# Welded tubing

Selecting welded tube by specification, manufacturing and delivery condition, seam acceptance and functional dimensions.

Reviewed: 2026-11-01

Tags: materials, stock-forms, tubing

Welded tubing has a wall joined by a manufacturing weld. The term describes a route, not a material grade, dimensional tolerance or service rating. A tube may subsequently be drawn, heat-treated, sized or finished, so **welded does not necessarily mean as-welded**. ASTM A513/A513M-25 explicitly covers several electric-resistance-welded mechanical-tube types, including as-welded and drawn-over-mandrel products. [ASTM A513/A513M-25](https://store.astm.org/a0513_a0513m-25.html)

## Manufacturing route and delivery condition

An ideal tube with **50.000 mm OD** and **2.500 mm uniform wall** gives **45.000 mm nominal ID**. A **44.800 mm insert** has **0.200 mm nominal diametral clearance** before seam, coating and form allowances. Verify the permitted internal bead and usable bore along the full engagement length.

For carbon-steel ERW tubing, Plymouth defines welding by electrical-resistance heating and pressure applied to strip; current can be introduced through electrodes or induction. This is a specific process description, not a definition of all welded tubular products. Identify the actual weld process rather than using ERW as a synonym for every welded tube. [Plymouth manufacturing glossary](https://www.plymouth.com/resources/terms-glossary/)

The subsequent operations also matter. Steel Tube Institute explains that DOM starts as ERW tube with flash removed and is drawn through dies and over mandrels; thermal treatment may follow drawing. Such a tube retains a welded manufacturing origin even when its finished surface no longer visibly identifies the seam. Do not reclassify it as seamless based on appearance or machining behavior. [STI DOM process](https://steeltubeinstitute.org/mechanical-tubing/drawn-over-mandrel/)

Keep these order fields separate:

| Field | What it resolves |
|---|---|
| Material specification and grade | Chemistry, applicable property and testing requirements |
| Welding/manufacturing route | How the tubular wall is formed and joined |
| Supplied condition | As-welded, drawn, annealed or other agreed condition |
| Seam and surfaces | Inside/outside bead acceptance, finish and cleanliness |
| Dimensions and inspection | Actual limits and evidence for the intended use |

Qualify any shop attachment or end weld separately from the mill seam.

## Choose the product family before comparing dimensions

Three current ASTM records illustrate distinct scopes:

- **A513/A513M-25:** ERW carbon and alloy **mechanical** tubing. Its named types distinguish hot-rolled versus cold-rolled starting material, sink drawing, DOM and special smooth ID. Grades, types and thermal conditions are separate selections. [A513 scope](https://store.astm.org/a0513_a0513m-25.html)
- **A500/A500M-23:** cold-formed welded and seamless carbon-steel **structural** tubing in rounds and shapes, for construction and general structural purposes. [A500 scope](https://store.astm.org/a0500_a0500m-23.html)
- **A269/A269M-25:** seamless and welded austenitic stainless tubing for general service. Its abstract identifies nominal-wall product and heat-treated supply, with applicable chemical and mechanical-test provisions. [A269 scope](https://store.astm.org/a0269_a0269m-25.html)

The shared words “welded tubing” do not make these interchangeable. A dimensionally convenient structural section is not thereby qualified for a fluid system, and an austenitic stainless tube still needs its actual grade and service conditions. Pressure, fatigue, corrosion, sanitary or low-temperature suitability must follow the governing application requirements and delivered product evidence. Avoid assigning a universal pressure rating or ranking all welded tube below all seamless tube.

## The seam can determine usable clearance

Plymouth distinguishes **flash-in**, where the internal weld bead remains, from **flash-removed**, where it has been mechanically removed. These descriptions concern the bore surface; they do not by themselves specify a maximum residual projection, a surface-roughness value or an inspection sensitivity. Define the required limit and method when the bore is functional. [Plymouth flash definitions](https://www.plymouth.com/resources/terms-glossary/)

For the HSS processes discussed in STI's *HSS Seam Welds* article, the exterior flash is removed but interior flash is normally retained. The article says inside removal must be requested and confirmed, and identifies telescoping and internal splice-plate connections as examples where the bead matters. This is HSS-specific guidance referencing the article's then-applicable standards, not a statement about every stainless, mechanical or pressure tube. [STI HSS seam-weld discussion](https://steeltubeinstitute.org/resources/hss-seam-welds/)

## Original dimensional example

**Assumptions:** an ideal concentric circular tube with 50.000 mm OD, uniform 2.500 mm wall and no internal bead, coating or local distortion.

- Nominal geometric ID: `50 − 2 × 2.5 = 45.000 mm`.
- Metal area: `π(50² − 45²)/4 = 373.064 mm²`.
- Metal volume for 1,000 mm length: `373,064 mm³ = 0.373064 L`.

A 44.800 mm diameter insert has only `45.000 − 44.800 = 0.200 mm` nominal diametral clearance, or 0.100 mm per side when centered. This calculation does **not** establish that it passes through delivered welded tubing. Any agreed residual seam projection and dimensional/form limits must be evaluated against the actual fit. Treat the example as geometry, not as a tolerance recommendation or an identified supplier product.

Likewise, calculating mass requires the selected alloy density, and calculating pressure or structural resistance requires the appropriate design basis. Neither follows from this cross-sectional area alone.

## Procurement and inspection decisions

1. **Define the application first.** Identify the service, specification/edition, grade and required delivery condition before comparing catalog sizes.
2. **Define controlled dimensions.** State OD, ID or wall requirements and how tolerances interact; include length, straightness and shape/corner requirements where relevant.
3. **Define the seam and finish.** Specify internal/external bead limits, retained surfaces, cleanliness and any orientation requirement needed by the component.
4. **Define inspection evidence.** Identify applicable mill tests, acceptance criteria, supplementary requirements and certificate/heat traceability. A test name alone does not establish full-volume coverage or a delivered tube's service rating.
5. **Qualify downstream operations.** Assess cutting, forming, machining, joining and finishing against the actual grade and condition; identify the stage at which final dimensions and surfaces are accepted.

For A513, optional supplementary requirements must be stated in the order; its inch-pound and SI systems are separately standard and should not be mixed. Resolve the intended unit system and complete dimensional requirements explicitly. [A513/A513M-25 ordering and units scope](https://store.astm.org/a0513_a0513m-25.html)

## Source versions and related reference

Reviewed 2026-11-01, America/Los_Angeles. ASTM's records identify A513/A513M-25 updated **19 May 2025**, A500/A500M-23 updated **21 November 2023**, and A269/A269M-25 updated **23 October 2025**. These are publisher record dates, not dates inferred from filenames. STI's HSS article cites 2013 standard editions and is used for its process explanation; current contractual requirements need their applicable edition. The cited Plymouth glossary and STI DOM page provide no explicit technical revision date. No PDF upload timestamp has been substituted for a printed revision.

[Stock forms and dimensions](index.md) · [Drawn-over-mandrel tubing](drawn-over-mandrel-tubing.md)