Stainless Steel Welded Heat Exchanger Coil Tube — GB/T 24592
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd. | Standard Reference: GB/T 24592 (Chinese National Standard for Welded Heat Exchanger Tubes) | Product Category: Heat Exchange Equipment — Coil Tube
1. Product Overview
The Stainless Steel Welded Heat Exchanger Coil Tube, manufactured in strict compliance with GB/T 24592 — the Chinese National Standard governing welded tubes specifically designed for heat exchanger applications — represents a premium-grade tubular product engineered for demanding thermal transfer environments. Unlike conventional fluid transport tubes, heat exchanger coil tubes are subjected to intensified quality control protocols, particularly regarding weld integrity verification, to ensure reliable performance under cyclic thermal loading, elevated pressures, and corrosive working media.
This product is supplied in coil (盘管) configuration, offering logistical advantages for downstream processing such as bending, forming, and direct installation into shell-and-tube heat exchangers, air coolers, condensers, and evaporators. The coil form factor reduces material handling costs and minimizes work-hardening during delivery.
2. Material & Properties
2.1 Applicable Stainless Steel Grades
GB/T 24592 accommodates a range of austenitic and austenitic-ferritic stainless steel grades commonly employed in heat exchange service. Typical grades include:
- Austenitic: 06Cr19Ni10 (equivalent to AISI 304), 06Cr17Ni12Mo2 (equivalent to AISI 316L), 06Cr25Ni20 (equivalent to AISI 310S)
- Austenitic-Ferritic (Duplex): S31803 (equivalent to 2205), S32750 (equivalent to 2507)
- Super-Austenitic: 06Cr24Ni35Mo4N (equivalent to 904L)
2.2 Mechanical Properties (Typical Values for 06Cr19Ni10 / AISI 304)
| Property | Requirement (GB/T 24592) | Typical Achieved Value |
|---|---|---|
| Tensile Strength (Rm) | ≥ 520 MPa | 580–720 MPa |
| Yield Strength (Rp0.2) | ≥ 205 MPa | 240–310 MPa |
| Elongation (A50) | ≥ 35% | 40–55% |
| Hardness (HBW) | ≤ 210 | 160–200 |
| Impact Energy (Charpy V, -29°C) | ≥ 47 J | 70–150 J |
2.3 Corrosion Resistance
The selected stainless steel grades provide excellent resistance to pitting, crevice corrosion, and intergranular corrosion (IGC). All heat exchanger tubes undergo a mandatory intergranular corrosion resistance test (acetic acid or sulfuric acid test per GB/T 4334) to verify solid solution treatment effectiveness and ensure long-term service integrity in chloride-containing environments.
3. Specifications
| Parameter | Specification / Range |
|---|---|
| Product Form | Coil Tube (盘管) — Welded & Cold-Worked |
| Governing Standard | GB/T 24592 (Welded Heat Exchanger Tubes) |
| Outer Diameter (OD) | Φ6.0 mm – Φ50.8 mm (as per standard schedule) |
| Wall Thickness | 0.5 mm – 3.0 mm | Coil Diameter | 300 mm – 1500 mm (customizable) |
| Coil Length | Up to 200 m per coil (typical) |
| Surface Finish | Bright Annealed (BA) or Pickled & Passivated (PP) |
| End Condition | Plain ends, not beveled (unless specified) |
| Welding Process | Automatic High-Frequency Induction Welding (HF-W) or TIG Welding |
| Tolerance — OD | ±0.05 mm to ±0.20 mm (depending on diameter) |
| Tolerance — Wall Thickness | ±10% of nominal |
| Roundness | ≤ 10% of OD tolerance |
| Material Certification | EN 10204 3.1 / 3.2 (Mill Test Certificate) |
4. Manufacturing Process
4.1 Process Flow
- Strip Preparation: Cold-rolled stainless steel strip is inspected for surface quality, dimensional accuracy, and chemical composition conformity.
- Coiling & Edge Preparation: Strip is slitted and coiled to target width; edges are cleaned to ensure weld quality.
- Forming & Welding: The strip is formed into a tubular shape and welded using high-frequency induction welding (HF-W) with inert gas (argon) shielding. For thinner walls or higher-integrity requirements, Tungsten Inert Gas (TIG) welding with back-purge is employed.
- Post-Weld Heat Treatment (PWHT): Where specified, the welded tube undergoes solid solution annealing (1050–1150°C) followed by rapid water quenching to restore full austenitic structure and eliminate residual stresses in the weld zone.
- Cold Drawing / Sizing: Tubes pass through precision dies to achieve final OD and wall thickness tolerances while improving surface finish and dimensional consistency.
- Pickling & Passivation: Chemical treatment removes mill scale, discoloration, and chromium-depleted weld heat-affected zones, restoring full corrosion resistance.
- Coiling: Finished tubes are coiled to specified diameter and length using automated coiling equipment to prevent mechanical damage.
- Final Inspection & Packaging: Each coil undergoes comprehensive NDT and dimensional verification before protective packaging and shipment.
