Recurso	Flange de aço inoxidável	Carbon Steel Flange
Main Alloy Elements	Ferro, Cromo (≥10.5%), Níquel	Ferro, Carbono (0.2–0.6%)
Resistência à corrosão	Excelente	Baixo (requires coating or lining)
Appearance	Silvery, brilhante, non-rusting	Dull gray, prone to rust
Magnetic Property	Usually non-magnetic (austenitic)	Magnetic
Custo	Mais alto	Mais baixo
Typical Grades	SS304, SS316, SS321	ASTM A105, A350LF2, Q235

1. Inspeção Visual

Flanges de aço inoxidável generally have a bright silver finish and resist oxidation. Even after extended exposure to air and moisture, they maintain a clean, shiny surface.

Carbon steel flanges, por outro lado, often appear dull gray or matte black. Without protective coatings like paint, galvanização, ou óleo, carbon steel flanges will rust over time.

Visual differences:

• Aço inoxidável: Polished or satin finish, clean look, no surface corrosion

• Aço carbono: Dull, may have red/brown rust spots or black oxide coating

sasa oblonga supplies flanges with mill finish or custom surface treatment to ensure easy identification and superior corrosion protection.

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2. Magnet Test

This is a quick and easy field test to identify the general category of steel:

• Aço carbono is always magnético

• Aço inoxidável varies:

  • Austenitic grades (por exemplo, SS304, SS316): Não magnético or slightly magnetic

  • Ferritic and martensitic grades: Magnetic

Place a magnet on the flange. If it sticks strongly, it’s likely carbon steel or ferritic stainless. If it barely reacts or does not stick, it is likely austenitic stainless steel.

Observação: Cold-working or machining austenitic stainless steel can make it slightly magnetic, so this test is not 100% conclusive.

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3. Spark Test

The spark test is commonly used in metal workshops:

• Aço carbono produces longo, branching orange sparks when touched with a grinder

• Aço inoxidável produces shorter, fewer sparks that are red or dull orange, often with less branching

This method requires experience and should be done with care. Always follow safety precautions when using grinders or spark tools.

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4. Weight Comparison

O aço inoxidável é slightly denser than carbon steel:

• Density of carbon steel: ~7.85 g/cm³

• Density of stainless steel (304/316): ~8.0 g/cm³

Although the difference is small, stainless steel flanges may feel slightly heavier than carbon steel flanges of the same size and design.

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5. Chemical Testing with Spot Kits

For more accuracy, chemical spot test kits are available to detect the presence of níquel, cromo, or molybdenum in stainless steel.

Por exemplo:

• Ácido nítrico: Stainless steel resists attack, while carbon steel shows rust or bubbling

• Copper sulfate: Reacts with carbon steel (copper plating visible) but not with stainless steel

These are semi-quantitative methods and give a reliable field indication of the material composition.

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6. Material Markings and Stamping

Reputable manufacturers like sasa oblonga mark each flange with:

• Grau do material (por exemplo, SS316, A105)

• Classificação de pressão (por exemplo, 150#, 300#)

• Size and schedule

• Padrão (por exemplo, ASME B16.5)

• Número de calor for traceability

Always check the stamping on the flange rim or hub. If a flange lacks clear markings, it should be tested before installation.

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7. Identificação Positiva de Material (PMI)

The most accurate way to distinguish flange material is Teste PMI using handheld analyzers like XRF (X-ray fluorescence) ou LIBRAS (laser-induced breakdown spectroscopy).

These devices provide:

• Elemental composition (por exemplo, Cr, Em, Fé, Mo)

• Grade matching (por exemplo, confirms 316L vs 304)

• Instant results in the field or warehouse

PMI is often required for critical systems in óleo & gás, vasos de pressão, and food processing equipment.

sasa oblonga offers full PMI testing and certification for stainless steel and carbon steel flange deliveries upon request.

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8. Corrosion Behavior

Expose a small, cleaned section of the flange to salt water spray or a humid environment for 24–48 hours.

• Aço carbono: Will show visible rust or reddish discoloration

• Aço inoxidável: Remains clean or may develop a light surface film, but no red rust

This simple exposure test helps confirm the corrosion resistance typical of stainless steel.

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Applications Based on Flange Material