Safety is a crucial issue in operational activities. When performing a hot work operation on a live pipeline, it is very important to isolate the pipeline to prevent any dangerous event. In this paper, a newly and innovatively designed approach has been presented which has been used to isolate a 32” and an 18” offshore and infield pipelines from sour gas and prepare them for hot work operation in order to substitute a T-piece with a pipe piece on the line.

The pipelines had been depressurized, but still filled with inflammable sour gas and not ready for hot work operation. In this designed approach, injection of Nitrogen as inert gas, launching pigs for batching the mediums, injecting MEG (Mono Ethylene Glycol) for washing out the remained condensed gas on inner pipe wall and finally usage of Medium Expansion AFFF foams have been implemented in order to prevent diffusion of inflammable gases and prepare a safe condition on the pipelines.

The implemented procedure resulted in a well-attained and fully safe condition which had an LEL and H2S amount of zero. The hot work operation, which included cutting a T-piece and welding a pipe piece instead, was performed safely and completed successfully.

This remarkable result in safe isolation of pipelines by using the implemented method was practically achieved with not a considerably high cost and a very low required time for preparation of equipment.