ISO 10439-3:2015 specifies minimum requirements and gives recommendations for axial compressors, single-shaft and integrally geared process centrifugal compressors, and expander-compressors for special purpose applications that handle gas or process air in the petroleum, petrochemical, and natural gas industries. ISO 10439-4:2015 specifies integrally geared centrifugal compressors in conjunction with ISO 10439‑1.