What Are Ultra High Purity Fittings
Ultra high purity fittings are components designed for gas and chemical delivery systems where even a few particles per billion can ruin a production batch. They are used in semiconductor manufacturing, LED production, solar panel fabrication, pharmaceutical bulk drug manufacturing, and any process where contamination must be below measurable limits.
The key differences from standard sanitary fittings: lower sulfur content in the stainless steel (≤ 0.005% sulfur), stricter surface finish (Ra ≤ 0.25 μm instead of Ra 0.8 μm), tighter dimensional tolerances, and clean packaging that prevents contamination before installation.
We manufacture UHP fittings in 316L high-purity stainless steel at our Wenzhou facility. Sizes from 6 mm to 154 mm OD. Compliance with ASME, 3A, and SEMI standards.
UHP Fitting Types
Ultra High Purity Elbows. 90° and 45° bends with electro-polished inner surfaces. The inner wall is smooth to reduce particle deposition and turbulent flow that could dislodge particles downstream. We radius the bend to keep pressure drop low — standard is long radius (R = 1.5D).
Ultra High Purity Reducers. Concentric reducers with a streamlined transition. The inner surface transitions gradually between diameters to avoid creating dead zones where particles could accumulate. Standard surface finish Ra ≤ 0.25 μm.
Ultra High Pressure Fixtures. Used to support and position critical connection points in UHP systems. Common at high-pressure joints, diaphragm valve interfaces, and connection segments of key process tools.
VCR Fittings for UHP Systems
VCR fittings are metal gasket face seal fittings designed for ultra-high purity and vacuum systems. They use a thin metal gasket that is compressed between two precision-machined beads to form a gas-tight metal-on-metal seal.
Standard VCR. Made from 304 or 316 stainless steel. Standard industrial finish. For general high-purity applications.
UHP VCR. Made from 316L VAR (Vacuum Arc Remelt) stainless steel with electropolishing. Meets SEMI standards for semiconductor use. Helium leak rate ≤ 1×10⁻⁹ atm·cc/sec.
High-Flow (H-Type) VCR. Designed for higher flow rates. Provides the capacity of a 3/8″ system within a 1/4″ VCR footprint. Common in bulk gas delivery systems.
Key Specifications for UHP Fittings
| Parameter | Standard | UHP |
|---|---|---|
| Material | 304/316L | 316L VAR (sulfur ≤ 0.005%) |
| Surface finish | Ra ≤ 0.8 μm | Ra ≤ 0.25 μm |
| Leak rate | 1×10⁻⁷ atm·cc/sec | ≤ 1×10⁻⁹ atm·cc/sec |
| Temperature range | -30°C to 200°C | -196°C to 300°C |
| Packaging | Standard | Double-bagged, clean room |
Surface Finish and Cleanliness
The surface finish is the most critical spec for UHP fittings. We measure it with a profilometer at three points on each fitting. For semiconductor applications, we use electropolishing to reach Ra ≤ 0.25 μm. At this finish, the surface is smooth enough that particles do not adhere — they pass through with the gas flow rather than accumulating and later releasing as a burst of contamination.
After electropolishing, we clean each fitting in a multi-stage process: deionized water rinse, ultrasonic cleaning, hot DI rinse, and clean-room drying. Each fitting is then double-bagged in certified clean packaging with a desiccant sachet.
Common Selection Mistakes
1. Using standard fittings in a UHP line. Standard fittings have higher surface roughness and higher sulfur content. The surface roughness traps particles, and the sulfur content causes outgassing that contaminates the gas stream.
2. Over-tightening VCR nuts. VCR nuts are silver-plated internally to prevent galling. Over-tightening deforms the gasket past its elastic limit and causes the joint to leak at the next thermal cycle. Torque to spec: 1/4″ VCR at 18 Nm, 1/2″ at 35 Nm.
3. Mixing VCR seal types. A standard VCR gasket and a UHP VCR gasket are not interchangeable. They have different hardness levels and surface finishes. Match the gasket to the fitting grade.
FAQs
Q: What is the difference between UHP fittings and sanitary fittings?
A: UHP fittings have stricter material purity (low sulfur 316L), smoother surface finish (Ra ≤ 0.25 μm vs Ra 0.8 μm), tighter tolerances, and clean packaging. Sanitary fittings are designed for hygienic processing (food, pharma, dairy) where cleanability is the priority. UHP fittings are designed for gas purity.
Q: Can I use VCR fittings for liquid?
A: VCR fittings are designed for gas and vacuum service. For liquid UHP service, use welded or orbit-welded connections to avoid the dead space in the VCR gasket cavity.
Q: What is the leak rate guarantee on your UHP fittings?
A: ≤ 1×10⁻⁹ atm·cc/sec for helium at rated pressure. We provide a test certificate with each batch.
Q: Do you supply orbital welding data for your UHP fittings?
A: Yes. We provide recommended weld schedules for common tube sizes and wall thicknesses. We also offer weld samples for process validation.
Q: How long does a VCR gasket last?
A: A VCR gasket is single-use by design — once compressed, it stays compressed. Replace the gasket each time you break and remake the joint. The nut and gland body last for hundreds of cycles.
Technical Review
Chen Li, Quality Manager — responsible for UHP and VCR product quality and clean-room packaging at OMSS.
onemo@onemoss.com
