Detailed Product Description
Application & Compliance
The ASTM A179 / ASME SA179 carbon steel U-bend tube is specified for shell and tube heat exchangers operating in low-pressure, non-corrosive or mildly corrosive service where carbon steel is the economic material selection. In refinery crude preheat trains, the U-bend tube bundle absorbs differential thermal expansion between the shell and tubes without inducing stress at the tube-to-tubesheet joints. In power plant condensers, it conveys cooling water on the tube side while steam condenses on the shell side. In boiler feedwater heaters, it transfers heat from extraction steam to boiler feedwater. The U-bend configuration allows both tube ends to expand into a single heat exchanger tubesheet, reducing the number of flanged connections and eliminating the need for a floating head assembly.
The tube is manufactured and tested in accordance with ASTM A179 / A179M, ASME SA179 / SA179M, and ASME Boiler and Pressure Vessel Code Section VIII Division 1 for pressure boundary applications. Certification is available per EN 10204 Type 3.1 or 3.2. Third-party inspection by ABS, GL, DNV, NK, PED, AD2000, and CCS is available upon request.
Problem Solved
The U-bend configuration addresses the differential thermal expansion problem inherent in fixed tubesheet heat exchangers. When the tube side fluid and shell side fluid operate at different temperatures, the tubes and shell expand at different rates. A fixed tubesheet design transfers this differential expansion into the tube-to-tubesheet joints, causing premature joint failure. The U-bend tube allows each tube to expand and contract independently, eliminating thermal stress at the joints. This design also allows the entire tube bundle to be removed from the shell for cleaning and inspection without disturbing the shell-side piping.
Material Specification – ASTM A179 / ASME SA179
ASTM A179 / A179M covers minimum-wall-thickness, seamless cold-drawn low-carbon steel tubes for tubular heat exchangers, condensers, and similar heat transfer apparatus. The specification covers tubes from 1/8 to 3 inches [3.2 to 76.2 mm] in outside diameter. Tubes shall be made by the seamless process and shall be cold drawn. Heat and product analysis shall be performed wherein steel materials shall conform to required chemical compositions of carbon, manganese, phosphorus, and sulfur. The steel materials shall also undergo hardness test, flattening test, flaring test, flange test, and hydrostatic test.
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 |
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 |
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, bending of tubes is done with a mandrel inserted in the tubes. The U-bend portion is subsequently stress relieved in controlled conditions and cycles to provide longer service life. The bend portion and six-inch leg is stress relieved by resistance heating. Inert gas (Argon) is passed through the tube at the required flow rate to avoid oxidation on the inner diameter. Each U-bend tube is fabricated to the required radius as per customer drawings.
Dimensional Tolerances (per ASTM A179 / ASME SA179)
Wall thickness tolerance for cold-finished tubes: for outside diameter 1-1/2″ (38.1 mm) and under, the tolerance is +20% / –0%; for outside diameter over 1-1/2″ (38.1 mm), the tolerance is +22% / –0%. Outside diameter tolerance for cold-finished seamless tubes: for tubes under 1″ (25.4 mm), the permissible variation is +0.004″ (+0.1 mm) / –0.004″ (–0.1 mm); for tubes 1″ to 1-1/2″ (25.4 to 38.1 mm) inclusive, the permissible variation is +0.006″ (+0.15 mm) / –0.006″ (–0.15 mm).
Size Range
Outside diameter: 1/8″ to 3″ [3.2 mm to 76.2 mm]. Length under 26 m. Bending radius and leg length are custom-manufactured per customer drawings.
Testing and Quality Control
Each U-bend tube is subjected to the following tests in accordance with ASTM A179 / ASME SA179:
Hydrostatic Test – 100% of U-bent tubes are tested for hydrostatic leak integrity.
Dye Penetrant Test (PT) – 100% of U-bend tubes are DP tested after hydrostatic testing.
Eddy Current Testing (ET) – For detection of surface and subsurface defects.
Hardness Testing (HT) – For verification of material condition per HRB scale.
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 less than 10% of the outside diameter.
Chemical Composition Analysis – Spectrometric or wet chemical analysis to verify alloy composition.
Dimensional Inspection – Verification of outside diameter, wall thickness, length, and U-bend radius.
Documentation
Each shipment is supplied with complete documentation including Mill Test Certificates (EN 10204 Type 3.1), heat treatment records (stress relief charts), hydrostatic test reports, DP test reports, NDE reports (ET, HT as applicable), dimensional inspection reports, and material traceability records.
For a rapid quotation on ASTM A179 / ASME SA179 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
Surface treatment requirement (oiled or black painting)
End preparation (plain ends or beveled ends)
Delivery period required
