Stainless Steel Coil Tube with Head Groove Assembly — Technical Specification

1. Product Overview

The Stainless Steel Coil Tube with Head Groove Assembly (hereinafter referred to as "Coil Tube Head Groove Product") is a precision-engineered stainless steel tubular component manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product integrates a coiled stainless steel tube (Coiltube) with a precisely machined head groove (Head Coil Tube Groove), designed to facilitate secure welding, mechanical fastening, or sealing interfaces between the coil tube and end fittings or pressure vessel heads (Dished Heads, Ellipsoidal Heads, or Flat Heads).

The manufacturing of head coil tube grooves represents a critical process in the fabrication of heat exchangers, pressure vessels, and high-temperature coil assemblies. The groove geometry, dimensional accuracy, and surface integrity directly determine the structural integrity, leak-tightness, and service life of the final assembly. This product line reflects advanced expertise in groove machining, material selection, and quality control within the stainless steel pipe and tube industry.

Key Insight: The manufacturing of head coil tube grooves requires an understanding of metallurgical properties, stress concentration effects, and welding compatibility. Improper groove preparation can lead to fatigue failure, stress corrosion cracking (SCC), or loss of pressure containment in critical service environments.

2. Material & Properties

2.1 Base Material Grades

2.2 Mechanical Properties

Property AISI 304/304L AISI 316/316L 2205 Duplex 904L
Tensile Strength (Rm) — MPa ≥ 515 ≥ 515 ≥ 550 ≥ 590
Yield Strength (Rp0.2) — MPa ≥ 205 ≥ 205 ≥ 450 ≥ 290
Elongation (A5) — % ≥ 40 ≥ 40 ≥ 25 ≥ 40
Corrosion Resistance (Pitting) — Excellent Moderate Good Very Good Excellent
Maximum Service Temperature — °C 870 870 300 1100
Chromium (Cr) Content — % 18–20 16–18 22–23 19–23
Nickel (Ni) Content — % 8–10.5 10–14 4.5–6.5 23–25

2.3 Physical Properties

3. Specifications

Parameter Specification / Range Applicable Standard
Outer Diameter (OD) Φ6.0 mm – Φ508.0 mm ASTM A312 / EN 10216-5
Wall Thickness 0.5 mm – 12.0 mm ASTM A312 / GB/T 12771
Coil Diameter (Minimum Bend Radius) 3 × OD (minimum); 5 × OD (recommended) Internal Specification
Coil Length (Per Spool) 10 m – 500 m (configurable) Customer-Specific
Head Groove Angle 60° ± 2° (V-groove); 37° ± 1° (Bevel) ASME Section IX / AWS D1.6
Groove Depth 0.5 mm – 6.0 mm (per wall thickness) ASME B31.3 / EN 13480
Groove Root Radius 1.5 mm – 3.0 mm ASME Section IX
Surface Finish (Ra) ≤ 0.8 μm (Polished); ≤ 3.2 μm (Pickled & Passivated) ASTM A240 / EN 10088
Dimensional Tolerance (OD) ± 0.05 mm (Precision); ± 0.5% (Standard) ASTM A312
Dimensional Tolerance (Wall) ± 10% (Standard); ± 5% (Precision) ASTM A312
Welding Method TIG (GTAW) / Orbital / Manual AWS D1.6 / EN ISO 15614
Packaging Wooden crate / Export-grade pallet with protective wrapping ISO 4180

4. Manufacturing Process

4.1 Process Flow

  1. Raw Material Inspection & Receiving: Incoming stainless steel seamless or welded tubes are verified against material certificates (MTC, EN 10204 Type 3.1/3.2). Chemical composition analysis (CMA) and mechanical testing are performed per lot.
  2. Cutting & Straightening: Tubes are cut to required lengths using precision plasma or laser cutting systems. Straightening ensures uniform geometry prior to coiling operations.
  3. Coiling (Tube Coiling): The straight tube is wound into a helical coil using CNC-controlled coiling machines. The coil diameter, pitch, and number of turns are controlled to maintain dimensional accuracy and avoid cold-work hardening beyond acceptable limits.
  4. Head Groove Preparation: The critical step — machining of the head coil tube groove — is performed on the tube end that will interface with the vessel head or end cap. This involves:
  • Welding (if applicable): Groove welds are executed using Tungsten Inert Gas (TIG / GTAW) welding with appropriate filler metals (e.g., ER308L, ER316L, ER2209). Back-purging with high-purity argon (≥ 99.995%) ensures the internal surface remains free of oxidation.
  • Post-Weld Heat Treatment (PWHT): Solution annealing at 1040–1120°C followed by rapid water quenching restores full austenitic structure and eliminates residual stresses. Stress-relief annealing may be applied for specific duplex grades at controlled temperatures (≤ 300°C).
  • Pickling & Passivation: Acid pickling removes heat-affected zone discoloration and chromium-depleted layers. Passivation with citric acid or nitric acid solutions restores the protective chromium oxide film (Cr₂O₃), enhancing corrosion resistance.
  • Non-Destructive Testing (NDT): Radiographic Testing (RT), Ultrasonic Testing (UT), Penetrant Testing (PT), and Magnetic Particle Testing (MT) are applied per customer specifications or applicable codes.
  • Final Inspection & Packaging: Dimensional verification, surface quality assessment, and hydrostatic pressure testing (per ASTM A530) are conducted prior to protective packaging and dispatch.

    • 4.2 Key Technical Considerations in Head Groove Manufacturing

    Critical Learning Point: The manufacturing of head coil tube grooves demands meticulous attention to the following factors:

    5. Applications

    5.1 Primary Application Sectors

    5.2 Typical Service Conditions

    Application Temperature Range (°C) Pressure Range (bar) Recommended Grade
    Oil Refinery Heat Exchanger 50 – 450 10 – 200 316L / 904L
    Cryogenic LNG Equipment -196 – -30 5 – 50 304L / 316L
    Pharmaceutical Bioreactor 20 – 130 1 – 15 316L (EP)
    Power Plant Boiler Coil 200 – 650 50 – 250 321 / 347H
    Chemical Reactor 30 – 350 5 – 100 2205 / Hastelloy C-276

    6. Quality Certifications & Compliance

    6.1 Applicable Standards & Codes