Recent research has shown that sour top of line corrosion (TLC) is different from sweet TLC. The steel surface temperature is the most important factor for sour TLC while condensation is less important. Failures due to sour TLC are relatively rare, but some cases have been documented the last decades.
In this work, sour TLC was systematically studied in autoclaves with a special holder that exposed one side of the TLC coupon while the back side was exposed to cooling liquid. The coupon surface temperature could be controlled by adjusting the temperature of the cooling liquid. The effect on TLC of various parameters like bulk temperature, condensation rate, organic acids, MEG and methanol was studied.
Methanol was clearly the most important factor affecting TLC corrosion. Although the mass loss corrosion rates increased somewhat with methanol, the major effect was that it resulted in significant localised corrosion compared to all other conditions that were tested. This is important because methanol sometimes is used in pipelines to prevent hydrates. A related literature review showed that methanol was involved in seven of ten field failure cases, further supporting the negative effect of methanol on sour TLC.
Key words: Top of Line Corrosion, H2S corrosion, methanol