ASTM A688 U Bend Stainless Steel Tube for Heater

We offer ASTM A688 seamless and welded U bend stainless steel tube for feedwater heater, Austenitic stainless steel and Ferritic stainless steels, surface condition in annealing and pickling, or bright annealing finishing, used in heat exchanger, boiler, condenser, heat transfer system.

ASTM A688 / A688M covers seamless and welded Austenitic stainless steel feedwater heater tubes including stainless steel U bending tube for application in tubular feed-water heaters, the tubing sizes covered shall be 5⁄8 in to 1 in. [15.9 to 25.4 mm] inclusive outside diameter, and average or minimum wall thicknesses of 0.028 in. [0.7 mm] and heavier.

ASTM A688 U Bend Stainless Steel Tube specification

  • Heat treatment shall be applied to the U-bend area plus approximately 6 in. [150 mm] of each leg beyond the tangent point of the U-bend after bending, if specified.
  • Straight length: max 30000 mm
  • Leg length: 12000 mm, points of tangency of the bend to the leg end
  • Bending radius: max 1500 mm
  • Manufacturing method: cold drawing, cold worked
  • Straight length equal to 2 x leg length + 3.1416 x R

Chemical Composition

Elem-ent Grade TP304 TP304L TP304LN TP316 TP316L TP316LN TP XM-29 TP 304N TP 316N
% UNS S30400 S30403 S30453 S31600 S31603 S31653 S24000 S30451 S31651
C, max   0.08 0.035 0.035 0.08 0.035 0.035 0.060 0.08 0.08
Mn, max   2.00 2.00 2.00 2.00 2.00 2.00 11.50-14.50 2.00 2.00
Ph, max   0.040 0.040 0.040 0.040 0.040 0.040 0.060 0.040 0.040
S, max   0.030 0.030 0.030 0.030 0.030 0.030 0.030 0.030 0.030
Si,,max   0.75 0.75 0.75 0.75 0.75 0.75 1.00 0.75 0.75
Ni   8.00-11.00 8.00-13.00 8.00-13.00 10.00-14.00 10.00-15.00 10.00-15.00 2.25-3.75 8.00-1.00 10.00-14.00
Cr   18.00-20.00 18.00-20.00 18.00-20.00 16.00-18.00 16.00-18.00 16.00-18.00 17.00-19.00 18.00-20.00 16.00-18.00
Mo   2.00-3.00 2.00-3.00 2.00-3.00 2.00-3.00
N   0.10-0.16 0.10-0.16 0.20-0.40 0.10-0.16 0.10-0.16

Dimensional Tolerance

ASTM A688 U bend tube tolerance of outside should be accordance with specification A1016/M, bent portion of U tubes for R =2 X D or greater, tolerance shall deviate from the nominal diameter prior to bending by more than 10 %, if less than 2 X D is specified, tolerances could be greater, minimum wall thickness shall not exceed +20 % − 0, average wall thickness are 10 % of the nominal wall thickness, bent area wall tolerance shall not be less than value determined by the equation: 4RT/(4R+D).

Tube Leg Length Tolerance

Leg Length, ft (m) Plus Tolerance, in (mm)
<= 20 (6) 1/8  (3.2)
>20(6), <=30(9) 5/32  (4.0)
>30 (9), <=40 (12.2) 3/16  (4.8)

Squareness of Ends Tolerance

Tube OD, in, (mm) Tolerance, in, (mm)
<=5.8 (15.9) 0.010 (0.25)
>5.8 (15.9), <=1 (25.4) 0.016 (0.4)

Compared to ASTM A249/A268 specification, ASTM A688 requires more and specific tests to ensure high quality tube, and more tighter tolerances.

testing & inspection

  • Tensile Strength
  • Reverse bending test
  • Flattening test
  • Flare test
  • Flange test
  • Dimensional
  • Hydrostatic Test
  • Pneumatic Test
  • Hardness
  • Eddy Current test
  • Intergranular Corrosion (option)
A688 U bend stainless steel tube for heater

U tube packing

U bend stainless steel tube should be packed in box, each tube should be separated.

welded seamless stainless steel U bending tube