Lined Pipe for Steel Pickling and Metal Finishing

Every coil of cold-rolled or galvanized sheet, every length of wire and every anodized extrusion has been through an acid bath, and the acid has to reach the bath, leave it and pass through a regeneration plant or a waste treatment system in pipe that it does not eat. Marspec Technical Products fabricates PTFE-, PVDF- and polypropylene-lined steel pipe spools and supplies the lined fittings, valves and accessories for pickling, galvanizing, plating and anodizing lines, shipping nationwide from Fairhope, Alabama. Call 251-625-4949 or contact us online with the acid, the temperature and a line list.

After more than half a century of lining steel pipe, pickle liquor is a service we know well.

Pickling: hydrochloric, sulfuric and nitric-hydrofluoric

A continuous hydrochloric acid pickling line pushes hot band through a cascade of shallow tanks against a counterflow of acid, fresh acid at roughly 18 percent entering the last tank and spent liquor leaving the first with most of its acid converted to ferrous chloride, at bath temperatures around 160 to 200 °F. Spent liquor goes to an acid regeneration plant, where a spray roaster or fluidized bed converts the iron chloride to iron oxide and hydrogen chloride that is absorbed back to about 18 percent acid and returned to the line. Fresh and regenerated acid headers, spent liquor transfer, the absorber loops, rinse water loaded with iron chloride and fume scrubber recirculation are all lined-pipe service, because hot hydrochloric acid attacks every common alloy except tantalum. Our hydrochloric acid page covers the chemistry; in short, PTFE in vented housings is the liner we recommend and quote across the pickling line, since HCl permeates PTFE faster as temperature climbs and the vents let it out, PVDF is an option for regenerated acid within its 275 °F limit, and polypropylene is available within its 225 °F rating where a specification calls for it.

Wire, bar and batch pickling often runs on sulfuric acid at 8 to 20 percent and 140 to 180 °F, with ferrous sulfate crystallizing from the spent bath; dilute hot sulfuric is far more corrosive to steel than the 93 percent acid it is made from, and our sulfuric acid page explains why PTFE lining is the answer. Stainless and specialty alloy mills pickle in a nitric and hydrofluoric acid mixture that attacks glass as well as metal; those lines are PTFE, with PVDF an option at lower temperatures, as our nitric and mixed acids and hydrofluoric acid pages explain. Aluminum finishing adds hot caustic etch, nitric desmut and phosphoric-nitric bright dip.

Galvanizing, plating and finishing

A hot-dip galvanizer degreases in caustic or acid, pickles in ambient hydrochloric acid, rinses and fluxes in hot zinc ammonium chloride before the kettle; continuous galvanizing lines add alkaline cleaning and chromate or trivalent passivation. Plating shops run chromic acid, nickel sulfate and chloride baths, acid copper, chloride and cyanide zinc and electroless nickel near 190 °F, with sulfuric and chromic anodizing, phosphating, caustic etch and nitric or citric passivation beside them. Circuit board and chemical milling shops etch with ferric chloride, cupric chloride and ammoniacal etchants. The waste treatment behind all of it reduces hexavalent chrome with bisulfite and acid, oxidizes cyanide with hypochlorite and caustic, and precipitates metals as hydroxides with caustic or lime, the chemistry on our water and wastewater page. Bath makeup, transfer and filtration loops, tank heating and treatment plant feeds are the lined-pipe runs in a finishing shop.

