Tính năng	Stainless Steel Flange	Carbon Steel Flange
Main Alloy Elements	Sắt, crom (≥10.5%), Niken	Sắt, Cacbon (0.2–0.6%)
Chống ăn mòn	Xuất sắc	Thấp (requires coating or lining)
Appearance	Silvery, sáng, non-rusting	Dull gray, prone to rust
Magnetic Property	Usually non-magnetic (austenitic)	Magnetic
Trị giá	Cao hơn	Thấp hơn
Typical Grades	SS304, SS316, SS321	ASTM A105, A350 LF2, Q235

1. Kiểm tra trực quan

Mặt bích thép không gỉ generally have a bright silver finish and resist oxidation. Even after extended exposure to air and moisture, they maintain a clean, shiny surface.

Mặt bích thép carbon, mặt khác, often appear dull gray or matte black. Without protective coatings like paint, mạ điện, hoặc dầu, carbon steel flanges will rỉ sét theo thời gian.

Visual differences:

• Thép không gỉ: Polished or satin finish, clean look, no surface corrosion

• Thép cacbon: Dull, may have red/brown rust spots or black oxide coating

sasa thuôn dài 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:

• Thép cacbon is always magnetic

• Thép không gỉ varies:

  • Austenitic grades (ví dụ., SS304, SS316): Không có từ tính 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 thép không gỉ austenit.

Ghi chú: 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:

• Thép cacbon produces long, branching orange sparks when touched with a grinder

• Thép không gỉ 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

Thép không gỉ là 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 niken, crom, or molybdenum in stainless steel.

Ví dụ:

• Axit nitric: 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 thuôn dài mark each flange with:

• Lớp vật liệu (ví dụ., SS316, A105)

• Đánh giá áp suất (ví dụ., 150#, 300#)

• Size and schedule

• Tiêu chuẩn (ví dụ., ASME B16.5)

• Số nhiệt 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. Xác định vật liệu tích cực (PMI)

The most accurate way to distinguish flange material is Kiểm tra PMI using handheld analyzers like XRF (X-ray fluorescence) hoặc LIBS (laser-induced breakdown spectroscopy).

These devices provide:

• Elemental composition (ví dụ., Cr, TRONG, Fe, Mo)

• Grade matching (ví dụ., confirms 316L vs 304)

• Instant results in the field or warehouse

PMI is often required for critical systems in dầu & khí đốt, bình áp lực, and food processing equipment.

sasa thuôn dài 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.

• Thép cacbon: Will show visible rust or reddish discoloration

• Thép không gỉ: 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