Re: Use of Nitrogen as a pipeline preservative

1 - The introduction of biocide, O2 scavenger & corrosion inhibitor is to clean the pipeline internal and provide a layer of the chemical mixtures after the hydrotest stage. I agree that the best dewatering mechanism will still leave water spots especially at low points/bends within the pipeline length. If your pipeline is a high pressure transmission for oil/gas/condensate/etc, i would prefer to do vacuum drying prior to purging the N2, where the cost of vacuum drying worth to keep the pipeline in your wanted condition. Vacuum drying will simply dry the pipeline to the max, that if we pump out the air from the pipeline, the pressure inside the pipeline will drop hence reach to the thermodynamics equilibrium of water which will boil it off until the inside pressure reach the absolute zero milibar.

2 - Should there still be water spots within the pipeline, N2 was meant to prevent the little traces of water left from corroding the pipeline <---as being explained in one of the replies (it's nothing to do with chemical reaction whatsoever).

3 - To contain leakage of N2 - it is best if we prevent the leak prior to purging N2, or while we are vacuum drying the line. The common practice which i have been involved for a pipeline from platform to platform offshore is to do the in-leak check when we first started the vacuum drying. During the stage, we shall be able to find/detect the leak on the weakest point of a topside piping where flanges, spectacle blinds, instrument connection or even the launcher/receiver door. This may involve flogging of them flanges and bolt tensioning where applicable. Once it is done, then can the vacuum drying be continued till it reach the absolute zero milibar.

4 - It should be i believe so, because the pipeline i have been involved with, it was all designed according to the mentioned code ASME B31.8. Thats my 2cents. Received on Wed Sep 01 22:34:00 2004