Stainless Steel Coil Tube (Coiltube) for Startup Heating Furnace Applications
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd. | Product Catalog No.: 1481 | Classification: Industrial Tubular Products — Literature & Technical Reference Series
This technical specification is derived from the engineering study and technical transformation experience documented in the reference work “Startup Heating Furnace Coil Tube Technical Retrofit — Learning and Practice Review”, reflecting field-proven engineering knowledge accumulated in high-temperature process environments.
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered tubular product manufactured in continuous coil form, specifically designed for high-temperature process applications including startup heating furnaces, reformers, and heat exchangers. Unlike conventional cut-length pipes, coil tubes are supplied in rolled coil configuration, which offers significant advantages in terms of material utilization, welding continuity, and installation efficiency.
Wenzhou Jixing Metal Materials Co., Ltd. specializes in the production and supply of stainless steel coil tubes that meet rigorous metallurgical standards. These products are integral to the technical transformation (technical retrofit) of startup heating furnaces, where enhanced thermal performance, corrosion resistance, and mechanical integrity under cyclic thermal loading are critical requirements.
The coil tube product line addresses the industry-wide challenge of improving furnace efficiency, reducing maintenance downtime, and extending service life in petrochemical and energy processing environments.
2. Material Composition and Properties
2.1 Base Material Grades
Stainless steel coil tubes for heating furnace applications are typically manufactured from the following austenitic and austenitic-ferritic stainless steel grades, selected based on operating temperature, corrosive medium, and mechanical requirements:
- SAE 304 / ASTM 304 (UNS S30400): General-purpose austenitic stainless steel with excellent corrosion resistance and formability; suitable for temperatures up to 870 °C.
- SAE 316 / ASTM 316 (UNS S31600): Molybdenum-enhanced austenitic stainless steel offering superior resistance to pitting and crevice corrosion; suitable for temperatures up to 870 °C.
- SAE 321 / ASTM 321 (UNS S32100): Titanium-stabilized austenitic stainless steel providing enhanced resistance to intergranular corrosion during welding; suitable for temperatures up to 900 °C.
- SAE 310 / ASTM 310 (UNS S31000): High-temperature austenitic stainless steel with excellent oxidation resistance; suitable for temperatures up to 1090 °C.
- SAE 347 / ASTM 347 (UNS S34700): Niobium-stabilized austenitic stainless steel for high-temperature service; suitable for temperatures up to 900 °C.
2.2 Mechanical Properties (Typical Values at Room Temperature)
| Property | SAE 304 | SAE 316 | SAE 321 | SAE 310 |
|---|---|---|---|---|
| Tensile Strength (MPa) | 515–720 | 515–720 | 515–720 | 515–720 |
| Yield Strength (0.2% Offset, MPa) | ≥ 205 | ≥ 205 | ≥ 205 | ≥ 205 |
| Elongation (%) | ≥ 40 | ≥ 40 | ≥ 40 | ≥ 40 |
| Density (g/cm³) | 8.00 | 8.03 | 8.00 | 8.00 |
| Thermal Conductivity at 100 °C (W/m·K) | 16.3 | 14.6 | 16.3 | 16.3 |
| Thermal Expansion Coefficient (10−6/K, 20–100 °C) | 17.3 | 16.0 | 17.3 | 18.5 |
2.3 Chemical Composition Requirements (wt%)
| Element | C | Cr | Ni | Mo | Ti / Nb | Si | Mn | P | S |
|---|---|---|---|---|---|---|---|---|---|
| SAE 304 | ≤0.08 | 18.0–20.0 | 8.0–10.5 | — | — | ≤0.75 | ≤2.00 | ≤0.045 | ≤0.030 |
| SAE 316 | ≤0.08 | 16.0–18.0 | 10.0–14.0 | 2.0–3.0 | — | ≤0.75 | ≤2.00 | ≤0.045 | ≤0.030 |
| SAE 321 | ≤0.08 | 17.0–19.0 | 9.0–12.0 | — | 5×C–0.70 | ≤0.75 | ≤2.00 | ≤0.045 | ≤0.030 |
| SAE 310 | ≤0.20 | 24.0–26.0 | 19.0–22.0 | — | — | ≤1.50 | ≤2.00 | ≤0.045 | ≤0.030 |
