ASTM A179 / ASME SA179 Seamless Carbon Steel U-Bend Tube for Shell and Tube Heat Exchanger and Heat Exchanger Tubesheet
ASTM A179 / ASME SA179 is a standard specification for minimum-wall-thickness, seamless cold-drawn low-carbon steel tubes intended for tubular heat exchangers, condensers, and similar heat transfer apparatus. The specification covers seamless tubes from 1/8 to 3 inches [3.2 to 76.2 mm] in outside diameter, inclusive. These U-bend tubes are manufactured by the seamless process and cold drawn to achieve precise dimensional tolerances and consistent mechanical properties.
The U-bend configuration allows tubes to be inserted into a single tubesheet at both ends, forming a compact U tube bundle that accommodates thermal expansion without inducing differential stress between the tubes and shell. This design is widely used in shell and tube heat exchangers where the tube bundle must be removable for cleaning and maintenance.
Base Tube Manufacturing Requirements
Seamless tubes shall be made by the seamless process and shall be cold drawn. After the final cold drawing pass, the base tubes are heat treated at a temperature of 1200°F [650°C] or higher. The finished tubes shall have a clean surface condition and shall be free from harmful scale and visible defects. A slight amount of surface oxidation may be accepted according to the applicable standard and purchase order. The maximum hardness requirement for the SA179 base tube is 72 HRB.
Chemical Composition (per ASTM A179 / ASME SA179)
| Element | Composition (%) |
|---|---|
| Carbon (C) | 0.06 – 0.18 |
| Manganese (Mn) | 0.27 – 0.63 |
| Phosphorus (P) | 0.035 max |
| Sulfur (S) | 0.035 max |
| Silicon (Si) | 0.25 max |
Chemical composition per ASTM A179 / ASME SA179 specification.
Mechanical Properties (per ASTM A179 / ASME SA179)
| Property | Requirement |
|---|---|
| Tensile Strength, min | 325 MPa (47,000 psi) |
| Yield Strength, min | 180 MPa (26,000 psi) |
| Elongation in 50 mm, min | 35% |
| Hardness, max | 72 HRB |
Mechanical properties per ASTM A179 / ASME SA179 specification.
U-Bend Manufacturing Process
U-bend tubes are manufactured after straight tubes are produced. The bending operation is performed in the cold state on an automatic U-bending machine. To ensure that wall thinning and diameter ovality are kept under control, a mandrel is inserted into the tubes during the bending process. The U-bend portion is subsequently stress relieved under controlled conditions and cycles to provide longer service life. Finished U-bent tubes undergo 100% hydrostatic leak testing and dye penetrant testing prior to dispatch.
Dimensional Tolerances (per ASTM A179 / ASME SA179)
Outside Diameter Tolerances
For tubes under 1″ (25.4 mm) OD, the tolerance is +0.10 mm / –0.10 mm. For tubes 1″ to 1-1/2″ (25.4 to 38.1 mm), the tolerance is +0.15 mm / –0.15 mm. For tubes 1-1/2″ to 2″ (38.1 to 50.8 mm), the tolerance is +0.20 mm / –0.20 mm. For tubes 2″ to 2-1/2″ (50.8 to 63.5 mm), the tolerance is +0.25 mm / –0.25 mm. For tubes 2-1/2″ to 3″ (63.5 to 76.2 mm), the tolerance is +0.30 mm / –0.30 mm.
Wall Thickness Tolerances
For tubes 1-1/2″ (38.1 mm) OD and under, the wall thickness tolerance is +20% / –0%. For tubes over 1-1/2″ (38.1 mm) OD, the tolerance is +22% / –0%.
Bending Radius and Leg Length
Bending radius ranges from 1.5 * OD (outside diameter) to 3600 mm. Leg length (straight portion) ranges from a minimum of 0.3 meters to a maximum of 16,500 mm.
Required Mechanical Tests
Flattening Test – One flattening test shall be made on specimens from each of two tubes from each lot or fraction thereof.
Flaring Test – One flaring test shall be made on specimens from each of two tubes from each lot or fraction thereof.
Flange Test – When specified as a substitute for the flaring test, for tubes having a wall thickness (actual mean wall) less than 10% of the outside diameter, one test shall be made on specimens from each of two tubes from each lot or fraction thereof. For tubes other than specified above, the flange test shall not be required.
Hydrostatic Test – Each base tube is subjected to hydrostatic testing unless a permitted non-destructive electric test is specified as a substitute by the purchaser.
Non-Destructive Examination (NDE)
Eddy Current Testing (ET) – For detection of surface and subsurface defects
Ultrasonic Testing (UT) – For detection of internal discontinuities
Hardness Testing (HT) – For verification of material condition
Magnetic Particle Testing (MT) – For surface defect detection where specified
Applications
ASTM A179 / ASME SA179 U-bend tubes are widely used in shell and tube heat exchangers, condensers, boilers, and similar heat transfer apparatus. Specific applications include feedwater heaters, evaporators, steam generators, and heat recovery systems. The U-bend configuration is particularly suited for applications requiring a removable tube bundle for cleaning and maintenance access.
Available Material Grades
Yuhong Group also supplies U-bend tubes in the following grades upon request: ASME SA178 Grade A and Grade C, ASME SA192, ASME SA210 Grade A1 and Grade C, ASME SA209 Grade T1, T1a and T1b, ASME SA213 Grade T1, T11, T12, T22, T5, T9 and T91.
Documentation
Each shipment is supplied with complete documentation including Mill Test Certificates (EN 10204 Type 3.1), heat treatment records, hydrostatic test reports, NDE reports (ET, UT, HT, MT as applicable), dimensional inspection reports, and surface condition reports.
For a rapid quotation on ASTM A179 / ASME SA179 Seamless Carbon Steel U-Bend Tube, please provide the following information:
Quantity (number of pieces or weight)
Outside diameter and wall thickness
Bending radius (centerline radius) and leg length (tangent length)
Straight length before bending (if applicable)
Surface treatment requirement (black painting, oiled, or bare)
End preparation (plain ends or beveled ends)
Delivery period required
