API 661 Air Cooler Heat Exchanger For Oil Refinery Services

Scope of API 661

• Applies to forced or induced draft air-cooled heat exchangers.

• Covers mechanical design, thermal performance, and operational requirements.

• Does not apply to:

  • HVAC systems.

  • Refrigeration units.

  • Radiators for internal combustion engines.
    

  • Tube Bundles:

    • Tubes typically in carbon steel, stainless steel, or alloys (e.g., Cu/Ni, Titanium).

    • Arranged in horizontal, A-frame, or V-frame configurations.

  • Fans & Drivers:

    • Electric motors, steam turbines, or hydraulic drives.

    • Fan diameter ≤ 6.7 m (22 ft) (larger sizes require special consideration).

  • Headers & Nozzles:

    • Designed per ASME BPVC Section VIII.

    • Nozzles must allow for thermal expansion.
      
      Materials & Corrosion Protection

    • Fin Tubes:

      • Aluminum fins (most common) or stainless steel for corrosive environments.

    • Structural Supports:

      • Carbon steel with protective coatings (galvanizing, epoxy paint).

    • Corrosion Allowance:

      • Minimum 1.5 mm (1/16 in) unless specified otherwise.
        

        Performance & Testing Requirements

        A. Thermal Performance

      • Design ambient temperature: Typically 38°C (100°F) unless specified.

      • Heat duty verification: Vendor must guarantee performance.

      • B. Mechanical Testing

      • Hydrostatic Test:

        • 1.5 × design pressure for tubes & headers.

      • C. Inspection & Quality Control

      • Dimensional checks (tube alignment, fin spacing).

      • Non-Destructive Testing (NDT):

      • Radiography (RT) for critical welds.

      • Dye penetrant (PT) or Magnetic particle (MT) for surface defects.

      • • API 661 vs. Other Standards

          Feature	API 661	ISO 13706	ASME BPVC
          Scope	Refinery ACHEs	General ACHEs	Pressure parts only
          Design Rules	Detailed mechanical & thermal	Similar to API 661	Only pressure containment
          Testing	Hydro, vibration, NDT	Similar	Hydro & NDT
          Materials	Corrosion-resistant alloys	Similar	Any ASME-approved

          

          Radiography (RT) for critical welds.

        • Dye penetrant (PT) or Magnetic particle (MT) for surface defects.

      • Air Leak Test:e stability.