Thanks, this was really very informative and useful. regards

Bigpond Apply TEMA Class C and ASME Sec VIII Div 1 rules for high pressure exchanger fabrication from design approval, fabrication drawing approval, stage wise III party inspection approval (including mock drill test, welding qualification to meet ASME code for tube to tube sheet welding) For ammonia high pressure service in tube side, light expansion in double groove to meet TEMA Class C and strength welding is the best option. You can add an additional precaution at the tube to tube sheet light expanded stage from performing pneumatic test (in Purchase order). This will ensure more guarantee that you had not missed any light rolled tube had not developed leaks after strength welding. Choose a well known and capable high pressure design / fabricator company than going by cheap cost fabricator. Apply stage wise III Party Inspector (choose a qualified and integrity related III Party Inspector who would be practical / experienced and high quality with integrity in such high pressure vessel fabrication inspection - stage wise inspection from material identification, welding qualification including mock drill test, stage wise fabrication including light expanded tubes and witnessing the pre- strength welded tube to tube sheet joint leak testing), P.O should be good to cover all aspects of material spec, welding and III party inspection responsibilities. Staggered tube to tube sheet welding, final S.R of tube to tube sheet should meet ASME code stipulations. Final hydro/pneuamtic (including helium leak test of tube to tube sheet joints) should be insisted and witnessed thoroughly and record kept by III Party inspector / fabricator / client. Hope this helps C.V.Srinivasan Nishi Engineers Pvt Ltd India August 24, 2010 E-mail: nishi@vsnl.com >hi, > >Tube repairs attempted in the past but found not very >successful due to contaminants, with re-tubing option >during an annual shutdown becoming critical in terms of >time, its been decided to go for a new cooler, I would like >to capture your thoughts on what additional precautions >shall be considered for its design and fabrication? Should >the tube to tubesheet weld design to strengh expanded and >seal welded or light expansion followed by strength welded. > >regards