Rethinking Roll Cage Tubing: A Comparative Analysis of CDS, DOM, and HFIW (ERW)

When safety and structural integrity matter – whether in motorsport, engineering, or performance fabrication – the quality of the tube behind the manufacturing process matters. In motorsport, regulations such as Motorsport Australia’s Schedule J may specify materials like “CDS/CDW carbon steel” or require a minimum tensile strength of 350 MPa. The FIA (Fédération Internationale de l’Automobile) has similarly mandated the use of CDS (cold-drawn seamless) tube with a minimum yield strength of 350 MPa since at least the early 1990s. These established guidelines provide important benchmarks, though as materials technology evolves, there may be opportunities to further enhance the criteria that define a safe and high-performing tube.

Legacy preferences for CDS often stem from historical limitations in older welded tube manufacturing – particularly contact-electrode ERW methods, which frequently resulted in inconsistent weld quality and limited formability in the finished tube. However, advances in high-frequency induction welding (HFIW), tighter forming control, and vastly improved weld integrity have significantly closed that performance gap. Coupled with the output of modern hot strip mills – producing flatter, cleaner, and mechanically uniform strip – today’s welded tube meets or exceeds CDS performance in many aspects.

Modern HFIW tube is now a high-performing, cost-effective alternative for structural and safety-critical applications. This has been proven in service, with Industrial Tube Manufacturing supplying over 165,000 metres of locally manufactured MSNZ-Q29 roll cage tube over the past 15 years – enough for up to 8,000 safety cages across multiple motorsport disciplines, as well as ROPS used in other safety-critical applications throughout Australasia. The product was developed in conjunction with Motorsport New Zealand by local tube mills, including Industrial Tube Manufacturing, using tube-designated base material from New Zealand Steel.

(Safety Cages made from ITM-MSNZ-Q29 tube by Mitchell Race Xtreme)

To advance the discussion and clarify terminology, we’ve tested and compared various tube types – including Cold Drawn Seamless (CDS), Cold Drawn Welded (CDW/DOM), and our High-Frequency Induction Welded (HFIW) product – to assess how manufacturing methods, base materials, and mechanical consistency influence real-world performance. In some regions, HFIW tube is still referred to as ERW, EWS, CREW (cold-rolled input material) or HREW (hot-rolled input material).

It’s important to clarify that ‘CDS’ and ‘CDW’ (or ‘DOM’) describe manufacturing processes, not material grades or standards. So, does tubing made using these methods offer better consistency or superior strength compared to HFIW tube?

To answer this, we first need to understand how these methods differ. Both HFIW (welded) tube and CDW/DOM begin with the same strip-based processes, whereas CDS follows a fundamentally different manufacturing route, which we’ll explore in more detail below.

 

(Basic process flow of various tube manufacturing methods)

 

Cold Drawn Welded (CDW) / Drawn Over Mandrel (DOM)

This process begins with a welded tube – typically produced using high-frequency induction welding (HFIW) – which is then cold drawn over a mandrel and through a die to improve concentricity, dimensional accuracy, and surface finish. While the weld seam remains visible, the drawing process helps refine and blend it.

The DOM (Drawn Over Mandrel) and CDW (Cold Drawn Welded) methods originated in the early 20th century as ways to enhance the performance of welded tube – improving strength, roundness, and dimensional consistency as a cost-effective alternative to seamless tubing. Although the terms are often used regionally – with DOM more common in North America and CDW in Europe and Asia – the underlying process is largely the same in modern production. DOM is typically associated with tighter tolerances and precision applications, but the final properties depend heavily on input steel quality and post-processing, such as normalising or internal weld bead removal.

Today, modern HFIW tube mills can achieve excellent roundness, straightness, and surface quality directly off the mill – particularly when using high-grade strip and advanced forming control – reducing the need for redraw in many structural applications.

