Corrosion rate in sour service 1

[halba1359]

Hello to all,
I know nothing about corrosion, but I need to read a report about corrosion assessment in a pipeline.
H2S partial pressure is 9.7bar and CO2 partial pressure is 2.81bar in this pipe, so I think the H2S is dominate corrosive component. But the partial pressure of CO2 is considered as a yardstick to predict corrosion rate with using De Waard and Milliams equation.
I'm very confused about this! Would you help me?
Regards
Amin

 

[brimmer]

This is because it is very difficult to predict corrosion rates from sour service as it is very complex depending on numerous factors, no predictive model exists for this application. I will assume your pipeline is multiphase, and contains free water. Some general guidelines, the higher the concentration of H2S, the higher the corrosion rate, or at least potential corrosion rate. Also, corrosion rates generally increase with increasing CO2 and H2S partial pressures and temperatures. Generally speaking, H2S and CO2 together you will form a semi-protective film, depending on the ratio of H2S to CO2, you will get a different film. Since you have more H2S than CO2, it will most likely form a semi-protective tighter film of Iron Sulfide, as opposed to a less protective film of Iron Carbonate(s). However, you need to take into account such factors such as Cl ions in the system as well, Cl ions will disrupt the scales formed and lead to pitting, so this is an important piece of info. Also, you want to know where your areas of water hold up will be, as you will find correlation to these locations and corrosion. Other factors include amount of solids, which can also disrupt films formed. If there is elemntal sulfur in the system, this will increase corrosion rates as well. Anyway, you get the idea, there is not just one factor, which makes the corrosion rate difficult to predict. There are a fair amount of papers on this topic you should be able to research to get background info. I have attached a paper to get you started.

 

[stanweld]

Corrosion rates will also depend on how much water you have and how much water you will have in the future and the fluid temperature.

 

[SJones]

We will not be able to teach you the finer points of H2S weight loss corrosion, never mind the pitting, on a forum such as this. I'm still learning after 25 years in the game! Brimmer has got you started, but if you cannot readily access NACE papers, and other associated literature, you will not get very far. Tell your supervisor you need to attend a NACE pipeline corrosion course.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

 

[halba1359]

thank you all

 

[strider6]

You can find a lot of useful papers on corrosion in oil&gas in these websites:

http://www.corrosioncenter.ohiou.edu/publications/

http://www.ife.no/en/publications/p...374b4c0dfe8d911fce1a&getAuthor=&submit=Search

hope this help

V.

Corrosion Control