BS 6323-5 Electric Resistance Welded and Induction Welded Steel Tubes

BS 6323-5 electric resistance welded and induction welded steel tubes are carbon steel mechanical tubes manufactured from steel strip by continuous electric resistance welding or high-frequency induction welding. The specification was developed for automobile, mechanical, and general engineering applications where controlled outside diameter, wall thickness, weld quality, mechanical properties, and forming performance are required.

BS 6323-5:1982 covers ERW1, ERW2, ERW3, ERW4, and ERW5 grades with progressively higher strength levels. Tubes may be supplied in as-welded, annealed, or normalized delivery conditions according to the required fabrication process and final mechanical properties.

BS 6323-5:1982 is a withdrawn British Standard. It was withdrawn on 24 June 2003 and superseded principally by BS EN 10305-3, BS EN 10305-5, and BS EN 10296-1. For replacement or legacy automotive components, BS 6323-5 material can still be specified where the original drawing, customer specification, or approved material list requires it.

Specifications

Main Characteristics

Controlled Dimensional Accuracy

Defined Strength Levels

The five ERW grades provide a structured range of mechanical properties. In normalized condition, minimum yield strength ranges from approximately 155 MPa for ERW1 to 340 MPa for ERW5, enabling material selection according to forming load, structural strength, and component design.

Controlled Formability Through Delivery Condition

As-welded tubes provide higher strength generated by the tube-forming process, while annealing or normalizing reduces residual forming stress and improves ductility. This distinction is important where the tube will subsequently undergo bending, end forming, swaging, flattening, welding, or brazing.

Consistent Longitudinal Weld

The strip edges are continuously joined by resistance or induction heating without conventional filler metal. Correct control of strip preparation, welding energy, pressure, and weld-bead removal provides a continuous longitudinal joint suitable for mechanical fabrication.

Our Advantages

1. How Is Weld Integrity Controlled for Components That Require Bending or Flattening?

For automotive and fabricated mechanical parts, nominal tensile strength alone is insufficient. A tube may meet chemistry requirements while still failing during bending if weld quality or heat input is inconsistent.

Production can therefore be controlled through strip-edge preparation, welding-current monitoring, weld-bead control, dimensional inspection, and representative flattening or forming tests. For parts involving severe deformation, the intended bending radius and subsequent forming operation should be supplied before production so that the appropriate grade and delivery condition can be selected.

2. How Are Dimensional Changes After Annealing or Normalizing Managed?

Heat treatment can change tube diameter, ovality, straightness, and mechanical properties. This is particularly important for buyers machining the tube or inserting it into closely toleranced assemblies.

Dimensions should therefore be specified together with the required delivery condition. KM as-welded tubes can achieve tighter OD tolerances, while GKM/GZF or NKM/NZF heat-treated tubes are assessed using the tolerance class applicable to the final heat-treated condition. Final OD, wall thickness, straightness, and length inspection is performed after the specified thermal processing rather than relying only on pre-treatment dimensions.

3. How Can Legacy BS 6323-5 Requirements Be Managed in Current Projects?

BS 6323-5:1982 has been withdrawn, but many established automotive and machinery drawings continue to reference ERW1-ERW5 grades.

For legacy orders, the material specification should remain traceable to BS 6323-5 when contractually required. For new designs, BS EN 10305-3, BS EN 10305-5, or BS EN 10296-1 should be evaluated depending on tube shape, dimensional precision, delivery condition, and intended application. Grade substitution should not be based only on tensile strength; chemistry, yield strength, elongation, tolerances, heat treatment, and test requirements should also be reviewed.

Execution Standards

Application

Automotive Seat Frame Cross Tube

A specific application is the tubular cross member used in an automotive seat frame.

The component requires a controlled outside diameter for fixture positioning and mating parts, sufficient elongation for bending and end forming, repeatable weld integrity during deformation, and adequate tensile and yield strength to withstand service loads.

Lower- and medium-strength BS 6323-5 grades such as ERW1, ERW2, or ERW3 may be selected depending on the seat structure design, tube diameter, wall thickness, bending radius, and required post-forming strength. Annealed or normalized delivery conditions can be considered where severe forming is required.

Chemical Composition

Mechanical Properties

For comparison, the KM as-welded condition provides different mechanical-property levels because of the forming and welding process.