Stainless Steel Cold-Drawn Coiltube — Re-Drawn Welded Pipe

Product Overview

The Stainless Steel Cold-Drawn Coiltube (also referred to as Re-Drawn Welded Pipe) is a premium intermediate-grade tube product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product represents a hybrid manufacturing approach that bridges the gap between conventional welded stainless steel pipe and fully seamless stainless steel tube. By subjecting a cold-welded stainless steel coil pipe to a secondary cold-drawing (cold re-drawing) process, the final product achieves the dimensional precision and mechanical integrity characteristic of seamless tubing, while retaining the cost-efficiency and extended length advantages inherent to the welded starting material.

This product is classified under Manufacturing Process → Forming Process → Re-Drawn Tube (重拉管), and is specifically designated as Welded Pipe Cold Re-Drawing (焊管再冷拔) within the industry taxonomy.

Material & Properties

Base Material

• Primary Grades: SUS 304, SUS 304L, SUS 316, SUS 316L, SUS 321, SUS 310S (AISI equivalents: 304, 304L, 316, 316L, 321, 310S)
• Alternative Grades: Custom alloy compositions available upon request (e.g., duplex stainless steel 2205, super austenitic 904L)

Mechanical Properties (Typical, Post Cold-Draw)

• Tensile Strength (UTS): 520–750 MPa (depending on grade and reduction ratio)
• Yield Strength (0.2% offset): 205–500 MPa
• Elongation (A50): ≥ 35% (annealed condition); ≥ 20% (cold-worked condition)
• Hardness: 95–320 HV (variable based on degree of cold work)

Key Metallurgical Characteristics

• Grain structure refinement achieved through controlled cold-drawing reduction ratios
• Elimination or near-complete removal of visible weld seam marks on both internal and external surfaces
• Homogenization of microstructure across the tube cross-section
• Improved surface finish (Ra ≤ 0.8 μm achievable on outer diameter; Ra ≤ 1.6 μm on inner diameter)

Specifications

Parameter	Specification / Range	Notes
Outer Diameter (OD)	6.0 mm – 168.3 mm (1/4" – 6")	Custom diameters available
Wall Thickness (WT)	0.3 mm – 6.0 mm	OD/WT ratio up to 100:1 achievable
Coil Length	10 m – 50 m (standard); up to 100 m on request	Continuous coil delivery format
OD Tolerance	±0.02 mm – ±0.10 mm	Significantly tighter than standard welded pipe
WT Tolerance	±0.01 mm – ±0.05 mm	Seamless-equivalent precision
Roundness	≤ 0.1% of nominal OD	Circularity maintained throughout coil
Surface Finish	BA (Bright Annealed), 2B, No.4, No.8, Mirror (#1200)	Post-draw surface treatment options
Heat Treatment	As-cold-drawn (CW), Annealed (SA), Solution Treated	Final temper condition per customer requirement
Weld Seam Residue	≤ 0.05 mm height (internal); effectively invisible externally	Key differentiator from standard welded pipe
Applicable Standards	ASTM A213/A213M, ASTM A269/A269M, EN 10216-5, GB/T 12771	Multi-standard compliance

Manufacturing Process

The production of Cold-Drawn Coiltube follows a multi-stage process engineered to transform a standard welded stainless steel coil pipe into a high-precision, seamless-equivalent product:

1. Stage 1 — Welded Pipe Fabrication (Starting Material):
   Stainless steel strip (coil) is fed through an Electric Resistance Welding (ERW) or Induction Welding (IW) line to produce a continuous welded coil pipe. This initial stage provides the cost advantage and long-length capability of welded manufacturing.
2. Stage 2 — Pre-Treatment:
   The welded coil pipe undergoes surface cleaning, scale removal (pickling and passivation if applicable), and inspection to ensure material readiness for cold working.
3. Stage 3 — Cold Re-Drawing (Secondary Cold Drawing):
   This is the critical differentiating process. The welded coil pipe is drawn through precision-die reduction stations (single-pass or multi-pass), achieving wall thickness reductions of 10%–40% per pass. This process:
   • Flows material over and through the weld seam, effectively eliminating visible weld marks
   • Reduces dimensional tolerances to seamless-pipe levels
   • Induces beneficial work hardening for improved mechanical properties
   • Homogenizes the microstructure across the tube circumference
4. Stage 4 — Intermediate Annealing (Optional):
   If multi-pass drawing is required to achieve target dimensions, intermediate solution annealing may be performed to relieve accumulated cold-work stresses and restore ductility.
5. Stage 5 — Final Surface Treatment:
   Post-drawing surface finishing (polishing, electropolishing, or passivation) is applied to achieve the specified surface grade.
6. Stage 6 — Final Inspection & Coiling:
   Comprehensive dimensional, mechanical, and surface quality verification is conducted. Product is then coiled and packaged for shipment.

