Lined Pipe for Chlorine and Hypochlorite Service

Dry chlorine is a carbon steel service; wet chlorine is a problem. The moment chlorine meets moisture it makes hydrochloric and hypochlorous acid, and a steel header that carried dry gas for years will pit through in weeks once a drying tower slips. Sodium hypochlorite, chlorine's most common downstream form, corrodes stainless steel and decomposes faster in contact with it. Marspec Technical Products fabricates PTFE- and PVDF-lined pipe spools in Fairhope, Alabama, supplies the lined fittings and Swissfluid PFA- and PTFE-lined valves, shipping nationwide from Fairhope. Call (251) 625-4949 or contact us online to start a quote.

Wet chlorine, dry chlorine and what each does to metal

Chlorine gas straight from an electrolytic cell is saturated with water, and that wet gas, along with chlorine water, cell-room vent gas, scrubber circuits and any chlorine line that has lost its dryness, is severely corrosive to carbon steel, stainless steel and the chromium-free nickel alloys. The metals that tolerate it are titanium and the high-molybdenum nickel-chromium alloys, and titanium carries its own trap: it stays passive only while the chlorine is wet, and in dry chlorine it can ignite. Fluoropolymer liners resolve the dilemma. PTFE and PVDF resist chlorine wet or dry, which is why lined steel is a proven choice for wet chlorine lines through 12 inches, for chlorine water, and for scrubber and vent systems; the main cell-gas headers from the cells to the drying towers are usually FRP or titanium and often larger than 12 inches. Dry gas and liquid chlorine under pressure remain a steel service by long-standing practice; lined valves and short lined sections go where moisture contamination is possible, and liquid chlorine, which expands sharply when trapped and warmed, is a service to discuss with us first.

Sodium hypochlorite: a product that is always decomposing

Bleach is made by absorbing chlorine in caustic and sold at 10 to 15 trade percent. From the day it is made it decomposes by two routes, to chlorate and to oxygen, and the oxygen route is the one a piping engineer feels. Heat, sunlight and higher concentration speed it up; nickel, copper, cobalt and iron ions catalyze it, so a steel or stainless component in a hypochlorite line not only corrodes but makes the product decompose faster. A lined system with no wetted metal keeps both the pipe and the bleach in specification. The released oxygen collects at high points, in strainers, in horizontal runs and in dead legs; it air-binds metering pumps, makes feed rates erratic and, trapped between two closed valves, builds enough pressure to split a valve body. So: slope lines to a vent that returns to the tank, keep runs short, point branches down, eliminate dead legs, keep velocity high enough to sweep bubbles along, and never block in a hypochlorite line without a path for gas to leave.

Liner selection, permeation and vacuum

• PTFE, minus 20 °F to 450 °F (minus 29 °C to 232 °C): our standard for wet chlorine gas, chlorine water, hypochlorite at any strength, and the mixed streams that swing between chlorine, caustic and hydrochloric acid in scrubber and tail-gas systems.
• PVDF, 0 °F to 275 °F (−18 °C to 135 °C): resists wet and dry chlorine to about 200 °F (93 °C) and is the hardest of the three liners, so it is often specified for chlorine gas in larger sizes. It is not for bulk bleach: 12.5 to 15 percent hypochlorite carries free caustic at about pH 12 to 13, which attacks PVDF over time, so bulk bleach goes in PTFE and PVDF is limited to dilute or on-site hypochlorite at pH 12 or below. Keep it out of streams that also carry caustic, at any strength; those go in PTFE.
• Polypropylene, 0 °F to 225 °F (−18 °C to 107 °C): chlorine attacks it, so chlorine lines go in PTFE. We recommend PTFE for hypochlorite too, and can provide polypropylene there wherever a customer specification requires it.

Chlorine, like hydrogen chloride, is a small molecule that permeates fluoropolymers, more quickly as temperature rises. Every spool and fitting housing has drilled vent holes as standard; they relieve permeant pressure between the liner and the housing to prevent liner collapse. A wet chlorine line should have its flange faces inspected on a schedule. Vacuum is routine here, in cell-gas headers, vacuum-regulated gas feed and scrubbers, so tell us where a line runs under vacuum; liner temperature limits, liner thicknesses, flange dimensions and torque tables are on our technical details page.

