Abstract
This paper describes a very simple model built to predict the quantities of dissolved iron and corrosion products which can be produced from sweet gas condensate pipelines. The key drivers of this model are fully described and compared to practical operational experience.
Several documented field cases are used to confront the hypotheses used and to determine relevant corrosion criteria.
In particular, it is shown that corrosion mitigation using MEG + pH control reduces the average bottom line corrosion rate down to 1 to 3 µm/yr, while corrosion inhibition will only reduce it to the range of 20 to 50 µm/yr depending on the operating temperatures, or up to 75- 80 µm/yr for temperatures higher than 80- 90°C. These corrosion rates still do not jeopardize pipeline integrity.
It is also shown from these field results that iron contents exceeding 100 to 200 mg/l at the outlet of sweet gas pipelines are not necessarily alarming. For quite long pipelines these counts correspond to fully acceptable residual corrosion rates. In case of such high iron levels, the present model and the associated residual corrosion criteria can be used to compare these iron contents with predictions.
Pre-existing corrosion products from mill scale and atmospheric rusting are also evaluated in this approach. The huge amount of rust formed on the surface of pipes prior to laying is particularly troublesome when no precaution is taken to minimize atmospheric corrosion during storage or to remove this rust after installation. Large pipelines of a few hundred kilometers may contain up to several hundreds of tons of rust which may dramatically impact downstream gas receiving facilities. This is a key factor in the decision to apply an internal coating in long and large gas export pipelines.
