Leading manufacturer of Stainless Steel 304 Welded Capillary Tubes in Mumbai, India
Stainless steel 304 welded capillary tubing sets the standard in micro-bore fluid control systems because they are designed specifically to operate under conditions of constant capillary flow, regardless of the effects of gravity. The manufacturing process uses high-precision longitudinal welding along with the innovative technique of multi-pass drawing.
Due to their smooth internal finish and precise bore consistency, 304 and 304L capillary tubes are critical components in sensitive measurement and fluid-conveyance assemblies including pressure transducers, sheath sheathing, Coriolis flow meters, hydraulic sensing units, and precision 1/16-inch flexible grips.
While small-scale capillary tubes are designed for micro-bore fluid channels, large-scale fluid networks often rely on standard industrial line sizes such as our ASTM A312 TP304 stainless steel pipes and tubes.
Manufacturing Process of Welded SS 304 Capillary Tubing
The production of high-precision 304 stainless steel welded capillary tubes starts with selecting certified, high-purity cold-rolled strip stock, slit to exact micro-dimensional widths.
For projects requiring specialised raw material specifications or primary coil sourcing, you can review our full inventory of 304 stainless steel plates and sheets..
The strip material is continuously formed into a tubular profile and longitudinally welded using automated TIG or laser welding under continuous argon shielding. The tube then undergoes cold sink drawing and floating plug die reductions. This essential cold working phase serves key functional purposes:
- Seamless Bead Integration: Eliminates the internal weld seam projection completely, creating a smooth, uniform inner wall profile.
- Strict Tolerance Control: Ensures outer and inner dimensions match exact design specs with wall variation kept within narrow limits.
- Enhanced Strength Profile: Work hardens the austenitic matrix to meet required temper specs ranging from soft annealed to hard drawn conditions.
Technical Data
Specifications for Stainless Steel 304 Welded Capillary Tubes
| Specification Parameter | Technical Detail / Standard |
|---|---|
Material Grade | Stainless Steel 304 (UNS S30400 / Werkstoff 1.4301) |
Low Carbon Variant | |
Production Standards | ASTM A269 welded bright annealed tubing, ASTM A632, DIN 17458 |
Outer Diameter (OD) | 0.30 mm to 5.00 mm (0.012 inch to 0.197 inch) |
Wall Thickness (WT) | 0.08 mm to 0.50 mm (0.003 inch to 0.020 inch) |
Temper Conditions | Bright Annealed (BA), Half Hard, Full Hard |
Surface Roughness | Internal bore Ra less than or equal to 0.40 micrometres |
Supply Formats | Straight cut lengths (0.1 metre to 6 metres), continuous micro coils |
Chemical Composition of UNS S304 Capillary Lines
| Chemical Element | Symbol | Minimum Weight (%) | Maximum Weight (%) |
|---|---|---|---|
Chromium | Cr | 18.00 | 20.00 |
Nickel | Ni | 8.00 | 10.50 |
Carbon | C | 0.00 | 0.08 |
Manganese | Mn | 0.00 | 2.00 |
Silicon | Si | 0.00 | 0.75 |
Phosphorus | P | 0.00 | 0.045 |
Sulphur | S | 0.00 | 0.030 |
Iron | Fe | 0.00 | Remainder |
Mechanical Properties of UNS S30400 Capillary Tubes
| Condition | Tensile Strength (MPa) | Yield Strength 0.2% (MPa) | Elongation (%) | Hardness Range |
|---|---|---|---|---|
Brightly Annealed | Minimum 515 | Minimum 205 | Minimum 35 | Maximum 90 HRB |
Half Hard | 750 to 950 | 550 to 750 | 10 to 20 | 25 to 32 HRC |
Full Hard | 900 to 1250 | 750 to 1050 | Maximum 8 | 32 to 40 HRC |
Dimensional Tolerances (ASTM A269 / ASTM A632)
| Outer Diameter Range (mm) | OD Tolerance (mm) | Wall Thickness Tolerance (%) | Cut Length Tolerance (mm) |
|---|---|---|---|
0.30 to 1.00 | +0.02 / -0.00 | +/- 10% | +/- 0.50 |
1.01 to 3.00 | +0.03 / -0.00 | +/- 10% | +/- 0.50 |
3.01 to 5.00 | +0.05 / -0.00 | +/- 7.5% | +/- 1.00 |
SS 304 Welded Capillary Tubes Working & Burst Pressure Ratings (Annealed Condition at 20°C)
| Nominal OD (mm) | Wall Thickness (mm) | Working Pressure (Bar) | Calculated Burst Pressure (Bar) |
|---|---|---|---|
1.00 | 0.15 | 360 | 1440 |
1.50 | 0.20 | 320 | 1280 |
2.00 | 0.25 | 300 | 1200 |
3.00 | 0.30 | 240 | 960 |
4.00 | 0.40 | 240 | 960 |
5.00 | 0.50 | 240 | 960 |
Industry Applications of Welded SS 304 Capillary Tubing
- HVAC and Refrigeration Systems: Used as precision restrictor coils, expansion loops, and thermostat sensing lines for the constancy of refrigerant flow and pressure drops.
- Analytical Instruments and HPLC: Necessary for the liquid chromatography columns, autosampler loops, and reagent lines where the ultra-smooth bore provides laminar flow and prevents contamination of samples.
- Industrial Sensors and Pressure Gauge: Serves as a high-pressure transmission lines for dial thermometers, remote diaphragm seals, Coriolis mass flow meters, and thermocouple sheaths.
- Medical and Precise Dispensing: Made into the micro-fluidic diagnosis nozzles, biopsy cannulas, and lab dosing tips which require burr-free cut ends and bio-passivated surfaces.
- Aerospace and Automotive: Used in high-pressure hydraulic sensing manifolds, fuel injection test loops, and compact fluid control lines where narrow spatial constraints put high demands on hoop strength.
Frequently Asked Questions
How is the internal weld seam eliminated in SS 304 welded capillary tubing?
Cold drawing over a floating plug die works the seam into the parent matrix. This creates a smooth inner surface without inner ridges.
What is the main advantage of welded capillary tubing over seamless tubing?
Welded capillary tubes provide consistent wall thickness and tighter concentricity at a lower cost, matching seamless performance after cold drawing.
Can stainless steel 304 capillary tubes be bent without bore collapse?
In the bright annealed condition, SS 304 capillary tubes offer excellent bend ductility. Proper bending tools prevent wall flattening or bore restriction during forming.
What cut length tolerances are achievable for micro capillary tubes?
Standard cut lengths are held within tight tolerances using precision wire EDM or electrochemical cutting to deliver clean, square ends without internal burrs.
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Related Products
304 family: SS 304 Seamless Capillary Tubes, SS 304L Pipes & Tubes, ASTM A312 TP304 Pipes & Tubes, SS 304 Plates & Sheets, ASTM A269 Welded Bright Annealed Tubing, SS 304 Coil Tubing
