pnBAS ISO 21905:2025

This document specifies requirements and gives recommendations for the design, materials of construction, modelling, controlling, fabrication, inspection, testing, installation, start-up and operation of industrial gas turbine (GT) exhaust systems with or without waste heat recovery unit (WHRU). Gas turbines can be on-shore or off-shore for such sectors as oil and gas, chemical and process industries, utilities, or other intensive energy users. For this document, the exhaust system means all items in the turbine exhaust gas stream between the GT exhaust gas collector outlet flange and the termination/s to the atmosphere. The following items are not covered by this document: — heat recovery steam generator equipment (HRSG); — supplementary fired systems; — auxiliary fired systems; — exhaust gas collector (also known as exhaust plenum); — fire detection and extinguishing systems; — emissions controls equipment intended to modify the gaseous composition of the exhaust gas; — WHRUs that are of the firetube type, where the turbine exhaust gas (TEG) passes through the tubes.