Stainless Steel Coil Tube for High-Pressure Steam Superheater Applications
Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product specifically designed for high-pressure steam superheater systems in metallurgical primary reforming furnaces (Primary Furnace). This product category addresses the critical demand for durable, high-performance coil tubing in extreme thermal and pressure environments encountered during natural gas reforming, hydrogen production, and ammonia synthesis processes.
Unlike conventional straight-length stainless steel tubing, coil tubes are formed in a continuous helical or serpentine configuration, enabling compact heat exchanger designs with superior thermal transfer efficiency. The coil geometry allows for extended heating surface area within a confined furnace volume, making it indispensable for high-pressure steam superheater (HPSS) applications where steam temperatures routinely exceed 450°C under pressures of 3.0–5.0 MPa.
Material & Properties
Base Alloy Selection
Coil tubes for high-pressure steam superheater duty are typically fabricated from the following stainless steel grades, selected based on operating temperature, pressure, and corrosive medium:
- SAE 310 / UNS S31008 — Austenitic chromium-nickel steel with excellent hot strength and oxidation resistance up to 1150°C; preferred for superheater outlet zones.
- SAE 310S / UNS S31008 (low-carbon variant) — Enhanced weldability and reduced sensitization risk during fabrication.
- SAE 309 / UNS S30908 — High-temperature structural applications with moderate corrosion resistance.
- SAE 321 / UNS S32108 — Ti-stabilized austenitic grade for intermediate temperature zones.
- SAE 347 / UNS S34708 — Nb-stabilized alternative offering superior resistance to intergranular corrosion at elevated temperatures.
Mechanical Properties (Typical at Room Temperature)
| Property | SAE 310 | SAE 310S | SAE 321 | SAE 347 |
|---|---|---|---|---|
| Tensile Strength (MPa) | ≥ 520 | ≥ 520 | ≥ 515 | ≥ 515 |
| Yield Strength (MPa) | ≥ 205 | ≥ 205 | ≥ 205 | ≥ 205 |
| Elongation (%) | ≥ 40 | ≥ 40 | ≥ 40 | ≥ 40 |
| Density (g/cm³) | 7.94 | 7.94 | 7.93 | 7.93 |
| Thermal Conductivity (W/m·K at 100°C) | 22.8 | 22.8 | 16.3 | 16.3 |
| Maximum Continuous Service Temperature (°C) | 1150 | 1150 | 870 | 870 |
Corrosion & Oxidation Resistance
The high chromium (≥ 24–25 wt%) and nickel (≥ 19–20 wt%) content in SAE 310-series alloys provides exceptional resistance to scaling, oxidation, and carburization in reducing and oxidizing furnace atmospheres. In the context of primary furnace high-pressure steam superheater retrofitting, these materials demonstrate minimal scale formation rates under continuous cyclic thermal loading, directly translating to extended service intervals and reduced maintenance downtime.
Specifications
| Parameter | Specification |
|---|---|
| Product Name | Stainless Steel Coil Tube (Coiltube) |
| Manufacturer | Wenzhou Jixing Metal Materials Co., Ltd. |
| Item Number | 543 |
| Outer Diameter (OD) | Φ 19.0 mm – Φ 76.0 mm (customizable) |
| Wall Thickness | 1.5 mm – 5.0 mm (per ASME B36.19M) |
| Coil Diameter | Φ 600 mm – Φ 3000 mm (adjustable to furnace layout) |
| Tube Length (Uncoiled) | Up to 300 m continuous coil |
| Surface Finish | 2B / BA / Pickled & Passivated |
| Operating Pressure | Up to 5.0 MPa (gauge) |
| Operating Temperature | Up to 1150°C (material-dependent) |
| Applicable Standards | ASTM A213, ASME SA-213, EN 10216-5, GB/T 12771 |
| Heat Treatment | Solution Annealed (1050–1150°C, water/quench) |
| Non-Destructive Testing | Eddy Current (ECT), Ultrasonic (UT), Hydrostatic |
Manufacturing Process
The production of high-performance stainless steel coil tubes for superheater applications follows a rigorously controlled multi-stage process:
- Raw Material Verification — Ingot or hot-rolled coil sourced from certified mills undergoes full chemical composition analysis (OES, wet chemistry) and mechanical property validation prior to acceptance.
- Hot Rolling & Annealing — Billet or slab is hot-rolled into seamless tube blanks per ASTM A213 specifications, followed by solution annealing to achieve uniform austenitic microstructure.
- Piercing & Pilgering — Seamless tube is produced via Mannesmann piercing or cross-rolling, then pilgered to intermediate dimensions with tight dimensional tolerances (±0.1 mm).
- Pilot Rolling & Sizing — Cold or hot pilot rolling refines wall thickness and OD to final specifications, ensuring uniformity critical for coil forming.
