Lined Pipe for Solvent Service

Most solvents do not corrode steel, and that is exactly why solvent piping gets specified wrong. The reasons to line a solvent header are product purity, the acid a wet chlorinated solvent makes, and the multipurpose line that carries solvent today and hydrochloric acid next week. Marspec Technical Products fabricates PTFE-, PVDF- and polypropylene-lined steel pipe for solvent service and supplies the lined valves, strainers and jacketing to go with it. Call (251) 625-4949 or contact us online with the solvent list.

Why a solvent line gets lined at all

Dry toluene, hexane or ethyl acetate will sit in carbon steel indefinitely. What they will not do is stay clean: rust and mill scale shed iron into the product, and in pharmaceutical and electronic work a few parts per million of iron is a rejected batch. Chlorinated solvents such as methylene chloride, chloroform, ethylene dichloride and perchloroethylene hydrolyze in the presence of water to hydrochloric acid, so a damp chlorinated line becomes an acid-chloride line that attacks carbon steel and pits stainless. Then there are the mixed streams: hydrogen chloride in methanol, hydrogen bromide in acetic acid, bromine in a chlorinated carrier. Stainless suits a clean, dedicated solvent line. A fluoropolymer liner is the answer when the line is not clean, not dedicated, or carries something the solvent is merely dissolving.

Matching the liner to the solvent

PTFE

PTFE is unaffected by essentially every industrial solvent: chlorinated and aromatic hydrocarbons, ketones, esters, ethers, amines, alcohols, glycols and the polar aprotic solvents such as DMF, DMSO and NMP, across its rating of -20 °F to 450 °F (-29 °C to 232 °C). It is our default for any solvent line that also sees acid, halogen or heat. The qualification is permeation. Small halogenated molecules pass slowly through PTFE at elevated temperature, and absorbed solvent can swell the liner slightly. Neither harms the liner. For hot halogenated service, send us the temperature.

PVDF

PVDF handles alcohols, glycols, aliphatic hydrocarbons and fuels, but its limit in some aromatic and chlorinated solvents is well below its 275 °F (135 °C) rating: about 175 °F (79 °C) in toluene and 125 °F (52 °C) in methylene chloride and chloroform. Send us the solvent and the temperature. Its weakness is polarity: ketones such as acetone, MEK and cyclohexanone, esters such as ethyl and butyl acetate, and the polar aprotic solvents DMF, DMAc, NMP and DMSO swell or dissolve it. Amines and bases above about pH 12 attack it too, and its resin maker does not recommend it in tetrahydrofuran. Let PTFE take the ketones and esters and the hot aromatic and chlorinated solvents; PVDF suits alcohols, glycols, aliphatic hydrocarbons and fuels.

Polypropylene

Polypropylene is available for alcohols, glycols and water-miscible solvents at moderate temperature, rated 0 °F to 225 °F (−18 °C to 107 °C), where a specification calls for it; PTFE is what we quote for those lines by default. It is not for aromatic or chlorinated hydrocarbons: published data rate toluene unsatisfactory even at room temperature and benzene and ethylene dichloride unsatisfactory above it, because the polymer absorbs the solvent and softens. If your specification names it for methanol, ethanol or glycols we will quote it; send us the conditions for anything else.

Permeation, static charge and vacuum

• Every spool and fitting housing has drilled vent holes as standard; they relieve permeant pressure between the liner and the housing to prevent liner collapse.
• Low-conductivity flammable solvents such as toluene, hexane and ethers accumulate static charge as they flow, and a plastic liner insulates the liquid from the grounded housing; a discharge can ignite the vapor or punch a pinhole through the liner. Follow NFPA 77: bond and ground every housing and flange, provide grounding paths across flanged joints, keep velocity moderate, use anti-static PFA-AS valves, and tell us if your specification calls for an anti-static liner.
• Solvent recovery stills and vacuum distillation put lines under vacuum every day, so mark those lines on the line list. Liner temperature limits, liner thicknesses, flange dimensions and torque tables are on our technical details page.
• The steel housing sets the thermal growth, as in any steel line, so jacketed lines get anchors and lined expansion joints, and joints are retorqued after the first hot cycle.

