ISO 2314 / API 616 Derating & Performance
ISO base rating: 59°F (15°C). Use site design max temperature.
Typical pipeline quality: 1,000-1,050 Btu/scf
8,760 = 24/7 operation. Typical: 8,000 hr/yr (91% availability)
Understand Brayton cycle thermodynamics, turbine types, derating methods, and gas turbine selection for midstream service
Gas turbine output decreases approximately 3.5% per 1,000 feet of altitude above sea level. This is because air density decreases with elevation, reducing the mass flow rate through the compressor section. At 5,000 ft elevation, a turbine loses roughly 17% of its ISO-rated power.
Derating is the reduction in gas turbine output from ISO base-rated conditions (59 deg F, sea level, 60% RH) to actual site conditions. Key derating factors include altitude (3.5%/1000 ft), ambient temperature (0.7% per deg F above 59 deg F), humidity, and inlet/exhaust pressure losses. Proper derating ensures the selected turbine can deliver required power at worst-case site conditions.
Simple-cycle gas turbine heat rates range from about 7,500 to 9,500 Btu/HP-hr depending on size class. Small turbines (<5,000 HP) typically have heat rates around 9,500 Btu/HP-hr (27% efficiency), medium turbines (5,000-20,000 HP) around 8,500 Btu/HP-hr (30% efficiency), and large turbines (>20,000 HP) around 7,500 Btu/HP-hr (34% efficiency). Combined-cycle configurations can achieve overall efficiencies above 50%.
ISO 2314 defines gas turbine performance testing and acceptance conditions, establishing the ISO base rating at 59 deg F (15 deg C), sea level, 60% RH. API 616 covers gas turbines specifically for petroleum, chemical, and gas industry services, addressing mechanical design, materials, controls, and acceptance testing requirements for refinery and pipeline applications.