Acceptance criteria for 304 stainless steel pipe

1. Chemical Composition

The pipe must meet the standard chemical composition for 304 stainless steel as per applicable standards (e.g., ASTM A312, ASME, etc.):

Chromium (Cr): 18.0–20.0%

Nickel (Ni): 8.0–10.5%

Carbon (C): Max 0.08%

Manganese (Mn): Max 2.0%

Phosphorus (P): Max 0.045%

Sulfur (S): Max 0.030%

Silicon (Si): Max 1.0%

Nitrogen (N): Max 0.10%

2. Mechanical Properties

The following mechanical properties are typically required for 304 stainless steel pipes:

Tensile Strength: Minimum 515 MPa (75,000 psi)

Yield Strength (0.2% offset): Minimum 205 MPa (30,000 psi)

Elongation: Minimum 35% for pipes of smaller diameters.

Hardness: Usually measured in Rockwell B or Vickers hardness scale. Max Rockwell B hardness is often limited to 92.

3. Dimensional Tolerances

Pipes must meet specific dimensional tolerances based on relevant standards (e.g., ASTM A269, A312):

Outer Diameter (OD): Tolerances are generally within ±0.5%.

Wall Thickness: Typically within ±10% of the specified nominal thickness.

Length: Tolerances for length can vary depending on whether the pipe is cut to fixed lengths or random lengths.

Ovality: The difference between maximum and minimum OD should be controlled within permissible limits.

4. Surface Finish

Internal and External Surface: Should be free from defects such as cracks, gouges, pits, or visible impurities that may affect performance.

Polishing: For some applications (e.g., sanitary), a specific surface finish may be required (e.g., a No. 4 or 2B finish).

Pickling and Passivation: Post-fabrication treatment processes like pickling and passivation may be required to improve the corrosion resistance of the pipe.

5. Weld Quality

Weld Bead: The welded seam must be smooth, free from defects such as cracks, undercutting, or excessive convexity/concavity.

Non-Destructive Testing (NDT): Welds are often inspected using methods like X-ray or ultrasonic testing to ensure the integrity of the welds.

Fusion: No lack of fusion or incomplete penetration should be present in the weld area.

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