Lined Pipe for Refineries and Petrochemical Plants
Most of a refinery is carbon steel and the alloys hydrocarbon service calls for, and lined pipe has no business in a crude line. It has every business in the units around the edges: the alkylation acid system, caustic treating, the amine and sour water loops, the water plant and the wastewater plant, wherever the fluid is acid, caustic or brine. Marspec Technical Products has fabricated PTFE-, PVDF- and polypropylene-lined spools and supplied the lined fittings, valves and accessories for those units for more than half a century. Call (251) 625-4949 to put a turnaround package on the schedule.
The petrochemical complexes next door, crackers, oxide and glycol units, sulfonation, acetyls and isocyanates, use the same liners for their caustic washes, acid catalysts and corrosive intermediates. Contact us online with a line list and we will quote it.
Refinery units that run on lined pipe
Alkylation
A sulfuric acid alkylation unit takes fresh acid at about 98 percent and discards it near 90 percent, diluted with water and loaded with acid-soluble oils. Concentrated fresh acid is handled in carbon steel at low velocity, but spent acid, the acid and hydrocarbon emulsion from the contactors, settler drains, acid wash water and anything that condenses in the acid regeneration plant eat steel quickly, and that is where PTFE-lined spools, PFA-lined cylindrical plug valves and lined sight glasses go. Hydrofluoric acid alkylation is a different case: anhydrous HF stays in carbon steel under tight controls, while the relief neutralizer, the potassium hydroxide scrubber loop, acid-soluble oil neutralization and any wet HF belong in fluoropolymer. HF attacks glass and silica, so glass-lined equipment is out and PTFE lining is in.
Caustic treating, amine and sour water
Caustic prewash and extraction units take 50 percent caustic from the tank farm, dilute it to 10 to 20 percent and send it out as spent caustic loaded with sulfides, mercaptides, cresylics and naphthenates. Fresh and spent caustic both run in PTFE-lined pipe, since spent caustic carries dissolved aromatics, whether it heads to a spent caustic oxidation unit or the wastewater plant; polypropylene is available for dilute fresh caustic where a specification calls for it. Amine regeneration builds heat-stable salts that are removed with caustic or ion exchange, and sour water strippers, sulfur plant quench loops and tail-gas scrubbers produce weak acid, ammonium bisulfide and caustic scrubbing solution. A PTFE-lined carbon steel housing replaces the alloy the specification would otherwise demand; send us the temperature and hydrogen sulfide content with the line list, since H2S permeates the liner faster as the line runs hotter.
Water, utilities and wastewater
Demineralizer and condensate polisher regeneration uses sulfuric or hydrochloric acid and caustic. Cooling towers are dosed with sulfuric acid for pH and sodium hypochlorite for biological control. The wastewater plant neutralizes with acid and caustic, coagulates with ferric chloride or alum and feeds polymer to the flotation unit. All of it is lined-pipe service: PTFE for the acid regenerant headers, the caustic, the coagulants and bulk hypochlorite, with PVDF only for dilute or on-site hypochlorite at pH 12 or below.
Petrochemical services
A steam cracker's caustic wash tower is the busiest lined-pipe service on the olefins side: fresh caustic in, spent caustic with sulfides and polymer out, often to a wet air oxidation unit. Ethylene oxide and glycol plants run caustic scrubbers and purify glycol under vacuum. Sulfation and sulfonation of alcohols and alkylbenzene run on sulfur trioxide and oleum followed by caustic neutralization, and oleum needs PTFE, because PVDF is attacked by fuming sulfuric acid. Hot acetic acid and acetic anhydride can attack stainless steel, and acetic and acrylic acid corrode carbon steel and pick up iron; isocyanate units turn chlorine into phosgene and send hydrochloric acid out the back. Aromatic and chlorinated solvents swell polypropylene, so PTFE is the default liner on the petrochemical side. Those solvents can build a static charge that pinholes a plain lining or ignites vapor, so bond and ground the spools and use anti-static PFA-AS valves; tell us if your specification calls for an anti-static liner.
