Presented by: James Watson
It is very common for pipelines to be purged of their product (line fill). The reasons to purge a pipeline
vary from preparation for repairs, line relocation, change in service, deactivation, or abandonment.
Recommended Purge Fluid
The recommended fluid for purging a pipeline is nitrogen since it is inert and is appropriate whether the fluid is a hydrocarbon (natural gas, natural gas liquids, crude oil, refined products, petrochemicals) or industrial gases (carbon dioxide, hydrogen, oxygen, ammonia, chlorine).
The use of air to displace a hydrocarbon pipeline is not recommended due to the potential for a combustible mixture of vapors to form in the pipeline.
Safety Concerns Using Nitrogen
Nitrogen under pressure and at low temperature must be handled properly. Nitrogen in liquid form will freeze unprotected skin on contact. Approved hearing protection should be worn when nitrogen is being vented to atmosphere to prevent possible hearing loss. Nitrogen gas can gather in low lying areas and may cause an oxygen deficient environment.
A pig launcher and receiver is needed. The receiver should be long enough to receive 2 to 3 pigs. The nominal pipe section is the same diameter as the pipeline. The barrel is typically 2 diameters larger than the pipeline diameter. The image below includes a launcher and a pig loader. The launcher can be simplified by using a blind flange.