Inhabited Pitting Rate 2

[Hajiwaji]

Dears,

Is corrosion inhibitors effective against pitting cased by H2S and CO2 for gas flowlines? The salt content is very low, so the line has low risk of scaling and under deposit corrosion. The ECE model gives around 20 MPY of maximum pitting rate and less than 1 MPY for general corrosion rate. Can we use NACE publication 01055 to calculate inhabited pitting corrosion rate? Then use the value as basis for the required corrosion inhibitor efficiency?

Thank you

 

[0707]

Normaly inhibitors are used to combat topping of columns corrosion against H2S and chlorides mantaining Ph arround 6. I sugest you to contact Baker Hughes or Nalco, they are specialized in corrosion inhibitors and for sure will give you advices.

 

[Hajiwaji]

0707

Thank you for your reply. My inquiry is about pipelines corrosion caused by acid gas dissolved in water phase condensed from compressed gas. Top of columns corrosion happen at high temperatures. Severe damage can occurred in distillation columns and other equipment during downtime. Corrosive chloride salts such as ammonium or amine chloride salts can cause corrosion at the rate of over 1000 mpy if exposed to moisture and air.

 

[0707]

Again I sugest you to contact Baker Hughes or Nalco, they are specialized in corrosion inhibitors and for sure will give you advices.

 

[SJones]

They can be if they are qualified correctly. Refer to NACE SP21469. The ECE manual should tell you about whether the model is able to apply an inhibition factor to the pitting rate.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

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

 

[Hajiwaji]

Thank you Dr. SJones. My client uses Champion KR-2237X or ATROS Dodigen 1641X for downstream gas pipelines. I will contact the vendor and post the result here.

 

[LittleInch]

Condensed water tends to end up with top of line corrosion which is difficult to inhibit.

Do you have any free water at the start of the line or is it all condensed.

Not sure too many inhibitors work without being able to create a film over the inner surface and that's difficult with condensation. I think. It's been a while since I did this sort of stuff now.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Hajiwaji]

Hi LittleInch,

This is compressed gas coming from GOSP HP compressor. The inlet of the pipeline is about 170 F which is above the dew point of water. The arrival temperature is 160 F. ECE predict condensation and pitting rate higher than 5 MPY which mandate corrosion control as per clint standard. One corrosion control method is the use of corrosion inhibitor. So I was wondering if it is a common practice to use the equation in NACE 01055 to get a value for the inhibited pitting rate. If corrosion inhibitor fails to bring the corrosion rate below 5 MPY, internal FBE coating will be used to protect the pipeline.

 

[SJones]

Judging by the terminology, sounds like Aramco. Surprised that they haven’t called for both inhibitor AND internal FBE

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

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

 

[Hajiwaji]

Correct Dr. Jones. This is Aramco. Curranty we are making the case for CS + CI + scrapping program which is inline with SAES-L-132 (Figure-1) and SAES-A-133 (Appendix A) CS evaluation for pipelines.