Lined Pipe for Slurries and Abrasive Service

An acid slurry wears pipe faster than the acid or the solids would alone, because each removes the protection the other would leave. The grit scours off the corrosion film that would otherwise slow the attack, the acid goes to work on fresh metal, and the next particle takes that layer off too. Marspec Technical Products fabricates PVDF-lined steel pipe for slurry and abrasive service, with polypropylene and PTFE where the chemistry calls for them, and supplies the full-port lined valves, strainers and tracing that keep solids moving. Call (251) 625-4949 or contact us online with the slurry analysis and the line list.

Erosion plus corrosion: why these lines fail fast

Wet-process phosphoric acid leaves the filter carrying gypsum, silica fines and fluoride, which rules out glass and pits stainless. A limestone flue-gas desulfurization absorber runs its slurry at a pH of about 5 to 6, but chlorides concentrated from the coal push local pH toward 1, and the published alloy answer at that point is a nickel-chromium-molybdenum grade, with slurry impingement opening fresh sites for pitting and crevice attack. Sulfuric acid leach slurries in mining, titanium dioxide digestion, lime and lime-mud circuits in pulp mills, crystallizer magmas of salt and sodium sulfate, and spent pickle liquor carrying scale all pair a corrosive liquid with a solid that scrubs. Rubber lining, or UHMW polyethylene, is the traditional answer and often outwears a fluoropolymer in neutral slurry; it holds up until the chemistry or temperature exceeds the rubber's limits. High alloys cost what they cost and still thin at the elbows. A plastic liner gives the slurry a surface that neither corrodes nor passivates, so the erosion-corrosion cycle has nothing to feed on.

Liner choice: PVDF first for abrasion

PTFE leads on chemical resistance and trails badly on abrasion, while PVDF is the hardest, most abrasion-resistant of the three liners, which is the puzzle of this service.

• PVDF is the hardest and most abrasion-resistant of our three liners, with published abrasion resistance its producers call excellent for pump and pipe service. It is our first recommendation for acidic abrasive slurries within its 0 °F to 275 °F (−18 °C to 135 °C) rating: phosphoric acid with gypsum, FGD absorber bleed, sulfuric acid leach pulps.
• Polypropylene stands up well to abrasion and is available where a specification calls for it on alkaline and near-neutral slurries at moderate temperature, rated 0 °F to 225 °F (−18 °C to 107 °C): lime slurry, lime mud, gypsum dewatering, caustic leach residues, salt and sodium sulfate crystallizer slurries. It is not for slurries carrying strong oxidizers such as hypochlorite.
• PTFE has the broadest chemistry and the widest temperature range, -20 °F to 450 °F (-29 °C to 232 °C), and the lowest abrasion resistance of the three. Use it when the liquid phase leaves no choice, hot or concentrated acid and hot mixed acids for example, and keep velocity at the low end. Send us the solids loading, particle size and temperature and we will be candid about liner life.

Whichever liner, the smooth, low-energy surface also resists the gypsum and calcium scale that bonds to steel and rubber, keeping the bore open longer between cleanings. Spools, elbows, tees and reducers come as lined pipe and fittings from 1/2" through 12", custom lengths to 20 ft, carbon steel or stainless housings.

Laying out a slurry line that lasts

• Velocity decides liner life. Run above the deposition velocity so solids stay suspended, but as little above it as the hydraulics allow: published slurry-pipeline guidance puts wear rising roughly with the cube of velocity at the high end, so a line that lasts years at 7 ft/s may last months at 13 ft/s.
• Use long-radius elbows and keep bends away from the pump discharge where turbulence peaks. In the worst services a plugged tee at the change of direction lets the slurry impact a cushion of its own solids instead of the liner.
• Rotating flanges, standard on our spools, let maintenance turn a horizontal spool a quarter or half turn at an outage so a settling slurry wears fresh liner instead of the same invert.
• Elbows, tees and reducers are standard lined fittings, so keep spares of the ones at the wear points, and a worn one unbolts and swaps out at an outage. Put lined tees for drains and flush water at the low points.
• Filter feed and filtrate lines on vacuum belt and drum filters run under vacuum, so mark those lines on the line list. Liner temperature limits, liner thicknesses, flange dimensions and torque tables are on our technical details page.

