Lined Pipe for High-Purity Water Service

Water with nothing in it wants everything it touches. Strip the ions out of water and it becomes a solvent for the pipe that carries it, pulling iron from carbon steel and iron, chromium and nickel from stainless at the parts-per-billion levels that fail a resistivity spec or stain a drug product. Marspec Technical Products fabricates PTFE-, PVDF- and polypropylene-lined steel pipe for deionized, demineralized and high-purity water and supplies the PFA-lined valves that keep the loop metal-free. Call (251) 625-4949 or contact us online with the water spec and the line list.

Pure water is a solvent for everything it touches

Ultrapure water at 18.2 megohm-centimeters has had essentially every ion removed, and it recovers them from whatever surface it meets. Early semiconductor plants piped it in steel and learned that the metal extractables cost yield; the move to plastic cut the metals and introduced a different problem, organic extractables from the additives in commodity resins. Demineralized boiler makeup and condensate carry dissolved oxygen and carbon dioxide and attack carbon steel freely, because there is no hardness scale to protect it. And in pharmaceutical purified water and water-for-injection systems built entirely of electropolished 316L, hot water still draws iron out of the alloy as rouge, a film of iron oxides that gets worse the hotter the loop runs and that, by the industry's own account, cannot be completely prevented. The liner answer to all of this is a wetted surface that contributes no metal ions at all and very little else.

Which liner for which water

• PTFE, rated -20 °F to 450 °F (-29 °C to 232 °C), is our first recommendation for high-purity water: it contributes no metal ions, no pigment and very little else, resists ozone and hydrogen peroxide sanitizers, and takes 176 °F (80 °C) hot-water sanitization or 250 °F (121 °C) steam-in-place well inside its rating. It also covers lines that alternate between water and acid, as in acid-dilution and rinse systems that see hydrofluoric or mixed acid.
• PVDF, rated 0 °F to 275 °F (−18 °C to 135 °C), is smooth, tough and resistant to ozone, peroxide and 176 °F (80 °C) hot water, but our PVDF liner is black-pigmented, so it suits utility deionized and demineralized water rather than loops held to a tight resistivity, TOC or metals specification. Ultrapure water at that level runs in solid natural PVDF or PFA pipe, not lined steel.
• Polypropylene, rated 0 °F to 225 °F (−18 °C to 107 °C), is available for demineralized water, RO permeate and plating-line rinse water where a specification calls for it and the purity spec is moderate. It is degraded by ozone, so it stays out of ozonated loops, and its extractables are higher than the fluoropolymers', so send us the TOC spec before choosing it.

All three liners come in lined pipe and fittings from 1/2" through 12", carbon steel or 304/316 stainless housings, with custom spools to 20 ft and rotating flanges standard.

Where lined steel fits in a high-purity system

We will be direct about this: inside a wafer fab, ultrapure water and electronic-grade chemicals run in solid natural PVDF or PFA pipe, and that is the right choice there; in a fab, lined pipe and lined valves are for bulk chemical supply, acid waste and neutralization. Lined steel earns its place where the strength of a steel housing matters: utility deionized water mains with long support spans, demineralized water headers in power plants and chemical complexes, rinse-water distribution through pickling and plating lines where a dropped coil would crush plastic pipe, hot sanitization return lines, acid-dilution makeup water in chemical plants, and deionized utility water in pharmaceutical plants that already standardize on lined piping for their acids and caustics. In each of those the liner delivers the purity and the steel delivers the pressure rating, fire resistance and toughness.

Design details that keep the water clean

Flanges and dead legs

Lined flanges seal liner to liner, so there is no elastomer gasket to leach plasticizer or to form a crevice where biofilm starts. Where a spacer is needed, use solid PTFE rather than rubber. Keep branches short and full-bore, close-couple instrument tees and sampling valves to the header, and keep the loop recirculating; a stagnant spool is a bacteria count waiting to happen regardless of liner.

