Standard for U bend Tubes

The semi-finished product for U bend tubes are heat exchanger tubes, manufactured and supplied according to DIN 28180 and ASTM A179. Tubes for heat exchangers are made of steel according to:

U-bend or U-shape

U bend tubes for heat exchangers applied mostly in oil and gas plants, chemical and petrochemical plants, refineries, power plants and renewable energy plants. Low fin tubes can be supplied in the form of U bends.

U-Bend Fabrication Tolerances

U-bend tubes are widely used in heat-exchanger systems. Heat-exchanger equipment on the basis of seamless stainless U-tubes is essential in strategically important and critical fields — nuclear and petrochemical machine building.

Item Condition (when) Tolercance
  Nominal bend radius ≤ 2 x nominal OD less than or equal to 12%
Ovality 2 x nominal OD < Nominal bend radius ≤ 4 x nominal OD less than or equal to 10%
  Nominal bend radius > 4 x nominal OD  less than or equal to 5%
  Nominal bend radius ≤ 2 x nominal OD 0.75 x nominal wall
Mimimum wall thickness 2 x nominal OD < Nominal bend radius ≤ 4 x nominal OD 0.8 x nominal wall
  Nominal bend radius > 4 x nominal OD 0.9 x nominal wall
  Nominal bend radius ≤ 8" (200mm) +/-3/64"(1mm)
Bending Radius 8" (200mm) < Nominal bend radius ≤ 16" (400mm) +/-1/16"(1mm)
  Nominal bend radius >16" (400mm) +/-5/64"(1mm)
Disrance between legs   Max 1/16"(1.5mm)
Wall thinning of bending area   Max 17%
Difference between leg lengths at the ends Leg length ≤ 16' (4.88m) +1/8"(3mm)
Leg length > 16' (4.88m) +3/16"(5mm)
Deviation from plane of bend   ≤ 3/16"(1.5mm)
Flattening on bend   ≤ 10% nominal diameter
Straight leg length ≤5m +1/8"(3mm)
>5m +3/16(5mm)
Total tube length including radius ≤6m +3/16(5mm)
>6m +5/16"(8mm)
Dimension control on U bend tubes

Heat treatment of U bend tubes

Post bending heat treatment by electrical resistance (Joule effect) is applied. The temperature is monitored and controlled during the process. It is possible to perform the heat treatment in a nitrogen atmosphere.

U bend tubes can be tested as follows

Sizes tolerances of U bend tubes are to fulfil the requirements of: ASTM A556 / 556M and DIN 28 179

At present Sunny Steel has purchased the equipment for production of the following product range:

Carbon & Alloy Ferrite Austenite Duplex

Tubes of other alloys and steel grades can be produced upon agreement.
Technical requirements

Straight tubes for bending:

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.




Seamless pipe Specification, standard and identification

Seamless pipes are extensively applied for the nuclear device, gas, petrochemical, ship building and boiler industries. Seamless pipes dominates 65% of market share in Chinese boiler industry.