Lined Pipe for Power Plants

A generating station is a steam plant surrounded by chemical plants: a scrubber circulating chloride-laden limestone slurry, a demineralizer regenerated with sulfuric acid and caustic, a cooling system dosed with hypochlorite and acid, and a wastewater plant that must meet effluent limits on all of it. Marspec Technical Products fabricates PTFE-, PVDF- and polypropylene-lined steel pipe spools and supplies the lined fittings, valves and accessories those systems need, with spools shipping nationwide from Fairhope, Alabama. Call (251) 625-4949 or contact us online.

We have lined steel pipe for these services in coal, gas and geothermal plants for more than half a century.

Four plant systems that run on lined pipe

Wet flue-gas desulfurization

A limestone forced-oxidation scrubber grinds limestone to a slurry, sprays it through the absorber, oxidizes the calcium sulfite to gypsum and dewaters the gypsum for sale or landfill. Chloride from the coal has nowhere to go but the recycle slurry, where it climbs into the tens of thousands of parts per million, and a purge stream is bled off to hold it there. The absorber recycle itself is large-bore alloy or rubber-lined work; the 2" through 12" lines around it are where lined steel belongs: limestone slurry feed, gypsum bleed to the hydrocyclones, mist eliminator wash, absorber purge, reclaim water, and the lime, ferric chloride and organosulfide feeds of the purge treatment plant. Slurry at pH 5 to 6 with high chloride and abrasive solids defeats unlined steel two ways at once; rubber lining is the usual answer for the slurry itself, and PVDF-lined spools with lined plug and diaphragm valves are the alternative where chloride resistance and inspection at the flange matter, and polypropylene-lined spools are available for the same lines where a specification calls for them. Our slurry and abrasive service page covers liner wear.

Makeup demineralizers and condensate polishing

Boiler makeup passes through cation and anion exchangers and a mixed bed, regenerated with sulfuric or hydrochloric acid and caustic soda diluted from bulk strength to a few percent. Bulk 93 percent sulfuric acid sits in carbon steel; the dilute acid regenerant leaving the eductor dissolves steel, and the warm caustic used to strip silica off the anion resin barely corrodes it but picks up iron that fouls the resin. Dilution headers, the valve nest on each vessel, eductors, the neutralization tank and its recirculation loop, and the waste discharge are all lined-pipe service, and so are the acid, bisulfite and cleaning chemicals of a reverse osmosis pretreatment train. Condensate polishers regenerated on site run the same chemistry at a purity standard where a liner that sheds no iron matters as much as one that does not corrode. See our sulfuric acid, caustic soda and high-purity water pages.

Cooling water and wastewater

Circulating water is dosed with sulfuric acid for alkalinity control, sodium hypochlorite or bromine for biofouling and scale inhibitor for the condenser, and seawater-cooled plants chlorinate every day. Cooling tower blowdown, FGD purge and demineralizer waste meet in a wastewater plant that neutralizes, precipitates metals with lime, ferric and organosulfide and, at plants headed for zero liquid discharge, concentrates the chloride brine in evaporators and crystallizers. Hot concentrated brine from a brine concentrator is among the harshest streams on a plant site, and PTFE is the liner for it; our brine and seawater page and our chlorine and sodium hypochlorite page cover the others.

Combined cycle and geothermal

A combined-cycle plant runs a smaller version of the same demineralizer, polisher and circulating water chemistry, plus aqueous ammonia for the SCR. A geothermal plant moves hot brine with scale inhibitor, acid and sulfide abatement chemicals, and PTFE's 450 °F (232 °C) rating makes lined steel workable there; send us the temperature and hydrogen sulfide content with the line list, since H2S permeates the liner faster as the line runs hotter.

