PTFE-Lined Static Mixer

Product Overview

The ywmixing PTFE-lined static mixer is a heavy-duty industrial mixer built around a carbon-steel (or 316L stainless) pressure shell that is internally lined with a 3-5 mm virgin-PTFE tube. All wetted parts — the liner, the mixing elements, and the gaskets — are PTFE or PTFE-derivative, so the process fluid never contacts the steel. This construction gives the operator the mechanical strength and pressure rating of a steel pipe (PN10, PN16, or PN25) combined with the near-universal chemical resistance of PTFE.

The mixer is the workhorse of aggressive-chemistry service in chlor-alkali plants, sulfuric and nitric acid facilities, herbicide and pharmaceutical manufacture, and bromine handling. Where all-PTFE mixers are too expensive at large diameter, and all-PVC or all-PP mixers are limited in temperature and pressure, the PTFE-lined design offers the optimal balance: 200°C continuous service, full vacuum capability, and a pressure rating equal to the equivalent steel pipe. The trade-off is that PTFE is a poor heat conductor, so the mixer is not suitable for service that requires heat transfer across the wall.

Internally, the PTFE-lined mixer uses a left-right helical element set of solid PTFE, in 4 to 8 elements depending on the required coefficient of variation. Element twist is selectable at 180° (default) or 270° (for higher-viscosity media up to 5,000 cP). Element rod diameter is typically 0.10-0.15 × DN, and the L/D ratio of the housing is 6-12 depending on the target σX. End connections are PTFE-lined flanges (ANSI B16.5 Class 150, DIN PN16, or JIS 10K) with PTFE envelope gaskets.

Material Properties

Polytetrafluoroethylene (PTFE) is the benchmark corrosion-resistant polymer. Its chemical resistance is essentially universal: it is unaffected by all mineral acids (HCl, H₂SO₄, HNO₃, H₃PO₄, HF) at any concentration and at all temperatures below 200°C, by all organic solvents (with the limited exceptions of molten alkali metals, elemental fluorine, and some fluorinated solvents at extreme conditions), by all halogens, and by strong oxidizers including aqua regia, concentrated hydrogen peroxide, and ozone. PTFE's only real chemical weakness is alkali metals (sodium, potassium) and certain fluorinated compounds at high temperature.

The mechanical properties of PTFE are modest: tensile strength 20-35 MPa, elongation at break 200-400%, density 2.15-2.20 g/cm³. PTFE has no real melt point — it transitions from solid to a gel-like state above 327°C, and continuous service temperature is limited to 200°C (260°C short-term for filled grades). The thermal expansion coefficient is high (100-130 × 10⁻⁶ /°C), so the liner must be designed to accommodate differential expansion against the steel shell — typically a 2-3 mm radial gap, vented to atmosphere.

For higher-pressure and higher-temperature service, the PTFE can be replaced by PFA (perfluoroalkoxy), which has the same chemical resistance as PTFE but with a true melt point of 305°C and improved mechanical strength (PFA can be used up to 260°C continuous). FEP (fluorinated ethylene propylene) is selected for very low temperatures down to -200°C. For service that sees mechanical wear (slurries with sharp particles), modified PTFE with carbon or graphite filler is available; the filler improves wear resistance and reduces creep but slightly reduces chemical resistance.

The pressure shell — the steel component that never contacts the process — is typically SA-516 Gr.70 carbon steel for cost, or 316L stainless for elevated temperature (above 150°C) or for offshore / marine installations. The shell is hydrostatically tested to 1.5× the design pressure before the liner is installed, and a final pressure test of the complete assembly is performed after liner installation. The 4:1 design safety factor on PTFE creep at the rated temperature is built into the standard wall-thickness calculation.

Construction Design

The PTFE-lined mixer is built in three concentric layers. The outermost is the pressure shell — a carbon-steel or stainless-steel pipe spool with welded or flanged end connections, designed to ASME B31.3 or the equivalent regional pressure-piping code. Inside the shell sits the PTFE liner, a 3-5 mm thick tube manufactured from virgin or modified PTFE sheet that is welded (PFA/PVDF liner) or isostatic-molded (PTFE liner) into a seamless cylindrical form. Between the shell and the liner is a vented annular gap of 2-3 mm.

The vented gap is the safety feature that distinguishes a properly designed PTFE-lined mixer from a generic rubber-lined pipe. Each end of the mixer carries a small tell-tale port — typically a 1/2" NPT plugged connection — that is piped to a local sight glass or to the plant's continuous emissions monitoring system. If the PTFE liner ever develops a pinhole leak, process fluid enters the vented gap and is detected at the tell-tale before it can attack the steel shell. This early warning prevents the catastrophic shell-wall corrosion that has caused several serious incidents in lined-piping service.

