What is ASTM A688?
ASTM A688 Tube defines a type of welded austenitic stainless steel tubing mainly employed for high temperature service applications including nuclear power and other industries. This specification consists of seamless and welded tubes produced from grades including 304, 316, 347 and others showing high corrosion resistance and strength.The tubes are normally used where high pressure, high temperature and radiation effects are expected. ASTM A688 tubes have close tolerance limits that in addition to the mechanical tests, also undergo hydrostatic and dimensional tests to meet the needed conditions for use in various environments.
ASTM A688 U-Bend Stainless Steel Tubes are specifically designed for feedwater heater applications, providing high temperature and corrosion resistance due to their austenitic stainless steel composition, often grade 304/304L or 316/316L. These tubes are manufactured using an automatic welding process for welded tubes or a cold working process for seamless tubes, which are then U-bent to form the required shape. Post-bending, the U-bend area and adjacent leg sections typically undergo heat treatment to relieve stress and enhance mechanical properties and corrosion resistance.
ASTM A688 Stainless Steel 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 |
ASTM A688 U Bend Stainless Steel Tube Dimensional Tolerance
ASTM A688 U bend tube tolerance of outside should be accordance with specification A1016/M, the 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) |
What is the price of ASTM A688 stainless steel U tubes per kg?
Prices range from USD 4.50 – 8.50 per kg, depending on grade, size, and order quantity.
ASTM A688 Stainless Steel U Shape Steel Tube Production Process
We offer ASTM A688 seamless and welded U bend stainless steel tube for feedwater heaters, Austenitic stainless steel and Ferritic stainless steels, surface condition in annealing and pickling, or bright annealed finishing, used in heat exchanger, boiler, condenser, heat transfer system. Mail:es@gescosteel.com
ASTM A688 / A688M covers seamless and welded Austenitic stainless steel feedwater heater tubes including 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.
