Low Fin Tube bundle requirement
15.9 mm (5/8 in) outside tube diameter may be used only when approved by the Principal.
below shows the outside tube diameters and minimum required tube gauges for bare tubes of copper alloys, carbon steel, low alloy steel, aluminium and high alloys. The actual thickness provided shall be suitable for both internal and external design pressure, any vacuum conditions, design temperature, tube thinning in U-bends, and any specified corrosion allowance for the tubes.
Where the tube thickness is specified as minimum wall, the tube thickness used for thermal design and pressure drop calculation purposes shall be 1.1 times the minimum wall thickness.
In services that are specified on the data/requisition sheet to require mechanical cleaning on the tube side, the mean radius of U-bends shall not be less than 75 mm (3 in) for tubes of an outside diameter less than 25.4 mm (1 in) or two (2) times the nominal outside diameter of the tube for tube diameters greater than or equal to 25.4 mm (1 in).
Where titanium U-tubes are specified, the minimum bend radius shall be two times the nominal outside tube diameter for tube diameters less than 25.4 mm (1 in), and 3.3 times the nominal tube diameter for tube diameters greater than o「equal to 25.4 mm (1 in), unless a larger bend radius is required for mechanical cleaning.
Where standard duplex stainless steel (e.g., S31803 or S32205) U-tubes are specified, regardless of the need for mechanical cleaning, the minimum bend radius shall not be less than 3.3 times the nominal outside diameter of the tube for all tube diameters. For benign services (e.g., non sour or wet H2S), consideration may be given to using a minimum bend radius of two times the nominal tube diameter when approved by the Principal.
Where super duplex stainless steel (e.g., S32750) is used, U-tubes may be provided with a minimum bend radius of two times the nominal outside diameter of the tube regardless of service and tube diameter
The tube side pressure drop may be calculated using smooth tube friction factors for stainless steel and other high alloy tubes, where corrosion is not expected. Commercial pipe friction factors shall be used for carbon and low alloy steel tubes.
Where possible, the number of tubes in any pass shall not be greater than 10 % above or vacuum, if specified, on the other side unless otherwise specified or approved by the purchaser.
Where welded tubes are used, re-dressing or "scarfing" of the weld seam is required when an expanded only tube-to-tube sheet joint is specified. The Contractor shall specify any additional testing requirements for welded tubes.