DOM remains popular in North American motorsport due to its availability and good formability, and it continues to be widely used in automotive and industrial components where internal weld bead removal is critical — such as hydraulic and pneumatic cylinders, or tooling tubes. As with CDS, the final mechanical properties of DOM depend on the base material –  often SAE 1010, 1020, or 1026 – and should not be assumed superior based on manufacturing method alone.

Cold Drawn Seamless (CDS)

Cold Drawn Seamless (CDS) tube manufacturing dates back to the 1920s and builds on the Mannesmann rotary piercing process developed in the 1880s. It continues to be a trusted method for producing seamless tubing. The process begins with a solid steel billet that is heated and pierced to form a hollow shell. This initial hollow can be produced using different methods, most commonly mandrel piercing (as in the Mannesmann process) or pilger rolling. In mandrel piercing, a rotating piercer is forced through the heated billet to create a rough hollow shell. Pilger mills, on the other hand, use grooved rolls and a mandrel to progressively reduce the diameter and wall thickness of the tube while improving roundness and surface finish.

After this hot-forming stage, the hollow tube undergoes cold drawing, where it is pulled through a series of dies and over a mandrel at room temperature. This process further reduces dimensions, refines the grain structure, enhances mechanical properties like strength and hardness, and achieves tight tolerances with a smooth internal surface. However, because the process starts from a pierced shell rather than a formed strip, achieving consistent wall thickness and internal concentricity is inherently more difficult – especially over long lengths – due to minor misalignments in the piercing or cold drawing stages and variations in how the material flows during reduction.

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(A basic process image showing the stages of Seamless tube manufacturing)

When manufactured to a high standard, CDS tubing offers consistent mechanical properties, excellent dimensional accuracy, and uniform wall thickness, making it well-suited for demanding structural, hydraulic, and high-pressure applications. When sourced from reputable mills such as Mannesmann, Vallourec, Plymouth Tube, or Webco Industries, it delivers strong performance in terms of concentricity and strength. However, not all CDS tubing is created equal – variations in feedstock quality, cold-drawing parameters, and heat treatment can lead to significant differences in strength, ductility, and dimensional control.

There is a number of differing standards and heat treatment options available such as C+ (normalised and tempered), N+ (normalised), A (annealed), H (stress relieved) or with no suffix it is often ‘as drawn’. We also found it difficult to source ‘true’, CDS mild steel which has made like-for-like comparisons difficult. Chemical analysis revealed that some tube sold in Australia as “CDS 1026” was actually 20CrMo4 – a chromium-molybdenum alloy with higher strength (577 MPa yield) but with inherently different weldability and material behaviour. We would be speculating to a degree, but it’s likely that the product was ordered based on meeting specific mechanical properties only. The mill may have chosen to use a material like 20CrMo4 to achieve these targets more consistently – particularly if heat treatment or work hardening of a mild steel grade alone wasn’t sufficient or reliable.

Other CDS tubes we tested were made from higher-manganese CMn steel, which differs from mild steel by offering greater strength and toughness due to its increased Mn content. This makes CMn steel well suited for demanding structural applications, though the welding parameters and filler material typically have different requirements to mild steel.

CDS is typically supplied with surface scale from hot working or normalising, and may require additional processing (e.g., pickling or machining) if a clean or smooth finish is required.

Mechanical Testing and Chemistry

Testing was conducted in accordance with AS 1391:2020 (or ISO 6892-1:2019) using a Universal Grade 1 Testing Machine (UTM). Hardness testing uses the Rockwell B/HRB scale. All tested tube is 2.6×44.5mm. All testing conducted in 2025.

Destructive Testing

We put all tubes we tested through our standard destructive testing regime at Industrial Tube Manufacturing. This includes cone/flare tests and flattening tests, which while typically used for welded tube (alongside the reverse bend test) have some relevancy here to test ductility and the integrity of the profile. As expected, all tube passed a standard flare test to 30%. The 20CrMo4 tube was the first to split when pushed past this, failing at 46% flare/from 44.5-65mm and it visibly embrittled and exhibited surface cracking during the flattening test – typical of many alloyed steels made using the CDS process.

