Purging

Prior to commissioning and during maintenance activities, pipelines, process equipment, and process piping must be purged with nitrogen gas to reduce the oxygen concentration to an acceptable level. Residual oxygen within the system can combine with hydrocarbon vapors to create flammable or explosive mixtures, especially after pressure containment has been broken. Therefore, whenever a system is opened, depressurized, or otherwise compromised, appropriate measures must be taken to ensure that

• An explosive atmosphere is not present while inspection, maintenance, or repair activities are being performed.
• An explosive atmosphere is not present within the equipment or piping before reinstatement and return to hydrocarbon service.
• The integrity of pressure containment is fully restored, tested, and verified before the system is returned to operation

Nitrogen purging and inerting of process vessels, equipment, pipelines, and piping systems are two commonly applied—but functionally distinct—methods used to control and reduce oxygen concentration. These practices minimize fire and explosion hazards by maintaining oxygen levels below flammability limits and also help preserve internal surfaces by preventing oxidation and moisture ingress, thereby extending the longevity and reliability of the system