Square Alloy 718 Tube
Square alloy 718 tube is a hollow structural tube with a square cross-section made from Inconel 718 (a high-strength nickel-chromium-based high-temperature alloy,UNS N07718).Because it is a high-strength,corrosion-resistant nickel-chromium superalloy,this tube is commonly used in extremely harsh environments, such as those involving high pressure,high temperatures,or severe corrosion.
Specification of Square Alloy 718 Tube
| Product | Square Alloy 718 Tube |
| Working Temperature | Up to 705°C (1300°F) |
| Dimension Range | Outside Diameter (OD): 6 – 200 mm Wall Thickness (THK): 0.35 – 6 mm Length (L): 0.5 – 12 m The size can be customized according to ASME B36.10 / ASME B36.19 |
| Schedules | SCH 5, 10, 40, 80, 160, XXS, XXH |
| Materials | Inconel 718 | UNS N07718 | W.Nr. 2.4668 | DIN NiCr19Fe19Nb5Mo3 |
| Standards | ASTM B163 / ASME SB163 / ASTM B670 / ASTM B983 / ASME SB983 |
| Surface Finish |
Annealed and Pickled Polished/Bright Annealed Electropolished Low-Burr/Burr-Free/Trovalised |
| Corrosion Resistance Specifications |
Excellent Resistance To: Oxidation Resistance Corrosion Resistance Stress-Corrosion Cracking Creep and Stress Rupture Resistance Post-Weld Cracking Resistance Fatigue Resistance |
| Applications | Aerospace Oil & Gas Nuclear & Power Generation Chemical & Medical Precision Engineering |
| Our Strength | Over 10 Years Experience Exporting Pipes & Tubings Stock Available In Common Sizes Customized Fabrication Available Package Supplying of Piping Materials Strict QC With PMI Testing For Every Batch Experience in Exporting to the US,Germany,UAE,etc. Third Party Inspection Available |
For more information on inconel 718 pipe and other products, please contact us.
Square Alloy 718 Tube Chemical Composition (%)
| Ni(+ Co) | Cr | Fe | Nb(+ Ta) | Mo | Ti | Al |
| 50.00 – 55.00 | 17.00 – 21.00 | Balance | 4.75 – 5.50 | 2.80 – 3.30 | 0.65 – 1.15 | 0.20 – 0.80 |
| Co | C | Mn | Si | P / S | B | |
| 1.00 Max | 0.08 Max | 0.35 Max | 0.35 Max | 0.015 Max | 0.006 Max |
Why are the material composition standards for
square tubes the same as those for round tubes?
Whether the tubing is square or round,its chemical composition remains the same.The difference in shape is determined by subsequent cold drawing or roll forming processes,but its metallurgical properties and corrosion resistance are entirely determined by the chemical composition described above.
Square Alloy 718 Tube Mechanical Properties(Typical value range)
| Tensile Strength | Yield strength | Elongation | Hardness |
| 1240 – 1450 MPa (180 – 210 ksi) | 1030 – 1200 MPa (150 – 175 ksi) | 12% – 25% | 36 – 44 HRC(331 – 415 HB) |
What is its modulus of elasticity?
At room temperature,the elastic modulus (Young’s modulus) of Alloy 718 is approximately 200–211 GPa (29.0–30.6 MPa).This value decreases gradually as the temperature rises.
Physical Properties of Square Alloy 718 Tube
Density:8.19 g/cm³ (0.296 lb/in³)
Melting Range:1260°C – 1336°C (2300°F – 2437°F)
Specific Heat:0.104 Btu/lb · ℉(70℉)
Poisson’s Ratio:0.29 to 0.30
Magnetic Permeability:Non-magnetic
Thermal Properties of Square Alloy 718 Tube
| Temperature | Thermal Conductivity | Mean CTE |
| 20°C | 11.4 W/m·K | – |
| 200°C | 13.4 W/m·K | 13.5 µm/m·°C |
| 400°C | 16.1 W/m·K | 14.1 µm/m·°C |
| 600°C | 18.8 W/m·K | 15.1 µm/m·°C |
| 800°C | 21.6 W/m·K | 16.0 µm/m·°C |
Manufacturing Process for Square Alloy 718 Tube
The manufacturing of square alloy 718 tube is a complex process due to the material’s high hardness and rapid work hardening rate.The principle of “round-to-square” is typically followed,and the main steps are as follows.
Melting & Casting
VIM + VAR:
To ensure extreme purity of the alloy,vacuum induction melting (VIM) is typically used,followed by vacuum arc remelting (VAR) to eliminate impurities and reduce segregation.
Mother Tube Production
Square tubes are typically produced from high-quality seamless round tubes.
Hot Extrusion:
An alloy ingot is heated to approximately 1,100°C and pressed through an extruder to form a hollow round tube blank.
Hot Piercing:
Efficient continuous deformation is achieved using a two-roll or three-roll system.
Cold Working
Cold Drawing:
Round tubes are forcefully drawn through a square die and an internal mandrel.Multiple drawing passes are typically required to achieve precise square dimensions and wall thickness.
Turks Head Rolling:
A round tube is gradually squeezed into a square cross-section using a set of adjustable rollers (in four directions).This method provides very precise control over dimensional tolerances.
Intermediate Annealing
Because Alloy 718 is highly susceptible to work hardening,solution annealing (at approximately 980–1040°C) must be performed between successive cold drawing operations to relieve stress and restore ductility;otherwise, the tubing will crack.
Final Heat Treatment
To achieve its final mechanical strength,the square tube must undergo precipitation hardening.
Double Aging:
Typically,the tube is held at 718°C for 8 hours,then furnace-cooled to 621°C and held there for another 8 hours.This step determines the final yield strength and hardness of the square tube.
Finishing & Inspection
Straightening:
Correcting any warping that may occur during heat treatment.
Pickling/Passivation:
Removing surface scale.
Non-Destructive Testing (NDT):
Eddy Current Testing (ET) or Ultrasonic Testing (UT):Inspecting the tube wall for cracks or defects.
Dimensional Inspection:Measuring the side length,wall thickness,and fillet radius (R) of the square tube.
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