Lined Pipe for Chlorine and Sodium 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 supplies PTFE- and PVDF-lined pipe spools, fittings and valves for both, built in Fairhope, Alabama and shipped nationwide. 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: in dry chlorine it ignites, at temperatures reported as low as 0 F. Fluoropolymer liners resolve the dilemma. PTFE and PVDF resist chlorine wet or dry, which is why lined steel is the usual choice for wet chlorine headers from the cells to the drying towers, for chlorine water, and for scrubber and vent systems. 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: 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: rated for halogens and strong oxidizers, with the highest strength of the three liners, so it is often specified for chlorine gas in larger sizes and for hypochlorite where lower permeation and stiffness under vacuum are wanted. Keep it out of streams that also carry strong caustic.
• Polypropylene, 0 F to 225 F: not for this service at strength. Chlorine and commercial hypochlorite are strong oxidizers that attack polypropylene; it suits only very dilute hypochlorite at ambient temperature, and even then send us the conditions.

Chlorine, like hydrogen chloride, is a small molecule that permeates fluoropolymers, more quickly as temperature rises. Permeant reaching the steel housing makes acid with whatever moisture it finds there, and a sealed housing then corrodes from the inside and lets the liner collapse. Our lined pipe and fittings are vented through the housing so permeant leaves to atmosphere, and a wet chlorine line should be inspected at its vents and flange faces on a schedule. Vacuum is routine here, in cell-gas headers, vacuum-regulated gas feed and scrubbers; vacuum ratings by size and liner 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 PTFE- or PFA-lined ball valves and PTFE-sleeved plug valves with no wetted metal, which sidesteps the titanium question entirely. On hypochlorite the first choice is a lined diaphragm valve, because it has no cavity; then a sleeved plug valve; and where a ball valve is required, one with a vent hole in the ball toward the upstream side 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 small-bore chlorine and sample lines.

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. Where a hypochlorite or chlorine-water line must be kept above freezing, 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 part 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?

Yes; that header is a textbook application for PTFE- or PVDF-lined steel. Specify vented housings, confirm the vacuum rating for the size and liner, 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 or PVDF; both resist hypochlorite at that strength. Polypropylene is not suitable for bleach at commercial concentration. 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.