316Ti Welded Capillary Tube: Material Properties, Manufacturing Tolerances, and Application Guide

When designing medical devices, analytical instruments, or aerospace components that require corrosion resistance beyond standard 316L stainless steel, engineers often encounter a specific need: a welded capillary tube that can withstand higher temperatures and resist intergranular corrosion without sacrificing the tight tolerances expected of small-diameter tubing. This article addresses the material properties, manufacturing tolerances, and application considerations for 316Ti welded capillary tube, helping you evaluate whether this grade fits your design and procurement requirements.

Applicable Scenarios and Industries

316Ti welded capillary tube is selected where the welded joint must resist sensitization during welding or subsequent exposure to elevated temperatures (e.g., 425–850 °C). Typical applications include:

• Chemical injection lines in pharmaceutical processing
• Heat exchanger tubing in analytical instruments
• High-temperature sensor sheaths
• Hydraulic and pneumatic control lines in aerospace
• Medical device subassemblies where autoclave sterilization is required

The titanium stabilization reduces carbide precipitation at grain boundaries, making 316Ti a preferred choice over standard 316 or 316L when welding is unavoidable and post-weld heat treatment is not feasible.

Material Grades and Designations

316Ti (UNS S31635) is a titanium-stabilized austenitic stainless steel. Key designations include:

• UNS: S31635
• EN: 1.4571 (X6CrNiMoTi17-12-2)
• JIS: SUS 316Ti

Chemical composition (typical, per ASTM A240):

Mechanical properties (annealed condition, per ASTM A249 for welded tube):

• Tensile strength: ≥ 515 MPa (75 ksi)
• Yield strength (0.2% offset): ≥ 205 MPa (30 ksi)
• Elongation in 2 in.: ≥ 35%

Compared to 304 or 321, 316Ti offers improved pitting resistance due to molybdenum content, while the titanium addition provides stabilization similar to 321 but with better high-temperature creep resistance up to about 800 °C.

OD, ID, Wall Thickness, and Length Considerations

316Ti welded capillary tube is typically produced in the following dimensional ranges (though custom sizes depend on drawing and process route):

For capillary applications, the ID is critical. ID is typically calculated as OD minus 2 × wall thickness. When specifying, note that welded tubes often have a slight internal bead that may require post-weld sizing or mandrel drawing to achieve the required ID tolerance. For very small IDs (< 0.5 mm), drawn welded tube may be necessary to reduce the weld bead.

Tolerances (Typical Ranges for Capillary Tube)

Tolerances for 316Ti welded capillary tube depend on the manufacturing route (as-welded, drawn, or annealed) and mutual agreement between buyer and supplier. Common industry-accepted ranges for small-diameter welded tube:

These values are typical for drawn welded tube. For as-welded tube without drawing, tolerances may be wider. Always confirm with the supplier based on your specific drawing.

End Condition and Burr Control

End condition is critical for capillary tube used in fluidic connections, sensor insertion, or welding into assemblies. Common requirements:

• Square cut: Cut-off wheel or saw, with end perpendicularity within 0.5°
• Deburred ends: Internal and external burrs removed; typical burr height ≤ 0.05 mm (or per drawing)
• Chamfered ends: Optional, specified by angle and depth
• No internal flash: For welded tube, the weld bead is typically reduced via cold drawing or bead conditioning. If a completely smooth ID is required, specify “ID bead-free” or “drawn welded” tube.

Burr control is verified by visual inspection under magnification (10×–20×) or by profilometry when specified.

Surface Finish and Cleanliness Requirements

Surface finish for 316Ti welded capillary tube is typically specified by roughness average (Ra) or by process condition:

• As-welded / annealed: Ra ≤ 1.6 µm (63 µin) typical
• Drawn / polished: Ra ≤ 0.8 µm (32 µin) or finer
• Electropolished: Ra ≤ 0.4 µm (16 µin) achievable, depending on starting condition

Cleanliness requirements are application-dependent. For medical device or analytical applications, tubes may be:

• Cleaned to remove oils, lubricants, and particulate
• Packaged in clean-room conditions (e.g., Class 1000 or better)
• Supplied with capped ends to prevent contamination

No standard claim of “medical grade” or biocompatibility is made here; such claims require specific testing and certification per applicable regulatory standards (e.g., ISO 10993).

Inspection Documentation

Standard documentation for 316Ti welded capillary tube includes:

• Material test certificate (MTC) per EN 10204 Type 3.1 or 3.2, showing chemical analysis and mechanical properties
• Dimensional inspection report listing OD, ID, wall thickness, length, and straightness measurements
• Surface finish report (if specified)
• Hydrostatic or pneumatic test report (if required for pressure applications)
• Welding process qualification records (e.g., per ASME Section IX or equivalent)

Additional testing (e.g., eddy current, ultrasonic, intergranular corrosion test per ASTM A262 Practice E) can be requested but must be agreed upon at the RFQ stage.

Packaging Considerations

Proper packaging prevents damage, corrosion, and contamination during transit:

• Individual tubes: Wrapped in acid-free tissue or plastic film
• Bundles: Tied with non-abrasive straps, separated by foam or cardboard
• End caps: Plastic or silicone caps on both ends to prevent ingress of debris
• Outer packaging: Corrugated boxes or wooden crates, with desiccant if required
• Labeling: PO number, material grade, dimensions, quantity, and heat number

For clean-room applications, tubes may be double-bagged in anti-static polyethylene and sealed under nitrogen.

RFQ Information Checklist

To ensure accurate quotation and manufacturing, include the following in your request for 316Ti welded capillary tube:

• Material grade: 316Ti (UNS S31635) with reference standard (e.g., ASTM A249, ASTM A269, or EN 10217-7)
• Dimensions: OD, wall thickness, length, and tolerances
• Quantity: Number of pieces or total length (m or ft)
• End condition: Square cut, deburred, chamfered, or other
• Surface finish: Ra value or process (as-welded, drawn, polished, electropolished)
• Cleanliness: Standard clean, medical-device clean, or particulate-free
• Inspection requirements: MTC type, dimensional report, additional tests
• Packaging: Individual wrap, capped ends, clean-room bagging
• Delivery schedule: Required date and shipping terms

To request a quotation for 316Ti welded capillary tube, submit your drawings, material grade, quantity, tolerance, surface finish, and inspection requirements through the Healsmed website. The engineering team will review and respond with a technical evaluation.