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Lately, have been experienced tube leak in DHDS stripper feed-effluent exchanger, Tubes were plugged and hydro-tested.
Four months later, again leak developed and found tubes in bad condition, and was recommended for full bundle re-tubing.
I would like to know what could be root cause for this tube failure in short time? Any specific improvement need to be done on internals of exchanger?
 
Answers
21/03/2014 A: Narendra Naidu, NWR, nbpnnaidu@gmail.com
Stripper feed/Effluent exchanger is usually at the Ammonium chloride deposition temperature, this were the Ammonium Chloride salts deposit, it could move upstream if the chloride content of your feed has increased but based on your chloride content this exchanger should have water wash to dissolve the salts and wash it to the sour water.
if do not have continuous wash water, try adding wash water to this exchanger on weekly basis for at least four to six hrs and the amount should be so that 25% of water stays as liquid.
15/01/2014 A: Eric Vetters, ProCorr Consulting Services, ewvetters@yahoo.com
How long had the bundle been in service before the first failure? Were non leaking tubes inspected after the first failure? It is possible that you had damage on more tubes than just the ones that leaked initially. When that happens it often doesn't take long for new leaks to develop if the original cause of the corrosion has not been addressed.
You might want to see if you are getting water carry over from your cold separator. As ammonium bisulfide in entrained water heats up in the feed/bottoms exchanger it can become corrosive.
15/01/2014 A: keith bowers, B and B Consulting, kebowers47@gmail.com
Additional information is necessary for us to offer any opinion. What caused the leaks? Corrosion, vibration, under deposit corrosion, crevice corrosion at tube sheet?
Was failure internal or external side? Bad Condition? in what way?
15/01/2014 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
If you are water washing the effluent condenser for removal of ammonium salts, an emulsion in the effluent settling vessel could allow water carry-under. Wet H2S would flow through the stripper feed/ bottoms exchanger, requiring alloy metallurgy. If you already have alloy, try stepping up to a higher alloy.
Sometimes a temperature adjustment in the settling vessel helps break emulsions.
15/01/2014 A: Morgan Rodwell, Fluor Canada Limited, morgan.rodwell@fluor.com
You should determine the cause of the tube corrosion/damage, and check with a metallurgist about the material selected. if you have switched to a higher sulfur feed, you may have higher sulfur / H2S content that is causing the corrosion. Other considerations may be that if you are not dewatering effectively in the upstream separator you could have salty sour water corroding the tubes. Check chloride levels in the upstream separator.