CP for uncoated oil treater

[andygo11]

Hi, an issue was raised by our client which is about CP for FWKO drums and oil treaters. Because of the high operating temperature and pressure, the vessels are not internal coated. The size for the vessels is about 4 m by 27 m. The question is what type of CP is suitable for this big vessel. Cient wants the sacrifical anode because of the low cost, but the CP vendor suggests the impressed current due to the large uncoated surface which needs high current. In this case, the sacrifical anode could be comsumed fast and a big amount of anodes needed to be intalled at the bottom of vessel.

The vessels are emulsion serive. The process information for the emulsion is:

T= 138 C, P= 835 kPag
H2O = 0.7171 mass fract. CO2 < 0.00005 mass frac.
H2S = 0.00000403 mass frac.
Cl in produced water separated from emulsion is 1140.5 ppm.

So, which type of CP is better to apply? If SA is used, is there any method to estimate the comsuption rate?

 

[SJones]

138 deg C is not overly high for a coating. On the other hand, you will only need to account for CP up to the high-high liquid trip point. What is the owner's planned vessel entry programme, as all they would have to do is add full anode replacement to the work pack? However, that chloride level is probably not high enough to go with aluminium sacrificial anodes and zinc will probably be a no-no at those temperatures because of potential reversal.

Start with sorting a coating out and then consult NACE SP0575. The only way to get a consumption rate is to run some tests.

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.