- Pickling & Passivation — Tubes are pickled in mixed acid baths (HNO₃/HF or HNO₃/HCl) to remove scale, followed by passivation to form a stable chromium oxide protective layer.
- Coil Forming (Coiling) — Using precision coil-bending machines with CNC-controlled roll stations, straight tubes are formed into the required helical or serpentine geometry without inducing residual stresses or work hardening that would compromise fatigue life.
- Post-Forming Annealing — Stress-relief annealing (850–950°C, furnace cool) eliminates residual stresses introduced during coiling, restoring ductility and ensuring dimensional stability.
- Final Inspection & Testing — Comprehensive quality assurance including dimensional gauging, surface defect inspection (magnetic particle or visual), ECT scanning for internal wall thickness variation, and hydrostatic pressure testing at 1.5× design pressure.
Applications
Primary Application: Primary Furnace High-Pressure Steam Superheater Retrofit
The primary application context for this coil tube product relates to the renewal and retrofit of primary furnace high-pressure steam superheater systems in large-scale natural gas reforming plants. Key application scenarios include:
- Natural Gas Steam Reforming (SMR) — Coil tubes serve as superheater elements within or adjacent to primary reformer tubes, recovering waste heat to generate high-pressure superheated steam for power generation or process use.
- Ammonia Synthesis Plants — HPSS coil systems integrated into the primary furnace outlet section, recovering thermal energy at 450–550°C under 3.0–5.0 MPa.
- Hydrogen Production Facilities — Steam superheater coils in gas-to-liquids (GTL) and hydrogen production units requiring long-term thermal cycling reliability.
- Methanol Synthesis — Waste heat recovery superheater systems in shift converter and methanol synthesis loops.
- Existing Plant Retrofits — Replacement of aged or failed superheater coil tubes in operational facilities, addressing issues of scaling, creep deformation, and thermal fatigue cracking.
Retrofit Engineering Considerations
In the context of primary furnace superheater retrofitting, coil tube selection must account for:
- Thermal Fatigue Resistance — Cyclic temperature excursions between startup/shutdown and steady-state operation demand materials with superior low-cycle fatigue performance.
- Creep Resistance — At sustained temperatures above 600°C, materials must resist creep deformation to maintain dimensional integrity and coil geometry over extended service periods.
- Scale Spallation Resistance — Oxide scale formation and subsequent spallation in reducing atmospheres (H₂, CO-rich) must be minimized to prevent tube blockage and flow restriction.
- Weldability — Field installation requires reliable welding of coil tube ends to headers; materials must exhibit minimal sensitization and good weld metal toughness.
Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system ensuring product conformity to international standards:
- ISO 9001:2015 — Quality Management System certification covering all manufacturing processes.
- ISO 14001:2015 — Environmental Management System certification.
- ISO 45001:2018 — Occupational Health and Safety Management System.
- EN 10204 3.1 — Material Test Certificates (MTC) issued for all product batches, verifying chemical composition, mechanical properties, and dimensional compliance.
- ASME "S" Stamp — Authorization for pressure vessel component fabrication (where applicable).
- Third-Party Inspection (TPI) — Available upon request; SGS, Bureau Veritas, or TÜV inspection services supported for critical project orders.
Testing & Inspection Protocol
| Test Method | Standard Reference | Frequency |
|---|---|---|
| Chemical Composition (OES) | ASTM E415 | Per heat |
| Tensile Test | ASTM A370 | Per heat |
| Hardness Test (Rockwell B) | ASTM E18 | Per heat |
| Eddy Current Examination | ASTM E309 / ASTM E709 | 100% of tube length |
| Hydrostatic Pressure Test | ASTM A530 | 100% of coils |
| Intergranular Corrosion Test | ASTM A262 Practice E | Per heat (qualifying) |
| Dimensional Inspection | ASME B36.19M | 100% of coils |
Unique Selling Points
- Specialized Retrofit Expertise — Products engineered specifically for primary furnace superheater renewal projects, incorporating lessons learned from extensive field performance data on thermal fatigue and scale degradation.
- Continuous Coil Integrity — Long-length continuous coil production minimizes weld joints, reducing potential failure points in high-pressure steam service.
- Custom Coil Geometry — Flexible manufacturing capability to produce coil diameters and configurations tailored to specific furnace outlet geometries and support structure layouts.
- Extended Service Life — Optimized alloy selection and post-forming annealing processes deliver 2–3× the service life compared to standard-grade coil tubes in equivalent duty.
- Full Traceability — End-to-end material traceability from ingot heat number through final coil delivery, ensuring complete supply chain accountability.
Technical Note: For high-pressure steam superheater retrofit applications, it is strongly recommended to conduct a metallurgical fitness-for-service assessment of existing coil tubes prior to determining replacement scope. Wenzhou Jixing Metal Materials Co., Ltd. provides technical consultation services to assist plant engineers in evaluating remaining service life and optimizing retrofit strategies for maximum economic and operational benefit.