arbon SA 213; ASTM B 163; ASTM B 729; ASTM B 407; ASTM B 423; ASTM A 789 U-bend Tubes: -TEMA RCB 2.31 Standards of the Tubular Exchanger Manufacturers Association (9th edition). -ASTM A688 Standard specification for welded tubes of austenite corrosion resistant steel grade designed for feed water boilers. -ASTM B163 Standard technical requirements for tubes of nickel and nickel alloy for condensers and heat exchangers. -Customer specifications.? ? ? ? ? ??u bendingBENDING RADIUS: from 1.