Valves, gaskets and accessories for solvent duty

Elastomers are the weak point: nitrile swells in ketones and aromatics, EPDM in hydrocarbons, and a swollen gasket leaks. Lined flanges seal liner to liner with no gasket, and where a lined flange meets a glass-lined nozzle we use a PTFE envelope gasket. The same thinking governs valves. PFA-lined ball valves with PTFE seats handle charging and transfer, PFA-lined cylindrical plug valves (1/2" through 2" full port and 3" through 6" reduced port, cavity-free, with no in-line adjustment) give tight shutoff with no cavity to hold a previous batch, PTFE-lined butterfly valves cover larger headers, and PFA-lined diaphragm valves meter solvent at dosing points. A diaphragm valve's PTFE face is backed by an elastomer, so tell us the solvent and we will confirm the backing. Lined check and sampling valves complete the set, with automated packages tested in-house. See our plastic-lined valves page.

Lined Y strainers catch catalyst fines ahead of pumps, sight glasses show phase separation, PTFE spectacle blinds isolate solvent tanks for hot work, and solid PTFE dip pipes and spargers serve the tanks. See our piping accessories page.

Tracing, glass-lined vessels and where solvents run

Several common solvents freeze in an unheated pipe rack: dimethyl sulfoxide at about 65 °F (18 °C), glacial acetic acid at 62 °F (17 °C), tert-butanol at 78 °F (26 °C), benzene at 42 °F (6 °C), cyclohexane at 44 °F (7 °C) and para-xylene at 56 °F (13 °C). 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: 15 psig steam at about 250 °F (121 °C) and 50 psig steam at nearly 300 °F (149 °C) are both inside its rating.

Solvent chemistry is also glass-lined chemistry. Borosilicate glass fused to a steel shell resists solvents and acids alike and cleans easily between products, which is why reactors, receivers and columns in solvent-based synthesis are glass-lined while the transfer lines and valves are PTFE and PFA. Glass is never used with hydrofluoric acid or fluorides and does not tolerate hot strong caustic, thermal shock or impact. We supply glass-lined pipe and equipment, including reglassing.

The plants that need all of this are pharmaceutical and biotech sites running solvent-based synthesis, semiconductor fabs with bulk solvent supply and solvent waste lines, refineries and petrochemical plants with aromatics extraction and solvent deasphalting, chlor-alkali and chemical complexes making chlorinated solvents and vinyls, and food and beverage plants extracting oils with hexane. Related streams are on our hydrochloric acid service and high-purity water service 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 Solvents

Can PVDF-lined pipe carry acetone or methyl ethyl ketone?

No. Ketones, esters and polar aprotic solvents such as DMF, NMP and DMSO swell or dissolve PVDF, which is the property that makes them casting solvents for PVDF film. Specify PTFE for ketone and ester service and for hot aromatic or chlorinated solvents; PVDF suits alcohols, glycols, aliphatic hydrocarbons and fuels.

Does a PTFE liner stop static charge in a flammable solvent line?

No liner does; a nonconductive liner actually isolates the liquid from the grounded housing. Bond and ground the steel housings and flanges per NFPA 77, provide grounding paths across each flanged joint, keep velocity moderate, use anti-static PFA-AS valves, and tell us if your specification calls for an anti-static liner.

Why does our methylene chloride line corrode when the solvent is supposed to be non-corrosive?

Chlorinated solvents hydrolyze to hydrochloric acid when water gets in, so a damp methylene chloride or ethylene dichloride line is really an acid-chloride line. PTFE-lined pipe handles both the solvent and the acid it makes.

Which steam pressure can I use to jacket a solvent line?

For jacketed or traced service, we recommend specifying PTFE. Low-pressure steam at about 15 psig, roughly 250 °F (121 °C), and 50 psig steam at nearly 300 °F (149 °C) are both inside the PTFE liner rating.