Nitrogen Preservation of equipment and pipelines is carried out to prevent corrosion of the metal of inner surfaces, both as process shutdown (switch to standby mode for a defined and indefinite time, out of service for the current and midlife repair, general maintenance, emergency shutdown), and at shutdown in a long term standby or maintenance (reconstruction) for a period of more than 6 months, as well as before commissioning, after chemical cleaning.
Inert gas (nitrogen) is utilized for preservation of the internal surfaces of critical parts (heat exchangers, tanks, etc.) manufactured from ferrous and non-ferrous metals and can be sealed. Nitrogen preservation is also used for chemical equipment designed for operation in an explosive environment or for the equipment with special requirements regarding the purity of the internal surfaces in contact with the product.
Nitrogen preservation is one of the final steps in the pipeline preparation before startup. After hydraulic-pressure test and pipeline drying (including vacuum) nitrogen is used to finally displace water vapor and oxygen to prevent oxidation of the pipes inner surface.
The essence of nitrogen preservation is to fill the circuit and maintain gas overpressure to prevent ambient oxygen access. The basic requirement for the preservation by gas is the sufficient nitrogen purity. The oxygen content in the nitrogen used for preservation as well as in the gas space of the equipment must not exceed 0.5%.
The merit of the nitrogen preservation is defined by reliability, continuance and comprehensive protection, method efficiency and fast equipment startup after such storing.