Q & A > Question Details
i have corrosion problem in overhead system reflux pump and accumulator this system consist of atmospheric tower and overhead condenser (4 bundles with crude in tube side) then accumulator with water boot the and reflux pump to atmospheric again. we just add corrosion inhibitor in overhead line without neutralizing amine due to old recommendation based on high accumulator temperature. temp in accumulator 115-130 c and pressure 1.1-1.4 barg .note that no water accumulated in vessel boot .
16/01/2018 A: NS Murthy, GE, murthy.ns@ge.com
Best way to deal this issue is that look at the area impacted by corrosion and have detailed analysis of corroded surface. As crude does bring in tramp amines, it could be the result of localized precipitation of amine salt which are at times well above the dew point of water. Request contacting nearest Suez (earlier GE Water team) representative and carryout audit on the OH system. Looking at past conditions, one can assess potential 'hot spots' in your system. Many designers do say no condensation in the first drum. However, varying crude and desalters' performance there could instances of water formation leading to such, which most occasions do go un-noticed. Also, check the effectiveness of CI in working under varying ICP pH range.
10/01/2018 A: Stefan van der Wal, Mettler-Toledo Process Analytics, stefan.vanderwal@mt.com
Probably there is no water in the boot as at those pressures and temperatures water will still be steam (check steam tables) .
pH may very well be the reason of your corrosion. Sour water is notorious for causing alkaline corrosion though at pH > 7.6
As acid corrosion needs to be avoided too, it's important to carefully and continuously control pH in the overhead bootwater. This requires an inline pH measurement and obviously the presence of water; This requires that you'll reduce the temperature in the boot and allow steam to condense.
03/01/2018 A: Lindsay McRae, Pall Corporation, Lindsay_McRae@pall.com
The corrosion issue may well be as a result of carryover or sour water back to CDU. By adding corrosion inhibitor this negatively impacts on the IFT (Interfacial Tension) and makes the HC . sour water emulsion more stable. This emulsion is likely much too stable for OH drum to make the separation effectively. I would expect IFT in region of 5-7 dynes/cm in a case like this. For OH drum to work better, IFT should be >20 dynces/cm. This is probably why you see no water in boot.
High efficiency PhaseSep Liquid Liquid coalescer installed after reflux pump can break this emulsion and prevent sour water recycle back to CDU and break the corrosion cycle. Sour water can be then diverted back to SWS. You may want to consider lowering the temp as well.
Are you seeing sour water carryover to debutanizer also? That might also be a possibility where OH drum separation is underperforming.
03/01/2018 A: Eric Vetters, ProCorr Consulting Services, ewvetters@yahoo.com
In addition to what Sam Lordo said, choride salts from tramp amines and/or ammonia in the overhead system could also be causing corrosion. Corrosion outside of the bundles is especially likely when the bundles are alloy. The shock condensation forms on the alloy bundle but does not corrode there. The salts or water then migrate to a non alloyed location where they cause corrosion - often the exchanger shell.
03/01/2018 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
Chemical salesmen will have several recommendations for the overhead protection program, based on the crude being processed and your desalter efficiency. Note that 50% of crude units worldwide inject caustic in the heat exchanger area. How can you not have water in the boot if you are using stripping steam?
03/01/2018 A: Sam Lordo, Nalco Company, salordo@comcast.net
if you have corrosion, you have some water present, most likely from shock condensation in the exchangers and dripping down into the accumulator.. this water would typically be very low ph especially if no neutralizer is used.. is the reason the neutralizer is not use is because this is a double drum system?