Rolled Tube Joints

Welded Tube Joints When suitable materials of construc tion are used, the tube ends may be welded to the tube sheets. Welded Joints may be seal-welded Tor additional tightness beyond that of tube rolling or may be strength-welded. Strength-welded Joints have been found satisfactoiw in veiy severe seivdces. Welded Joints may or may not be rolled before or after welding. 

Stress relieve carbon and chrome steel welds and cold bends in amine service regardless of service temperature. For all concentrations of carbonate solutions and in concentrations of caustic up to 30 percent stress relieve for service temperatures above 140 F (60 C). For 30 to 50 percent caustic, the service temperature where stress relief is required decreased from 140 >F(60°C) to 118T (4B C). Welded tubing does not require heal treatment in addition to that required by the ASTM specifications. Rolled tube-to-tube sheet joints do not require stress relief. 

As a caution, the rolling of tubes into their tubesheets is a very special job that requires experience and feel, even though today there are electronically controlled rolling and expanding tools. The tubes must be just right, not over nor under expanded, to give a good joint and seal. 

Greater care should be taken and proper procedures followed by the condenser manufacturer when rolling the tube ends to avoid excessive wall reduction and tube extrusion. To prevent crevice corrosion in the tube-to-tubesheet joint, the tube end should be rolled for the full thickness of the tube sheet.12... 

M. Podhorski, Hydraulic expansion of tubes , International Conference on Expanded and Rolles Joint technology, Toronto (1993). 

For the structural consideration, the graphitic monolayer tube can be treated as a rolled-up graphite sheet that matches perfectly at the closure line. Choosing the cylinder joint in different directions leads to different helicities. One single helicity gives a set of discrete diameters. In order to obtain the diameter that matches exactly the required interlayer spacing, the tube layers need to adjust their helicities. Therefore, in general, different helicities for different layers in a multilayer tube are expected and were indeed found in our experiment. 

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