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We are operating a kettle reboiler connected to a distillation column. Heating is in a 3 metre long U-tube steam heat exchanger. Steam is at 10 kg/cm2 pressure. In the shell side dilute alcohol is evaporated at temperature of 100 deg C.U-tubes are welded in the tube sheet. we are facing the problem of frequent leakage from welding. Tubes and tube sheet are SS316 material. The tube bundle is adequately supported.
Does condensing steam create vibration in the u-tube? Welding leakage from top few rows are predominant.Would appreciate for suggestion to avoid such problem.
 
Answers
20/08/2015 A: keith bowers, B and B Consulting, kebowers47@gmail.com
What type of cracking? YES condensing steam inside U-tubes can cause high amplitude and high frequency vibration. Steam should be on shell side and tube bundle should be a floating head with Rolled tube ends, not welded. Liquor should be either pumped or a thermosiphon to ensure high circulation rates and minimal tube wall temperatures.
20/08/2015 A: Tom Podwell, ProSonix LLC, tpodwell@pro-sonix.com
Yes, steam condensate can lead to steam or water hammer if all of the condensate is not removed. The condensate can build-up and not allow steam movement which I believe is sometimes referred to as "exchanger stall". Your steam trap rep should be able to help trouble shoot this.
Also possible that hot steam entering the exchanger may be causing thermal shock depending on the temp of the exchanger. This can damage welds. Some of our customers with large heat exchangers or HRSGs will pre-heat the system with circulating hot water and ramp up the metal temp prior to adding steam.