CO2 corrosion and condensate effects in wet gas piping and equipment

[timbones]

I am in the process of working out some corrosion rates for piping and equipment at the inlet of gas processing plant. I am using NACE 69 as a guide for calculating corrosion rates.

The only known corrosive contaminant I have is CO2 which makes up 2 mol% of my inlet gas. The inlet gas comes it at approx 93 bar and 30°C. At the inlet of the plant, all the liquids (including any inhibitor) from the pipeline are removed in slug catcher or separator vessel. Downstream of the slug catchers is a long line (about 1 km)that leads into another separator vessel.

The liquid stream off of the bottom of the second separator consists of about 20% water, 2% CO2 and the rest is natural gas condensates. These liquids form through condensation in the pipeline. The question is, will the condensates sufficiently "oil wet" the steel to protect it from corrosion? NACE 69 suggests that you cannot expect NG liquids to "oil wet", but I'm not convinced.

 

[SJones]

Short answer: No! Take the advice of NACE and don't be so sceptical. You might be lucky at 20% water but need to take flow regimes and flow disturbance into account. Surf through the following:

http://search.nace.org/query.html?c...=mponline&qt="oil+wetting"&charset=iso-8859-1

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/

 

[stanweld]

I am in full agreement with Steve; piping in highly similar services in some of my former company's lines experienced severe corrosion and required replacement.

 

[timbones]

Ok, I guess I better start looking at that drain a little more closely.

There must be a threshold below which I don't need to worry about the water content. For instance, I have several drains that are further downstrem that are 98% condensate, 1% water and 1% dissovled CO2. In these lines I likely will not have to worry about the corrosion.