Stainless Steel for Oil and Gas piping

[nickypaliwal]

Is stainless Steel not considered for produced water, injection water, lift gas, test separator water and oil outlets even if the chloride content and other process parameters allow ?

Does stainless steel face problems of under deposit corrosion in long run even if the chloride content in the flow is in tolerable limits of SS?

 

[blacksmith37]

I never recommended austenitics because the Cl is never low enough.If you really want to spend money on alloy, why not ferritic/martensitic like down hole ?

 

[nickypaliwal]

Thanks.. I have not seen ferritic/martensitic for onplot .. I have only seen duplex and Austenitic..

Also what should be the reason to reject austenitic.. ? and I have not seen my client using ferritic/martensitic...

 

[MagBen]

Generally specking, austenitic SS is better than ferrite/martensitic SS at corrosion resistance.

Is not 316 commonly used for oil and gas piping? Mo is added in this alloy to withstand attack by many industrial chemcials and solvents, in particular, inhabits pitting caused by chlorides. For those severe corrosion environmmnets where 316 is inadequate, 20Cb-3 is very economical choice available.

 

[nickypaliwal]

IN my case chlorides are not higher than SS316 tolerable limits...Temperature is not high and no H2S is present.. So on what basis shoul i reject ss316.. what about ferritic/martensitic as advised above..

 

[EdStainless]

If you have low Cl and NO oxygen then why not use carbon steel (0.25% Cr)?

The Cl limits for 316 are a lot lower than most people think. I wouldn't go over 200ppm.
You have to watch out for issues like under deposit corrosion, crevice corrosion, and attack of welds.
In general if it is produced water with NO oxygen then a 5% Cr or 9%Cr alloy will work fine.
If you have Cl and oxygen then you have to balance the costs, either of using full time inhibitor injection or using a high alloy austenitic (6% Mo).

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P.E. Metallurgy, Plymouth Tube

 

[nickypaliwal]

CO2 is present which gives a high corrosion rate so CS is not advised.... This limit to chloride content given above (200 ppm) is discussed anywhere ? Oxygen is not present in the system ....

 

[EdStainless]

There have been dozens of papers given at NACE over the last ten years.
Don't use a reference older than that.
There have been a lot of failures in 316 systems at 300-500ppm Cl.
Especially if there is CO2 to drive the pH down.

So this is two phase flow?
Are you sure that oxygen is below 0.2ppm?

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P.E. Metallurgy, Plymouth Tube

 

[nickypaliwal]

yes oxygen is below 10ppb ...it is water system...