317L Small Diameter Tubing: Material Properties, Manufacturing Tolerances, and Application Guide

When engineering for high-corrosion environments such as chemical injection systems, pharmaceutical processing equipment, or offshore instrumentation, standard 316L stainless steel often falls short. Engineers and procurement specialists sourcing 317L small diameter tubing are typically solving for pitting resistance in chloride-rich media or for improved mechanical strength at elevated temperatures. This article provides a technical reference for selecting, specifying, and procuring 317L small diameter tubing based on material properties, manufacturing tolerances, and application-specific requirements.

Applicable Scenarios and Industries

317L small diameter tubing is specified where 316L’s resistance to localized corrosion is inadequate. Typical environments include:

• Chemical processing: handling sulfuric acid, hydrochloric acid, or chloride-bearing process streams
• Pharmaceutical and bioprocessing: high-purity fluid transfer where trace metal contamination must be minimized
• Oil and gas: downhole instrumentation lines and hydraulic control systems exposed to sour gas or seawater
• Marine and offshore: sensor housing capillaries and sampling lines in splash-zone or submerged conditions
• Pulp and paper: bleach plant components where chlorine dioxide is present

Material Grade and Designation

317L is a molybdenum-bearing austenitic stainless steel with a low carbon content (max 0.03%) to prevent sensitization during welding. The higher molybdenum content (3.0–4.0% by weight per ASTM A269 / A213) provides significantly improved pitting resistance compared to 316L (2.0–3.0% Mo). Key designations include:

• UNS S31703 (wrought form)
• ASTM A269 (small diameter seamless and welded tubing)
• ASTM A213 (seamless ferritic and austenitic tubing for boilers, superheaters, and heat exchangers)
• EN 1.4438 (European equivalent)

Compared to 304 or 321, 317L offers superior resistance to reducing acids and chloride stress corrosion cracking. For applications requiring even higher pitting resistance, 317LMN (UNS S31726) with added nitrogen may be considered, but 317L remains the standard for most small-diameter tubing needs.

OD / ID / Wall Thickness / Length Considerations

Small diameter tubing for capillary applications typically ranges from 0.5 mm (0.020″) to 6.0 mm (0.236″) outer diameter. Wall thickness selection depends on pressure requirements and machinability:

When specifying, note that ID tolerance becomes tighter as wall thickness decreases. For thin-wall capillary (<0.1 mm wall), expect that dimensional control depends on drawing, material condition, process route, and mutual agreement between parties.

Tolerances (Typical Ranges for Capillary Tube)

Tolerances for 317L small diameter tubing are typically defined per ASTM A269 or by customer drawing. Standard commercial tolerances for cold-drawn tubing include:

For capillary applications where concentricity (wall variation) is critical, specify ovality limits and runout requirements. Note that tightest tolerances may require multiple cold-drawing passes and intermediate annealing, increasing lead time and cost.

End Condition and Burr Control

End conditions are specified based on the assembly method (compression fitting, welding, or swaging). Common options include:

• Square cut: deburred on both ends, typical for general instrumentation
• Chamfered: for easier insertion into fittings
• Precision deburred: ID and OD burrs removed to prevent particle entrapment

Burr size limits (e.g., max 0.05 mm burr height) should be stated on the drawing. For medical device or pharmaceutical applications, specify that ends are free of loose particles and visible burrs under 10x magnification.

Surface Finish and Cleanliness Requirements

317L small diameter tubing can be supplied in various surface conditions:

• Bright annealed: smooth, oxide-free surface, typical for clean environments
• Pickled: matte finish with thin oxide layer removed
• Electropolished: Ra ≤ 0.4 µm achievable, reduces surface area for bacterial adhesion
• Mechanically polished: for cosmetic or sealing applications

Cleanliness level (e.g., degreased, ultrasonically cleaned, packaged in cleanroom) must be specified. For oxygen service or pharmaceutical use, declare residual oil and particulate limits per relevant standards.

Inspection Documentation

Standard documentation for 317L small diameter tubing includes:

• Material test report (MTR): per EN 10204 Type 3.1 or 3.2, showing heat analysis, mechanical properties, and chemical composition
• Dimensional inspection report: OD, ID, wall, length, and ovality measurements
• Surface finish report: Ra values if electropolished or polished
• Hydrostatic or pneumatic test certificate: if required by specification

Third-party inspection (e.g., by customer representative or accredited agency) can be arranged upon agreement.

Packaging Considerations

Packaging must protect the tube from mechanical damage, moisture, and contamination during transit. Common options:

• Individually sleeved or bundled with foam separators
• Heat-shrink sealed ends for cleanliness
• Desiccant and VCI (vapor corrosion inhibitor) for long-term storage
• Wooden crates or metal racks for large quantities

Specify packaging if the tubing will be used directly in cleanroom assembly without re-cleaning.

RFQ Information Checklist

To receive an accurate quotation for 317L small diameter tubing, provide the following:

• Material grade and applicable standard (e.g., UNS S31703 per ASTM A269)
• OD, ID, wall thickness, and length with tolerances
• End condition and burr requirements
• Surface finish and cleanliness specification
• Quantity (pieces or total length)
• Required inspection documentation
• Packaging and delivery requirements

To request a quotation for 317L small diameter 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.