We also flared our HFIW tube (MSNZ-Q29) to failure (66% flare/from 44.5- 74mm), and it split well away from the weld zone (HAZ), consistent with the weld zone’s higher hardness (HRB 95) compared to the base material (HRB 86). Importantly, this hardness remains well within the typical ductile range for structural steel, indicating the weld zone is not a brittle or weak point. This enhanced hardness contributes to section strength while maintaining sufficient ductility, helping the tube retain overall integrity under stress.

Destructive testing – cone/flare and flattening tests. Top Left flare at 30% for all four tubes. Top right ITM-MSNZ-Q29 flare at 66%, ‘3’ top centre is 20CrMo4 CDS at 46%.

Building on the mechanical performance and ductility insights from our destructive testing, it’s important to consider how tubing specifications align with various regulatory requirements across motorsport disciplines.

Navigating Dual Compliance: Tubing Standards Across Motorsport Disciplines

With crossover between disciplines such as circuit racing and drag racing, questions often arise around tubing compliance. Motorsport New Zealand’s MSNZ-Q29 standard allows locally manufactured 44.5 x 2.6 mm HFIW mild steel tubing, which meets structural and safety standards for many applications. However, SFI standards for drag racing (and local interpretation) require a minimum wall thickness of 3.0 mm, particularly for cars under 10.0 seconds E.T.

In the New Zealand market, 3.0 mm roll-cage designated tubing with the required strength and certification is not commonly available. This presents challenges for competitors wishing to use a mild steel roll cage in both disciplines. NZDRA and IHRA NZ maintain relatively strict adherence to SFI specifications, which limits cross-category eligibility unless using approved alternatives like 4130 Chromoly or Docol R8. These high-strength materials often allow for thinner wall sections to reduce weight, but would require engineering sign-off under Motorsport New Zealand regulations to meet safety compliance for non-standard designs.

From an engineering perspective, a 44.5 x 2.6 mm steel tube with a 350 MPa yield strength offers notably better performance than a 42.4 x 3.2 mm nominal bore (NB) pipe with a 250 MPa yield strength. NB pipe is typically a China sourced commodity product with broader dimensional tolerances and variable material properties. Despite the thinner wall, the higher yield strength of the 350 MPa tube more than compensates for differences in section modulus. Calculations show that under a central point load over a 1.0 m unsupported span, the 350 MPa tube can resist approximately 47.3 kN before yielding – over 30% greater than the 35.8 kN capacity of the thicker, lower-strength pipe. This clearly demonstrates that structural performance depends not just on wall thickness but critically on material yield strength and the tube’s section modulus.

Manufacturing a ROPS or motorsport roll cage from NB pipe product also carry risks around varying standards, as not all importers specify minimal yield strengths when ordering AS 1074 pipe and motorsport rule books rarely require specific pipe standards, which can lead to the use of suboptimal material, as low as 195 MPa yield strength in critical safety structures. Purpose-engineered, high-strength tubing offers better strength-to-weight efficiency and more reliable safety for demanding structural applications compared to commodity NB or schedule pipe.

The Case for Locally Made Tubing

High Frequency Induction Welded (HFIW) tubing, often categorised as Electric Resistance Welded (ERW), has evolved significantly since the 1990s. At Industrial Tube Manufacturing, our HFIW ‘Roll Cage’ tubing, designated ITM-MSNZ-Q29 offers practical advantages for fabricators and race teams:

• Local Production with local standards: Manufactured at our precision tube mill in Hamilton from New Zealand Steel supplied hot-rolled coil, meeting AS/NZS 1594 and AS/NZS 1365. Finished tube exceeds AS 1450 tolerances and is certified to the Motorsport New Zealand standard, ‘MSNZ-Q29’.
• Tight Tolerances: Outside diameter tolerance of 0.13 mm for consistent, reliable fit-up. Minimal internal weld upset.
• Fabricator-Friendly: Pickled and oiled finish improves weldability, cutting consistency, and paint/coating adhesion, making it ideal for downstream fabrication.
• Proven on the track: Over 165,000 metres supplied through Industrial Tube alone – trusted in more than 8,000 roll cages across circuit, rally, and off-road motorsport.

