The SA335 P11 SS409 HFW (High-Frequency Welded) Finned Pipe combines a high-temperature-resistant SA335 P11 chromium-molybdenum alloy steel base pipe with corrosion-resistant SS409 stainless steel fins, utilizing advanced high-frequency welding technology to create a durable, efficient heat transfer solution for power plants, petrochemical systems, and industrial boilers operating under extreme temperatures (up to 540°C) and corrosive environments.

1. HFW SA335 P11 Fin Pipe Overview

High-Frequency Welded Finned Tubes are high-efficiency heat exchange components where metal fins are securely welded to the outer surface of a base pipe through high-frequency induction welding technology. Their core function is to significantly increase heat transfer surface area, improving thermal conduction efficiency for applications in high-temperature, high-pressure, and corrosive environments.

2. Analysis of Base Pipe Material SA335 P11

2.1 Material Standard and Chemical Composition

• Standard: ASTM SA335 (Seamless Ferritic Alloy-Steel Pipe for High-Temperature Service)
• Grade Equivalent: P11 (Similar to Chinese 15CrMoG, German 13CrMo4-5)

2.2 Mechanical Properties and High-Temperature Characteristics

• Room Temperature Mechanical Properties:
  • Tensile Strength (σb): ≥415 MPa
  • Yield Strength (σs): ≥205 MPa
  • Elongation (δ): ≥30%
• High-Temperature Creep Strength (at 550°C):
  • 100,000-hour rupture strength: ≥80 MPa
• Heat Treatment Process: Normalization + Tempering (Typically 930°C normalization, 650°C tempering)

2.3 Corrosion Resistance and Welding Properties

• Oxidation Resistance: Forms stable Cr₂O₃ protective film below 540°C
• Welding Key Points:
  • Preheat to 200~300°C (to prevent cold cracking)
  • Recommended welding material: E8018-B2 (AWS standard)

3. Comprehensive Analysis of Fin Material SS409

3.1 Material Characteristics and Composition

• Standard Equivalent: ASTM A240 (UNS S40900), ferritic stainless steel

3.2 Corrosion Resistance and Thermal Stability

• Corrosion Resistance:
  • Better atmospheric corrosion resistance than carbon steel, but weaker than austenitic stainless steel
  • In sulfur-containing environments (e.g., flue gas dew point corrosion), temperature should be controlled ≤400°C
• High-Temperature Performance:
  • Continuous service temperature: -20~650°C
  • Oxidation limit: 800°C (short-term)

3.3 Fin Forming Process

• Processing Method: Cold rolling (fin height up to 16mm, pitch 3~8mm)
• Surface Treatment: Sandblasting or pickling passivation can be applied to enhance corrosion resistance

4. Technical Details of High-Frequency Welding Process

4.1 Welding Principle

High-frequency current (100~400kHz) generates skin effect at the contact surface between the fin root and base pipe, instantly heating to 1200~1300°C to achieve metallurgical bonding without filler material.

4.2 Process Advantages

• Small heat-affected zone (≤1mm), preventing base pipe performance degradation
• High welding speed (up to 20m/min)
• Bonding strength: Shear strength ≥200 MPa

4.3 Quality Inspection

• Non-destructive testing: Eddy current testing (ET) + Ultrasonic testing (UT)
• Metallographic examination: Welds must be free from defects like lack of fusion or porosity

5. Parameters for Engineering Selection

6. Solutions for Special Operating Conditions

• High-sulfur environments: Recommend internal cladding with Alloy 625
• Chloride corrosion: Switch to duplex stainless steel fins (e.g., S31803)
• Severe wear scenarios: Apply tungsten carbide coating on fin surface

SA335 P11 SS409 HFW Finned Pipe