Threaded Static Mixer

Product Overview

The threaded static mixer is the smallest and most economical structural variant in the ywmixing range. It is built as a one-piece housing with male tapered (NPT) or parallel (BSP) threads machined directly on each end. The internal mixing element is permanently fixed inside the housing — there is no removable cartridge — which is the reason this variant is restricted to small-bore DN15 to DN50 service where fouling is not expected and the unit is treated as a consumable fitting.

Threaded mixers are the workhorse of chemical-injection skids. On a typical 2 m × 1 m metering skid, you will find eight to twelve threaded mixers handling the dilution of polymers, scale inhibitors, biocides, and oxygen scavengers. They are quick to install, require no special tools, and the spare cost is small enough that the operator simply replaces the entire unit if the elements foul. The unit price is typically 30-50% of the equivalent flanged mixer, which is why the threaded version dominates in skid-mounted OEM applications.

The standard pressure rating is PN40 (40 bar at 120°C) for SS316L housings and PN25 (25 bar) for carbon steel. The temperature envelope spans -20°C to +200°C, with PTFE-jacketed EPDM seals used for the threaded interface. Above 200°C, the thread joint loses its sealant capability and the connection should be flanged or welded. Above DN50, the wall thickness required to maintain a pressure-tight thread becomes impractical, so the customer is moved to the flanged platform.

Design Features

The threaded housing is machined from solid bar stock or thick-walled pipe. For SS316L units, the body is a single CNC-turned piece, with the threaded ends, hex flats for wrench engagement, internal bore, and shoulder stops for the mixing element all machined in one setup. This construction gives a homogeneous grain structure and avoids the weld HAZ that would otherwise exist in a fabricated housing. For carbon steel units, the body is hot-forged and machined; for PVC/PP, it is injection-molded with threaded sockets.

The mixing element is press-fit or pinned into the housing bore. For SV corrugated plate technology, the plate pack is captured between two machined shoulders and held in compression by a small disc-spring at the upstream end — this accommodates thermal expansion and prevents axial movement. For SK helical technology, the elements are twisted from flat bar and welded end-to-end to form a continuous helix, with the upstream end pinned to a shoulder and the downstream end free to slide.

Thread forms are produced to ASME B1.20.1 (NPT) or ISO 228 (BSP) as standard, with crest and root profiles inspected with a ring/plug gauge set. The hex flats are dimensioned per ASME B16.11 for the corresponding class, so the unit can be installed with a standard pipe wrench. A witness mark is laser-etched on each hex flat indicating the recommended installation torque and the thread standard, so the fitter does not have to consult a manual.

For OEM skid builders, we offer a custom thread service. Send a sample fitting or print, and we will replicate the thread form on the mixer housing. This is common with European skid builders who use JIS B0203 PT threads on their internal piping, and with Chinese OEMs who use the GB/T 7306 55° tapered thread. There is no engineering charge for custom threads above DN25.

Technical Specifications

Parameter	Value
Connection Standard	NPT (ANSI B1.20.1), BSP (ISO 228), JIS B0203 PT, GB/T 7306
Pipe Diameter Range	DN15 (1/2") to DN50 (2") — special to DN80
Pressure Rating	PN40 (SS316L) / PN25 (carbon steel) / PN10 (PVC/PP)
Temperature Range	-20°C to +200°C (metallic) / -10°C to +60°C (PVC/PP)
Housing Material	SS316L (default), SS304, Carbon Steel, PVC, PP, PVDF
Mixing Element	SK helical (default) or SV plate — fixed in housing
Element Count	4 to 8 elements (DN15 = 4, DN50 = 8)
Hex Flat Dimension	Per ASME B16.11 Class 2000/3000
Sealant	PTFE tape (default), anaerobic resin, or PTFE O-ring
Installation Torque	DN15 = 25 Nm / DN25 = 60 Nm / DN50 = 130 Nm
Length-to-Diameter (L/D)	5 to 12 (geometry dependent)
Weight (DN25 SS316L)	0.8 to 1.5 kg depending on element count

Connection Options

NPT (National Pipe Taper) is the most common thread form for North American process plants. The 1:16 taper provides the seal — no gasket is required, only thread sealant. We taper-tap the male thread to a precision matched to the customer-supplied female fitting. Standard NPT sizes stocked are 1/2", 3/4", 1", 1-1/2", and 2", corresponding to DN15 to DN50.

BSP (British Standard Pipe) is the standard in Europe, Asia (except Japan), and most of the Middle East. BSP comes in two variants: BSPT (tapered, ISO 7) and BSPP (parallel, ISO 228). For pressure-tight service we use BSPT. For BSPP we add an O-ring or bonded seal to achieve the seal. The default thread is right-hand; left-hand threads for trace chemical service (e.g., oxygen lines) are available on request.

JIS B0203 PT threads are used in Japanese skid packages. The thread angle is 55° (compared to 60° for NPT) and the taper is the same 1:16. We stock JIS-threaded mixers for OEM export to Japan, and the witness mark indicates the JIS standard for the fitter.

For OEM customers with non-standard threads (e.g., autoclave, marine, or special-process fittings), we offer a custom thread service. The customer supplies a thread gauge or a sample fitting, and we replicate the thread on the mixer housing. There is no engineering charge for threads above DN25; for DN15 with a non-standard pitch, a small setup fee applies.

Applications

Chemical injection skids. Threaded mixers are the default in metering skids for oilfield chemicals — scale inhibitors, corrosion inhibitors, biocides, demulsifiers, and paraffin dispersants. A typical 8-pump skid carries 6-10 threaded mixers, each handling one chemical dilution stage. The compact length (typically 150-300 mm) fits the limited envelope of a wall-mounted skid.

Instrument-air systems. Pneumatic control loops require clean, oil-free, dry air. Threaded SK mixers are used to blend desiccant-regeneration air with the main supply and to mix trace amounts of instrument-air additives. The PN40 rating covers the 8-10 bar instrument-air header pressure.

Water-treatment pilot plants. Pilot and laboratory units use threaded mixers because they can be swapped between experiments in minutes. The 1/2" and 3/4" NPT sizes match the flexible tubing and compression fittings used in pilot rigs.

Cooling-water chemical dosing. Closed-loop cooling systems dose biocides, scale inhibitors, and corrosion inhibitors into the recirculating water. Threaded mixers handle the chemical blend in the side-stream injection line. The 1" NPT size is the most common, processing 1-5 m³/h of dosed water.

Laboratory and R&D. Bench-scale mixers in chemistry labs use threaded connections because they are easy to clean, easy to swap, and the small size matches the typical 0.5-2 L/min flow rates of lab experiments. SS316L threaded mixers down to DN8 (1/4") are available for analytical applications.

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