Stainless Steel Coil Tube (Coiltube) — Metallurgical & Eddy Current Verified

Product Overview

The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product designed for demanding industrial and commercial applications. Unlike conventional seamless stainless steel tubing, coil tubes are produced through a continuous cold-drawing or cold-rolling process that yields superior dimensional consistency, surface finish, and mechanical properties. This product line is subject to rigorous verification protocols—specifically Metallographic Examination (金相验证) and Eddy Current Testing (涡流验证)—to ensure authenticity and prevent the substitution of welded tubes for seamless equivalents (a practice known as "weld-pass-off-as-seamless" fraud).

In the stainless steel pipe and tube industry, the visual distinction between high-quality welded coil tubes and true seamless tubes can be negligible. This creates a significant supply chain integrity risk. Wenzhou Jixing Metal Materials addresses this challenge by implementing a dual-verification system that provides the only reliable means of differentiation when appearance alone is insufficient.

Material & Properties

Coil tubes are typically fabricated from austenitic stainless steel grades, including but not limited to:

Key Mechanical Properties (Typical Values for Grade 304):

Specifications

Parameter Specification Standard Reference
Product Type Stainless Steel Coil Tube (盘管) —
Material Grades 304, 304L, 316, 316L, 321, 310S ASTM A213 / ASTM A269 / EN 10216-5
Outer Diameter (OD) 6.0 mm – 50.8 mm (1/4" – 2") ASTM A554 / DIN 2391
Wall Thickness 0.5 mm – 3.0 mm Per customer specification
Coil Weight 500 kg – 3,000 kg per coil —
Surface Finish BA (Bright Annealed), 2B, No.4, Hairline ASTM A478
Tolerance (OD) ±0.10 mm (Standard) / ±0.05 mm (Precision) ASTM A269
Tolerance (Wall) ±10% (Standard) / ±5% (Precision) EN 10216-5
Heat Treatment Solution Annealed (固溶退火) 1050–1150°C, water quench
Verification Method Metallographic Examination + Eddy Current Testing ASTM E309 / GB/T 6394
End Condition Plain, Beveled, or Custom Per customer requirement

Manufacturing Process

The production of stainless steel coil tubes follows a tightly controlled multi-stage process:

  1. Coil Cutting (开卷) — Cold-rolled stainless steel strip is slit to precise width and fed into the forming station.
  2. Forming & Welding (成型焊接) — The strip is cold-formed into a tube shape and joined via Argon Arc Welding (TIG) or Laser Welding, ensuring a high-integrity weld seam.
  3. Heat Treatment (热处理) — The welded tube undergoes solution annealing at 1050–1150°C followed by rapid cooling to homogenize the microstructure and restore corrosion resistance in the Heat-Affected Zone (HAZ).
  4. Pickling & Passivation (酸洗钝化) — Removal of mill scale and oxide layers, followed by passivation to restore the protective chromium oxide film.
  5. Cold Drawing / Sizing (冷拔定径) — Precision sizing to achieve tight dimensional tolerances and improved surface quality.
  6. Coiling (盘卷) — Finished tubing is coiled at controlled tension to prevent deformation during storage and transport.
  7. Quality Verification (质量验证) — Metallurgical and eddy current inspection to confirm product authenticity and structural integrity.

Quality Verification: Metallurgical & Eddy Current Testing

This product category is subject to a mandatory dual-verification protocol, which constitutes the industry's only reliable method for distinguishing genuine seamless tubing from welded tubing when visual and dimensional inspection yields identical results.

Metallographic Examination (金相检验)

Metallographic examination involves cross-sectional sampling of the tube wall, specifically targeting the weld zone. Under optical microscopy (typically 100×–500× magnification), a genuine seamless tube exhibits a uniform, homogeneous grain structure throughout the entire wall thickness. In contrast, a welded tube displays:

Reference Standard: GB/T 6394 — Microstructural Examination of Metallic Materials; ASTM E3-94 — Standard Guide for Preparation of Metallographic Samples

Eddy Current Testing (涡流检测)

Eddy Current Testing (ECT) utilizes electromagnetic induction to detect discontinuities and structural anomalies in conductive materials. A probe generates alternating magnetic fields that induce eddy currents within the tube wall. Any structural variation—such as a weld seam, seam offset, or HAZ microstructural change—alters the impedance signal, producing a detectable deviation from the baseline of a homogeneous seamless tube.

Reference Standard: ASTM E309 — Standard Practice for Eddy Current Examination of Seamless and Welded Stainless Steel Tubing; ISO 15771

Industry Note: When the external appearance, dimensional accuracy, and surface finish of a welded coil tube are engineered to closely replicate those of a seamless tube, metallurgical and eddy current verification represent the sole reliable means of differentiation. This makes these protocols indispensable for risk mitigation in high-value procurement scenarios.

Applications

Stainless steel coil tubes verified through metallurgical and eddy current protocols find application in sectors where material authenticity and structural integrity are critical:

Quality Certifications & Compliance

Wenzhou Jixing Metal Materials Co., Ltd. maintains adherence to the following international and national standards:

Unique Selling Points