Acid Gas Injection Pipeline
Acid Gas Injection Pipeline
(OP)
I have a mixture of acid gas that is (by mass) 73% CO2, 26% H2S, and about 0.2% H2O with trace hydrocarbons. The acid gas is compressed to 1100 psig and then flows to the injection well through a buried carbon steel pipeline.
My concern is that of an aqueous phase may condense one the gas hits the colder pipeline and cause localized corrosion. Should I be worried? Are there any good epoxy coatings for this type of application? I had originally planned on dehydrating the gas, but I have run into some budgetary and time constraints.
My concern is that of an aqueous phase may condense one the gas hits the colder pipeline and cause localized corrosion. Should I be worried? Are there any good epoxy coatings for this type of application? I had originally planned on dehydrating the gas, but I have run into some budgetary and time constraints.





RE: Acid Gas Injection Pipeline
RE: Acid Gas Injection Pipeline
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Steve Jones
Materials & Corrosion Engineer
http://www.pdo.co.om/pdo/
RE: Acid Gas Injection Pipeline
quite a bit actually. Any where from 90% CO2 to the design conditions.
East Texas probably a couple of feet deep.
Fully turbulent. Somewhere around 300,000 to 500,000 Reynolds number if liquid and 1.3 million if gas.
RE: Acid Gas Injection Pipeline
RE: Acid Gas Injection Pipeline
RE: Acid Gas Injection Pipeline
Even though water is present as a small percentage to be mostly in the form of a liquid -- droplets and surface film, probably. Carbon steel will be attacked by the acids formed by gases disolved in the water.
Carbon steel is not acceptable. Don't put any faith in epoxy coated pipe.
Use a nonferous alloy. A nickel alloy might be best, but I can't say for sure. You must investigate. Buena suerte.
RE: Acid Gas Injection Pipeline
RE: Acid Gas Injection Pipeline
RE: Acid Gas Injection Pipeline
Steve Jones
Materials & Corrosion Engineer
http://www.pdo.co.om/pdo/
RE: Acid Gas Injection Pipeline
RE: Acid Gas Injection Pipeline
That is the whole point of engineering, isn't it. Do the calculations; then if a bad condition is revealed by the calculations, change the design.
Read Engineering Design for Process Facilities, McGraw-Hill (1993).
RE: Acid Gas Injection Pipeline
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..particularly the ones that inject acid gas with formation water.
I have also read a few papers on the subject. There is no real consensus on the appropriate material for pipeline construction. Generally, if the acid gas is compressed to the dense phase or has a water content of less than 0.2%, carbon steel is acceptable since there isn't sufficient free water to form an aqueous phase. In this case it is borderline, but probably will not form. Currently we are looking into chilling the acid gas into the dense phase to save horsepower going into the well, so that should remove the potential for corrosion as well.
RE: Acid Gas Injection Pipeline
RE: Acid Gas Injection Pipeline
RE: Acid Gas Injection Pipeline
Steve Jones
Materials & Corrosion Engineer
http://www.pdo.co.om/pdo/
RE: Acid Gas Injection Pipeline
RE: Acid Gas Injection Pipeline
Jim
RE: Acid Gas Injection Pipeline
psia psia
lbs lb-moles mole-fr Pp degF Pv
______ _________ ________ _______ _______ ________
CO2 | 73 | 1.659 | .682 | 760 || 100 | 0.943 |
H2S | 26 | 0.763 | .314 | 350 || 110 | 1.28 |
CO2 | 0.2 | 0.0111 | .0046 | 5.13 || 120 | 1.69 |
Sum = 2.4331
degF Pv
_____ _____
100 | .943
110 | 1.28
120 | 1.69
Stated water content is 0.2 lbs. This is a mole fraction of 0.0046. Multiply this times 1115 psia to obtain partial pressure of 5.13 psia. This pressure is compared to vapor pressure, Pv, (the last column of the table) at 100, 110, and 120 degF. For example at 120 degF the vapor pressure is 1.69 psia. Therefore, water will condense until its concentration is: mole-fr = .0046*(1.69/5.13) = .00152, or a gas composition of 73% CO2, 26% H2S, .066% H2O.
RE: Acid Gas Injection Pipeline
From the originator's response on conditions prevailing, it is clear that the gas is compressed, cooled and sent for re-injection. He does mention cooler performance. Under the circumstances, it would be logical to assume the gas to be water saturated (is the KOD having water after the final cooling?) and any further cooling can and will drop out water. Rest follows...
We have an application where we have a separate dewpointing unit to dewpoint the gas - and the gas is heated up to near ambient to give a 15 deg C superheat or so. We dont expect any cooling (ambient conditions, length of pipe etc).
I would be very concerned also (especially if the length of pipeline is large) about upset / startup/shutdown conditions.
I can suggest one thing though...leave some of the superheat in the compressed gas to avoid condensation...if acceptable. Or better still, use some of the compression heat (in another exchanger) to superheat the final gas after the cooling / knock out. The degree of superheat will have to be decided based on the ground conditions (ambient, length of pipe etc). These methods should also be used along with something else to address the upset / startup / shut down conditions.
Hope this helps.
RE: Acid Gas Injection Pipeline