Appearance quality requirements for seamless stainless steel pipes

The appearance quality of seamless stainless steel pipes directly affects their performance, processing performance and corrosion resistance, so they must be strictly controlled. The following are common appearance quality requirements, usually referring to ASTM A312, ASTM A269, EN 10216-5, GB/T 14976 and other standards. It is mainly reflected in the following aspects.

1. The inner and outer surfaces should be smooth and flat, without obvious defects such as bumps, wrinkles, scratches, etc.

These defects may affect the performance of seamless pipes, such as reducing their pressure resistance and increasing fluid resistance. During visual inspection, the surface roughness should be uniform and there should be no obvious differences.

2. There should be no penetration defects such as cracks and cracks.
Cracks may cause seamless pipes to break during use, which seriously threatens safety. For tiny cracks, professional testing equipment is required to ensure the quality of seamless pipes.

Surface defect control, specific requirements are as follows:

(1) Defects that are not allowed to exist (scrap criteria)
Cracks (surface or end face)
Folds (overlapping defects formed during rolling or drawing)
Scars (protrusions formed by metal adhering to the surface)
Delamination (separation of inner and outer layers)
Severe scratches (depth exceeds the wall thickness tolerance)

(2) Minor defects that are allowed to exist (restricted)
Minor scratches: depth ≤ 0.05mm, and do not affect use.
Pits/pits: local, small amount, do not affect wall thickness and strength.
Oxidation color (such as slight discoloration after heat treatment): can be removed by pickling or polishing.

3. The color should be uniform.
Seamless stainless steel pipes are usually silver-white or stainless steel color. If color difference or local discoloration occurs, it may be due to uneven material or improper surface treatment.

The surface finish of seamless stainless steel pipes affects corrosion resistance and aesthetics. Common treatment methods and requirements:
a. Pickling surface: no residual oxide scale, uniform color, and slight color difference is allowed.
b. Polished surface: Ra≤0.8μm (mirror polishing can reach Ra≤0.4μm).
c. Electrolytic polishing: no microscopic burrs, improve corrosion resistance.

4. The ends of seamless pipes should be neat, without burrs, flash and other phenomena.

The quality of the ends of seamless pipes directly affects the connection and use of seamless pipes. Neat ends are convenient for welding, cutting and other processing operations.

Cut verticality: deviation ≤1° (high-precision pipes require higher requirements).
Burr control: burrs need to be removed to prevent scratches or affect welding.
Port protection: plastic end caps need to be installed during transportation to prevent bumps.

5. Straightness and ovality requirements
The straightness and ovality of stainless steel pipes affect assembly and processing:
Straightness: generally ≤1.5mm/m, high-precision pipes ≤0.5mm/m.
Ovality (out-of-roundness): outer diameter ≤±1% (high-precision pipes are more stringent).

6. Special purposes

For some stainless steel seamless pipes for special purposes, such as food hygiene grade seamless pipes, the surface is also required to be free of rust, oil and other impurities to ensure the safety and hygiene of food.

7. Steel pipe marking
The markings of seamless stainless steel pipes should be clear and complete, including information such as material, specification, and production, to facilitate installation, maintenance, and management.

8. Inspection method

The appearance inspection of seamless stainless steel pipes usually includes:

Visual inspection (VT): Check surface defects under sufficient light.
Eddy current flaw detection (ET): Detect tiny cracks on the surface.
Ultrasonic flaw detection (UT): Detect internal defects (such as inclusions and pores).
Surface roughness meter: Measure Ra value (such as polished pipe).

In short, the appearance quality requirements of seamless stainless steel pipes are strict. Only by meeting these requirements can the safe and reliable use of seamless pipes in various applications be guaranteed.

Read more: 7 Things to consider when purchasing stainless steel ERW pipes or Stainless Steel Seamless Pipe Manufacturing Process