Krish 123 Rolling in C.S Tube sheet with T 5 tubes - how differential expansion comes to give an off-set to increase diameter by 3-5 mm of the tube sheet at one end only (floating end) . Basically there is not much difference in T.S values for C.S and T 5 grades even though T 5 grade material is little harder. Ideal could have been A 182 F 5 forged tube sheet with T 5 tube for both fixed and floating head ends. Exchanger design if made to TEMA Class C or R, and rolling grooves in tube sheet of 60 mm with either double groove light rolling and strength welded at tube sheet end, this problem could not have come. Contractor is allowed only double rolling to meet TEMA Class C or R with grooving depth to suit this 60 mm tube sheet. Why he used triple rolling? Probably, T 5 tubes had come with tight tolerances than the original C.s tubes (this could be one reason for the over-all expansion in diameter). What is the sequence of tube rolling practice contractor adopted if he had adopted triple sequential rolling (which he may not be allowed in 60 mm tube sheet design exchanger). I guess contractor could have chosen or selected , from his own judgement, after seeing tube sheet to tube clearance to decide additional rolling expansion due to the gap between existing C.S tube sheet and the T 5 tube to have more tight expansion and this could have affected the over all diametral expansion of tube sheet by 5 mm. He is not allowed such leeway as per TEMA Class C or Class R. What is the sequence of tube rolling he adopted- you could check. Normally in such used old tube sheet to new tube expansion rolling is done in a staggered way so that tube rolling stresses are minimized or balanced . It is preferable from outer periphery to inner periphery or centre tubes to avoid such diametral expansion of tube sheet. What is the type of jigs and fixture he used for avoiding distortion and diametral expansion when he did triple rolling- you could check? Hope this helps C.V.Srinivasan Nishi Engineers Pvt Ltd India June 3, 2010 E-mail: nishi@vsnl.com >Due to corrosion issue we have upgraded the existing carbon >steel tubes(19.00 mm ODX2.71 thk A201) with T5 >Material(5Cr-0.5 Mo) and retained the CS Tube sheet(60 mm >thick).However,after tube expansion we noticed increase in >diameter for about 3-5 mm especially at the floating head >cover gasket seating area. The exchanger fabricator claiming >that this is mainly due to rolling of hard alloy steel tube >to soft carbon steel tube sheet. I would like to know >whether if we change the carbon steel tube sheet with alloy >steel tube sheet will solve the above issue.If not is there >any method to avoid increase in diameter of tube sheet while >rolling?It is be noted that the fabricator has used adequate >jixs& fixture while rolling even then the change in tube >sheet diameter was experienced. Any improvement can be made >in rolling practice?Contactor used 3-roll for rolling the >tubes with sequential rolling method. Your suggestion is >much appreciated in this regard. > >with advance thanks,