Unique Selling Points

"Seamless Performance, Welded Economy" — The Cold-Drawn Coiltube uniquely combines the extended-length and cost-efficiency advantages of welded pipe manufacturing with the dimensional precision, surface quality, and mechanical homogeneity of seamless tube.

• Eliminated Weld Seam: The cold re-drawing process effectively removes visible weld seam traces on both the internal and external tube surfaces, achieving a near-seamless appearance.
• Superior Dimensional Accuracy: Tolerances are tightened to ±0.02 mm (OD) and ±0.01 mm (WT), far exceeding standard welded pipe specifications.
• Cost Efficiency: Compared to fully seamless tube (produced via hot-rolled or cold-finished seamless processes), this product offers 20%–35% cost savings while maintaining comparable performance.
• Extended Coil Length: Continuous production format enables coil lengths up to 100 meters, reducing downstream fabrication joints and improving material utilization.
• Enhanced Mechanical Properties: Controlled cold work imparts improved tensile strength and surface hardness without sacrificing corrosion resistance.
• Consistent Microstructure: Unlike standard welded pipe, the re-drawn product exhibits uniform grain structure around the entire circumference, eliminating the anisotropic behavior near the weld line.

Applications

Primary Industries

• Petrochemical & Oil/Gas: Downstream processing tubing, heat exchanger tubes, instrument piping (where seam-free internal surfaces are critical for flow uniformity)
• Food & Beverage Processing: Hygienic-grade process piping, CIP (Clean-In-Place) compatible tubing for dairy, brewery, and pharmaceutical applications
• Medical & Pharmaceutical: Equipment tubing, fluid transfer lines, sterilization-compatible components
• Automotive & Aerospace: Fuel lines, hydraulic tubing, exhaust system components, structural tubing
• Construction & Architecture: Decorative guardrails, structural supports, elevator guide tubes
• General Engineering: Precision hydraulic cylinders, pneumatic systems, fluid conveyance systems

Typical Use Cases

• High-pressure fluid systems requiring tight bore tolerances
• Applications where internal weld protrusion would cause flow turbulence or stress concentration
• Long-run installations where minimizing butt-weld joints is critical
• Projects requiring seamless-equivalent performance at reduced budget

Quality Certifications & Standards Compliance

Management System Certifications

• ISO 9001:2015 — Quality Management System
• ISO 14001:2015 — Environmental Management System
• ISO 45001:2018 — Occupational Health & Safety Management System

Product Standards & Compliance

• ASTM A213/A213M — Standard Specification for Seamless, Welded, and Heavy-Walled Austenitic Stainless Steel Tubes for High-Temperature Service
• ASTM A269/A269M — Standard Specification for Seamless, Welded, and Heavy-Walled Austenitic Stainless Steel Tubing for Chemical and Similar Severe Service
• EN 10216-5 — Non-ferrous metallic tubes and their fittings for pressure purposes — Technical delivery conditions — Part 5: Austenitic stainless steels
• GB/T 12771 — Welded steel tubes and fittings for general purposes (Chinese National Standard)
• GB/T 21832 — Stainless steel welded tubes for general industrial purposes

Testing & Inspection Protocols

• Hydrostatic pressure testing (per ASTM A269, typically 2–5× working pressure)
• Eddy current testing (ECT) for internal/external surface defect detection
• Dimensional inspection via ultrasonic thickness gauging and laser micrometry
• Spectroscopic chemical analysis (OES) for alloy composition verification
• Mechanical testing per ASTM E8/E8M (tensile) and ASTM A370 (hardness)
• Surface roughness verification per ISO 4287

Technical Summary

The Stainless Steel Cold-Drawn Coiltube manufactured by Wenzhou Jixing Metal Materials Co., Ltd represents a technically sophisticated intermediate product that leverages the Welded Pipe Cold Re-Drawing (焊管再冷拔) process to deliver seamless-grade quality at a competitive price point. With its ability to eliminate weld seam artifacts, achieve sub-0.1 mm dimensional tolerances, and maintain continuous coil delivery formats, this product occupies a strategically important niche in the stainless steel tubing market — particularly for applications demanding high precision, superior surface quality, and extended installation lengths.