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hydrotest pressure of fractionator ovhd finfan cooler

Home Forums Coking hydrotest pressure of fractionator ovhd finfan cooler

This topic contains 2 replies, has 1 voice, and was last updated by  Anonymous 8 years, 6 months ago.

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  • #1875

    Freddy Martinez
    Participant

    Can you suggest on the following?

    In refinery turn around, it was found that distillation column overhead fin fan cooler thickness is lost by around 50%(3mm becomes 1.5mm). In order to sustain operation, it is advised by inspection deptt. to carry out hydrotest of fin fan cooler at 3.5kg/cm2 instead of original hydrotest pressure of 6.75. At the same time, we are also decided to bring down the distillation column psv set pressure from original 4.5 to 3.5kg/cm2. will there be any problem when the unit will be in operation? Please help?

    Bipul

  • #4623

    Anonymous

    Hi! It appears from your post that the air cooler HEADER BOXES have lost approximately 50 percent of their original corrosion allowance of 3 mm. If this is the case, there is no concern since at least 1.5 mm of corrosion allowance is still available (note that rigorous engineering calculations performed today might find that more than 1.5 mm corrosion allowance still remains). If the TUBES have lost approximately 50 percent of their original wall thickness of 3 mm, I would proceed to hydrotest the air cooler at its original test pressure of 6.75 kg/cm2, plug off any leaking tubes, return the air cooler to operation, and follow-up with ordering a replacement tube bundle. A tube wall thickness of 1.0 to 1.5 mm is normally considered the absolute minimum required for SHORT-TERM reliability. Reducing the maximum operating pressure of the distillation column and the air cooler will not provide any real increase in remaining life of the air cooler since the operating pressure is so low to begin with. Good luck!

  • #4622

    Anonymous

    Thanks for your reply. The thickness reduction I had mentioned was actual tube thickness, not the corrosion allowance. In fact, there was no corrosion allowance considered in design of the tubes.
    We have already going ahead for replacement of fin fan tubes. For short term reliability, we have already hydrotested the fin fan tubes at 3.5kg/cm2 and bring down the fractionator column PSV set point to 3.5kg/cm2 instead of earlier 4.5kg/cm2. Our normal operating pressure at fractionator top is 2kg/cm2 and temp 116 degree C. Some time in previous operations we had encountered problem of pressure surging to 4kg/cm2 at column top due to mostly water present in our feed. our unit will be operational very shortly. You may please suggest for preventive course of action as a short term reliability.

    Your further comment on the above will be appreciated.

    Bipul

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