Sanitization and thermal cycling

A loop that cycles from ambient to 176 °F (80 °C) hot water, or to steam, works the liner against the housing every cycle. The steel housing sets the thermal growth, as in any steel line, so anchor the run, fit lined expansion joints where the layout needs them, and retorque flanges after the first hot cycle, since PTFE cold-flows under bolt load. Liner temperature limits, liner thicknesses, flange dimensions and torque tables are on our technical details page.

Vacuum and venting

Vacuum degasifiers and membrane degassing put suction on the line; PTFE liners are rated for vacuum by size and temperature, so send us the vacuum and temperature for the size you are running. Water vapor permeates the liner at temperature, and the vent holes drilled as standard in every spool and fitting housing relieve that permeant pressure to prevent liner collapse.

Valves, strainers, tracing and where this water runs

The high-purity valve is the PFA-lined weir diaphragm valve: no packing, no body cavity, drainable, with a PTFE-faced diaphragm as the only moving wetted part. We supply it for isolation, throttling and point-of-use duty. PFA-lined ball valves serve utility deionized water, PTFE-lined butterfly valves the large demineralized headers, lined check valves the pump discharges, and lined sampling valves the conductivity and TOC grab points. No valve we quote for this service has metal in the flow path, and automated packages are assembled and tested in-house. See our plastic-lined valves page.

Lined basket strainers protect reverse-osmosis skids and polisher resin from carryover, PTFE spectacle blinds isolate a train for sanitization, and solid PTFE pipe handles small-bore polish lines. Outdoor demineralized water lines at power plants are electrically traced against freezing with the controller held below the liner limit, and hot sanitization loops are insulated and, where needed, fitted with clamp-on heaters. All of it is on our piping accessories page.

The plants that run this water are semiconductor and high-purity manufacturers, pharmaceutical and biotech plants, power plants with demineralizer trains and condensate polishing, steel pickling and metal finishing lines with rinse circuits, and battery and lithium plants making electrolyte and hydroxide. The acid side of the same systems is on our hydrofluoric acid and nitric and mixed acid pages, and sanitizer handling on our chlorine and sodium hypochlorite page. Our lined pipe and fittings 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 passes a minimum 10,000-volt spark test. More than half a century in, we ship nationwide from Fairhope, Alabama. Call (251) 625-4949 or contact us online.

FAQ: Lined Pipe for High-Purity Water

Does a lined pipe add anything to 18 megohm water?

A PTFE liner contributes no metal ions, no pigment and very little organic extractable, which is why it is our first choice for deionized and purified water loops; our PVDF liner is black-pigmented, so we keep it to utility deionized and demineralized water. Inside a wafer fab the ultrapure water itself runs in solid natural PVDF or PFA, and lined pipe there is for bulk chemical supply, acid waste and neutralization. We still ask for your resistivity and TOC specification and the sanitization method so the liner and the flange details match them.

Can lined pipe handle hot-water or steam sanitization?

PTFE-lined pipe takes hot-water sanitization at 176 °F (80 °C) and steam-in-place at 250 °F (121 °C) well inside its 450 °F (232 °C) rating, and PVDF-lined pipe takes 176 °F (80 °C) hot water within its 275 °F (135 °C) rating. Either way, anchor the run for thermal growth, as with any steel line, and retorque the flanges after the first hot cycle.

Will lined pipe stop rouging in our hot deionized water loop?

In the piping, yes. Rouge is iron oxide drawn out of stainless steel by hot pure water, so a line with no stainless in contact with the water cannot rouge. A PTFE or PVDF liner separates the water from the steel housing completely, which is the point of using it in this service.

Is polypropylene-lined pipe acceptable for deionized rinse water?

Where a specification calls for it, yes, for demineralized and rinse water at moderate purity and temperature; our recommendation for water service is still PTFE. Polypropylene is attacked by ozone and leaches more organics than the fluoropolymers, so loops that are ozonated or carry a tight TOC spec should go to PTFE; send us the water spec and we will say which.