Well Integrity Technical Section

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  • 1.  Pitting causes

    Posted 10-26-2023 08:21 AM
    Edited by Binh Nguyen 12-12-2023 06:25 AM

    Dear technical experts,

    Could you please give me some example of what causes pitting on CRA & carbon steel pipes downhole and on surface?

    I know it's oxygen in the mud that causes local corrosion but what else? not all the pipes coming back from downhole have pitting, while some others are severly damaged?

    Can we duplicate this defect in lab condition? how to?

    Thanks and best regards,

    Binh



  • 2.  RE: Pitting causes

    Posted 10-26-2023 11:59 PM

    Hello Binh, 

    Please see the attached link that is a paper on the lab experiments aimed to understand corrosion mechanism in thermal wells. While your application might be different, you might like the methodology used.

    Studies of Aqueous Hydrogen Sulfide Corrosion in Producing SAGD Wells | NACE CORROSION | OnePetro

    Cheers,

    Barkim




  • 3.  RE: Pitting causes

    Posted 10-27-2023 09:56 AM
    A major source of pitting is CO2. CO2 can create localized pitting in an area of the well where gas is breaking out of the produced fluid or where the static or even flowing fluid level is in a well. It can also create pits in J areas of tubing. It can create random pitting anywhere fluid with CO2 can sit and work on the metal.

    You mention Oxygen as a pitting agent. That is true but has to be introduced into the well as it isn't usually native to a flow stream. Keep it out and you won't have Oxygen corrosion.

    Other sources of pitting comes from carbonic acid being created by the produced fluid mixing with the salts and scales being produced that go through phase change on their way out of the well.

    Mike Chaffin
    Valence Operating Company




  • 4.  RE: Pitting causes

    Posted 10-28-2023 04:22 PM
      |   view attached

    Binh,

    You don't mention what steel grades you are using but API does not restrict the metallurgy of lower grade steels like J55 or K55, L80, N80 and even P110 (see attached).  This means the composition of these steels may vary from batch to batch and supplier to supplier. This makes these grades the cheapest grades of steel you can buy.

    Take a look at the attached and we can discuss what this chart means when it comes to corrosion resistance.



    ------------------------------
    Dan Gibson
    aka The Well Doctor
    Completion & Well Integrity Advisor
    Houston, Texas
    ------------------------------



  • 5.  RE: Pitting causes

    Posted 10-29-2023 09:55 PM

    Binh

    If you could share some photos of the damage we could point you to the likely cause but in general chemistry of all of the alloy steel grades will have similar behavior and low grade CRAs may be influneced by similar damaging species like bacteria or acid attack in addition to Oxygen as stated.


    Original Message