Flanges, gaskets and isolation

A chlorine leak is a toxic release, so the flanged joints in a lined chlorine system deserve more attention than the pipe. Lined spools seal flare to flare without a gasket; against alloy or glass-lined equipment use a PTFE envelope gasket, torque in a cross pattern to the technical details table, and retorque after the first thermal cycle, because fluoropolymer flares relax. Rotating flanges are standard and simplify alignment in a congested cell room. For positive isolation during maintenance, use PTFE spectacle blinds and spacers, not a closed valve, and on hypochlorite remember that a blinded section still off-gasses and needs a vent. Custom spools to 20 ft cut the joint count, and PTFE-bellows expansion joints take up growth on hot headers. Glass-lined reactors remain the standard vessel for chlorination and bromination chemistry, and we supply them; the transfer lines and valves around them belong in PTFE.

Valves, accessories, temperature and where it is used

On chlorine gas we quote PFA-lined ball valves and PFA-lined cylindrical plug valves, 1/2" through 2" full port and 3" through 6" reduced port, cavity-free, with no in-line adjustment; neither puts metal in the wetted path, which sidesteps the titanium question entirely. On hypochlorite the first choice is a lined diaphragm valve, because it has no cavity, with the PTFE/FPM diaphragm, since hypochlorite permeates the PTFE face and the FPM backing resists it; where a ball valve is required, use one with a vented ball, the vent facing upstream, so trapped liquid cannot pressurize. Lined butterfly valves serve the larger scrubber and chlorine-water lines, lined check valves protect metering pumps, and lined sampling valves draw a sample without a cloud of gas. Automated packages are assembled and tested here. Accessories include lined strainers mounted where trapped gas can escape, sight glasses that let operators see bubbles in a hypochlorite suction line, spargers for chlorinating caustic to make bleach, and solid PTFE pipe for short, low-pressure chlorine gas and sample lines, never liquid chlorine.

Temperature maintenance here is mostly about keeping things cool: hypochlorite decomposes faster warm, so bleach tanks and lines are shaded and insulated rather than heated. Keep chlorine-water and wet-chlorine lines above about 50 °F (10 °C), below which solid chlorine hydrate forms. Hypochlorite lines only need to stay above freezing: bleach can freeze in deep cold, so trace it only to keep it from freezing, and never overheat it, since heat speeds its decay. For both, electric tracing at a low setpoint under heat-transfer compound is the right tool, and we supply it.

Chlor-alkali plants carry wet chlorine from the cells to the drying towers and make hypochlorite from tail gas. Water and wastewater plants feed hypochlorite, and in some cases gas, for disinfection. Pulp mills generate chlorine dioxide and handle its chlorine-bearing side streams; power plants chlorinate cooling water, and food plants sanitize with hypochlorite. See the pages for chlor-alkali and chemical plants, water and wastewater treatment, pulp and paper mills, power plants and food and beverage plants, and the hydrochloric acid, caustic soda and brine and seawater pages for the chemicals chlorine comes from and goes to.

Our lined pipe and fittings, 1/2" through 12" in carbon steel or 304/316 stainless housings with ANSI B16.5 flanges, comply with ASTM F1545; fittings conform dimensionally to ANSI B16.5 and are welded to ASME B31.3 by welders certified to ASME Section IX, and every lined spool and fitting is spark tested at a minimum of 10,000 volts. We have built lined piping for more than half a century. Send us the stream, concentration, temperature and vacuum conditions; call (251) 625-4949 or contact us online.

FAQ: Lined Pipe for Chlorine and Hypochlorite

Can we use lined pipe on the wet chlorine header between the cells and the drying tower?

Through 12 inches, yes: PTFE- or PVDF-lined steel is a proven choice for wet chlorine lines, though main cell-gas headers are usually FRP or titanium and often larger than 12 inches. Tell us the vacuum the line sees, and inspect flange faces at turnarounds.

Our hypochlorite feed pumps keep losing prime. Is it the piping?

Usually. Oxygen from decomposition collects in strainers, horizontal runs and dead legs and air-binds the pump. Slope the suction line up to a vent, remove the dead legs, replace cavity ball valves with lined diaphragm valves or vented balls, and keep metal out of the wetted path so decomposition slows.

Which liner for 12.5 percent sodium hypochlorite at a water plant?

PTFE. Commercial 12.5 percent bleach carries excess caustic at about pH 12 to 13, which attacks PVDF over time, so PVDF is an option only for dilute or on-site hypochlorite at pH 12 or below. We can provide polypropylene wherever a customer specification requires it. We ask for the summer temperature of the storage area before we quote, because warm bleach gasses more.

Is lined pipe acceptable for liquid chlorine?

Liquid chlorine under pressure is handled in carbon steel by long-standing industry practice, and its thermal expansion when trapped is severe. We do not recommend lined pipe for it without a review; send us the service and we will say where lined valves and spools can and cannot be used.