Liner and valve selection by stream
- Spent alkylation acid, acid emulsions and regeneration condensate: PTFE
- Fresh dilute caustic, coagulants and neutralized effluent at ambient: PTFE, or polypropylene where the specification names it
- Spent caustic with dissolved aromatics: PTFE
- Ferric chloride dosing: PTFE or PVDF; bulk hypochlorite: PTFE, with PVDF only for dilute or on-site hypochlorite at pH 12 or below
- Oleum, sulfur trioxide and concentrated sulfuric acid: PTFE
- Wet HF, KOH scrubber loops and HF neutralization: PTFE
PFA-lined cylindrical plug valves, 1/2" through 2" full port and 3" through 6" reduced port, cavity-free, with no in-line adjustment, serve acid and spent caustic. PFA-lined ball valves give quarter-turn shutoff where a body cavity is acceptable, lined diaphragm valves serve hypochlorite and coagulant dosing, lined butterfly valves cover the large caustic and water headers, lined check valves protect dosing pumps and lined sampling valves draw spent caustic safely. The patterns and linings are on our lined valves page. Automated packages leave our shop with actuators, positioners and switches mounted and tested.
The spool package, vacuum and temperature
A refinery package from us is typically 1" through 8" PTFE-lined carbon steel built to the unit isometrics in lengths up to 20 ft with class 150 ANSI B16.5 rotating flanges, plus lined elbows, tees, reducers and laterals, PTFE spacers at the tie-ins, spectacle blinds at the battery limits for positive isolation during a turnaround, lined Y-strainers ahead of acid and caustic pumps, lined sight glasses on acid transfer lines and PTFE-bellows expansion joints on long outdoor racks. Sizes, liners and housings are on our lined pipe and fittings page; the rest is under piping accessories.
Vacuum shows up in glycol purification, spent caustic degassing and solvent recovery, and PTFE liners are rated for vacuum by size and temperature, so tell us the vacuum level and we will confirm the rating; liner temperature limits, liner thicknesses, flange dimensions and torque tables are on our technical details page. On the cold side, 50 percent caustic crystallizes near 54 °F (12 °C), fresh 98 percent sulfuric acid freezes near 32 °F (0 °C) (stronger acid higher), and glacial acetic acid solidifies at 62 °F (17 °C), so outdoor caustic, fresh acid and acetyl lines get clamp-on steam heaters or electric tracing with heat-transfer compound from our temperature maintenance line, sized to keep the liner inside its limit. Acrylic acid lines are the exception: overheating can set off runaway polymerization, so they take tempered water at 95 °F (35 °C) or less or temperature-limited electric tracing holding 59 to 77 °F (15 to 25 °C), never steam. For jacketed or traced service, we recommend specifying PTFE.
Where the industry is, and how to order
American refining is concentrated on the Gulf Coast: the Houston Ship Channel, the Golden Triangle of Beaumont and Port Arthur, Corpus Christi, the Baton Rouge corridor and Lake Charles, and Pascagoula on the Mississippi coast. California, the third-largest refining state, the Delaware River below Philadelphia, the Whiting refinery and its Chicago-area neighbors, Ohio and the Mid-Continent, the Puget Sound refineries, Montana and Minnesota fill out the map, and the crackers and derivative units cluster beside the Gulf Coast refineries. Many of the same sites run chlor-alkali units and water and wastewater plants.
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 is spark tested at a minimum of 10,000 volts before it ships. Send the isometrics, the line list or the valve schedule, call (251) 625-4949 or contact us online. Custom spools leave Fairhope, Alabama, for plants nationwide.
FAQ: Lined Pipe for Refineries and Petrochemical Plants
Can lined pipe handle fresh 98 percent alkylation acid as well as spent acid?
PTFE handles sulfuric acid across the concentration range at ambient temperature, so one liner covers fresh, spent and intermediate strengths. Many plants leave concentrated fresh acid in carbon steel and line the spent acid, emulsion and regeneration lines, where dilution and heat make steel fail. Send us the temperatures and we will confirm the liner.
What do you recommend for spent caustic from a cracker or a caustic treating unit?
PTFE. Spent caustic carries dissolved benzene and other aromatics along with sulfides, and aromatics swell polypropylene. We quote PTFE for fresh dilute caustic as well; polypropylene is available for it where a specification calls for it, and in a finished spool the liner is a small part of the cost.
Is PVDF suitable for the oleum and sulfur trioxide lines in a sulfonation unit?
No. PVDF is attacked by fuming sulfuric acid and by hot concentrated sulfuric acid. We quote PTFE-lined spools and PFA-lined cylindrical plug valves for oleum and absorber loops, and PVDF only on the dilute acid and neutralized product side.
Can you support a refinery turnaround with spools built to our isometrics?
Yes. Custom spools to field dimensions are most of what we build, and lined pipe to ASTM F1545 with ANSI B16.5 flanges bolts up to whatever lined system is already in the unit. Call (251) 625-4949 early in the planning and we will tell you where the package fits on the schedule.