The Oil & Gas Petroleum Refining and Gas Processing

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The Oil & Gas Petroleum Refining and Gas Processing Technical Community of Interest is a group of people (both AMPP members and nonmembers) who have come together for the purpose of furthering a common cause by sharing wisdom, knowledge, information, and/or data for application and evaluation of methods of corrosion control and control of materials deterioration for petroleum refining and gas processing operations.

  • 1.  Clarification on API 581 Threshold for ACSCC(Carbonate SCC ) in FCC Gascon Unit Section

    Posted 01-16-2025 05:49 AM
      |   view attached

    I am seeking clarification regarding the threshold specified in API 581 for the likelihood of Alkaline Carbonate Stress Corrosion Cracking (ACSCC) in the FCC Gascon unit section. The document mentions a threshold of 100 ppm above which ACSCC becomes likely.

    Could you please confirm whether this threshold of 100 ppm refers specifically to the concentration of the carbonate ion (CO32−CO32−), or if it encompasses the total carbonate concentration, which includes both carbonate ions (CO32−CO32−) and bicarbonate ions (HCO3−HCO3−)?

    Understanding this distinction is crucial for accurate monitoring and prevention strategies in our refinery processes. Any additional insights or references to relevant sections in API 581 or other related standards would be greatly appreciated.

    Thank you for your assistance.

    Best regards,



    ------------------------------
    Harsh Zala
    Larsen and Toubro(L&T)
    hzala408@gmail.com
    +917984512098
    ------------------------------


  • 2.  RE: Clarification on API 581 Threshold for ACSCC(Carbonate SCC ) in FCC Gascon Unit Section

    Posted 01-17-2025 04:26 AM

    Harsh,  I would suggest that you review the NACE Publication 34108, "Review and Survey of Alkaline Carbonate Stress Corrosion Cracking in Refinery Sour Waters" as this should answer your questions.

    1. The ion that is implicated in causing ASCC is CARBONATE (CO3=).
    2. Measuring CO3= as a standalone species is very difficult and not necessarily relatable to total carbonates (CO3=, HCO3-, CO2).
    3. Closed cup pH of the sour water is an essential determination for assessing this potential for ASCC. See Figure D1. 
      1. pH determines the concentration split between the species with higher pH indicating higher CO3= potential. Determination of CO3= will typically require electrolytic modelling.
      2. The pH/CO3= concentration to potentially trigger ASCC concerns can be found in the Kmetz and Truax Figure C1 in the NACE publication.
    4. The susceptibility for high pH and hence higher CO3= is a function of FCC feed and processing. Highly hydroprocessed FCC feed has the highest potential to create a high pH , higher CO3= environment. 

    Hope this helps. 

    Andy Gysbers
    Refining Metallurgical & Corrosion Engineering Expert

    CMI Division

       agysbers@becht.com
       becht.com

     




    Original Message


  • 3.  RE: Clarification on API 581 Threshold for ACSCC(Carbonate SCC ) in FCC Gascon Unit Section

    Posted 01-20-2025 05:30 AM

    Dear Harsh,

    ACSCC primarily occurs in alkaline environments with pH levels between 8 and 10. At higher pH values, carbonate (CO₃²⁻) becomes the predominant species, while bicarbonate (HCO₃⁻) becomes less stable. For example, when the pH reaches 10, carbonate makes up over 90% of the species present.

    ACSCC doesn't occur below pH 8 because bicarbonate is the dominant species in this range. Without a significant presence of NH⁴⁺, the conditions aren't suitable for ACSCC. This explains why API 581 specifically identifies carbonate (CO₃²⁻) as the species responsible for cracking, rather than bicarbonate. In fact, bicarbonate acts as a buffer, helping to prevent pH increases and actually reducing the likelihood of ACSCC occurring.

    Best Regards,



    ------------------------------
    Dr Mohammd Hosseini, PhD, CEng, CSci, FIMMM, FICorr, AMPP CS/SICT, API 571/580
    Technical Director
    London Petrotech Engineering Ltd
    London, UK
    +44 (0) 3289 9991
    ------------------------------

    Original Message


  • 4.  RE: Clarification on API 581 Threshold for ACSCC(Carbonate SCC ) in FCC Gascon Unit Section

    Posted 01-20-2025 05:31 AM

    Hi Harsh,

    ACSCC primarily occurs in alkaline environments with pH levels between 8 and 10. At higher pH values, carbonate (CO₃²⁻) becomes the predominant species, while bicarbonate (HCO₃⁻) becomes less stable. For example, when the pH reaches 10, carbonate makes up over 90% of the species present.
     
    ACSCC doesn't occur below pH 8 because bicarbonate is the dominant species in this range. Without a significant presence of NH⁴⁺, the conditions aren't suitable for ACSCC. This explains why API 581 specifically identifies carbonate (CO₃²⁻) as the species responsible for cracking, rather than bicarbonate. In fact, bicarbonate acts as a buffer, helping to prevent pH increases and actually reducing the likelihood of ACSCC occurring.
    Kind regards,
    Dr. Mohammad Hosseini, PhD, CEng, CSci, FIMMM, FICorr, AMPP-Certified Corrosion Specialist, API 571/580
    London Petrotech Engineering Ltd


    ------------------------------
    Seyed Mohammad K. Hosseini
    Subsea 7
    Epsom
    +44203289991
    ------------------------------

    Original Message


  • 5.  RE: Clarification on API 581 Threshold for ACSCC(Carbonate SCC ) in FCC Gascon Unit Section

    Posted 01-20-2025 05:31 AM

    Hi Harsh,

    ACSCC primarily occurs in alkaline environments with pH levels between 8 and 10. At higher pH values, carbonate (CO₃²⁻) becomes the predominant species, while bicarbonate (HCO₃⁻) becomes less stable. For example, when the pH reaches 10, carbonate makes up over 90% of the species present.
     
    ACSCC doesn't occur below pH 8 because bicarbonate is the dominant species in this range. Without a significant presence of NH⁴⁺, the conditions aren't suitable for ACSCC. This explains why API 581 specifically identifies carbonate (CO₃²⁻) as the species responsible for cracking, rather than bicarbonate. In fact, bicarbonate acts as a buffer, helping to prevent pH increases and actually reducing the likelihood of ACSCC occurring.


    ------------------------------
    Dr Mohammd Hosseini, PhD, CEng, CSci, FIMMM, FICorr, AMPP CS/SICT, API 571/580
    Technical Director
    London Petrotech Engineering Ltd
    London, UK
    +44 (0) 3289 9991
    ------------------------------

    Original Message