Materials Performance

DEC 2014

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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59 NACE INTERNATIONAL: VOL. 53, NO. 12 MATERIALS PERFORMANCE DECEMBER 2014 solubility did not allow the chemical to get to the corrosive area. Te chemical companies, if given all the data, can design and laboratoryqualif y the right inhibitor. Te only diference between subsea and aboveground piping are the logistics and cost of getting the chemical to the injection points. A: I guess the signifcant diference between on and ofshore pipe lines is corrosion monitoring, not corro sion control. It is virtually impossible to monitor corrosion in subsea pipelines— inlet and outlet probes and coupons often fail to pick up issues within the pipeline, especially in lowfow conditions. Subsea corrosion monitors frequently fail to pro duce any data, despite their high cost. You might have better luck with a subsea tieback, as opposed to a pipeline, as you can tie the interrogation system into the subsea well control pod, but I wouldn't pin too many hopes on these devices. The problem is that you don't want to run a pig at some time in the future and f ind you have a severely degraded asset. I don't know the answer, except to put in place the best and most reliable inhibitor system you can, prefera bly with some builtin redundancy. A: Inhibitors are usually efective, provided they are designed for the particular conditions. In my experi ence, the major failing, especially ofshore, is failure of the injection system or lack of attention by operators. If you have to inject a hydrate inhibitor or fow modifer, I recommend you blend the inhibitor with the productioncritical component. You will stand a much better chance of having the inhibitor injected without interruption. A: Pigging will have to form an inte gral part of the corrosion control program. So, is the line piggable? If slug fow is a possibility, then batch pigging may be the only option, as the high shear of the slug will strip a flm. Mercaptan corrosion Q: Would anyone have information on mercaptan corrosion or its mechanism? Is the corrosion mode the same as hightemperature sulfidation? A: Your assumption that the corro sion mechanism for mercaptan corrosion is the same as hightempera ture sulfdation is correct. Unfortunately, very little has been published on this subject. I believe that speciation of sulfur components in an oil stream is equally important compared to speciation of naphthenic acids. Not all naphthenic acids behave the same, and not all sulfur species behave the same. An old, but very good reference paper on this subject is by Z.A. Foroulis, "High Temperature Degradation of Structural Materials in Environments Encountered in the Petroleum and Petrochemical Industries: Some Mechanistic Observations," Anti-Corrosion 32, 11 (1985): pp. 49.

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