Stainless Steel Coil Tube with Compression Fitting — Two-Step Pre-Assembly & Final Tightening System

Product Overview

Wenzhou Jixing Metal Materials Co., Ltd. presents a high-performance stainless steel coil tube (Coil Tube) engineered for reliable fluid conveyance in installation and maintenance applications. This product is specifically designed for use with compression fittings (Compression Fitting / 卡套接头), incorporating a proprietary two-step tightening procedure — consisting of pre-assembly (Pre-Assembly) and final assembly (Final Assembly) — to ensure leak-free, repeatable, and field-serviceable connections. The coil tube is supplied in a coiled configuration, enabling efficient on-site deployment without the need for additional bending or forming, thereby preserving the metallurgical integrity of the tube wall.

Material & Properties

The coil tube is manufactured from high-grade austenitic stainless steel, selected for its exceptional combination of corrosion resistance, mechanical strength, and formability. The material composition ensures long-term durability in demanding industrial environments.

Specifications

Parameter Specification Standard / Reference
Product Category Installation & Maintenance — Connection Process —
Sub-Category Compression Fitting (Compression Fitting) ISO 13879-2 / ASME B16.3
Tube Form Coil Tube (Coiled Configuration) ASTM A213 / ASTM A269
Material Grade 304 / 316 Austenitic Stainless Steel ASTM A270
Outer Diameter (OD) 3.18 mm – 50.8 mm (1/8" – 2") ASTM A269 / EN 10216-5
Wall Thickness (WT) 0.5 mm – 3.0 mm (based on pressure rating) ASME B31.3
Maximum Working Pressure Up to 6.3 MPa (914 psi) at 20 °C ASME B31.3 / EN 13480
Coil Diameter Standard coil diameters from 0.5 m to 1.5 m Manufacturer Specification
Surface Treatment Precision cold-drawn; optional passivation ASTM A967
Dimensional Tolerance OD tolerance: ±0.05 mm; WT tolerance: ±10% ASTM A269 / EN 10217
Elongation ≥ 40% ASTM A270
Tensile Strength ≥ 515 MPa (Grade 304) ASTM A270

Manufacturing Process & Two-Step Tightening Procedure

3.1 Coil Tube Production

The coil tube is produced through a precision cold-drawing process that ensures dimensional accuracy and surface quality critical for compression fitting compatibility. The manufacturing sequence includes:

  1. Hot Rolling: Production of seamless steel tube blanks from ingots or continuous casting billets
  2. Pickle & Decarb: Removal of scale and decarburization to restore full alloy chemistry
  3. Precision Cold Drawing: Multi-pass cold drawing through calibrated dies to achieve tight dimensional tolerances and smooth surface finish
  4. Solution Annealing: Heat treatment to restore full austenitic microstructure and eliminate cold-work stresses
  5. Precision Coil Winding: Automated coiling onto standardized spools with controlled tension to prevent deformation
  6. Passivation: Chemical treatment to enhance surface chromium oxide layer and improve corrosion resistance

3.2 Two-Step Tightening Procedure (Pre-Assembly + Final Assembly)

The integrity of the compression fitting connection is governed by a strict two-step tightening protocol. This methodical approach ensures proper engagement of the compression ring (Compression Ring / 卡套) against the tube outer surface, creating a reliable metal-to-metal seal without over-compression that could cause tube wall deformation or fitting damage.

Step 1 — Pre-Assembly (Pre-Tightening):
Insert the tube end fully into the fitting body (Insert Tube to Bottom), ensuring the tube end contacts the internal shoulder. Hand-tighten the nut (Hand-Tighten) until the compression ring is seated against the tube outer surface. This step aligns the fitting components and establishes initial contact geometry.
Step 2 — Final Assembly (Final Tightening):
Using an appropriate wrench (Wrench), rotate the nut an additional 1.25 turns (1¼ turns) beyond hand-tight position. This precise angular rotation deforms the compression ring inward, creating uniform radial clamping force on the tube OD and forming a leak-tight seal.

3.3 Critical Failure Modes & Prevention

Based on extensive field experience and engineering analysis, the following factors are identified as the primary causes of connection leakage. Strict adherence to quality control at each stage is essential:

Unique Selling Points

Applications

Quality Certifications & Compliance

Installation & Handling Guidelines

  1. Tube Preparation: Cut tube square (perpendicular to axis) with a precision tube cutter. Deburr and chamfer both ends. Inspect OD surface for scratches or ovality — reject any damaged tube.
  2. Insertion: Insert tube fully into the fitting body until the tube end contacts the internal shoulder. Do not force or tap the tube.
  3. Pre-Tighten: Hand-tighten the nut until the compression ring is visibly and audibly seated against the tube OD.
  4. Final Tighten: Using a wrench of the correct size, rotate the nut exactly 1.25 turns beyond hand-tight. Do not exceed this specification.
  5. Verification: Pressure-test the assembly to 1.5× the maximum working pressure and hold for a minimum of 30 minutes. Inspect for any signs of leakage at the fitting interface.
Warning: Exceeding the 1.25-turn specification will over-compress the tube wall, causing permanent deformation and potential catastrophic failure. Insufficient tightening will result in incomplete compression ring engagement and gradual leakage under cyclic pressure loading.