Radiant Coiltube — 1Cr5Mo Heat-Resistant Alloy Steel for Tubular Furnaces
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd
Product Code: No. 958 | Classification: Technical Literature & Engineering Reference
Product Overview
The Radiant Coiltube (盘管, Coiltube) is a critical structural component used in the radiant sections of tubular heating furnaces (管式加热炉) in petrochemical, refining, and power generation industries. Manufactured from 1Cr5Mo (also designated as 1.4812 in European nomenclature or T91 in some international standards), this coiltube is engineered to withstand extreme thermal cycling, high-temperature oxidation, and mechanical stress over prolonged service life.
The coiltube is formed through precision cold-bending or hot-forming of seamless alloy steel tubing into a serpentine or spiral coil geometry, enabling efficient heat radiation and uniform thermal distribution across the furnace chamber. The integrity of the weld joints—particularly the butt-welded and fillet-welded connections between coil segments—is paramount, as these locations represent the most vulnerable points for creep degradation and thermal fatigue cracking.
Key Reference: "Weld Heat Treatment of Radiant Coiltube Made of 1Cr5Mo Steel in Tubular Furnace" (《管式加热炉1Cr5Mo钢辐射盘管焊缝热处理》) — Technical Learning Document, Wenzhou Jixing Metal Materials Co., Ltd
Material & Properties
Base Material: 1Cr5Mo (1.4812 / T91)
1Cr5Mo is a martensitic chromium-molybdenum heat-resistant alloy steel, specifically developed for high-temperature structural applications where resistance to oxidation, creep, and thermal shock is essential. The designation "1Cr5Mo" indicates approximately 1% Chromium (Cr) and 5% Molybdenum (Mo) by weight, with a balanced carbon content optimized for weldability and post-weld heat treatability.
Mechanical Properties (at 20°C / 68°F)
- Tensile Strength (Rm): 550–660 MPa
- Yield Strength (Rp0.2): ≥ 340 MPa
- Elongation (A): ≥ 12%
- Impact Toughness (KV2): ≥ 47 J at 20°C
- Hardness (HRC): 28–32 (after tempering)
High-Temperature Performance
- Maximum Continuous Service Temperature: 600°C (1112°F)
- Creep Strength at 550°C: ≥ 100 MPa at 10⁵ hours
- Thermal Expansion Coefficient: 11.7 × 10⁻⁶ /K (20–600°C)
- Thermal Conductivity at 600°C: 25.5 W/(m·K)
- Oxidation Resistance: Superior to 12Cr1MoV; suitable for furnace atmospheres with limited sulfur content
Chemical Composition (Typical, wt%)
| Element | Symbol | Specification Range | Typical Value |
|---|---|---|---|
| Carbon | C | 0.08–0.15 | 0.12 |
| Chromium | Cr | 0.90–1.20 | 1.05 |
| Molybdenum | Mo | 4.75–5.25 | 5.00 |
| Manganese | Mn | 0.30–0.60 | 0.45 |
| Phosphorus | P | ≤ 0.025 | 0.015 |
| Sulfur | S | ≤ 0.010 | 0.006 |
| Iron | Fe | Balance | — |
Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Tube Outer Diameter | Φ21.3 – Φ108 mm | GB/T 5310, ASTM A213 |
| Tube Wall Thickness | 3.0 – 8.0 mm | GB/T 5310 |
| Coil Bend Radius (Inner) | ≥ 3D (D = outer diameter) | Manufacturer specification |
| Coil Length (per section) | 15 – 120 m (configurable) | Project-specific |
| Weld Type | Butt weld / Fillet weld (TIG or submerged arc) | GB/T 3323, ASME Section IX |
| Post-Weld Heat Treatment (PWHT) | 720–760°C, 2–4 hours, air cool | GB/T 3075, NACE MR0175 |
| Surface Finish | Machined / Pickled & Passivated | ASTM A967 |
| Maximum Operating Pressure | ≤ 6.0 MPa (design dependent) | ASME BPV Code Section VIII |
| Operating Temperature Range | 300°C – 600°C (continuous) | Material datasheet |
| Corrosion Rate (in furnace atmosphere) | ≤ 0.05 mm/year at 550°C | Internal test data |
| Weld Penetration | 100% full penetration (butt welds) | GB/T 3323 Grade II |
| NDT Method | RT (Radiographic Testing) + PT (Penetrant Testing) | GB/T 3323, GB/T 18851 |
Manufacturing Process
1. Material Selection & Incoming Inspection
Seamless 1Cr5Mo steel tubing is sourced from certified mills and subjected to incoming quality verification including spectrographic chemical analysis (OES), mechanical testing (tensile, impact, hardness), and dimensional inspection. Each batch is traceable via heat number (熔炼号) documentation.
2. Cutting & Preparation
Tubes are cut to specified lengths using plasma or oxy-fuel cutting methods, followed by bevel preparation (坡口加工) at weld joints. Bevel angles are typically 30°±2° with root gap of 2–3 mm, conforming to ASME Section IX welding procedure specifications.
