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)
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