Valves that pass solids

The slurry valve has no cavity for solids to pack and no seat that a partial opening will erode. PFA-lined cylindrical plug valves, 1/2" through 2" full port and 3" through 6" reduced port, with no in-line adjustment, lead the list: they are cavity-free, so solids have nothing to pack into. PFA-lined diaphragm valves with PTFE-faced diaphragms, in weir and straight-through patterns, are the classic choice for throttling and isolating slurry. Full-port lined ball valves work on finer slurries where the body cavity can be flushed. PTFE-lined butterfly valves cover the big lines, on-off only, since a throttled disc erodes at the edge. Lined swing check valves are preferred to lift checks, which foul, and full-bore lined sampling valves pull a representative sample. Ball, plug and diaphragm valves are PFA-lined and butterfly valves PTFE-lined, with automated packages assembled and tested in-house. See our plastic-lined valves page.

Lined basket strainers catch tramp material ahead of spray nozzles and pumps, sight glasses show settling and plugging before the pressure gauge does, PTFE spectacle blinds give positive isolation on filter feed, and solid PTFE dip pipes and spargers serve agitated tanks. Lined expansion joints handle the growth of a hot slurry line, placed where the line drains rather than at the bottom of a loop where solids collect in the convolutions. All are on our piping accessories page.

Hot slurry, cold weather, and where slurries run

Slurries set up when they cool. Gypsum and lime slurries settle and cement in a stopped line, saturated salt brine drops crystals, and sodium sulfate solutions crystallize as the decahydrate below about 90 °F (32 °C), so crystallizer and filter-feed lines outdoors are traced or jacketed. We supply steam-jacketed lined pipe and fittings, clamp-on steam heaters, electric tracing and heat-transfer compound. For jacketed or traced service, we recommend specifying PTFE, run within velocity limits. Where an abrasive slurry needs PVDF's abrasion resistance and must be traced as well, we leave that choice to you. Glass-lined equipment, which we also supply, is not for abrasive slurry; impact and abrasion are two of its hard limits.

The industries that live with these lines are fertilizer and phosphate plants, mining and metals operations, power plants with wet FGD, pulp and paper mills with lime and bleach-plant circuits, battery and lithium plants converting spodumene, and water and wastewater plants handling lime and ferric slurries. The liquid phases are covered on our sulfuric acid, hydrofluoric acid and caustic soda pages. 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. We have lined pipe for more than half a century and ship nationwide from Fairhope, Alabama. Call (251) 625-4949 or contact us online.

FAQ: Lined Pipe for Slurries and Abrasive Service

Which liner lasts longest in phosphoric acid slurry with gypsum?

PVDF, the most abrasion-resistant of our liners, which resists phosphoric acid and the fluorides that come with it within its 275 °F (135 °C) rating. Pair it with long-radius elbows, a velocity just above deposition, and rotating flanges so spools can be turned at outages.

Is PTFE-lined pipe a mistake for abrasive service?

Not a mistake, but a trade: PTFE has the widest chemical and temperature range and the lowest abrasion resistance of the three liners. We quote it for slurries whose liquid phase rules out PVDF, and we ask for particle size, solids loading and velocity so the life estimate is honest.

What valves do you recommend for FGD absorber bleed and limestone slurry?

PFA-lined cylindrical plug valves or PFA-lined diaphragm valves for isolation and throttling, lined swing check valves on pump discharges, and PTFE-lined butterfly valves for on-off duty on the larger headers. The fluoropolymer lining handles the chloride-rich, low-pH liquid; the valve pattern, with no cavity to pack and no seat to score, handles the solids, and on neutral limestone slurry rubber-lined valves often outwear fluoropolymer.

How fast should a lined slurry line run?

Fast enough to keep the solids suspended and no faster, because wear climbs steeply with velocity. Settling slurries typically need a few feet per second; send us the particle size and specific gravity and we will help you set a velocity that protects the liner.