ASTM A556/A556M is the specification for minimum-wall-thickness, seamless, cold-drawn carbon steel tubes, including tubes bent into U-shapes when specified, for use in tubular feedwater heaters. In a fossil or nuclear power plant these tubes sit inside the shell-and-tube feedwater heater, where extracted steam condenses on the outside while feedwater flows through the bore; preheating the feedwater before it returns to the boiler raises cycle efficiency and protects downstream equipment. Because the tubes are rolled or expanded into tube sheets and see repeated thermal cycling, the specification controls chemistry tightly, relies on cold drawing for dimensional accuracy, and requires a final heat treatment that restores ductility.
A556 is a carbon steel specification, not an alloy or heat-resistant grade. Tubes for superheater and reheater service - which run at much higher metal temperatures - are covered by a different specification (ASTM A213 alloy steel tubes).
Grades:ASTM A556 Grade A2, Grade B2, Grade C2
The three grades form a strength ladder set mainly by manganese content. A2 is the softest and most formable, B2 is the standard grade specified for most feedwater heaters, and C2 is used where higher design pressure allows a thinner, lighter tube. Grades B2 and C2 are the most frequently ordered for power-plant feedwater heaters.
Chemical Components (%) of ASTM A556 pipe
| Grade | C % | Si % | Mn % | P % | S % |
| A2 | 0.18 | ... | 0.27–0.63 | 0.035 | 0.035 |
| B2 | 0.27 max | 0.10 min | 0.29-0.93 | 0.030 max | 0.030 max |
| C2 | 0.30 max | 0.10 min | 0.29-1.06 | 0.030 max | 0.030 max |
All Mechanical Properties Tensile Requirements and Hardness of ASTM A556 alloy pipe
| Grade | Tensile strength, min, ksi [MPa] | Yield strength, min, ksi [MPa] | Elongation in 2 in. or 50 mm, min, % (longitudinal) | Hardness Requirements |
| A2 | 47 [320] | 26 [180] | 35 | HR B 72 |
| B2 | 60 [410] | 37 [260] | 30 | HR B 79 |
| C2 | 70 [480] | 40 [280] | 30 | HR B 89 |
Tolerances
Tolerances according to specification or by agreement. Standard tolerances are as follows:
| Processing Method | OD | Wall Thickness (WT) |
|---|---|---|
| Hot finished | ±1% | ±12.5% |
| Cold finished | ±0.75% | ±10% |
International Equivalents (indicative)
| ASTM A556 | DIN 17175 | JIS G3461 | Typical service |
|---|---|---|---|
| A2 | St 35.8 | STB 340 | Low-pressure feedwater heaters |
| B2 | St 45.8 | STB 410 | Standard feedwater heaters |
| C2 | 17Mn4 | STB 510* | High-pressure feedwater heaters |
*Cross-references are indicative. Confirm exact grade-to-grade equivalence against the current comparison standards and your project specification before substitution.
Applications
Tubular feedwater heaters in fossil-fuel and nuclear power plants (secondary loop).
Industrial boilers and process heat exchangers.
Any service where clean, dimensionally precise carbon-steel tubing is rolled into tube sheets.
Manufacturing and Heat Treatment
Tubes are made by a seamless process and then cold drawn to finished size. After the final cold-draw pass, every tube is heat treated at 1200°F [640°C] or higher so it has enough ductility to be expanded into the tube sheet and to meet the mechanical requirements. When U-bends are ordered, the bent section is stress-relief annealed in the 1100–1200°F [585–640°C] range.
Required Tests
Tension, flattening, and flaring tests on samples from each lot.
Hardness (Brinell or Rockwell) on specimens from two tubes per lot.
Full-section NDT - every tube is passed through an eddy-current (ASTM E309) or ultrasonic (ASTM E213) tester that examines the entire cross-section after final heat treatment.
Hydrostatic test - not required for straight tubes, but every U-tube must be hydrostatically tested with a non-corrosive fluid (or, by agreement, at 1½× the design working pressure).
U bend ASTM A556 feedwater heater tubes
A556 is commonly delivered as U-tubes. The bend must be made without visible flattening or wrinkling, wall thinning at the bend must stay within the minimum-wall requirement, and the bent portion is stress-relief annealed as noted above. The U-tube layout needs only one tube sheet, allowing the tubes to expand and contract freely and simplifying cleaning and maintenance.
GNEE Additional value-added services
UT(Ultrasonic examination)
AR(As Hot Rolled only)
TMCP (Thermal Mechanical Control Processing)
N(Normalized)
GNEE also supplies related cold-drawn carbon and alloy heater-tube specifications such as SA179 and SA192, and alloy grades including ASTM A213 T11/T22 for higher-temperature service.
Request a quote or mill test certificate:
Email sales@gneetube.com with your grade, size, length, and U-bend requirements.
certificate
ASTM A556 Feedwater Heater Tubes supplier
Gnee participated in the NECC exhibition
Customer visit
A556 seamless cold-drawn carbon steel tubes Factory
FAQ
1.Q: What is the difference between ASTM A556 Grades A2, B2, and C2?
A: The three grades share the same carbon-steel chemistry limits but differ in strength. A2 is the softest at 320 MPa minimum tensile, B2 rises to 410 MPa, and C2 reaches 480 MPa. Grade B2 is the most common choice for power-plant feedwater heaters, while C2 is specified when the heater sees higher pressure.
2. Q: How does ASTM A556 compare with ASTM A179 / SA179?
A: Both are seamless cold-drawn low-carbon steel tubes, but A179 is a general condenser and heat-exchanger grade with a single set of properties, while A556 is written specifically for feedwater heaters and offers three strength grades (A2, B2, C2) plus explicit U-bend and full-section NDT requirements. For feedwater heater retubing, A556 is usually the controlling specification.
3.Q: What size range does ASTM A556 cover?
A: The specification covers outside diameters from 5/8 in to 1-1/4 in (15.9 to 31.8 mm) with a minimum wall thickness of 1.1 mm. GNEE also supplies custom lengths up to 27 m and U-bend geometries to drawing.
4. Q: What tests are required by ASTM A556?
A: Each order is verified by tension, flattening, and flaring tests, plus Brinell or Rockwell hardness on specimens from two tubes per lot. Every tube is passed through an eddy-current or ultrasonic nondestructive test that examines the full cross-section after final heat treatment. Straight tubes are not hydrostatically tested, but U-tubes are.
5. Q: Can A556 tubes be supplied as U-bends?
A: Yes. A556 is frequently supplied bent into U-tubes for feedwater heaters. After bending, the bent portion must be stress-relief annealed in the 1100 to 1200°F (585 to 640°C) range, and every U-tube is hydrostatically tested with a non-corrosive fluid.
Hot Tags: ASTM A556 Feedwater Heater Tubes, China ASTM A556 Feedwater Heater Tubes manufacturers, suppliers, factory, seamless boiler pipe end of life, seamless boiler pipe taper, seamless boiler pipe delivery, seamless boiler pipe waveguide characteristics, seamless boiler pipe certification, seamless boiler pipe quenching
