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 PVDF-, PTFE- and polypropylene-lined steel pipe for deionized, demineralized and ultrapure 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

• PVDF, rated 0 F to 275 F, is the recognized high-purity water liner: smooth, low in extractables, resistant to ozone and hydrogen peroxide sanitizers, and comfortable with 176 F hot-water sanitization. It is our first recommendation for ultrapure and deionized loops with a tight resistivity or TOC specification.
• PTFE, rated -20 F to 450 F, takes over where the line alternates between water and acid, as in acid-dilution and rinse systems that see hydrofluoric or mixed acid, or where steam-in-place at 250 F is part of the sanitization cycle.
• Polypropylene, rated 0 F to 225 F, 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: the polish loop inside a wafer fab is usually solid PVDF or PFA pipe, and that is the right choice there. 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 fabs and chemical plants, and purified 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 hot water, or to steam, works the liner against the housing every cycle. Liners expand more than steel, 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. The torque tables, flange ratings and vacuum ratings by size and liner are on our technical details page.

Vacuum and venting

Vacuum degasifiers and membrane degassing put suction on the line; PTFE holds full vacuum in the smaller sizes and reduced vacuum in the larger ones at temperature, so check the rating for the size you are running. Our housings are vented so that water vapor permeating the liner at temperature escapes rather than collecting against the steel.

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 diaphragm as the only moving wetted part. We supply it for isolation, throttling and point-of-use duty. PTFE-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 products 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 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 PVDF liner add anything to 18 megohm water?

PVDF contributes no metal ions and very low organic extractables, which is why it is the accepted material for ultrapure water in semiconductor and pharmaceutical plants. 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?

PVDF-lined pipe handles hot-water sanitization at 176 F comfortably within its 275 F rating, and PTFE-lined pipe takes steam-in-place within its 450 F rating. Either way, anchor the run for liner expansion and retorque the flanges after the first hot cycle.

Will lined pipe stop rouging in our purified water loop?

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 PVDF or PTFE 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 PVDF, with PTFE where the line also sees acid. It is attacked by ozone and leaches more organics than PVDF, so loops that are ozonated or carry a tight TOC spec should go to PVDF; send us the water spec and we will say which.