Cold Pilgering vs Hot Extrusion for Seamless Pipe
Not all seamless pipe is created equal. The manufacturing route — cold pilgering or hot extrusion — determines surface finish, dimensional precision, microstructure, and ultimately the pipe's suitability for critical applications. For semiconductor, pharmaceutical, and data center cooling, cold-pilgered 316L is not just preferred — it's mandatory.
Process Comparison
| Parameter | Hot Extrusion | Cold Pilgering |
|---|---|---|
| Process Temperature | 1150-1250°C (above recrystallization) | Room temperature (cold working) |
| Surface Finish (Ra) | 3.2-6.3 μm (requires pickling) | ≤ 0.8 μm (bright anneal capable) |
| Dimensional Tolerance | ±10-12.5% on wall thickness | ±5-8% on wall thickness |
| Microstructure | Coarse grain (recrystallized at high temp) | Fine, uniform grain (strain + recrystallization) |
| OD Range | 21-610mm typical | 3-220mm typical (small-medium diameters) |
| Production Rate | High (tons/hour) | Lower (meters/minute) |
| Cost | Lower (commodity pipe) | Higher (precision pipe) |
| Best For | General process piping, large diameters | Precision tube, semiconductor, pharma, data center |
Why Cold Pilgering for Critical Applications?
Surface Finish: Ra ≤ 0.8 μm
Cold pilgering compresses the metal against polished mandrels and dies, producing an exceptionally smooth ID surface. Combined with bright annealing in hydrogen atmosphere, the result is a mirror-like finish with Ra ≤ 0.8 μm — ideal for high-purity gas delivery and liquid cooling where surface roughness promotes biofilm and particle entrapment.
Grain Refinement
Cold working introduces dislocations and strain energy that drive recrystallization during subsequent annealing. The result is a fine, uniform grain structure (ASTM 6-8) compared to the coarser grain (ASTM 3-5) of hot-extruded pipe. Fine grains improve strength, fatigue resistance, and ultrasonic inspectability.
TOKO TECH Cold-Pilgering Capability
TOKO TECH operates cold pilger mills for stainless steel and nickel alloy tube from 3mm to 114mm OD. Our integrated process — cold pilgering → degreasing → bright annealing → straightening → ultrasonic cleaning → helium leak testing → cleanroom packaging — ensures every tube meets the most demanding surface finish and cleanliness specifications for semiconductor, pharmaceutical, and AI data center liquid cooling applications.