Liner by bath

• Hydrochloric acid pickle, rinse and scrubber: PTFE in vented housings across the range, PVDF to 275 °F for hot regenerated acid, polypropylene to 225 °F where the spec names it
• Sulfuric acid pickling and anodizing: PTFE across the range, polypropylene available for dilute baths at moderate temperature if specified; no PVDF in hot concentrated acid
• Nitric-hydrofluoric, nitric desmut, bright dip and chromic acid: PTFE, or PVDF at lower temperatures; never polypropylene with these oxidizers
• Caustic etch, degreasing and hydroxide precipitation: PTFE, or polypropylene where specified; not PVDF
• Zinc ammonium chloride flux, chloride etchants, nickel and copper plating baths: PTFE or PVDF
• Rinse water and spent liquor carrying mill scale: PVDF, the strongest liner, where abrasion is the limit

Spools, valves and accessories

We fabricate custom lined spools from 1/2" through 12" in lengths up to 20 ft, with lined elbows, tees, reducers, laterals and instrument tees that conform dimensionally to ANSI B16.5, in carbon steel or 304 and 316 stainless housings. Rotating flanges are standard, which matters on a line built around rubber-lined pipe with its own flange quirks. Ratings by liner and size are on our technical details page.

PTFE-lined sleeved plug valves are the workhorse on pickle liquor, with no cavity for scale to pack into; lined diaphragm valves throttle acid dosing and handle liquor carrying solids; lined ball valves isolate fresh acid and caustic; lined check valves sit at every acid pump; and lined sampling valves draw liquor for titration. We also assemble the automated lined valves an acid concentration controller uses to add fresh acid on demand, actuators and switches mounted and tested before shipment. See our lined valves page.

Lined Y and basket strainers protect spray nozzles in turbulent pickling and the pumps on regeneration loops, sight glasses show acid flow, PTFE spacers and spectacle blinds isolate a tank nozzle while the tank is relined, expansion joints take up movement on long acid headers, and dip pipes and spargers serve tank heating; see our piping accessories page. Outdoors, spent liquor heavy in ferrous chloride thickens as it cools and 50 percent caustic crystallizes near 54 °F, so we supply electric tracing, clamp-on steam heaters and heat-transfer compound from our temperature maintenance line.

Where the mills and finishers are

The integrated mills on the Indiana lakefront at Gary, Burns Harbor and East Chicago pickle more hot band than anywhere else in the country, with Ohio's mills at Cleveland and Middletown and the Mon Valley sheet mill and Allegheny Valley stainless mills around Pittsburgh close behind. Electric-furnace sheet mills with their own pickling lines run at Decatur in Alabama and Huger near Charleston, one of the largest stainless producers in the country finishes at Ghent in Kentucky, and plating and anodizing shops cluster wherever aerospace and automotive work is, from Huntsville to Southern California.

Standards and a quote

Our lined 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 before it ships. Tell us the acid, its concentration and temperature, the solids and the flange standard, and we will confirm the liner and quote the order. Call 251-625-4949 or contact us online. Custom spools fabricated in our own shop ship nationwide from Fairhope, Alabama.

FAQ: Lined Pipe for Steel Pickling and Metal Finishing

Which liner do you recommend for hydrochloric acid on a continuous pickling line?

PTFE in vented housings for the pickle tanks, rinse and scrubber lines, including the hottest service, PVDF as an option where regenerated acid returns within its 275 °F limit, and polypropylene within its 225 °F rating where a specification calls for it. All three go in carbon steel housings with PTFE-lined plug valves.

Why vented housings for hot HCl in PTFE-lined pipe?

Hydrogen chloride permeates PTFE slowly, and faster as temperature rises. Vent holes in the steel housing let it escape instead of collecting behind the liner and blistering it, and a quick look at the vents and flange faces during an outage tells you how the line is doing.

Can lined pipe handle the nitric-hydrofluoric pickle at a stainless mill?

Yes. The mixture attacks glass and most alloys, but PTFE is unaffected at pickling temperatures and PVDF is an option on cooler lines. We supply spools, lined diaphragm and plug valves and sampling valves in the same liner so there is no weak joint in the line.

Will your lined fittings bolt to the rubber-lined pipe already on our line?

Our fittings conform dimensionally to ANSI B16.5 and our spools are built to your face-to-face dimensions with rotating flanges, so they mate with standard flanged rubber-lined or lined pipe. Send dimensions or a photo of the flange and we will confirm.