API 618 Pulsation and Vibration Control

API 618 is a standard issued by the American Petroleum Institute (API) that defines the minimum requirements for the design and construction of reciprocating compressors and their drivers, specifically for use in the petroleum, chemical, and gas industries. The standard addresses critical aspects such as safety, reliability, pulsation and vibration control, and mechanical integrity of compressors operating in demanding industrial environments.

Key Aspects of API 618

Scope: Covers reciprocating compressors (both lubricated and non-lubricated) used for process air or gas, especially in critical and continuous service applications.

Design Requirements: Sets minimum criteria for materials, design, fabrication, inspection, testing, and documentation to ensure safe and reliable operation.

Pulsation and Vibration Control: Provides detailed guidelines for analysing and mitigating pulsation and vibration, which are common issues in reciprocating compressor systems.

Testing and Acceptance: Specifies procedures for mechanical running tests, vibration limits, and acceptance criteria to verify compressor performance before commissioning.

Importance

API 618 is considered the industry benchmark for reciprocating compressor reliability, safety, and performance. Compliance is often required in contracts and can be mandated by regulatory authorities, especially for projects where safety and operational continuity are critical. 

API 618 is essential for ensuring that reciprocating compressor systems meet rigorous industry standards for performance, reliability, and safety in demanding service environments.

Latest (6th) Edition Highlights (May 2024)

Discharge Temperature Limits: Maximum allowable discharge temperature reduced to 135°C for all compressors (was 150°C), and 120°C for hydrogen and non-lubricated service (was 135°C).

Pulsation and Vibration Analysis: Design Approach 1 (empirical bottle sizing) removed; now only Design Approach 2 or 3 (detailed analysis) are accepted.

Lubrication Systems: Pressurized lube oil system requirements updated for compressors below 150 kW, referencing API 614.

Trip Speed: Minimum trip speed for constant speed compressors increased to 102% of maximum continuous speed (was 100%).

Cylinder Cooling: All compressors should have cylinder jackets; non-cooled or air-cooled cylinders require purchaser approval.

Alarms and Shutdowns: Mandatory trip for high gas discharge temperature replaced with an alarm; mandatory alarm and shutdown for high crosshead vibration.

Notable 2024 Updates 

Lower discharge temps

Stricter analysis, design approaches allowed:

• DA-2 (detailed analysis), 
• DA-3 (advanced FEA)