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Fluid conduction · Instrumentation tubing

TECHNICAL DATA SHEET

FT-TC-TUB-TBG-001

Issue date: July 22, 2026 · Rev. 001

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SKU VT-tubing-inoxidable · seamless 316/316L stainless steel tubing, 1/8 in to 1 in OD · 6 m lengths · made to order

1. TECHNICAL SPECIFICATIONS

Stainless steel tubing is precision tube designated by exact outside diameter (OD) in inches and wall thickness in thousandths — not by NPS nominal size with schedule — and is connected with twin-ferrule compression fittings. It is supplied to ASTM A269/A269M-25 in grades 316/316L and 304, seamless, annealed, in 6 m lengths, 1/8 in to 1 in OD, for instrumentation, pneumatics, hydraulics and sampling lines.

General product data

Dimensional tolerances (ASTM A269/A269M-25, Table 4)

Reference mechanical properties of the grade (annealed)

ASTM A269 controls hardness and forming tests (flaring for seamless tube, flanging for welded); it does not publish a minimum tensile table. Reference tensile values for annealed TP316 come from ASTM A213/A213M-24.

Chemical composition (ASTM A269/A269M-25, Table 1), mass %

Dual-certified 316/316L material simultaneously meets the lower maximum carbon of the L grade and the mechanical properties of the non-L grade.

2. ENGINEERING CALCULATIONS

The allowable working pressure of each OD × wall combination is calculated with equation (3a) of paragraph 304.1.2 of ASME B31.3-2024 — the code form of the Barlow formula with the Y stress-redistribution correction:

P = 2 · S · E · t / (D − 2 · Y · t)

Calculation values

The calculation uses the maximum OD and minimum wall the standard allows: the least favorable tube a compliant manufacturer may deliver. It is the same method used by industry reference MS-01-107 for A269 tubing. With S = 137.9 MPa against the grade's minimum ultimate tensile strength (515 MPa), the resulting design factor against rupture is 515 / 137.9 ≈ 3.7 (≈4:1); heavy-wall combinations not covered by code equation (3a) are validated in industry by repeated pressure testing with a 4:1 design factor.

Worked example: 1/2 in OD × 0.049 in wall

1. D = 12.70 + 0.13 = 12.83 mm (0.505 in) — maximum OD with tolerance.
2. t = 1.24 × 0.90 = 1.12 mm (0.0441 in) — minimum wall with −10 % tolerance.
3. P = 2 × 137.9 × 1.00 × 1.12 / (12.83 − 2 × 0.4 × 1.12) = 308.9 / 11.93 = 25.9 MPa.
4. 25.9 MPa = 259 bar = 3,755 psi.
5. Conservative round-down to the nearest 100 psi: 3,700 psi (255 bar).

Heavy wall (t ≥ D/6)

For small ODs with heavy wall (for example 1/8 × 0.035 in or 1/4 × 0.065 in) the wall exceeds D/6 and equation (3a) no longer applies per paragraph 304.1.2 itself; for those cells the matrix uses the thick-wall (Lamé) formulation:

P = S · E · (D² − d²) / (D² + d²)

where d is the inside diameter at minimum wall. All results are rounded down to the nearest 100 psi.

3. WORKING PRESSURE MATRIX OD × WALL

Allowable working pressure at ≤38 °C (100 °F) for seamless ASTM A269 TP316/316L tubing (also valid for TP304: same S = 137.9 MPa in ASME B31.3-2024, Table A-1). Each cell: psi · bar. Empty cells: non-standard combination for twin-ferrule fittings.

¹ Value limited to 7,500 psi by repeated pressure testing of the fitting with a 4:1 design factor (industry reference MS-01-107); the thick-wall calculation for the tube alone gives 8,600 psi.

Gas service (air, nitrogen, hydrogen, helium): select the heavier walls of each OD. A heavy wall resists ferrule action better and coins out minor surface defects that on a thin wall would leave gas micro-leak paths.

Temperature derating — grades 316/316L

Multiply the matrix pressure by the table factor. Factors from industry reference MS-01-107 (Table 26), derived from the ASME B31.3 S values at temperature.

Weld factor

The matrix applies to seamless tube (E = 1.00). If the lot is welded and drawn, multiply by 0.85 (double-welded) or 0.80 (single-welded), in line with the ASME B31.3 joint quality factors. Example: 1/2 in × 0.049 in single-welded = 3,700 × 0.80 = 2,960 psi (204 bar).

4. TUBING VS PIPE AND A269 VS A213

Is 1/2 inch tubing the same as 1/2 inch pipe?

No: 1/2 in tubing measures exactly 12.70 mm outside diameter, while NPS 1/2 pipe measures 21.34 mm outside diameter per ASME B36.10M-2022 — 68 % larger. In tubing, the size IS the actual outside diameter; in pipe, NPS is a nominal name whose actual OD comes from a table. That is why a 1/2 in compression fitting never fits 1/2 in pipe, and vice versa.

Which standard applies: ASTM A269 or ASTM A213?

ASTM A269/A269M-25 is the general-service tubing standard — corrosion and temperature resistance in instrumentation and process lines — and is the one covering this product. ASTM A213/A213M-24 governs seamless tubes for boilers, superheaters and heat exchangers, with minimum tensile requirements and service-specific tests. The same tube may carry dual A269 + A213 certification; the lot certification is confirmed on quotation.

What pressure does stainless steel tubing withstand?

It depends on the OD × wall combination: from 2,000 psi (137 bar) at 7/8 in × 0.049 in up to 10,900 psi (751 bar) at 1/8 in × 0.035 in at ≤38 °C, per this data sheet's matrix calculated with ASME B31.3-2024. Larger OD at the same wall means lower pressure; heavier wall at the same OD means higher pressure.

5. FITTINGS, BENDING AND CLEANLINESS

Twin-ferrule compression fitting: how it works

As the nut is tightened, the back ferrule bites into the tube surface (mechanical grip against pressure and vibration) and drives the front ferrule against the tapered seat of the body (primary seal). The system requires the tube to be softer than the fitting: that is why the tubing must arrive annealed at ≤90 HRB (200 HV) hardness — exactly the maximum ASTM A269/A269M-25 already guarantees for TP304/TP316.

Tightening sequence (no torque wrench)

1. Cut the tube square and deburr inside and outside.
2. Insert the tube until it bottoms firmly against the shoulder of the fitting body.
3. Tighten the nut finger-tight and mark its position.
4. With a wrench, tighten 1 1/4 turns from finger-tight for 1/4 in to 1 in OD; for 1/16, 1/8 and 3/16 in OD tighten 3/4 turn.

Installation is controlled by turns, not by torque: this is the instruction published by twin-ferrule fitting manufacturers. The fitting allows repeated disassembly and reassembly following the manufacturer's reassembly instruction.

Bend radii with a hand tube bender

R is the bend radius to the tube centerline; L is the minimum straight length between the end of the bend and the fitting so the tube can bottom fully. Data from industry reference MS-13-43 (hand tube bender, 1/8 to 1/2 in OD); 5/8 to 1 in ODs require a bench-top bender.

Cleanliness and handling

• Cleaning, descaling and passivation per ASTM A380/A380M-25 where the service demands it (analysis gases, oxygen, high purity).
• Do not drag lengths across rough surfaces or out of the rack: scratches in the sealing zone cause leaks in gas service.
• Use a sharp tube cutter with light passes; always deburr before inserting into the fitting.
• Cap the ends of stored lengths to prevent internal contamination.

6. Application notes

7. Technical notice and limitation of liability