Arnab TEMA code standards prescribe conditions for Class B, Class C, Class R type exchanger manufacture. This is based on leak tolerance permitted in joints from process fluids or vapor exchanges (tube to tube sheet roll tolerances) and the leak permitted with seal or strength welding and also based on the type of explosive limit to which crititcal solvent exchange takes place. For high pressure and high temperature > 150 deg cent and pressures > 40 KSC in highly explosive reacting liquid or vapor streams - strength weld joints are recommended in addition to double groove tube tight rolling in tube sheet grooves. Client has to specify clearly the process conditions, at the time of order, and the limit of leak tightness and for the type of liquid or vapor stream conditions for mechanical design to select either seal or strength weld conditions for tube to tube sheet joints in addition to tube to tube sheet rolling grooves. In some cases, a strength weld is done without tube to tube sheet groove rolling but with very tight tube to tube sheet clearances. This depends on fluid handled, fluid pressures, chances of vapor - liquid flow in the tube to tube sheet clearances etc. TEMA Code and ASME code for fabrication for leak tolerance and explosive limit (in case of vapor -liquid exchanve) decides the criticialy of seal weld versus strength weld selection. If there is a possibility of vortex effect in clearances between the tube and tube sheet grooves or with no grooving, then effect of corrosive fluid attacking the tube or tube sheet, then tube groove rolling and strength weld will be a better option than seal welding even if with tight tube to tube sheet groove rolling. Trust this is of help to you C.V.Srinivasan Nishi Engineers Pvt Ltd India April 5, 2006 E-mail:nishi@vsnl.com >What is the requirement for difference in seal welding and >strength welding of Heat excahnger tube to tube sheet joint. >What is the pressure/ temperature limitation where strength >welding is required?

Excellent answer. To add to the discussion, if a strength weld is used in addition to ring groves it is advised to check into hydraulic expansion of the tubes rather than the traditional rolling method. The rolling method expands the tubes radially as well as longitudionally. This imparts pressure on the strength weld joint. Hydraulic expansion expands the tubes in the radial direction only and does not adversly affect the seal weld.