Choosing the liner

• PTFE: the liner we recommend and quote by default, for reagent feed, regenerants, neutralization and bulk-strength hypochlorite as well as hot brine from evaporators and crystallizers, geothermal brine and mixed waste streams. Rated to 450 °F (232 °C)
• PVDF: gypsum and absorber purge where abrasion and chloride meet, dilute or on-site hypochlorite at pH 12 or below, and utility RO and deionized water. Rated to 275 °F (135 °C); not for caustic at any strength, which goes in PTFE
• Polypropylene: available where a specification calls for it on limestone slurry and reagent feed, dilute acid and caustic regenerants, neutralization and dilute cooling water acid feed. Rated to 225 °F (107 °C); for hypochlorite and other oxidizers we recommend PTFE

Spools, valves and accessories

We fabricate custom lined spools from 1/2" through 12" in lengths up to 20 ft, in carbon steel or 304 and 316 stainless housings, with lined elbows, tees, reducers, laterals and instrument tees that conform dimensionally to ANSI B16.5 and bolt to the class 150 flanges in the scrubber and water treatment buildings. Rotating flanges are standard so a replacement spool lines up with a rack that has moved. Liner temperature limits, liner thicknesses, flange dimensions and torque tables are on our technical details page.

The demineralizer regeneration sequence is a natural fit for automated lined ball and diaphragm valves with actuators, limit switches and positioners mounted and tested in our shop before the valve nest ships. Lined plug and diaphragm valves handle slurry, lined butterfly valves handle large-bore purge and reclaim water, lined check valves sit at chemical pump discharges, and lined sampling valves draw regenerant for titration. See our lined valves page.

Lined strainers protect mist eliminator wash nozzles and metering pumps, PTFE-bellows expansion joints take up thermal movement on absorber-area racks, PTFE spacers and spectacle blinds isolate an absorber module or a demineralizer vessel, sight glasses show reagent flow, and dip pipes and spargers serve neutralization tanks; see our piping accessories page. Where a plant sees winter, 50 percent caustic crystallizes near 54 °F (12 °C) and idle slurry lines freeze solid, so we supply clamp-on steam heaters, electric tracing and heat-transfer compound from our temperature maintenance line, sized to the liner's limit. For jacketed or traced service, we recommend specifying PTFE.

Where the plants are, standards and a quote

Scrubbed coal units line the Ohio River through West Virginia, Kentucky and southern Indiana and sit at mine mouth in Wyoming and North Dakota, and combined-cycle plants are wherever gas is cheap.

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 before it leaves the shop. Send the P&ID section or the tag numbers from the last outage, with fluid, concentration, temperature and solids, and we will confirm liners and quote the package. Call (251) 625-4949 or contact us online. Custom spools fabricated in our own shop ship nationwide from Fairhope, Alabama.

FAQ: Lined Pipe for Power Plants

Which liner do you recommend for FGD absorber purge and gypsum bleed lines?

PVDF where chloride and abrasion combine, because it is the hardest, most abrasion-resistant of the three liners and unaffected by chloride, and PTFE for reclaim water, with polypropylene available there where a specification calls for it. The limestone slurry itself usually runs in rubber-lined pipe, which outwears any fluoropolymer in neutral slurry. Lined plug or diaphragm valves go with any of them, and all three liners can be inspected at the flange without pulling the rubber lining apart.

Can lined pipe handle the dilute sulfuric acid and caustic in our demineralizer regeneration system?

Yes. Dilute acid is far harder on steel than the 93 percent acid in the bulk tank, and PTFE-lined spools carry both regenerants through dilution, the valve nest and neutralization, with polypropylene available where a specification calls for it. We also assemble the automated lined valves the sequence calls for.

Is lined steel suitable for the hot brine from a ZLD brine concentrator?

PTFE-lined pipe is the usual answer, rated to 450 °F (232 °C) and unaffected by concentrated chloride brine. Tell us the temperature, chloride level and whether the line sees vacuum, and we will confirm the liner and size the spools.

Can you build replacement spools to match the lined piping already in our scrubber building?

Yes. Send face-to-face dimensions, size, flange standard and liner, and we fabricate spools that bolt into the existing run, spark test them and ship from Fairhope, Alabama. Custom spools built to field dimensions are our normal work during an outage.