BS 6323-2 Hot Finished Welded Carbon Steel ERW Tubes for Automotive Applications

BS 6323-2 hot finished welded steel tubes are carbon steel mechanical tubes manufactured from flat-rolled strip with a longitudinal weld produced continuously without filler metal, followed by hot finishing. The standard was developed specifically for automobile, mechanical, and general engineering applications and covers material grades HFW 2, HFW 3, HFW 4, and HFW 5.

For automotive buyers, the principal technical advantages are controlled weld geometry, defined dimensional tolerances, and verified tensile/forming performance. BS 6323-2 specifies an outside-diameter tolerance of ±1% with a minimum tolerance band of ±0.5 mm, wall-thickness tolerance of ±10% for ERW tubes, complete removal of the external weld upset, and optional reduction of the internal weld bead to a residual height not exceeding 0.25 mm.

BS 6323-2:1982 has been superseded by BS EN 10296-1:2003. It remains relevant when an existing drawing, automotive component specification, replacement part, or legacy procurement document explicitly requires BS 6323-2.

Specification

Main Technical Characteristics

Controlled Outside Diameter and Wall Thickness

The specified outside-diameter tolerance is ±1%, including ovality, with a minimum tolerance value of ±0.5 mm. For electric-resistance-welded and induction-welded tubes, wall thickness including eccentricity but excluding the weld is controlled to ±10%.

These tolerances are particularly relevant for automotive components that are subsequently bent, cut, welded, expanded, or assembled into brackets and structural subassemblies.

Defined Weld-Bead Geometry

BS 6323-2 requires the external weld upset to be removed completely so that it is flush with the external tube surface.

The standard permits the internal weld bead to remain, but its maximum height is limited to 60% of the specified wall thickness. When specifically ordered, the internal weld upset can be reduced to a residual height not exceeding 0.25 mm. The minimum thickness in the weld area must remain within the same permitted thickness requirement as the tube body.

This is important for applications involving tube insertion, mandrel bending, internal sleeves, bushings, or components requiring predictable internal clearance.

Verified Formability

BS 6323-2 requires tensile testing and an additional forming test depending on outside diameter.

For tubes over 60.3 mm OD, a flattening test is specified. For tubes up to and including 60.3 mm OD, the complete tube is subjected to a bend test using a former with a radius equal to six times the original tube outside diameter.

This testing provides a direct assessment of both the tube body and welded area under deformation.

Grade-Specific Mechanical Strength

The standard provides four strength levels:

HFW 2: minimum yield strength 195 MPa
HFW 3: minimum yield strength 215 MPa
HFW 4: minimum yield strength 235 MPa
HFW 5: minimum yield strength 340 MPa

The corresponding minimum tensile strengths range from 320 MPa for HFW 2 to 490 MPa for HFW 5.

This grade progression allows designers to select material according to the required balance between forming capability and component strength.

Our Advantages

Weld Profile Controlled for Downstream Automotive Processing

A frequent concern with automotive ERW tubing is interference from the internal weld bead during bending, insertion, swaging, or assembly.

For BS 6323-2 production, the external weld bead is removed flush with the outside surface. Where the customer's component requires restricted internal clearance, the internal bead can be specified with a residual height not exceeding 0.25 mm rather than relying only on the standard maximum of 60% of wall thickness.

For purchasing specifications, the required internal-bead condition can therefore be defined before production instead of being treated as an uncontrolled post-production characteristic.

Dimensional Requirements Can Be Defined Against the Actual Assembly

Automotive buyers commonly need to control OD, ovality, wall thickness, straightness, and cut length because each parameter affects bending fixtures, welding fixtures, bush installation, and final assembly.

BS 6323-2 establishes OD tolerance at ±1% with a minimum of ±0.5 mm and wall tolerance at ±10%. Standard cut-length tolerances are +10/0 mm for lengths up to 6000 mm and +15/0 mm above 6000 mm. BS 6323-1 limits straightness deviation to 1.5 mm per metre unless another requirement is agreed.

Where the component drawing requires tighter control, dimensional requirements can be reviewed separately and agreed before order confirmation rather than assuming that standard tolerances automatically satisfy the finished component.

Testing Is Selected According to Tube Diameter and Deformation Risk

A welded tube may satisfy tensile strength requirements while still performing poorly during flattening or bending if the weld zone is inconsistent.

BS 6323-2 therefore does not rely only on tensile results. Tubes over 60.3 mm OD are subject to flattening testing, while tubes up to and including 60.3 mm OD are subject to whole-tube bend testing. During flattening, the weld is positioned at 90 degrees to the direction of flattening so that weld integrity is directly evaluated.

This testing approach is especially useful for automotive tubes that will subsequently undergo bending, pressing, welding, or other forming operations.

Execution Standards

BS 6323-2:1982
Hot finished welded steel tubes for automobile, mechanical, and general engineering purposes. The standard has been superseded by BS EN 10296-1.

ASTM A513/A513M
Electric-resistance-welded carbon and alloy steel mechanical tubing manufactured from hot-rolled or cold-rolled steel. Commonly specified for automotive and mechanical tubing in North American projects.

EN 10296-1
Welded circular steel tubes for mechanical and general engineering purposes. This is the successor standard identified for BS 6323-2.

JIS G3445
Carbon steel tubes for machine structural purposes. Applicable to mechanical components where dimensional and mechanical requirements are specified according to Japanese standards.

GOST 10705
Electric-welded steel pipes with technical delivery requirements, used for longitudinally welded carbon and low-alloy steel pipe applications.

GB/T 13793
Longitudinal electric-resistance-welded steel tubes used for mechanical and general engineering applications.

These standards should not be treated as automatically interchangeable. Grade chemistry, mechanical properties, dimensions, tolerances, testing, and delivery conditions must be reviewed against the customer's drawing before substitution.

Application Field

Automotive Seat Frame Cross Tube

A specific application for BS 6323-2 hot finished welded tubing is an automotive seat frame cross tube.

The tube can serve as a transverse structural member connecting left and right seat-frame components. During manufacturing, the tube may undergo cutting, bending, bracket welding, end forming, drilling, or insertion of sleeves and bushes.

For this component, the following properties are particularly relevant:

Controlled outside diameter supports repeatable location in welding and assembly fixtures.

Straightness control reduces positional variation across the seat-frame assembly.

A flush external weld bead improves contact with fixtures and welded brackets.

Optional reduced internal weld bead provides additional clearance for internal sleeves or inserted components.

Defined tensile and forming requirements provide a measurable basis for evaluating the tube before mass production.

The final grade should be selected according to seat-frame load requirements, forming severity, welding procedure, and vehicle-specific validation requirements.

Chemical Composition

BS 6323-2 itself defines four HFW steel grades rather than five. To avoid introducing a non-existent BS 6323-2 grade, the first four rows below are the complete BS 6323-2 grade set. E355 is included only as a clearly identified successor-standard reference under EN 10296-1 and must not be ordered as a BS 6323-2 grade.

Mechanical Properties

Forming Test Requirements

Standard Dimensional Series

Ordering Information

For technically complete procurement, the enquiry should define at least:

BS 6323-2 grade: HFW 2, HFW 3, HFW 4, or HFW 5

Outside diameter and wall thickness

Tube length and cut-length tolerance

Quantity

Required internal weld-bead condition

Surface protection requirement

Any tighter straightness or dimensional tolerance

Required inspection documentation

Additional forming or component-specific test requirements

Final automotive component approval should always be based on the customer's drawing and functional validation rather than grade designation alone.