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Understanding SAE J527-2017: Specifications for Brazed Double Wall Low-Carbon Steel Tubing
SAE J527-2017 is a stabilized standard that outlines the requirements for brazed double wall low-carbon steel tubing. This tubing is designed for automotive, refrigeration, hydraulic, and similar applications where bending, flaring, beading, forming, and brazing are essential. The standard ensures that the tubing meets specific dimensional, mechanical, and performance criteria, making it reliable for demanding environments.
🔍 Stabilized Notice: SAE J527-2017 has been declared “Stabilized” by the SAE Metallic Tubing Committee. Users are responsible for verifying references and continued suitability of technical requirements as newer technology may exist.
🛠️ Scope, Manufacture, and Dimensional Tolerances
The tubing is manufactured from a single or double strip of low-carbon steel (UNS G10080 or UNS G10100) shaped into a double-wall form and secured by copper brazing in a controlled atmosphere. The braze must be uniform with no internal or external beads. Standard tubing is available in coiled or straight condition, with straightness agreed upon between supplier and purchaser.
Key dimensional parameters are specified in Table 1 (partial listing below), including nominal diameters, outside diameter dimensions and tolerances, and wall thickness values. For instance, tubing with a nominal OD of 4.76 mm (dash size –3) has an OD tolerance of ±0.08 mm and a basic wall thickness of 0.71 mm ±0.08 mm.
| Dash Size | Nominal Tube OD (mm) | Outside Diameter Basic (mm) | OD Tolerance ±mm | Wall Thickness Basic (mm) | Wall Thickness Tolerance ±mm |
|---|---|---|---|---|---|
| –2 | 3.18 | 3.18 | 0.05 | 0.64 | 0.13 |
| –3 | 4.76 | 4.76 | 0.08 | 0.71 | 0.08 |
| –4 | 6.35 | 6.35 | 0.08 | 0.71 | 0.08 |
| –5 | 7.94 | 7.94 | 0.08 | 0.71 | 0.08 |
| –6 | 9.53 | 9.53 | 0.08 | 0.71 | 0.08 |
| –8 | 12.70 | 12.70 | 0.10 | 0.89 | 0.09 |
| –10 | 15.88 | 15.88 | 0.10 | 0.89 | 0.09 |
Other sizes and intermediate wall thicknesses can be specified by agreement. Tubing ends must be cut with minimal distortion, and surface imperfections (e.g., handling marks, shallow pits) are not considered injurious if they remain within tolerance and do not affect function. Sealing surfaces must be smooth and free from defects that could prevent proper sealing.
🔍 Mechanical Properties and Performance Requirements
Finished tubing must meet the following minimum mechanical properties:
- Yield Strength (0.2% offset): 170 MPa
- Tensile Strength: 290 MPa
- Elongation in 50 mm: 14%
- Hardness (Rockwell 30T scale): T65 max (not required for nominal wall thickness < 1.65 mm)
The standard mandates several performance tests conducted per SAE J1677 or ASTM A 254:
- Bending Test – verifies formability
- Flaring Test – assesses expandability
- Pressure Proof Test – confirms leak resistance (allowable unit stress = 140 MPa, 80% of minimum yield)
- Nondestructive Electronic Test – detects hidden flaws
- Flattening Test – checks ductility
- Inside Surface Cleanliness – per ASTM A 254
⚠️ Common Pitfall: Neglecting to agree on straightness requirements or failing to perform the required performance tests can lead to tubing that does not meet application needs. Always verify that the tubing supplier provides a certificate of compliance upon request.
Engineering Design Insight
The double wall construction combined with copper brazing provides a leak‑proof seam and excellent formability, making the tubing ideal for repeated bending and flaring operations. Designers should note that surface imperfections that do not compromise sealing or dimensional conformance are acceptable, but sealing surfaces must be pristine. Additionally, the specified corrosion protection—using a removable compound or extended coatings like tern coating or epoxy paint—ensures longevity during storage and shipment. When selecting tubing, ensure that the material (low‑carbon steel UNS G10080 or G10100) meets the required yield and tensile strengths to guarantee reliable performance under pressure and mechanical loading.
Frequently Asked Questions
What standard tubing sizes are defined in SAE J527?
The standard provides nominal diameters from 3.18 mm to 15.88 mm, with corresponding outside diameter tolerances and wall thicknesses. Other sizes can be supplied by agreement between supplier and purchaser.
What performance tests must the tubing pass?
Required tests include bending, flaring, pressure proof (by agreement), nondestructive electronic testing, flattening, tensile testing, and inside surface cleanliness check. These tests ensure that the tubing can withstand forming and service conditions.
What corrosion protection is specified?
The tubing must be protected against corrosion during shipment and normal storage. A removable compound may be used, or extended coatings such as tern coating, galvanizing, or epoxy paint can be applied per user request.
Can surface imperfections be allowed?
Yes, surface imperfections like handling marks or shallow pits are acceptable provided they do not affect the function of the tubing and fall within the dimensional tolerances. Slight seam lift or separation on the outside bevel edge is also acceptable if it does not impact the sealing area.