(High-frequency Induction Welding (HFIW) at Industrial Tube Manufacturing)

Structural Integrity Starts with Design, Not Just Material

While material quality is critical, roll cage performance depends on more than just the tube. It’s worth briefly noting that industry experience consistently shows failures often stem from factors beyond the material itself, including:

• Weld Imperfections: Poorly executed welds at joints or base plates can create stress concentrations and become failure points under load. Issues like lack of fusion, undercutting, or porosity can compromise the structure regardless of tube quality. Welds should be consistent, full-penetration where required, and ideally inspected – especially in critical areas.
• Design Flaws: Poor triangulation or inadequate bracing can limit the cage’s ability to distribute forces effectively. Without proper geometry, tubes may buckle or deflect during impact. Strategic placement of diagonals and load paths is essential for strength in all directions.
• Mounting Issues: Attaching cage tubes directly to thin sheet metal, without reinforcing underlying structures like chassis rails, can lead to serious failures in a crash. A strong cage starts with high-quality tube, but it must be paired with competent fabrication and proper load path integration to perform as intended under impact.

Supporting Consistency and Clarity in Safety Standards

Established frameworks like FIA Appendix J, Motorsport Australia’s Schedule J and Motorsport New Zealand’s Appendix Two, Schedule A provide critical safety benchmarks by specifying minimum materials and mechanical properties. From our experience working with fabricators and engineers, especially at the grassroots level, we’ve observed some areas where greater clarity could support both compliance and safety outcomes.

To that end, we believe the following ideas – developed through practical experience – could benefit the broader community:

• Standardised reporting formats for mechanical and chemical properties, making documentation clearer and easier to assess. This shows manufacturer commitment to the industry and illustrates fit-for-purpose products.
• Greater transparency around manufacturing processes such as normalising, cold working, and seam welding, which have a direct impact on real-world tube performance.
• Recognition of modern, certified HFIW tubing, which in many cases meets or exceeds CDS and DOM in terms of strength, ductility, dimensional control, and material consistency.
• Updated Yield Strength Criteria for Select Applications: Enabling the use of certified high-strength tubing with slightly thinner walls (e.g. 2.6 mm vs 3.0 mm) in Drag and Speedway categories could address the limited availability of >350 MPa yield mild steel material – while maintaining or improving safety margins.

We offer these suggestions not as criticisms, but as a contribution to ongoing conversations around safety, fabrication, and performance in motorsport.

Proven Performance in Practice

All the products we’ve tested in this case are broadly fit for purpose and performed well under destructive testing, with acceptable roundness and concentricity. But not all tubing is created equal – differences in steel grade, process control, and traceability can have a significant impact on weldability, consistency, and structural performance under load. In some instances, we found that tubes marketed under common designations varied significantly in their actual composition, highlighting the importance of verifying material properties rather than relying solely on nominal specifications.

Importantly, our testing confirmed what we’ve seen in practice for over a decade: properly manufactured HFIW tube not only holds up – it performs. With good ductility, high weld zone integrity, and consistent mechanical properties, it stands as a reliable alternative to CDS and DOM for safety-critical applications. At Industrial Tube Manufacturing, we believe safety starts with quality – not just in the tube, but in the standards, transparency, and traceability behind it. Our commitment to locally made, certified steel, precision manufacturing, and proven testing methods has earned the trust of fabricators and scrutineers.

For fabricators, engineers, and competitors alike, asking the right questions matters:

• Where was the tube made?
• Is it certified and traceable?
• Are the mechanical properties independently verified?

These questions aren’t just box-ticking – they’re the foundation of safer, stronger structures that hold up under pressure. When the right material is selected, and its specification is backed by verified properties, controlled processing, and full traceability, real-world performance isn’t just expected – it’s engineered.

For more information or to discuss your requirements, contact us today.