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DCU fractionator HCGO draw tray damage

Home Forums Coking Technical Fractionation & Process Fractionation DCU fractionator HCGO draw tray damage

This topic contains 3 replies, has 2 voices, and was last updated by  Mike Kimbrell 3 years, 5 months ago.

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  • #27487

    chiou
    Participant

    Recently, Our DCU suffered main fractionator HCGO draw tray(Chimney tray) leakage problem. The HCGO leaked down to bottom of the main fractionator. The recycle ratio of our DCU increased from 1.1 to 1.6 passed through one year. We shut down our DCU to check the damage condition of the HCGO draw tray. We found 44 cracks on the HCGO draw tray( the total length of the cracks is 7.7m). The tray had cracks but no deformation on it. The material of the trays is ASTM A240 TP410. We have a wash zone of shed deck design under the HCGO draw tray for main fractionator. Has anyone had suffered similar tray damage problem as our DCU main fractionator? Is the damage caused by drum switchs and cool downs upsetting the fractionator?

  • #27489

    Mike Kimbrell
    Participant

    This material is susceptible to cracking at welds or other areas of high induced stress, particularly in high H2S environments. Use of type 405 or 410S stainless steels is done to reduce the risk of this cracking. Bolted trays of type 410 have given good service as long as the bolts are 405 or 410S, otherwise they will crack. API 571 – Damage Mechanisms discusses 885 F (475 C) embrittlement discusses trays constructed of type 410 stainless steel that operate at temperatures in excess of 600 F (316 C) for long periods of time will lower the toughness of this material at lower temperatures. Multiple shutdowns and start-ups could cause damage to the trays if their toughness was low enough.

  • #27490

    chiou
    Participant

    Dear sir:
    I made a mistake. Our DCU HCGO draw tray(op. temperature 360C) material is 410S. And our CDU LGO draw tray(410s, op. temperature 325C) and VDU wash oil draw tray(410s, op. temperature 350C) also have cracks at welds.
    Do we need to upgrade the tray material or renew the tray in a period of operation?

  • #27492

    Mike Kimbrell
    Participant

    Trays constructed of 410S should give good results in the services you describe. If these are all welded trays, the weld procedure may be leaving hard welds that crack in operation. Changing the weld procedure could be enough to resolve your problems.

    I have had good luck with 410S trays in these services, both welded and bolted trays. If you converted the welded trays to bolted trays you would not have the cracking problem. Bolted trays have more leakage, which is why draw trays are typically welded. If you want to switch to bolted trays, you might need to have them gasketed to limit the leakage to acceptable levels.

    You should have a discussion with your tray supplier (Koch-Glitsch, Sulzer or ?) to make them aware of the leakage problem you are experiencing due to weld cracking. They may have specific advise on what is needed on your unit.

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