347H SS Capillary Tube: Material Properties, Manufacturing Tolerances, and Application Guide

When specifying capillary tubing for high-temperature environments that involve repeated thermal cycling, oxidation, or corrosive media, standard 304 or 316L grades may suffer from sensitization or reduced creep strength. The engineering challenge is to select a stainless steel grade that maintains structural integrity and corrosion resistance at elevated service temperatures. 347H SS capillary tube addresses this need through a stabilized, high-carbon austenitic composition that resists intergranular corrosion and offers improved high-temperature strength compared to non-stabilized grades.

Material Properties and Grade Designations

347H is a columbium (niobium)-stabilized austenitic stainless steel with a controlled carbon content of 0.04 to 0.10 %. The stabilization prevents chromium carbide precipitation at grain boundaries when the material is exposed to temperatures in the sensitization range (425–815 °C). The “H” designation indicates the higher carbon variant intended for elevated-temperature service.

Chemical Composition (Typical, per ASTM A213/A269)

Mechanical Properties (Annealed Condition, per ASTM A213)

• Tensile Strength, min: 515 MPa
• Yield Strength (0.2% offset), min: 205 MPa
• Elongation in 50 mm, min: 35%

These values apply to tube sizes typical for capillary applications; actual properties may vary with tube dimensions and heat treatment. The stabilized structure gives 347H superior creep and stress-rupture strength above 500 °C compared to 304H or 316H.

Applicable Scenarios and Industries

347H SS capillary tube is primarily specified for high-temperature and corrosive environments where repeated heating and cooling cycles occur. Typical applications include:

• Thermocouple sheaths and sensor probes in furnace systems
• Heat exchanger tubing in chemical and petrochemical processing
• Instrumentation lines in oil and gas downstream operations
• Aerospace fluid systems requiring oxidation resistance up to 800 °C
• Sample injection loops in high-temperature analytical equipment

The grade is not inherently “medical grade” and is not claimed here for implant or biocompatibility use. Engineers select 347H over 321 when higher creep strength or better resistance to polythionic acid stress corrosion cracking is needed.

OD / ID / Wall Thickness / Length Considerations

Capillary tube in 347H is typically manufactured in the following dimensional ranges (subject to drawing and process capability):

• Outer Diameter: 0.5 mm to 6.0 mm
• Wall Thickness: 0.1 mm to 1.0 mm
• Length: Straight lengths up to 6 m or coiled on spools

Custom dimensions for ID, OD, or wall thickness are produced to engineering drawings. Wall thickness below 0.1 mm may require specialized drawing and annealing cycles. Length tolerances are typically specified per customer requirements.

Tolerances

Tolerances for 347H SS capillary tube are governed by the applicable standard (ASTM A269 or A213) and customer drawing. Typical ranges for small-diameter tubing include:

For tighter tolerances, the achievable range depends on drawing specifications, material condition (annealed vs. cold-drawn), process route, and mutual agreement between parties.

End Condition and Burr Control

Capillary tubes require clean, burr-free ends to prevent flow obstruction, particle generation, or assembly issues. Standard end conditions for 347H capillary include:

• Square cut with edge deburring
• Chamfered ends (ID and/or OD)
• Laser-cut ends for minimal heat-affected zone and burr

Burr control is especially critical for tubes with wall thickness below 0.2 mm, where mechanical cutting can cause edge deformation. Specifying “deburred” or “burr-free” on the drawing is recommended.

Surface Finish and Cleanliness Requirements

Surface finish of 347H capillary tubes is typically specified as Ra ≤ 0.8 µm for both ID and OD, though smoother finishes (Ra ≤ 0.4 µm) are achievable depending on process route. For high-purity or clean-service applications, tubes can be supplied:

• Bright annealed (hydrogen atmosphere) for clean, oxide-free surface
• Electropolished ID for reduced surface roughness and enhanced cleanliness
• Degreased and packaged in a controlled environment

Cleanliness requirements (e.g., oil-free, particulate-free) should be stated on the inquiry. No specific cleanliness standard is assumed unless requested.

Inspection Documentation

The following documentation is typically available for 347H SS capillary tube, depending on the customer’s specification:

• Material Test Certificate per EN 10204 Type 3.1 (including heat number, chemical analysis, mechanical properties)
• Dimensional Inspection Report (OD, ID, wall, length measurements)
• Surface Finish Report (Ra values, visual inspection records)
• Third-Party Inspection (e.g., by customer representative or inspection agency)

All certifications are traceable to the specific heat and manufacturing lot. For critical applications, Type 3.2 certification can be arranged per the procurement specification.

Packaging Considerations

Capillary tubes are delicate and require protective packaging to prevent bending, scratching, or contamination during transit. Common packaging methods for 347H capillary include:

• Secure bundling with individual tube end caps
• Spool winding for long lengths (coiled tube)
• Moisture-proof wrapping (VCI paper or polybags) for export
• Custom labeling per customer requirements

Packaging should be verified with Healsmed during the quotation phase to match handling and storage conditions.

RFQ Information Checklist

To receive an accurate technical evaluation for 347H SS capillary tube, include the following in your inquiry:

• Material grade: 347H + applicable standard (ASTM A213/A269, EN 10216-5)
• OD / ID / wall thickness / length (with tolerances)
• End condition and burr requirement
• Surface finish (ID and OD) and cleanliness specification
• Quantity (meters or pieces)
• Inspection and certification requirements
• Packaging and delivery preferences

To request a quotation for 347H SS 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.