317L Welded Capillary Tube: Material Properties, Manufacturing Tolerances, and Application Guide

When your medical device or analytical instrument design calls for a capillary tube that must resist pitting and crevice corrosion in chloride-containing environments, standard 316L may not be sufficient. 317L welded capillary tube offers a higher molybdenum content for enhanced corrosion resistance, making it the material of choice for applications where 316L is borderline. This article provides the technical information needed to evaluate 317L welded capillary tube for sourcing, design, and procurement decisions.

Applicable Scenarios and Industries

317L welded capillary tube is typically specified where the service environment includes chlorides, acidic media, or elevated temperatures up to approximately 800°F (427°C). Common applications include:

• Chemical injection lines and sampling ports in pharmaceutical processing
• Gas chromatography and analytical instrument columns
• Hydraulic and pneumatic control lines in marine or offshore equipment
• Heat exchanger tubing in corrosive environments
• Medical device components requiring long-term corrosion resistance in saline or bodily fluids

Industries that regularly specify 317L include chemical processing, oil and gas, pharmaceutical manufacturing, analytical instrumentation, and medical device OEMs.

Material Grade and Designation

317L is a low-carbon austenitic stainless steel with a nominal composition of:

Common designations include UNS S31703 (ASTM A240/A240M for plate, sheet, and strip) and ASTM A269 for welded tubing. The low carbon content (0.03% max) minimizes carbide precipitation during welding, preserving corrosion resistance in the heat-affected zone.

Compared to 316L (2–3% Mo), 317L provides approximately 30–40% higher pitting resistance equivalent number (PREN) due to the additional molybdenum. This translates to better resistance in chloride environments such as seawater, bleach, and certain acidic process streams.

OD / ID / Wall Thickness / Length Considerations

Capillary tube is generally defined by small outer diameters, typically 0.020 in. (0.508 mm) up to 0.250 in. (6.35 mm). Wall thickness can range from 0.005 in. (0.127 mm) to 0.065 in. (1.651 mm), depending on the application.

For 317L welded capillary tube, common dimensional combinations include:

Lengths are typically supplied in random mill lengths (12–20 ft / 3.6–6.1 m) or cut to specified lengths with a tolerance that depends on the drawing, material condition, process route, and mutual agreement between parties.

Tolerances

Tolerances for 317L welded capillary tube are typically governed by ASTM A269 or ASTM A1016/A1016M, with tighter controls possible per customer specification. Typical ranges include:

• OD tolerance: ±0.003 in. (0.076 mm) for OD ≤ 0.125 in.; ±0.005 in. (0.127 mm) for OD > 0.125 in.
• Wall tolerance: ±10% of nominal wall thickness for wall ≥ 0.020 in.; tighter tolerances depend on drawing, material condition, process route, and mutual agreement between parties.
• Length tolerance: ±0.125 in. (3.2 mm) for cut lengths under 12 in.; ±0.250 in. (6.4 mm) for longer pieces.
• Straightness: 0.010 in./ft (0.833 mm/m) maximum deviation, per ASTM A269 unless otherwise specified.

For precision applications such as analytical columns or fluidic manifolds, tighter tolerances can be negotiated with the supplier, but these are not standard and must be verified for each production lot.

End Condition and Burr Control

End condition is critical for capillary tube used in compression fittings, ferrule connections, or welded joints. Standard end conditions include:

• Square cut: Ends cut perpendicular to the tube axis with minimal burr.
• Deburred: Internal and external burrs removed to a specified maximum (e.g., 0.005 in. max burr height).
• Chamfered: Ends beveled for easier insertion into fittings.

Burr control is especially important for small ID tubes where a burr can obstruct flow or cause particle generation. The acceptable burr size depends on the application and is typically specified on the drawing.

Surface Finish and Cleanliness Requirements

Surface finish for 317L welded capillary tube is typically supplied in the as-welded, annealed, and pickled condition. Common finishes include:

• ID surface finish: Typically 32–64 Ra µin (0.8–1.6 Ra µm) as-welded and pickled. For cleaner applications, a bright annealed finish (16 Ra µin or better) may be specified, but this requires additional processing and must be confirmed with the supplier.
• OD surface finish: 32–64 Ra µin (0.8–1.6 Ra µm) in the annealed and pickled condition. Mechanical polishing can achieve 16 Ra µin or lower, but this is not standard.
• Cleanliness: Standard capillary tube is cleaned to remove oils and particulates. For medical or analytical applications, cleanliness levels such as ASTM G93 Level C or equivalent may be required. Verify with the supplier what cleaning and packaging protocols are available.

Inspection Documentation

When sourcing 317L welded capillary tube, typical inspection documentation includes:

• Material test report (MTR): Certified chemical analysis and mechanical properties per ASTM A269 or A240 (strip).
• Dimensional report: OD, ID, wall thickness, and length measurements per lot.
• Surface finish report: Ra values for ID and/or OD if specified.
• Hydrostatic test report: Per ASTM A269, each tube is tested at 1000 psi (6.9 MPa) or as agreed.
• Nondestructive examination (NDE): Eddy current or ultrasonic testing per ASTM E309 or E213, if required.

All documentation should be traceable to the specific heat number and production lot.

Packaging Considerations

Packaging for 317L welded capillary tube depends on the quantity, length, and application cleanliness requirements. Common packaging options include:

• Bundles: Tied and wrapped in polypropylene or kraft paper for standard industrial use.
• Spools or coils: For continuous lengths, wound on metal or plastic spools.
• Individual tubes in plastic sleeves: For cut lengths requiring protection from surface damage.
• Clean-room packaging: Double-bagged in clean polyethylene with desiccant, for medical or analytical applications.

Specify packaging requirements at the time of RFQ to avoid rework or contamination.

RFQ Information Checklist

To obtain an accurate quotation for 317L welded capillary tube, provide the following information:

• Material grade: 317L (UNS S31703) or other as required
• OD, ID, and wall thickness with tolerances
• Length and quantity
• End condition (square cut, deburred, chamfered)
• Surface finish requirements (ID and OD)
• Cleanliness level
• Inspection documentation required
• Packaging requirements
• Applicable standard (ASTM A269, customer specification, etc.)

To request a quotation for 317L 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.