Stainless Steel Seamless Coiltube for Diesel Engine High-Pressure Common Rail Fuel Systems

Product Overview

The Stainless Steel Seamless Coiltube for High-Pressure Common Rail (HPCR) Fuel Systems is a precision-engineered tubular product designed specifically for the fuel delivery circuits of modern diesel engines. Operating under extreme conditions of 180–250 MPa (26,100–36,250 PSI) ultra-high injection pressure and continuous cyclic fatigue loading, this coiltube serves as the critical pressure conduit connecting the common rail accumulator to individual fuel injectors within the engine's fuel injection manifold.

Developed by Wenzhou Jixing Metal Materials Co., Ltd., this product addresses the demanding requirements of next-generation diesel fuel injection systems, where reliability, fatigue resistance, and dimensional integrity are paramount for engine performance, emissions compliance, and operational longevity.

Material & Properties

Base Materials

Mechanical Properties (Post-Manufacture)

Chemical Composition (Typical)

Element 304L (wt%) 316L (wt%)
C (Carbon) ≤ 0.030 ≤ 0.030
Cr (Chromium) 18.0 – 20.0 17.0 – 19.0
Ni (Nickel) 8.0 – 12.0 10.0 – 14.0
Mo (Molybdenum) — 2.0 – 3.0
Mn (Manganese) ≤ 2.0 ≤ 2.0
S (Sulfur) ≤ 0.030 ≤ 0.030
P (Phosphorus) ≤ 0.035 ≤ 0.035

Specifications

Parameter Specification
Product Form Seamless Re-Drawn Coiltube (盘管)
Outer Diameter (OD) 6.00 – 12.00 mm (0.236 – 0.472 in)
Wall Thickness 1.20 – 2.50 mm (0.047 – 0.098 in)
Coil Outer Diameter 200 – 600 mm (7.87 – 23.62 in)
Coil Length per Spool 500 – 3,000 m (1,640 – 9,843 ft)
Maximum Working Pressure 250 MPa (36,250 PSI)
Operating Temperature Range −40°C to +150°C (−40°F to +302°F)
Surface Finish (Inner) Ra ≤ 0.4 μm (post-shot peening)
Surface Finish (Outer) Ra ≤ 0.8 μm (electro-polished or passivated)
Dimensional Tolerance (OD) ±0.05 mm (±0.002 in)
Dimensional Tolerance (Wall) ±0.03 mm (±0.0012 in)
Minimum Bend Radius 3× OD (cold forming)
Applicable Standards ASTM A269 / ASME SA-269; ASTM A213 / ASME SA-213; EN 10216-5; GB/T 12771

Manufacturing Process

Process Flow

  1. Hot-Rolled Billet Preparation: High-purity austenitic stainless steel billets are reheated to 1,150–1,250°C and prepared for tube piercing.
  2. Seamless Tube Piercing (Plattner or Mannesmann Process): Solid billets are pierced to form seamless hollow tubes, ensuring homogeneity and absence of weld seams that could serve as fatigue initiation sites.
  3. Hot Rolling & Annealing: Tubes are hot-rolled to approximate dimensions and solution-annealed at 1,050–1,100°C followed by rapid quenching to achieve fully austenitic microstructure with maximum ductility.
  4. Pickling & Descaling: Surface scale and oxide layers are removed via acid pickling (HNO₃/HF blend) to expose clean metallic surfaces.
  5. Cold Re-Drawing (Multi-Pass): Tubes undergo 2–4 passes of cold drawing through precision tungsten carbide dies with graphite-based lubricants to achieve exact final dimensions (OD and wall thickness within ±0.05 mm tolerance). This process induces controlled work hardening, increasing tensile strength by 25–35%.
  6. Intermediate Annealing: Between drawing passes, tubes are annealed at 900–1,000°C to restore ductility and prevent cracking during subsequent deformation.
  7. Inner Wall Shot Peening (内壁喷丸强化): High-velocity ceramic or glass beads (0.3–0.6 mm diameter) are projected at the inner bore surface at 30–50 m/s. This creates a compressive residual stress layer (depth 0.05–0.15 mm) that significantly enhances fatigue resistance by inhibiting crack nucleation and propagation at the inner surface — the critical location for pressure-induced fatigue.
  8. Electro-Polishing / Chemical Passivation: Final surface finishing ensures smooth inner bore (Ra ≤ 0.4 μm) for minimal fuel flow resistance and passivation to prevent corrosion initiation.
  9. Coiling: Finished tubes are wound onto precision mandrels to form coils of specified diameter and length, with protective wrapping to prevent mechanical damage during storage and transport.

Key Manufacturing Innovation — Inner Wall Shot Peening

The inner wall shot peening process introduces a compressive residual stress layer with a depth of 50–150 μm and peak compressive stress of −300 to −500 MPa. This is the primary mechanism by which the coiltube achieves validated fatigue performance exceeding 10⁷ cycles at 250 MPa peak pulsating pressure — a critical requirement for high-pressure common rail systems operating at 1,500–2,500 RPM engine speeds.

Applications

Primary Application: Diesel Engine High-Pressure Common Rail (HPCR) Systems

The coiltube serves as the high-pressure fuel line in the following configurations:

Target Engine Platforms

Performance Advantages in Application

Quality Certifications & Testing Protocols

Applicable Standards & Certifications

Quality Assurance Testing

  1. Hydrostatic Pressure Testing: Each coil tested at 1.5× maximum working pressure (375 MPa) with minimum 5-second hold time; zero leakage tolerance.
  2. Eddy Current Inspection (ECI): 100% inline inspection for internal and external surface defects, wall thickness uniformity, and dimensional deviations.
  3. Residual Stress Measurement: X-ray diffraction (XRD) verification of compressive residual stress profile on inner surface post-shot peening.
  4. Fatigue Limit Verification (疲劳极限验证): Representative samples subjected to pulsating pressure cycling (0–250 MPa, sine waveform, 20–50 Hz) for minimum 10⁷ cycles in dedicated fatigue testing apparatus with strain-controlled loading.
  5. Chemical Composition Analysis: Spectrographic verification of each heat lot per ASTM E415 / ASTM E135.
  6. Mechanical Testing: Tensile testing per ASTM A370; hardness verification per ASTM E92 (Rockwell B) or ASTM E18 (Vickers).
  7. Surface Roughness Measurement: Confocal microscopy or stylus profilometry per ISO 4287 for Ra verification.
  8. Corrosion Testing: Salt spray testing per ASTM B117 (≥ 500 hours, no red rust); intergranular corrosion per ASTM A262 Practice E.

Unique Selling Points