特徴	ステンレス製フランジ	Carbon Steel Flange
Main Alloy Elements	鉄, クロム (≥10.5%), ニッケル	鉄, 炭素 (0.2–0.6%)
耐食性	素晴らしい	低い (requires coating or lining)
Appearance	Silvery, 明るい, non-rusting	Dull gray, prone to rust
Magnetic Property	Usually non-magnetic (austenitic)	Magnetic
料金	より高い	より低い
Typical Grades	SS304, SS316, SS321	ASTM A105, A350 LF2, Q235

1. 目視検査

Stainless steel flanges 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, 一方で, often appear dull gray or matte black. Without protective coatings like paint, 亜鉛メッキ, またはオイル, carbon steel flanges will rust over time.

Visual differences:

• ステンレス鋼: Polished or satin finish, clean look, no surface corrosion

• 炭素鋼: Dull, may have red/brown rust spots or black oxide coating

ササフランジ 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:

• 炭素鋼 is always 磁気

• ステンレス鋼 varies:

  • Austenitic grades (例えば, SS304, SS316): 非磁性 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.

注記: 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:

• 炭素鋼 produces 長さ, branching orange sparks when touched with a grinder

• ステンレス鋼 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

ステンレス鋼は 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 ニッケル, クロム, or molybdenum in stainless steel.

例えば:

• Nitric acid: 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 ササフランジ mark each flange with:

• 材質グレード (例えば, SS316, A105)

• 圧力定格 (例えば, 150#, 300#)

• Size and schedule

• 標準 (例えば, ASME B16.5)

• 熱数 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. 確実な物質識別 (PMI)

The most accurate way to distinguish flange material is PMIテスト using handheld analyzers like XRF (蛍光X線) または ライブラリ (laser-induced breakdown spectroscopy).

These devices provide:

• Elemental composition (例えば, Cr, で, 鉄, モー)

• Grade matching (例えば, confirms 316L vs 304)

• Instant results in the field or warehouse

PMI is often required for critical systems in 油 & ガス, 圧力容器, and food processing equipment.

ササフランジ 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.

• 炭素鋼: Will show visible rust or reddish discoloration

• ステンレス鋼: 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