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Overheat damage of carbon steel tubes

  • 1.  Overheat damage of carbon steel tubes

    Posted 05-08-2021 08:39

    The images shown here are replica micrographs for carbon steel pipe that was subjected to an overheat incident:
       
    Material: ASTM A106 Grade B
    Design temperature for the tubes is 335 °C.
    Temperature excursion exposed tubes to a temperature of 600 °C for 16 hours.
    Location: Base material of tube

    Description: ferrite and pearlite microstructure showing pearlite decomposition and spheroidization of carbides

    Comment: Overheating exposure caused pearlite decomposition (partial metallurgical damage)

    Degree of damage: Moderate damage
    What was recommended is to repeat replication after 3 years without any immediate action . How do feel about this recommendation?

    500X
    1000X



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    Waleed Khalifa
    Principal and CEO
    Arabic Consultancy Center for Engineering Materials, Inspection and Welding
    Maadi, Cairo
    Egypt
    01098163293
    accmiw@ymail.com
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  • 2.  RE: Overheat damage of carbon steel tubes

    Posted 05-10-2021 08:02
    I would also consider performing a field hardness test such as a portable Brinell hardness.  If the hardness results, converted to an approximation of the tensile strength, agree with the UTS of the original spec, then the 3 year reinspection is good.

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    Robert Franco
    President
    Franco Corrosion Consulting, LLC
    Bellaire TX
    (713) 304-0398
    RobertFranco
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  • 3.  RE: Overheat damage of carbon steel tubes

    Posted 05-14-2021 05:37
    Robert

    Thank you for your comments. Actually, we did the hardness testing and it supported our recommendation as you advised. I share here the discussion of this post at the ASM Community as well.

    "DAN, I believe this piping work was done according to the process piping code B31.3.  I am not sure of the initial heat treatment condition of the pipes . The heat damage occurred during commissioning of the heater, so the heater was not in service before the temperature excursion. 

    The scope of this work was initially based on characterizing the microstructure and the hardness at several locations of the hot oil heater. The Investigation covered locations of pipe base metal, HAZ, weld metal, and base metal at a bend location. Out of 36 locations, 21 locations did not show any significant microstructural changes. Slight metallurgical damage was observed in 12 locations, while only three locations showed moderate metallurgical damages similar to what appeared in the micrographs.  The hardness values were all above the lower limit (120 HB), but at the lowest range which might agree with low carbon level as noticed by PAUL . Based on these results, and after discussion with User, the three years of re-inspection was suggested. Additional work was done after that to confirm these recommendations.

    This is to physically simulate this heat overshot via heat treatment of an identical pipe spool.  This might be in line with SEAN commendation. The replicas of the simulated spool showed a moderate damage at three locations, and only the weld metal was free did not show any  microstructural changes.  The hardness were all above the lower limit as well. Tensile specimens were cut from the simulated pipe spool, but I am not aware of the results yet. 

    I reviewed the paper that NIHAD recommended: the paper showed that mcirotsrctural changes occurred after 50 hours at 630 C. I am not sure if this can be useful to compare with our case, since this was the shortest treatment time in the paper at this temperature. This means the changes might occurred  at shorter times but not recorded or observed. The starting microstructure of the pipe material of the paper might also be different from that of the oil heater. Even with this, the paper was very useful to understand the rate of changes in A106 grade B materials."        

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    Waleed Khalifa
    Principal and CEO
    Arabic Consultancy Center for Engineering Materials, Inspection
    Maadi, Cairo
    Egypt
    accmiw@ymail.com
    ------------------------------