# Rectangular Stainless Heat-Transfer Tubes: Specify the Profile and Flow Basis

Canonical: https://jundapipe.com/en-AU/blog/rectangular-stainless-heat-transfer-tube

Define a rectangular tube profile with corner radii, wall and flow dimensions. Includes a bounded hydraulic-diameter example for comparison.

Specify a rectangular stainless heat-transfer tube by its complete cross-section, not only width and height. Include wall requirements, internal and external corner radii, length, straightness, twist and end details. Thermal or hydraulic performance needs the actual internal geometry and operating conditions; the profile name alone does not establish an improvement.

Junda lists a [rectangular stainless steel heat-transfer tube](https://jundapipe.com/products/rectangular-stainless-steel-heat-transfer-tube). [Catalogue source](https://jundapipe.com/products) Confirm the required profile and applicable product requirements with a drawing.

## Which dimensions must the drawing distinguish?

| Feature               | What to define                                      | Why the distinction matters                            |
| --------------------- | --------------------------------------------------- | ------------------------------------------------------ |
| Width and height      | External or internal measurement basis              | Determines fit or flow area                            |
| Wall                  | Required basis, tolerance and measurement locations | A nominal value does not define every corner condition |
| Corner radii          | Internal and external radii                         | Changes the actual area and wetted perimeter           |
| Longitudinal geometry | Length, straightness and twist                      | Controls assembly alignment                            |
| Ends                  | Cut, finish and connection details                  | Defines the mating interface                           |

State the governing drawing revision and units. A sketch without corner definitions can describe several different cross-sections that share the same outer envelope.

## What can a simple flow calculation show?

For a fully wetted ideal rectangular duct, hydraulic diameter is defined as Dh = 4A/P, where A is flow area and P is wetted perimeter. For sharp internal corners with sides a and b, this reduces to Dh = 2ab/(a + b).

Using illustrative internal dimensions a = 20 mm and b = 10 mm gives A = 200 mm², P = 60 mm and Dh = 800/60 ≈ 13.33 mm.

This is a geometry example, not a Junda product size. Real corner radii change A and P. Hydraulic diameter is a characteristic length used in appropriate flow models; it does not establish that a rectangular tube performs identically to a round tube of that diameter or produces a particular heat-transfer gain.

## What else is needed for a thermal comparison?

Provide fluid properties and flow rates, inlet conditions, fouling assumptions, pressure-drop constraints, wall material and thickness, and the external heat-transfer arrangement. Ask the equipment designer to use a model applicable to the actual geometry and flow regime.

Keep calculated performance separate from physical test evidence. If a supplier supplies a performance figure, request the geometry, operating conditions, method and uncertainty or limits. Do not compare figures obtained under different conditions as if only the profile had changed.

## How should standards and inspection be agreed?

[ASTM A213/A213M-25](https://store.astm.org/a0213_a0213m-25.html) describes its seamless boiler, superheater and heat-exchanger tube scope. That public description is not proof that any arbitrary rectangular profile is certified under it. Confirm the applicable specification, dimensional provisions and additional drawing requirements using the complete documents.

For applicable tube specifications, [ASTM A1016/A1016M-24a](https://store.astm.org/a1016_a1016m-24a.html) explains the relationship among general, product and order requirements. Define the final geometry and examination scope explicitly.

Send the drawing, operating basis and inspection requirements through the [Junda contact page](https://jundapipe.com/contact). Request confirmation of manufacturable dimensions and documented deviations before using the proposed profile in an equipment design.