You need to specify if if you are planning to use stainless or carbon steel. The approx amount of sweet gas and temperature is also usefull to pick the correct alloy.
In the North Sea Norwegian sector, the oil companies use pipes with more 13% chromium if the CO2 level is high and the H2S level is low. If you have water in the pipe together with O2, then forget about carbon steel unless you have some sort of cathodic protection.
It might be usefull to check out duplex-sttels as well, if the temperature is above 40deg C (or 100deg F) and the pipe is in contact with chlodies and water.
thank you very much. is this similiar case with onshore gasline with the fluid content is wet gas, no H2S, no chloride? well gas Temp above 212deg F, so the duplex more suitable, isn't it?
I love it when people say 'no chlorides'. That is what keeps me in business.
If your CO2 is low then carbon steel or a 13%Cr grade might be the better options. At that temp I doubt that CS will be suitable though.
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Corrosion never sleeps, but it can be managed.
EdStainless, you are correct about someone saying "no chlorides". I have seen pipes of AISI316 that is trasporting CO2 at temperatures above 100deg F, and it is failing because there is actually moist of water and chlorides present in the pipe.
Xda
At a seminar a couple of years ago, CLI-FAFER (french company?) presented a case where they used 12-13% Cr steels at temperatues up to 212deg F (100deg C) with pressure of CO2 up to 290psi and pH as low as 3,5.
Ask a stainless steel supplier about thay think when you give them your data of the fluid. (content CO2, pH, pressure etc., length of pipe (line?)) Remember you might save weight and cost if the alloy is strong and stainless. The wallthickness can be reduced bacause of strength of the SS alloy compared to using a carbon steel alloy with cathodic protection (that also needs extra wallthickness due to corrosion)
Carbon steel can be used if H2O remains as vapor. Once condensate is formed, expect corrosion rates in excess of 80 mils/year for carbon steel piping. If this is initial well chemistry, remember that the concentrations, pressures and temperatures will change over time. Expect H2O to increase while pressure and temperature decrease. If condensate will not occur initially, expect it to occur sometime during the life of the well.
This is very much a life cycle cost question, i.e. do you want to load your capital expenditure with an expensive stainless steel or does the opex intensive chemical treatment option for carbon steel give an overall higher net present value of the project? The first step is to have some idea of the expected corrosion rate of carbon steel. Try putting the operating parameters into the Norsok model at:
Concurrently, the feasibility of chemical treatment and associated operations such as pigging can be investigated and some costs obtained for life cycle evaluation. Pipeline burial requirements play a part as the stainless steel will, like the carbon steel line, have to be coated and subjected to cathodic protection. It's a bit too involved to go into here. ISO 15663 gives guidance on life cycle costing.
Steve Jones
Petroleum Development Oman LLC
Muscat
Sultanate Of Oman
I concur with Steve. You really need to look at the economics of the pipeline that you are wanting to build. Carbon steel can be very cost effective, especially if it is only a short life that you want to have. If the asset is expoected to have a much longer life, then it may be prudent to look at other options.
This is a very complex matter, and companies spend lots of time and money in the decision as to what is the best way to go.
My first recommendation to you is to decide what is most important to you. Up-front CAPEX or lowest life cycle cost? When you start looking at material factors of 3 to 7 times that of carbon steel, many project managers get 'concerned'. Even when you can show a life cycle cost benefit for CRA, it is often hard to get support when it costs the project more up front - that's my experience anyway.
