Hi there, We have a high pressure water cooler to cool high temperature ammonia which is a single pass shell and tube exchanger and made in carbon steel with HP Amm gas on shell while cooling water on tube side. Due to the poor quality tube to tubesheet weld joint which is light expanded and strength welded construction, the ammonia gas leaks from few T/TS welds and forms salt deposits on the tubesheet. The repair to leaking tube by welding was tried but in vain as this opens up the adjacent welds and worsen the situation. I need your expert opinion on 1. How to carry our effective repair without affecting the adjacent welds, given that tube welds are close to each other. 2. What improvements should be carried out in the existing design should we decided to replace the unit with a new. regards

Bigpond HP Ammonia cooler (C.S material) repair welding of tube to tube sheet with pitch distance between tubes being less, higher weld heat input , during repair welding, will spread and affect near by tubes. The only choice left is to reduce heat input with some staggered repair welding approach for TIG root and final strength weld both combined. If you have excess capacity to meet TEMA Class C (which should be close to 10%), plug the near by tubes that are affected due to welding repair of tubes already leaking and have been attempted repair welding. This itself will be an improvement to both repair welding and also make utility of existing HP Ammonia cooler. This will greatly improve performance with slight loss in capacity utilization. Question of replacing with better design and avoiding pitfall in current design or repair approach comes only after careful repair approach to existing tube to tube sheet leaks and also taking care to plug nearby tubes likely to have been affected due to weld repair of tube to tube sheet. HP Ammonia cooler leaks is commonly experienced by most fertilizer users . By careful staggered welding repair approach this problem can be solved successfully. There may not be a need to review current design and current operating exchanger performance if you do that Hope this helps C.V.Srinivasan Nishi Engineers Pvt Ltd India march 30, 2010 E-mail: nishi @vsnl.com/cvsjsmeta@gmail.com >Hi there, >We have a high pressure water cooler to cool high >temperature ammonia which is a single pass shell and tube >exchanger and made in carbon steel with HP Amm gas on shell >while cooling water on tube side. Due to the poor quality >tube to tubesheet weld joint which is light expanded and >strength welded construction, the ammonia gas leaks from few >T/TS welds and forms salt deposits on the tubesheet. The >repair to leaking tube by welding was tried but in vain as >this opens up the adjacent welds and worsen the situation. > >I need your expert opinion on >1. How to carry our effective repair without affecting the >adjacent welds, given that tube welds are close to each >other. >2. What improvements should be carried out in the existing >design should we decided to replace the unit with a new. > >regards

Bigpond It is not compounded unless you have done a bad repair job welding execution. After identifying the leaky tube and take corrective action to repair the tube - not by just repair welding but first effective steps to plug the internal of the tube to be repair welded. Second before attempting repair welding on the tube leaking, ensure that the near by tubes had not developed signs of leaks. Take the nearest four tubes around the leaky tubes for plugging as a precautionary measure. Before plugging these nearest four or six tubes around the leaky tube to be repair welded (both by internal plug + strength weld of the leaky tube to tube sheet joint) ensure that you do quality staggered repair weld. Ensure by leak test from shell side with a gas which is lighter than air and observe if the nearby tubes had developed slight sweating or signs of slight tube to tube sheet leak after repair welding the leaky tube. Once you are sure, plug the sound tubes around the repair welded tube and test again by pneumatic with helium or even with nitrogen with soap sud around the whole tube sheet. This way you will ensure that repair welded leaky tube and the nearby tubes that have been plugged are leak proof for further operation of HP Ammonia cooler (Four or six nearby tubes are taken as a precautionary measure to avoid problems of leaks around them after starting the plant). Success is more or less ensured if you approach this way both repair weld and plugging nearby tubes as a caution. Hope this helps C.V.Srinivasan Nishi Engineers Pvt Ltd India April 1, 2010 E- mail: nishi@vsnl.com >Thanks for the valuable reply. Just to clarify, while we >plug nearby tubes (assuming we weld the plug) how do we >protect their neighboring tubes. It is compounded while the >leaking tubes are in the middle. >regards