316Ti Seamless Capillary Tubing: Material Properties, Manufacturing Tolerances, and Application Guide

When specifying stainless steel capillary tubing for applications that demand resistance to intergranular corrosion at elevated temperatures—such as heat exchangers, thermowells, or sensor probes in chemical processing—engineers often find that standard 316L lacks the necessary stability after welding or prolonged exposure in the 500–800 °C range. The keyword 316Ti seamless capillary tubing addresses this exact gap: a stabilized austenitic grade with titanium addition that prevents chromium carbide precipitation, maintaining corrosion resistance and mechanical integrity in service conditions where standard 316L would sensitize.

Applicable Scenarios and Industries

316Ti seamless capillary tubing is specified where the component experiences intermittent or continuous temperatures between 425 °C and 850 °C, or where post-weld heat treatment is impractical. Typical applications include:

• Thermocouple sheaths and temperature sensor probes in furnaces, kilns, and exhaust systems
• Heat exchanger tubing in chemical plants handling corrosive fluids at elevated temperatures
• Instrumentation lines for pressure and flow measurement in high-temperature environments
• Pharmaceutical and bioprocess equipment requiring cleanability and resistance to sensitization during steam-in-place (SIP) cycles
• Oil and gas downhole tools where H₂S resistance is required (subject to NACE MR0175/ISO 15156 verification per project)

Industries commonly sourcing this product include chemical processing, petrochemical, pharmaceutical, power generation (especially geothermal and solar thermal), and aerospace fluid systems.

Material Grade and Designation

316Ti is an austenitic stainless steel stabilized with titanium. The titanium content (typically five times the carbon content minimum) ties up carbon as titanium carbides, preventing chromium depletion at grain boundaries during heating. Relevant standards and designations include:

• UNS S31635
• EN 1.4571 (X6CrNiMoTi17-12-2)
• ASTM A213 / A269 (seamless tubing)
• ASTM A1016 (general requirements for ferritic, austenitic, and martensitic alloy steel tubing)

Key chemical composition ranges per ASTM A213 (weight %):

Mechanical properties (typical for annealed condition per ASTM A213): tensile strength ≥ 515 MPa (75 ksi), yield strength ≥ 205 MPa (30 ksi), elongation ≥ 35%.

OD / ID / Wall Thickness / Length Considerations

Capillary tubing is defined by small outside diameters, typically ≤ 6.35 mm (0.250 in). For 316Ti seamless capillary tubing, common dimensions include:

• Outside diameter: 0.50 mm to 6.35 mm (0.020 in to 0.250 in)
• Wall thickness: 0.10 mm to 1.65 mm (0.004 in to 0.065 in)
• Inside diameter: calculated as OD minus 2× wall; ID tolerances are derived from OD and wall tolerances unless otherwise specified
• Length: random mill lengths (typically 1–6 m) or cut-to-length per drawing; straightness tolerance depends on length and diameter

For applications requiring precise ID control—such as capillary flow restrictors or chromatography columns—the wall thickness tolerance becomes critical because ID is not directly measured. In such cases, specify the ID tolerance directly and indicate the measurement method (air gauge or pin gauge).

Tolerances (Typical Ranges for Capillary Tube)

Tolerances for 316Ti seamless capillary tubing are governed by ASTM A269 (general service) or ASTM A213 (boiler and superheater tubes). Typical values for capillary sizes:

For tighter tolerances—such as ±0.025 mm on OD or ±5% on wall—these are achievable through cold drawing and centerless grinding but must be agreed upon with the supplier and may affect lead time and cost.

End Condition and Burr Control

Capillary tubing is often used in compression fittings, ferrule connections, or welded joints. End conditions must be specified:

• Square cut: ends cut perpendicular to the tube axis, deburred inside and outside
• Deburred: removal of sharp edges to prevent particle generation or seal damage
• Chamfered: for easier insertion into fittings or for welding preparation
• Burr height: typically ≤ 0.10 mm (0.004 in) for capillary sizes; for critical applications (e.g., chromatography), burr-free ends may be required

Burr control is especially important in 316Ti because the titanium content can make the material slightly more abrasive during cutting, potentially leaving larger burrs if tooling is not optimized.

Surface Finish and Cleanliness Requirements

Surface finish for 316Ti seamless capillary tubing depends on the application:

• As-drawn (mill finish): typical Ra 0.8–1.6 µm (32–63 µin), suitable for general industrial use
• Bright annealed: smoother finish (Ra ≤ 0.6 µm / 24 µin), with a clean, oxide-free surface
• Electropolished: Ra ≤ 0.4 µm (16 µin) for pharmaceutical or high-purity applications; note that electropolishing may slightly enlarge the ID
• Cleanliness: for oxygen service, semiconductor, or pharmaceutical use, specify degreasing to a cleanliness level such as ASTM G93 Level C or equivalent

Note: 316Ti is not inherently “medical grade.” If the tubing is intended for implantable devices, the buyer must specify and verify applicable standards (e.g., ASTM F138 for implantable stainless steel) and biocompatibility testing per ISO 10993.

Inspection Documentation

Standard documentation for 316Ti seamless capillary tubing typically includes:

• Material test report (MTR / EN 10204 3.1) showing heat number, chemical composition, and mechanical properties
• Dimensional inspection report (OD, wall, length, straightness) per agreed sampling plan
• Surface finish measurement report (if specified)
• Cleanliness verification report (if specified)

Additional documentation (e.g., positive material identification (PMI) report, hydrostatic test report, NACE MR0175 compliance certificate) can be requested but must be confirmed with the supplier during quotation.

Packaging Considerations

Because capillary tubing is delicate and easily kinked, packaging must prevent bending, scratching, and contamination:

• Coiled or straight lengths: straight lengths are typically bundled and wrapped in protective paper or plastic, then boxed or crated
• For small quantities: individual tubes may be bagged with desiccant and placed in foam-lined boxes
• For export: vacuum-sealed with rust-preventive coating (if required) and packed in wooden crates
• Marking: each bundle or box should carry a tag with material grade, heat number, dimensions, and quantity

RFQ Information Checklist

To ensure accurate quotation for 316Ti seamless capillary tubing, provide the following in your request:

• Material grade: 316Ti (UNS S31635 / EN 1.4571)
• Applicable standard: ASTM A269, ASTM A213, or other
• Outside diameter and tolerance
• Wall thickness and tolerance (or ID and tolerance)
• Length: random or cut-to-length (specify exact length and tolerance)
• Quantity: total meters or pieces
• End condition: square cut, deburred, chamfered
• Surface finish: as-drawn, bright annealed, or electropolished (specify Ra value)
• Cleanliness requirement: degreased, oxygen service, or other
• Inspection documentation required: MTR, dimensional report, PMI, etc.
• Any special testing: hydrostatic, eddy current, ultrasonic, or NACE compliance
• Delivery location and desired lead time

To request a quotation for 316Ti seamless capillary tubing, 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.