L body with EPDM diaphragm; also used for sodium hypochlorite

Materials: A351 CF3M (SS316L cast) or A182 F316L forged; EPDM diaphragm

Standards: ASME B16.34, DIN 3202 (diaphragm valves)

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Titanium Ball Valve

Class 150 / 300

Why: Brine service and wet chlorine — Grade 2 titanium resists both Cl₂ and HCl; used in electrolysis cell connections

Materials: Titanium Grade 2 (UNS R50400) body, ball, and stem; PTFE seats

Standards: ASTM B265 (titanium sheet), ASME B16.34

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Critical Requirements

Wet chlorine gas — PVDF or PTFE-lined body, titanium disc; absolutely no iron, nickel-chromium alloys (attacked by wet Cl₂); no copper; FKM or PTFE packing only
Dry chlorine gas (< 20 ppm moisture) — carbon steel is surprisingly acceptable for dry Cl₂; however most plants keep SS316 or titanium as standard
Hydrochloric acid (all concentrations) — Hastelloy C-276 or titanium; SS316 only for dilute (<5%) cold HCl; NEVER use carbon steel
Caustic soda (NaOH) — SS316L acceptable for <70% NaOH; avoid aluminium (catastrophic SCC in NaOH); EPDM diaphragm valves preferred for slurry-free NaOH
Hydrogen gas from electrolysis — ATEX Zone 1; all electrical components on actuated valves must be Ex-certified
Brine (saturated NaCl) — titanium or rubber-lined butterfly; SS316 not reliable above 60°C in concentrated chloride

Fluid & Service Challenges

⚠Wet chlorine gas (Cl₂ + HCl + H₂O) — attacks iron, nickel alloys, and most stainless steels; requires PVDF or titanium wetted parts
⚠Hydrochloric acid (concentrated HCl) — one of the most aggressive mineral acids; Hastelloy C-276 or titanium required above 10%
⚠Caustic soda (50% NaOH, 80°C) — stress corrosion cracking in austenitic SS under tension; use CF3M (SS316L) cast body or duplex SS
⚠Chlorinated brine — combined attack of Cl₂ and NaCl; titanium is the only reliable general material
⚠Sodium hypochlorite (NaOCl) — unstable above 40°C; SS316L and CPVC; no rubber in contact (bleach attacks NBR/EPDM)

Material Selection Guidance

Wet chlorine: PVDF-lined body + titanium disc OR solid PVDF body for ≤ PN 10. Dry chlorine: carbon steel acceptable if confirmed dry (<20 ppm H₂O). HCl all concentrations: Hastelloy C-276 (N10276) — do not substitute with SS316. Caustic (NaOH 30–50%): SS316L (CF3M cast or F316L forged) with EPDM seats; avoid Ni-Cu alloys (Monel attacked by hot concentrated NaOH). Brine (saturated NaCl at 90°C): titanium only; rubber-lined butterfly acceptable for lower-temperature brine.

Typical Service Points

Chlorine gas main header — PVDF-lined butterfly valves (PN 10, titanium disc)
Electrolytic cell connections — titanium ball valves (Class 150, brine/Cl₂ service)
HCl synthesis furnace outlet — Hastelloy C-276 ball valves (concentrated HCl, 60°C)
Caustic evaporator and storage — SS316L diaphragm valves (50% NaOH, 80°C)
Hydrogen gas header — SS316L ball valves, ATEX-rated actuators (Zone 1, Ex-d)
Sodium hypochlorite production — SS316L butterfly and ball valves (NaOCl, ambient temp)

FAQ — Valve Selection for Chlor-Alkali Plants

Can I use SS316 valves for chlorine service in a chlor-alkali plant?
No — wet chlorine gas (Cl₂ with moisture) attacks austenitic stainless steel, including SS316. The chromium oxide passive layer that protects SS316 is destroyed by Cl₂ + HCl attack, causing rapid pitting and stress corrosion cracking. For wet chlorine, specify PVDF-lined butterfly valves (PN 10) or titanium ball valves. Dry chlorine (confirmed < 20 ppm moisture) can use carbon steel, but most plants maintain PVDF or titanium as a standard to eliminate moisture moisture monitoring from the maintenance programme.
What valve material handles both chlorine and caustic service?
Titanium Grade 2 is the rare material that resists both wet chlorine gas and dilute caustic soda — making it the preferred choice for brine and cell liquor service where both Cl₂ and NaOH are present. However, titanium is expensive and not suited for concentrated hot NaOH (>70%, above 80°C — risk of titanium stress corrosion cracking in very hot concentrated alkali). For pure caustic service, SS316L diaphragm valves are more economical.

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Chlor-Alkali Plants

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Key Standards

ASME B16.34
ISO 9001:2015
API 609 (Butterfly)
EN 12756 (Valve Stuffing Boxes)
ATEX / IECEx (Chlorine Zone 1)
Chlorine Institute Pamphlet 6

Products for This Application

Ball ValvesButterfly ValvesDiaphragm Valves

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