DSV have used Nitrogen extensively for replacing an active and explosive atmosphere because it is odorless, tasteless, non-toxic and practically inert. The objective are either to reduce oxygen content in the pipeline or to reduce the Hydrocarbon level to below its Lower Explosive Level (LEL) so that on contact with air, the Hydrocarbon concentration is sufficient to create an explosive mixture with atmospheric oxygen. Medium density foam pigs are employed for the displacement to be effective. The foam pigs will serve as a buffer for the displacement. Medium density foam pigs generally have sealing efficiency that greatly reduces any forward or bypass of liquids.

Based on our experience on past projects, our aim majorly, is to reduce the Hydrocarbon level to acceptable Lowest Explosive Level (LEL). During this operation, Nitrogen is continuously pumped into the pipeline at one point and the air or undesired composition leaves from another point. The purged gas is normally vented to atmosphere so that the systems remain at atmospheric pressure during the entire purging operation. The purging operation shall continue until the Hydrocarbon content of the system is less than 2% by volume and this will be determined by a calibrated Gas Meter. 

Gas Analysis

It is important to take gas samples from the system. Ensure that all gas meters used have up-to-date calibration certificates and are functioning properly before use. The two main gas meters used are the Oxygen meter for measuring Oxygen content in the system and a Hydrocarbon in Nitrogen meter, which is calibrated to LEL