5. Quality Certifications & Inspection Protocols
5.1 Weld Seam Non-Destructive Testing (NDT) — Key Differentiator
A critical distinguishing feature of GB/T 24592 heat exchanger tubes compared to general fluid transport tubes (e.g., GB/T 12771) is the significantly higher sampling ratio for Radiographic Testing (RT) and Ultrasonic Testing (UT) on weld seams. This elevated inspection intensity reflects the elevated consequences of weld failure in heat exchanger service, where leakage can result in cross-contamination, thermal efficiency loss, or catastrophic equipment failure.
| Inspection Method | Fluid Tubes (GB/T 12771) | Heat Exchanger Tubes (GB/T 24592) |
|---|---|---|
| Radiographic Testing (RT) — Weld Seam | 100% eddy current; RT optional / batch sampling | RT sampling ratio elevated above fluid tube requirement (typically ≥5% per heat, or as specified by end-user) |
| Ultrasonic Testing (UT) — Weld Seam | Supplementary / on-request | UT sampling ratio elevated above fluid tube requirement (mandatory for critical service) |
| Eddy Current Testing (ET) | 100% inline | 100% inline + additional verification |
| Hydrostatic / Pneumatic Pressure Test | 100% | 100% |
| Intergranular Corrosion Test | As specified | Mandatory per GB/T 24592 |
| Endoscopy Inspection (Weld Zone) | Not required | Recommended / available upon request |
5.2 Additional Quality Assurance Measures
- Chemical Analysis: Spectrometric verification of each heat lot against GB/T 24592 composition limits.
- Dimensional Inspection: 100% OD and wall thickness measurement using automated optical gauges during production; statistical process control (SPC) monitoring.
- Surface Quality: Visual and magnetic particle inspection (MT) for surface defects; surface roughness verification (Ra ≤ 0.8 μm for BA finish).
- Traceability: Full heat-number traceability from raw material mill certificate through final product delivery.
- Certification: Third-party inspection available via SGS, BV, TÜV, or DNV upon request.
6. Applications
Stainless steel welded heat exchanger coil tubes conforming to GB/T 24592 are designed for the following critical applications:
- Shell-and-tube heat exchangers in petrochemical, refinery, and chemical processing industries
- Air coolers and overhead condensers in distillation columns and gas processing facilities
- Refrigeration systems — evaporators, condensers, and economizers requiring high-purity thermal transfer
- Power generation — feedwater heaters, economizers, and condenser tube bundles
- Food and pharmaceutical processing — pasteurizers, sterilizers, and hygienic heat exchangers (with electropolished surface)
- Marine and offshore — seawater coolers, heat recovery units, and LNG processing equipment
- Heat recovery steam generators (HRSG) in combined-cycle gas turbine (CCGT) plants
7. Unique Selling Points
Elevated Weld Integrity Assurance: The RT/UT sampling ratio for weld seams in GB/T 24592 heat exchanger tubes exceeds that of standard fluid transport tubes, providing superior confidence in weld quality for thermally and mechanically critical service.
- Standard Compliance: Full conformity with GB/T 24592, the authoritative Chinese National Standard for welded heat exchanger tubes, ensuring compatibility with domestic and international engineering specifications.
- Coil Configuration Advantage: Supplied in coil form, enabling efficient downstream bending, U-tube forming, and direct installation — reducing fabrication time and material waste by up to 15%.
- Enhanced NDT Protocol: Mandatory RT and UT sampling at ratios exceeding fluid tube requirements, coupled with 100% eddy current and hydrostatic testing, delivers multi-layered quality assurance.
- Broad Grade Coverage: Availability across austenitic, duplex, and super-austenitic grades allows precise material selection for diverse corrosion environments and temperature ranges.
- Full Traceability: End-to-end material traceability from steelmaking heat number through final coil identification, supporting regulatory compliance and asset integrity management.
- Surface Excellence: Bright annealed or pickled & passivated finishes ensure optimal thermal transfer coefficients and resistance to fouling and corrosion.
8. Technical Note
GB/T 24592 supersedes earlier industry practices by formalizing elevated weld inspection requirements specific to heat exchanger service. Engineers specifying heat exchanger tubes should note that while fluid transport tubes (GB/T 12771) may rely primarily on 100% eddy current testing supplemented by limited RT/UT sampling, heat exchanger tubes under GB/T 24592 mandate a higher proportion of destructive-equivalent volumetric inspection (RT/UT) to detect subsurface weld defects such as lack of fusion, porosity, and cracks that are invisible to surface-sensitive methods. This reflects the design philosophy that heat exchanger tubes operate under continuous thermal cycling, pressure differentials, and often corrosive media — conditions under which even micro-scale weld defects can propagate and lead to premature failure.
Wenzhou Jixing Metal Materials Co., Ltd. maintains a dedicated production line for GB/T 24592 heat exchanger coil tubes, equipped with integrated HF welding, automated eddy current inspection, RT/UT stations, and post-weld heat treatment furnaces, ensuring consistent quality from coil to delivery.