In the oil and gas industry, reciprocating compressors are classified into different technical systems based on design, manufacturing and testing standards. API 618 and API 11P are two dominant specifications that serve separate scenarios: downstream refining & chemical processing, and upstream production & gathering, respectively. They differ greatly in operating conditions, installation, drive type, cooling system and structure. Meanwhile, API 11P has been updated and gradually replaced by the international standard ISO 13631. This article summarizes the application scope, core characteristics and evolutionary relationship of the two standards to provide guidance for equipment selection, engineering configuration and compliance.
1. API 618 Standard: Medium-Low Speed Reciprocating Compressors for Refining & Chemical Industry
API 618 is designed for downstream oil refining and chemical processing in the oil and gas industry. Compressors built to this standard are typically medium-to-low speed units.
They are applied in well-equipped environments such as refineries and chemical plants with sufficient space, stable power, water supply and complete infrastructure. API 618 units require high continuous operation: usually at least 8,000 hours of uninterrupted service, mostly supported by standby machines.
Structurally, API 618 compressors feature fixed foundation, motor drive, ample maintenance space and full water cooling systems to support long-term, high-load and stable process operation.
2. API 11P Standard: Compact Reciprocating Compressors for Upstream Oil & Gas Production
API 11P targets the upstream oil and gas sector, including natural gas production, gathering, transportation, storage and oil auxiliary production.
Compared with API 618, API 11P compressors operate under more severe conditions: remote fields, unattended stations, and harsh offshore platforms, often without full water and power infrastructure.
Key characteristics include: compact skid-mounted structure, small footprint, usually driven by gas engines and equipped with air cooling systems to adapt to field conditions with limited water supply.
3. Relationship Between API 11P and ISO 13631
API 11P and ISO 13631 are highly consistent in scope and technical content. In short:ISO 13631 is the internationally adopted and updated version of API 11P. With global standardization, ISO 13631 has gradually replaced the original API 11P as the common international standard for upstream reciprocating compressors.
Conclusion
API 618 and API 11P (now ISO 13631) are the two core standards for reciprocating compressors, serving downstream chemical processes and upstream production respectively. Understanding their application fields, configurations, drive and cooling differences supports accurate selection, efficient matching and stable operation in engineering and maintenance.
