YUHONG GROUP has extensive experience in supplying carbon steel, alloy steel, stainless steel, duplex steel, and nickel alloy seamless pipe and tube for heat exchanger and boiler applications. The A179 U‑bend tube is used across refineries, power plants, steel plants, chemical factories, fertilizer plants, and shipbuilding industries. Specific applications include shell & tube heat exchanger bundles, boiler feedwater heaters, condensers, air preheaters, finned tube coolers, and heat recovery steam generators (HRSG).
The ASTM A179 U‑Bend Tube is produced from straight tubes through a cold bending process using an automatic U‑bending machine. To control wall thinning and diameter ovality during the bending operation, a mandrel is inserted into the tube. After bending, the U‑bend portion is stress relieved under controlled conditions and cycles to extend service life. Each ASME SA179 U‑bending tube undergoes 100% hydrostatic leak testing and dye penetrant testing prior to dispatch.
These U‑bend tubes are widely used as the primary heat transfer elements in shell and tube heat exchangers, where they form part of the tube bundle assembly. They can be arranged as U‑tube bundles for applications with high thermal differential, or incorporated into finned tube bundles to enhance heat transfer surface area. The tubes are rolled or welded into heat exchanger tubesheets at both ends (or at a single tubesheet for U‑tube configurations) to create a leak‑tight seal between the tube side and shell side fluids.
| ASTM A179/A179M Chemical Components (%) | |||||||
| C | Si | Mn | P | S | Mo | Cr | V |
| 0.06-0.18 | / | 0.27-0.63 | ≤0.035 | ≤0.035 | / | / | / |
| Property | Requirement |
|---|---|
| Tensile Strength, min | 325 MPa |
| Yield Strength, min | 180 MPa |
| Elongation in 50 mm, min | 35% |
| Hardness (HRB) | 72 max (typical) |
| Outside Diameter | Tolerance (% Over / Under) |
|---|---|
| 1½″ (38.1 mm) and under | +20% / 0 |
| Over 1½″ (38.1 mm) | +22% / 0 |
| Outside Diameter | Permissible Variations (Over / Under) |
|---|---|
| Under 1″ (25.4 mm) | +0.004″ (+0.1 mm) / –0.004″ (–0.1 mm) |
| 1″ to 1½″ (25.4 to 38.1 mm), inclusive | +0.006″ (+0.15 mm) / –0.006″ (–0.15 mm) |
Outside diameter tolerance per ASTM A179 / ASME SA179.
Straight tubes are first manufactured by the seamless cold‑drawn process. The A179 U‑bending tube operation is then performed in the cold state on an automatic U‑bending machine. A mandrel is inserted into the tube during bending to maintain wall thickness uniformity and control diameter ovality. The U‑bend portion is subsequently stress relieved in controlled conditions to reduce residual stresses and enhance fatigue life. Finished ASME SA179 U‑bend tube products are 100% tested for hydrostatic leak integrity and dye penetrant inspection.
Each U‑bend tube is subjected to the following inspections and tests in accordance with ASTM A179 / ASME SA179 requirements:
Hydrostatic Test – 100% of tubes are hydrostatically tested to verify leak‑tight integrity
Dye Penetrant Test (PT) – Applied to detect surface defects
Hardness Test – Per HRB scale to verify material condition
Flattening Test – To assess ductility and soundness
Flaring Test – To evaluate resistance to deformation
Flange Test – To check tube end ductility
Non‑Destructive Examination (NDE) – Eddy Current Testing (ET), Ultrasonic Testing (UT), and Hardness Testing (HT) as specified
The ASTM A179 U‑Bend Tube is designed for direct integration into:
Shell and tube heat exchangers – as the primary tube bundle carrying one fluid
U‑tube bundles – where single tubesheet construction and independent thermal expansion are required
Finned tube bundles – when combined with helical fins to increase effective heat transfer area
Heat exchanger tubesheets – the tube ends are rolled, welded, or both into the tubesheet holes to form a pressure‑tight joint
U‑bend tubes are susceptible to damage during transit and require careful handling. Tubes are packed in specially designed steel frames fitted into wooden boxes to ensure protection during transportation. Packaging options include ply‑wooden cases, iron cases, plastic bags, plastic tube caps, and bundles.
Each shipment is supplied with complete documentation including:
Mill Test Certificates (EN 10204 Type 3.1)
Hydrostatic test reports
NDE reports (ET, UT, HT as applicable)
Dimensional inspection reports
Heat treatment records (stress relief charts)
Quantity (number of pieces or weight)
Outside diameter and wall thickness
Straight length and U‑bend radius (centerline radius)
Leg length (tangent length) and required orientation
Surface treatment requirement (oiled or black)
Delivery period required