Internal elements are solid PTFE rods, twisted 180° left and right in alternating pairs and locked into PTFE element holders that are welded or mechanically fastened to the liner at each end of the housing. The number of elements is selected from a chart that relates target σX, viscosity, and L/D ratio; standard offerings are 4, 6, or 8 elements. Element-to-liner attachment uses PTFE hot-gas welding, which produces a leak-tight, chemically resistant joint. Element-to-liner mechanical locking is used as a secondary retention in higher-pressure PN25 mixers.

End connections are PTFE-lined steel flanges with PTFE envelope gaskets (asbestos-free). The envelope gasket consists of a PTFE outer envelope with a non-asbestos fiber filler; the filler provides the mechanical seating force while the PTFE protects the filler from process attack. For services above 150°C, a flexible graphite filler is substituted. Bolting is 316L stainless with PTFE washers to prevent galling.

Technical Specifications

Parameter	Value
Liner Material	Virgin PTFE (standard), Modified PTFE, PFA, FEP
Liner Thickness	3.0 mm (DN25-50) / 4.0 mm (DN65-150) / 5.0 mm (DN200-500)
Shell Material	SA-516 Gr.70 carbon steel (standard), 316L stainless (high-temp/marine)
Element Material	Solid PTFE (standard), PFA, or modified PTFE
Internal Structure	180° / 270° left-right helical twist elements (4-8 elements)
Operating Temperature	-30°C to +200°C (PTFE) / -200°C to +200°C (FEP option) / -30°C to +260°C (PFA option)
Design Pressure	PN10 / PN16 (standard) / PN25 (DN25-150 option)
Vacuum Service	Full vacuum with vacuum breaker and stainless support ring
Connection Types	PTFE-lined flange (ANSI 150, DIN PN16, JIS 10K)
Pipe Diameter Range	DN25 to DN500
Flow Rate Range	0.5 to 1,200 m³/h
Viscosity Range	≤ 5,000 cP (PTFE) / ≤ 1,000 cP (PTFE with 270° elements)
Gasket Material	PTFE envelope with aramid or graphite filler
Safety Features	Vented annular gap with tell-tale port for leak detection

Applications

Chlor-alkali plants. PTFE-lined mixers are used for the dilution of 32% and 50% caustic soda, for hydrochloric acid absorption tail-gas scrubbing, and for the in-line neutralization of chlorine bleach with sodium hydroxide. The PTFE liner is one of the few materials that tolerates wet chlorine gas at 80-90°C without degradation, and it is the standard liner for the chlorine scrubber feed and discharge piping in chlor-alkali plants worldwide.

Sulfuric and nitric acid manufacture. 98% H₂SO₄ at 150°C and 60% HNO₃ at 120°C both require PTFE-lined equipment. The PTFE-lined mixer is used for acid dilution (98% → 78%, 78% → 50%), for SO₂ absorption in oleum plants, and for the acid-side feed of the nitric acid absorption tower. PFA liner is preferred for service above 180°C because of its higher mechanical strength at temperature.

Pharmaceutical API manufacture. Multi-product API plants use PTFE-lined mixers in the reagent-feed and product-collection headers because PTFE is the only material that can be cleaned with all standard cleaning agents (dilute acids, dilute bases, organic solvents, hot water, steam) without degradation. The mixer is typically specified with sanitary tri-clamp end connections for cleanability.

Bromine and bromine-compound production. Liquid bromine and bromine vapor are handled in PTFE-lined equipment because bromine attacks most elastomers and many metals. The PTFE-lined mixer is used for bromine absorption in NaBr/Br₂ scrubbing towers and for the in-line neutralization of residual bromine with sodium hydroxide or sodium sulfite before the effluent is discharged.

Herbicide and pesticide manufacture. Many herbicides (glyphosate, 2,4-D, atrazine) involve aggressive intermediates including chloroacetic acid, dimethyl sulfate, and various phosphorus chlorides. The PTFE-lined mixer is used at the reagent-addition points because it tolerates all of these compounds plus the sulfuric and hydrochloric acid catalysts used in the reaction.

Electronics and semiconductor wet-etching. Semiconductor fabs use PTFE-lined mixers for the in-line blending of HF/HNO₃/H₂O etchant baths and for the dilution of concentrated HF for BOE (buffered oxide etch) solutions. The PTFE liner is required because HF attacks glass, most metals, and many other plastics; only PTFE, PFA, and a few exotic alloys are compatible.

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