3. Technical Specifications
3.1 Dimensional Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 12.7 mm – 168.3 mm (0.500″ – 6.625″) | ASTM A213 / ASME SA-213 |
| Wall Thickness | 1.0 mm – 12.7 mm (0.040″ – 0.500″) | ASTM A213 / ASME SA-213 |
| Coil Length | 15 m – 300 m (per coil, customizable) | Manufacturer Specification |
| Coil Inner Diameter | 300 mm – 600 mm (adjustable) | Manufacturer Specification |
| OD Tolerance | ±0.05 mm – ±0.20 mm (depending on diameter) | ASTM A213 |
| Wall Thickness Tolerance | ±10% (minimum ±0.10 mm) | ASTM A213 |
| Straightness (per 3 m) | ≤ 3.0 mm | ASTM A213 |
| Coil Diameter Tolerance | ±10 mm | Manufacturer Specification |
3.2 Surface Finish and Condition
| Surface Condition | Description | Typical Ra (Surface Roughness) |
|---|---|---|
| Hot Finished & Annealed | Standard mill finish with oxide scale removed; suitable for general furnace applications | 1.6 – 3.2 µm |
| Pickled & Passivated | Acid pickled to remove scale, followed by passivation treatment for enhanced corrosion resistance | 0.8 – 1.6 µm |
| Machined / Ground | Mechanically finished for precision applications requiring tight dimensional tolerances | 0.2 – 0.8 µm |
3.3 Available End Forms
- Plain End: Standard cut end with deburring
- Beveled End: 37.5° or 60° bevel per ASME B16.25
- Threaded End: NPT, BSP, or custom thread per ASME B1.20.1
- Butt Weld Preparation: Per ASME B16.25A
4. Manufacturing Process
4.1 Process Flow
The manufacturing of stainless steel coil tubes follows a rigorous multi-stage process to ensure metallurgical integrity and dimensional accuracy:
- Raw Material Selection: Virgin stainless steel ingots or continuous cast slabs are sourced from certified steel mills with traceable heat numbers. Each heat is accompanied by a mill test certificate (MTC) verifying chemical composition and mechanical properties.
- Hot Rolling / Seamless Tube Production (Bundling & Piercing): For seamless coil tubes, the steel billet is heated to 1,150–1,250 °C and pierced through a mandrel to form a hollow tube. For welded coil tubes, hot-rolled strip is prepared for forming.
- Hot Forming / Tube Sizing: The tube blank is passed through a series of sizing rolls to achieve the target outer diameter and wall thickness. For welded tubes, the strip is formed into a round cross-section and the longitudinal seam is welded using High-Frequency Induction Welding (HF Welding) or TIG (Tungsten Inert Gas) Welding.
- Coil Winding: The continuous tube is wound onto a coil spool with controlled tension to ensure uniform curvature and prevent deformation. Coil diameter is controlled within specified tolerances.
- Heat Treatment (Annealing): The coil tube is subjected to solution annealing at 1,010–1,150 °C followed by controlled cooling (air cooling or furnace cooling depending on grade). This process relieves residual stresses, dissolves carbide precipitates, and restores full austenitic microstructure for optimal corrosion resistance and ductility.
- Pickling and Passivation: The annealed coil is immersed in a mixed acid bath (typically HNO3/H2SO4 or HNO3/HF) to remove oxide scale. This is followed by passivation with dilute nitric acid or citric acid to form a protective chromium oxide film on the surface.
- Dimensional Inspection and Quality Control: Each coil undergoes comprehensive inspection including dimensional measurement, visual examination, and non-destructive testing (NDT).
- Packaging and Marking: Coils are wrapped with protective material, labeled with product identification, heat number, and traceability information, and prepared for shipment.
4.2 Key Process Parameters for Startup Heating Furnace Coil Tubes
| Process Step | Key Parameters | Quality Objective |
|---|---|---|
| Solution Annealing |