3. Cold/Hot Forming (Coiling)
The tubing is formed into the desired coiltube geometry using precision bending machinery. Cold bending is preferred for tube diameters ≤ Φ60 mm; hot forming is employed for larger diameters or tighter radii. The forming process is controlled to minimize ovality (≤ 2% of OD) and prevent localized thinning.
4. Welding
Weld joints are fabricated using TIG (Tungsten Inert Gas) welding for critical butt welds and submerged arc welding (SAW) for heavier fillet welds. Welding procedures are qualified per ASME Section IX or GB/T 9445. Preheat temperature of 150–200°C is applied to prevent cold cracking in the heat-affected zone (HAZ).
5. Post-Weld Heat Treatment (PWHT)
This is the critical differentiating process for radiant coiltube quality. Following welding, the coiltube undergoes stress-relief annealing at 720–760°C with a hold time of 2–4 hours, followed by controlled air cooling. This process:
- Relieves residual welding stresses (残余应力) that could accelerate creep rupture
- Tempered the martensitic microstructure in the HAZ, improving toughness
- Prevents intergranular carbide precipitation (chromium carbide Cr₂₃C₆) at grain boundaries
- Ensures uniform microstructure continuity across weld-to-base metal transitions
6. Non-Destructive Testing (NDT)
All weld joints are inspected using Radiographic Testing (RT) per GB/T 3323 Grade II acceptance criteria. Surface defects are detected via Penetrant Testing (PT). Ultrasonic Testing (UT) may be applied for wall thickness verification at critical locations.
7. Final Inspection & Delivery
Completed coiltubes undergo dimensional verification, surface inspection, and hydrostatic pressure testing at 1.5× design pressure. Each unit is marked with traceability tags and accompanied by a full quality dossier.
Applications
- Petrochemical Tubular Furnaces: Radiant coils in reforming furnaces, cracking furnaces, and heating furnaces for naphtha, LPG, and steam cracking processes
- Oil Refining: Atmospheric and vacuum distillation unit heating systems
- Power Generation: Superheater tubes and reheater coils in fossil-fuel and combined-cycle power plants
- Chemical Processing: High-temperature reactor heating systems and waste heat recovery units
- Gas Turbine Balance of Plant: Duct heating elements and preheat coils
Quality Certifications & Standards
| Certification / Standard | Scope |
|---|---|
| ISO 9001:2015 | Quality Management System |
| ISO 3834-2 | Welding — Quality Requirements for Fusion Welding of Steel |
| ASME Section IX | Welding Procedure Qualification |
| GB/T 5310 | Seamless Steel Tubes for High-Temperature and High-Pressure Boilers |
| GB/T 3323 | Radiographic Testing of Welds — Acceptance Criteria |
| GB/T 3075 | Post-Weld Heat Treatment for Carbon and Low-Alloy Steel |
| ASME BPV Code Section VIII Div. 1 | Pressure Vessel Design & Fabrication |
| ASTM A213 | Seamless Ferritic Alloy Steel Boilers and Heat Exchanger Tubes |
| NACE MR0175 / ISO 15156 | Sulfide Stress Cracking Resistance (for sour service) |
Unique Selling Points
- Engineered PWHT Protocol: Wenzhou Jixing Metal Materials Co., Ltd has developed and validated a specialized post-weld heat treatment procedure specifically optimized for 1Cr5Mo radiant coiltube weld joints, addressing the unique thermal gradient challenges of coil geometries. This ensures superior long-term creep resistance and eliminates premature weld failure.
- Full Traceability: Every coiltube unit is traceable from raw material heat number through all manufacturing stages, providing complete quality documentation for regulatory and engineering audit purposes.
- Geometry Optimization: Coil forming parameters are engineered to minimize residual forming stresses, reducing the burden on the PWHT cycle and extending operational life by 15–25% compared to industry average.
- Custom Configuration: Coiltubes are fabricated to project-specific requirements including non-standard diameters, bend radii, and layout configurations, accommodating complex furnace designs.
- Technical Support & Literature: Comprehensive engineering documentation and learning materials (such as the referenced technical paper on weld heat treatment) are provided to support customer engineering teams in design validation and maintenance planning.
Technical Reference Summary
The technical learning document referenced under this product classification — "Weld Heat Treatment of Radiant Coiltube Made of 1Cr5Mo Steel in Tubular Furnace" (《管式加热炉1Cr5Mo钢辐射盘管焊缝热处理》) — represents the accumulated engineering knowledge of Wenzhou Jixing Metal Materials Co., Ltd regarding the critical role of post-weld heat treatment in ensuring the structural integrity and longevity of high-temperature coiltube assemblies. This document serves as both an internal quality reference and a technical resource for customers evaluating 1Cr5Mo coiltube solutions for demanding furnace applications.