Predicting Iron Production from Sweet Gas-Condensate Pipelines

There is an increasing number of long and large gas-condensate pipelines operated in a wet regime around the world. Although their long term integrity is well controlled with various corrosion mitigation solutions, a residual corrosion as low as a few tenth of microns per year may cause serious issues of scale deposition, plugging of filtration systems, emulsification of fluids, etc. due to tons of corrosion products which may be produced from the huge surface of these pipes.

 The present paper aims at quantifying the amount of iron products that a sweet gas pipeline may produce even in the case of well controlled bottom of line and top of line corrosions. This quantification is made from about 10 field cases of wet gas pipelines operated with or without MEG as an hydrate inhibitor and with either corrosion inhibitor or pH control as corrosion mitigation solutions. Average residual Bottom Line Corrosion rates ranging from 10 to 100 µm/yr over 5 to 20% of the surface are relevant to most cases, depending on the temperature and the flow regime of the pipeline.

 The possible contributions of mill scale, pre-rusting during storage of linepipes, and hydrotest water are also evaluated. A simple spreadsheet model including all these contributions is established to help carrying out such evaluations.