Export Pipeline CO2 Modelling
Export Pipeline CO2 Modelling
(OP)
Dear All
I am planning of modelling CO2 general corrosion on an export Condensate Pipeline(Cassandra) My understanding is that both CO2 content and Pressure input data should be from the last stage separator (where the gas is in equilibrium). I have seen a number of reports (from consultancies) which use the condensate export pipeline operating pressure (which is substantially higher than last stage separator Pressure)
I assume both cannot be right and would appreciate your input.
Many thanks
I am planning of modelling CO2 general corrosion on an export Condensate Pipeline(Cassandra) My understanding is that both CO2 content and Pressure input data should be from the last stage separator (where the gas is in equilibrium). I have seen a number of reports (from consultancies) which use the condensate export pipeline operating pressure (which is substantially higher than last stage separator Pressure)
I assume both cannot be right and would appreciate your input.
Many thanks





RE: Export Pipeline CO2 Modelling
RE: Export Pipeline CO2 Modelling
Cassandra is the historical BP take on the de Waard - Milliams, de Waard - Lotz work. Thus, it is likely to work with fugacity of CO2. The model generally derives this as a function of the gas phase partial pressure. This implies that you are going to have to come up with a gas phase composition. If your condensate line is single phase, how will you work out the gas phase composition? Has pumping the condensate pressure up increased or decreased the fugacity of the CO2 compared to the separator?
Steve Jones
Corrosion Management Consultant
http://www.linkedin.com/pub/8/83b/b04
All answers are personal opinions only and are in no way connected with any employer.
RE: Export Pipeline CO2 Modelling
The manual categorically states to use the last stage separator data for liquids.What confused me is to see so many reports using the pipeline Pressure when using Cassandra!
Wouldn't the partial Pressure remain same as it's linked to Henry Constant? Wouldnt any dissolved gases in the condensate be much lower than the last stage CO2 mol% used as an input hence the fugacity would remain constant?
Many thanks for your input.
RE: Export Pipeline CO2 Modelling
If it is close by this is quite accurate, problems may occur however if any degassing then occurs or if the liquid is subsequently pumped.
If the line pressure is greater than the separator operating pressure then it suggests that the condensate passes through a pump before it enters the pipeline, hydraulic pressure does not increase the concentration of dissolved acid gases in the liquid and therefore it is not correct to use the line pressure to calculate partial pressure of the gas to enter into the model.
A common problem in this type of example is to be provided only with dissolved liquid measurements of acid gas concentrations with no upstream equilibrium gas phase data available. In equilibrium with a gas phase the equivalent liquid concentration is much lower than the gas concentration and entering this data combined with the line operating pressure into a corrosion model is a frequent mistake that will result in the underestimation partial pressure and therefore corrosion rates.
In this case if upstream data is not available a “hypothetical equilibrium gas phase” must be calculated using henrys law and correcting for fugacity if needed to calculate an accurate rate.
RE: Export Pipeline CO2 Modelling
Anyway - you have your answer: do what the manual says.
Steve Jones
Corrosion Management Consultant
http://www.linkedin.com/pub/8/83b/b04
All answers are personal opinions only and are in no way connected with any employer.
RE: Export Pipeline CO2 Modelling
Many thanks. That's why I love this website. Such an immense knowledge sharing!
This is an eye opener for me to see these countless reports from "consultancies " with this issue not being highlighted by the end users!
Many thanks all.
RE: Export Pipeline CO2 Modelling
Steve Jones
Corrosion Management Consultant
http://www.linkedin.com/pub/8/83b/b04
All answers are personal opinions only and are in no way connected with any employer.
RE: Export Pipeline CO2 Modelling
Thanks
RE: Export Pipeline CO2 Modelling
Steve Jones
Corrosion Management Consultant
http://www.linkedin.com/pub/8/83b/b04
All answers are personal opinions only and are in no way connected with any employer.
RE: Export Pipeline CO2 Modelling
RE: Export Pipeline CO2 Modelling
CO2 corrosion can only occur in an all liquid condensate stream when there is a pH value (or some other parameter which correlates with pH) for the free water phase of the condensate stream.
RE: Export Pipeline CO2 Modelling
Steve Jones
Corrosion Management Consultant
http://www.linkedin.com/pub/8/83b/b04
All answers are personal opinions only and are in no way connected with any employer.
RE: Export Pipeline CO2 Modelling
Cassandra predicts the corrosion rate at water wetted locations only (The data the model is built upon is taken from flow loop tests in water) and the output is not corrected for any oil wetting effect.
If the condensate is a completely dry hydrocarbon then the corrosion rate would be zero yes, however the ability of condensate to entrain water is very limited and typically no oil wetting effect is considered for condensate. So if there was any water drop out in the pipeline there could be corrosion.
ECE includes an oil wetting correction factor.
RE: Export Pipeline CO2 Modelling
NACE has been trying to publish a couple of reports on corrosion modelling. Having just checked the NACE website, they don't appear to be having much success with the membership. One document is called "Prediction of Environmental Aggressiveness in Oilfield Systems from System Conditions," and the other is "Selection of Pipeline Flow and Internal Corrosion Models." Unfortunately, the drafts have been copyright marked so they cannot be attached.
That really only leaves the 2009 IFE Report as being of any use: IFE/KR/E - 2009/003
Steve Jones
Corrosion Management Consultant
http://www.linkedin.com/pub/8/83b/b04
All answers are personal opinions only and are in no way connected with any employer.
RE: Export Pipeline CO2 Modelling
Actually you cannot enter zero water to ECE.
RE: Export Pipeline CO2 Modelling
Steve Jones
Corrosion Management Consultant
http://www.linkedin.com/pub/8/83b/b04
All answers are personal opinions only and are in no way connected with any employer.
RE: Export Pipeline CO2 Modelling
So you can imagine what doesnt happen in these separators. These also wreak havoc on condensate-water separators when in MEG/water - hydrocarbon service where CI and MEG injection occurs far upstream of gathering pipelines at subsea wells.
RE: Export Pipeline CO2 Modelling
Steve Jones
Corrosion Management Consultant
http://www.linkedin.com/pub/8/83b/b04
All answers are personal opinions only and are in no way connected with any employer.
RE: Export Pipeline CO2 Modelling
Nesic team from Ohio university developed modelling of CO2 corrosion (free dl)
Nowadays DeWaard&Milliams is more or less obsolete (always gives very high corrosion rates whatever the operating parameters)
API RP941 for HT H2 service (annex, latest edition) provides several methods for evaluating equivalent partial pressures pp for full liquid streams while knowing conditions in previous separator, this includes change in total pressure :
RE: Export Pipeline CO2 Modelling
Steve Jones
Corrosion Management Consultant
http://www.linkedin.com/pub/8/83b/b04
All answers are personal opinions only and are in no way connected with any employer.