Tubes are fixed to the tube sheet (a thick circular metallic plate) by the method of tube rolling and brazing (non-removable) or ferrule connection (removable). Thickness of the tube, sheet is normally ____________ the outside diameter of the tube but in no case it should be less than 22 mm (7/8″)?

• A. Half
• B. Three fourth
• C. Equal to
• D. 1.5 times