Stainless Steel Coil Tube with Two-Step Ferrule Fitting Installation System

Product Overview

This product is a stainless steel coil tube (Coil Tube) designed specifically for applications requiring compact, pre-formed piping configurations with reliable leak-free connections. The tube is supplied in a coiled configuration, enabling rapid deployment and installation in confined spaces where straight-length tubing would be impractical. The system integrates a precision ferrule fitting (Compression Ferrule Fitting) connection methodology employing a proprietary two-step tightening procedure — comprising a pre-installation stage and a final assembly stage — to ensure optimal sealing integrity and mechanical stability at every joint.

Manufactured by Wenzhou Jixing Metal Materials Co., Ltd., this coil tube product falls under the Installation & Maintenance category, specifically within the Connection Process sub-classification. The two-step tightening technique is a critical engineering protocol that distinguishes this product from conventional single-step tightening methods, significantly reducing the risk of over-compression, galling, and premature seal failure.

Material & Properties

The coil tube is fabricated from high-grade austenitic stainless steel, selected for its superior corrosion resistance, mechanical strength, and formability. The material composition and properties are as follows:

Specifications

Parameter Specification Standard / Tolerance
Product Designation Coil Tube (盘管), Item No. 219 —
Tube Outer Diameter (OD) 3.0 – 51.0 mm (available in multiple sizes) ±0.1 mm (per ASTM A269)
Wall Thickness 0.3 – 3.0 mm (variable by application) ±10% of nominal
Coil Inner Diameter 150 – 600 mm (customizable) ±5 mm
Coil Length 5 – 50 m per coil (standard) ±0.5 m
Ovality (Out-of-Roundness) ≤ 0.5% of nominal OD Critical — primary leak prevention parameter
Surface Condition No scratches, nicks, or surface defects Visual inspection per ASME B31.3
End Preparation Deburred, chamfered to 15° for ferrule fitting engagement ASME B16.3
Material Grade ASTM A269 TP304 / TP316L / TP321 Mill Certificate (EN 10204 3.1)
Applicable Fitting Type Double Ferrule Compression Fitting (卡套接头) ASME B16.3 / ISO 1549

Manufacturing Process

3.1 Tube Production

  1. Hot Rolling & Annealing: Stainless steel strip or wire is hot-rolled into a hollow tube blank and annealed to relieve residual stresses and achieve the desired austenitic microstructure.
  2. Cold Drawing: The tube blank undergoes multi-pass cold drawing through precision-die tooling to achieve the target outer diameter and wall thickness within tight dimensional tolerances.
  3. Pickling & Passivation: The drawn tube is pickled in a nitric-hydrofluoric acid bath to remove oxide scale, followed by passivation treatment to restore the protective chromium oxide layer.
  4. Surface Polishing: Interior and exterior surfaces are polished (mechanically or via electropolishing) to achieve a smooth finish free of scratches, inclusions, or surface defects.
  5. Dimensional Inspection: Each tube undergoes 100% inspection for ovality, dimensional accuracy, and surface integrity using optical comparators and surface profilometers.

3.2 Coiling Process

  1. Controlled Coiling: The finished tube is coiled using precision coil forming equipment with controlled bending radius (minimum bend radius ≥ 5× OD) to prevent kinking, ovalization, or wall thinning.
  2. Stress Relief: Post-coiling stress-relief annealing is performed at 850–950 °C to eliminate coiling-induced residual stresses without grain growth.
  3. End Finishing: Tube ends are cut square, deburred, and chamfered to facilitate proper ferrule fitting engagement.

Two-Step Ferrule Fitting Installation Procedure

The connection integrity of this coil tube system relies on a rigorously defined two-step tightening methodology for the double ferrule compression fitting (卡套接头). This procedure is divided into a Pre-Installation Stage (预装) and a Final Assembly Stage (终装), each serving a distinct mechanical function:

Step 1: Pre-Installation (预装) — Seating the Rear Ferrule

  1. Tube Insertion: The prepared tube end is inserted fully into the ferrule fitting body until it bottoms out against the seat. The tube must be inserted to the full depth mark — partial insertion is a critical failure mode.
  2. Hand Tightening (Hand-Tight): The fitting nut is threaded onto the fitting body and tightened by hand only, until the nut contacts the front ferrule. This step ensures the rear ferrule is properly seated behind the tube and the front ferrule is positioned at the correct initial location.
  3. Purpose: The hand-tight step allows the rear ferrule to take its initial bite on the tube, establishing the primary seal. This prevents the rear ferrule from shifting during the subsequent wrench tightening.

Step 2: Final Assembly (终装) — Finalizing the Seal

  1. Wrench Tightening — 1.25 Turns: Using the appropriate open-end wrench, the fitting nut is rotated an additional 1.25 turns (3/4 turn beyond the hand-tight position plus an additional 1/2 turn, totaling 1.25 turns from hand-tight). This controlled over-tightening compresses the front ferrule against the tube outer surface, creating the secondary mechanical seal and locking the assembly.
  2. Leak Testing: After tightening, the joint must be pressure-tested to the design system pressure to verify seal integrity. No visible seepage or pressure drop is permissible.
Critical Installation Note: The 1.25-turn specification is calibrated for standard tube wall thicknesses (0.5–1.5 mm). For thicker-wall tubing, the tightening angle may need adjustment per the fitting manufacturer's published torque/angle chart. Deviation from the specified 1.25 turns — either under-tightening or over-tightening — will compromise seal integrity and may result in field leakage.

Leakage Prevention — Critical Quality Parameters

Based on extensive field experience and failure analysis, the following three factors are identified as the primary root causes of connection leakage in coil tube ferrule fitting systems:

Failure Mode Description Prevention Measure
Scratches (划伤) Surface scratches on the tube outer diameter, caused during handling, coiling, or cutting, create stress concentration points that prevent the ferrule from achieving uniform contact and sealing Handle with clean gloves; use non-marring cutting tools; inspect tube ends with magnification before installation
Ovality (椭圆) Out-of-round cross-section of the tube, resulting from improper coiling, transportation damage, or manufacturing defects, causes uneven ferrule bite and localized high stress Maintain ovality ≤ 0.5% of OD; perform 100% dimensional inspection; avoid dropping or compressing coils
Dimensional Out-of-Tolerance (尺寸超差) Tube OD or wall thickness deviating from specified tolerances results in improper ferrule engagement geometry, leading to incomplete seal formation Source material with mill certification; verify dimensions with calibrated micrometers; reject tubes outside ±0.1 mm tolerance

Applications

The stainless steel coil tube with two-step ferrule fitting connection system is widely deployed across the following industries and applications:

Quality Certifications & Compliance

This product is manufactured and certified in accordance with the following international standards and quality frameworks:

Unique Selling Points