Overview of API Standard 660 – Shell-and-Tube Heat Exchangers

API 660 is the established standard for shell-and-tube heat exchangers used in oil, gas, and petrochemical facilities. This page provides engineers with a detailed reference covering all critical aspects of design, material selection, fabrication, inspection, and testing. Understanding API 660 ensures equipment reliability, operational safety, and regulatory compliance without having to read the full standard.

Introduction

API Standard 660, titled “Shell-and-Tube Heat Exchangers,” is developed by the American Petroleum Institute to define requirements for the design, fabrication, inspection, testing, and shipment of shell-and-tube heat exchangers in petroleum, petrochemical, and natural gas industries. The standard ensures mechanical integrity, thermal performance, and operational safety, serving as a reference for engineers, designers, fabricators, and operators. It applies to heaters, condensers, coolers, and reboilers but excludes vacuum-operated steam surface condensers and feed-water heaters.

Scope and Applicability

API 660 covers heat exchangers operating under typical conditions found in oil, gas, and petrochemical facilities. Its key objectives include:

  • Ensuring mechanical integrity under design pressures and temperatures.
  • Providing thermal performance requirements to meet process needs.
  • Specifying materials suitable for corrosive and high-temperature environments.
  • Establishing inspection and testing protocols to guarantee safety and quality.

The standard applies to a variety of shell-and-tube heat exchangers commonly used in oil, gas, and petrochemical facilities, covering critical process applications:

  • Heaters: Devices designed to raise the temperature of process fluids, ensuring optimal reaction conditions, energy efficiency, and process continuity.
  • Condensers: Equipment that removes heat from vapors, converting them into liquid form to facilitate downstream processing, recovery, or reuse of valuable components.
  • Coolers: Systems that lower the temperature of fluids to meet process requirements, protect equipment, and maintain safe operational conditions.
  • Reboilers: Heat exchangers that supply the necessary thermal energy to distillation columns or similar separation processes, supporting efficient vaporization and fractionation.

Excluded equipment includes vacuum-operated steam surface condensers and feed-water heaters.

Design Considerations

1. Mechanical Design

Mechanical design under API 660 ensures the structural integrity and longevity of heat exchangers:

  • Shell Design: Determining shell thickness based on internal pressure, external loads, and material properties.
  • Tube Sheets: Thickness and material must accommodate thermal expansion and operational stresses. Tube-to-tube sheet joints are designed for strength and leak prevention.
  • Baffle Design: Proper baffle spacing and orientation optimize flow, improve heat transfer, and reduce vibration risks.
  • Nozzle and Flange Design: Must withstand operational loads, maintain alignment, and allow safe attachment to piping systems.
  • Expansion Provisions: API 660 requires allowances for thermal expansion to avoid excessive stress on tubes and shell.

2. Thermal Design

Thermal performance is critical to meet process requirements:

  • Heat Transfer Calculations: API 660 provides methods to calculate required heat transfer area, based on fluid properties and temperature differences.
  • Flow Arrangements: Counterflow, parallel flow, or multi-pass tube configurations are selected to maximize efficiency.
  • Pressure Drop Management: The design balances optimal heat transfer with acceptable pressure drops on both shell and tube sides.

  • Fouling Considerations: Fouling factors are applied in design to maintain long-term thermal efficiency.

3. Material Selection

API 660 emphasizes the importance of materials to resist corrosion, high temperature, and pressure:

  • Common Materials: Carbon steel, stainless steel, nickel alloys, titanium, and other corrosion-resistant alloys.
  • Corrosion Resistance: Selection considers process fluid chemistry, temperature, and operational conditions.
  • Thermal & Mechanical Properties: Materials must withstand operational stresses and thermal cycling without degradation.
  • Compatibility: Materials should prevent chemical reactions with process fluids and avoid fouling or scaling.

Fabrication and Construction

API 660 specifies requirements for the fabrication of heat exchangers to ensure quality and safety:

  • Welding Procedures: Adherence to approved welding procedures to maintain structural integrity.
  • Material Certification: Ensuring all materials used are certified and traceable.
  • Quality Control: Implementing rigorous quality control measures during fabrication to detect and rectify defects.
  • Preparation for Shipment: Proper packaging and documentation to ensure safe delivery and compliance with specifications.

Inspection and Testing

To verify the integrity and performance of heat exchangers, API 660 mandates:

  • Hydrostatic Testing: Applying internal pressure using water to check for leaks and structural weaknesses.
  • Pneumatic Testing: Using air or inert gases to detect leaks, especially in sensitive applications.
  • Non-Destructive Testing (NDT): Techniques like ultrasonic testing and radiographic inspection to detect internal flaws without damaging the equipment.
  • Dimensional Checks: Verifying that all components meet specified dimensions and tolerances.

These tests ensure that the heat exchanger meets the required standards for safety and performance.

Maintenance and Operation

API 660 provides guidelines for the operation and maintenance of heat exchangers:

  • Operational Procedures: Establishing standard operating procedures to ensure efficient and safe operation.
  • Maintenance Schedules: Implementing regular maintenance schedules to inspect and service components, preventing unexpected failures.
  • Fouling Management: Monitoring and managing fouling to maintain heat transfer efficiency.
  • Performance Monitoring: Regularly assessing performance metrics to detect any deviations from optimal operation.

Compliance and Certification

API 660 compliance is widely recognized in the oil, gas, and petrochemical industries as a benchmark for quality and safety in shell-and-tube heat exchangers. Manufacturers adhering to the standard demonstrate that their equipment meets globally accepted mechanical, thermal, and material integrity requirements.

Compliance with API 660 supports certifications such as ISO 9001 for quality management, ASME Section VIII for pressure vessel construction, and NACE MR0175 / ISO 15156 for corrosion-resistant materials in sour service. In practice, API 660 is often used in conjunction with piping codes like ASME B31.3 or B31.1 and, when applicable, other heat exchanger standards such as API 661 for air-cooled exchangers.

Following API 660 is essential for manufacturers seeking industry acceptance, EPC project approvals, and operator confidence. Non-compliance can result in rejection during inspections, procurement difficulties, and increased liability risk. By certifying equipment to API 660, manufacturers ensure that their heat exchangers are readily accepted by EPC contractors, operators, and inspection agencies worldwide.

Conclusion

API Standard 660 serves as a critical reference for engineers and manufacturers involved in the design, fabrication, and operation of shell-and-tube heat exchangers in the oil, gas, and petrochemical industries. By adhering to the guidelines specified in API 660, companies can ensure the efficient and safe operation of these essential components, thereby minimizing downtime and reducing operational risks.