WORK PACKAGE 4: INTERNAL CORROSION AND DEGRADATION

LEADER: PROF J. OAKEY

---

WP4.1 Corrosion of Metallic Materials and Welds in Pipeline and Compression Equipment (Dr K. Patchigolla)

For long distance transport of high pressure CO₂ by pipeline, carbon steel is the only economical material choice, as evidenced by the 2500km of carbon steel pipelines constructed and operated in the USA for high pressure CO₂ service. Pure, dry, supercritical CO₂ is not corrosive to carbon steel. However, if free water forms in the system then corrosion will occur at high rates. It is recognised that there may be situations when it is not possible to prevent free water formation, for example, due to failure of the dehydration unit at the capture plant. In case of such events, the effect on the pipe materials needs to be understood.

The present experimental database is not sufficient to be able to make these predictions or to specify inhibitor requirements to control corrosion under these circumstances. However, in locations where contact with wet CO₂ is more likely or unavoidable e.g. inlet piping to compressors, coolers and scrubbers, then it becomes economical to select a corrosion resistant alloy.

The purpose of this task is therefore to extend the experimental database for CO₂ containing impurities for a range of pipeline and compressor materials and to investigate the role of inhibitors in controlling corrosion during plant upset conditions. In particular, attention will be paid to the effects of aggressive contaminants such as H₂S and trace species which could lead to localised damage, such as environmentally assisted cracking in crevices, weld zones, etc..

In order to conduct these experiments a high pressure experimental rig will be designed and constructed at Cranfield University, which is capable of achieving the temperatures and pressures required to simulate operating conditions in the environments identified in WP1. Corrosion measurements will be made for stressed and unstressed materials, prepared in order to simulate their condition in service, using a number of techniques including weight loss coupons, LPR, EIS and ECN.

WP4.2 – Non-Metallic Material Investigation (Dr K. Patchigolla)

It has been shown that supercritical CO₂ can cause deterioration and explosive expansion of petroleum based elastomers such as nitrile, neoprene and viton and synthetic lubricants. Appropriate inorganic lubricants and sealing materials such as Teflon, nylon, EPDM rubber must therefore be specified in CO₂ service. However, the effect of impurities in the CO₂ on seal materials has not been studied in the literature and it is recommended that the currently specified CO₂ service seal materials are tested to ensure that they are still appropriate for the CO₂ compositions expected from the capture plant. The aim of this task is to conduct exposure testing of elastomers in supercritical CO₂ environments containing impurities to determine their suitability for this service. The experimental rig developed for WP4.1 will be used to conduct these exposure tests.