What is the chemical composition of ASTM b444 UNS N06625?
General introduction
Alloy 625 tubes are widely used in superheater or heat exchanger tubes and are typically manufactured to ASTM B444 (ASME SB-444) UNS N06625. It is a typical nickel-chromium-molybdenum-niobium alloy, commercially known as the proprietary brand "Inconel Alloy 625". Cold-worked Alloy 625 seamless pipe is available in two grades with different heat treatment conditions: Grade 1 (annealed) - pipe is typically used at operating temperatures up to 1100°F (593°C); Grade 2 (solution annealed) - Materials are typically used at operating temperatures above 1100°F (593°C) when resistance to creep and rupture is required. Generally supplied in Grade 1 unless otherwise stated.
ASTM B444 Alloy 625 Pipe
Cold-drawn alloy 625 pipe can be provided with polished surface or pickled matte surface according to customer requirements. In particular, UNS N06625's small diameter, light wall tubes are widely used in heat exchangers or instrumentation tubes. "Small diameter" refers to pipe with an outside diameter of 1-1/4 inches (31.8 mm) and less, while "light wall" refers to pipe with a specified wall thickness of 3% or less of the specified outside diameter.
Chemical composition requirements
Carbon: ≤0.10; Manganese: ≤0.50; Silicon: ≤0.50; Phosphorus: ≤0.015; Sulfur: ≤0.015; Chromium: 20.0~23.0; Columbium + Tantalum: 3.15~4.15; Cobalt: ≤1.0; Molybdenum: 8.0~10.0; Iron: ≤5.0; Aluminum: ≤0.40; Titanium: ≤0.40; Nickel: ≥58.0; All expressed in weight percentage.
Mechanical properties and heat treatment
Mechanical properties of Alloy N06625 Grade 1 (annealed) pipe: Tensile strength ≥ 120 ksi [827 MPa]; Yield strength ≥ 60 ksi [414 MPa]; 2-inch elongation ≥ 30%. Mechanical Properties of Alloy N06625 Grade 2 (Solution Annealed) Pipe: Tensile Strength ≥ 100 ksi [690 MPa]; Yield Strength ≥ 40 ksi [276 MPa]; 2-inch Elongation ≥ 30%. Annealing heat treatment shall be performed at a temperature not less than 1600°F [871°C]. Solution annealing heat treatment should be performed at a temperature not less than 2000°F [1093°C], followed by a stabilization anneal at a minimum of 1800°F [982°C] to improve resistance to sensitization.
Testing and inspection
Hydrostatic Testing: Each alloy 625 pipe (seamless and cold worked) with an outside diameter of 3 mm and above and a wall thickness of 0.38 mm and above shall be tested in accordance with ASTM B829. The allowable fiber stresses for UNS N06625 Levels 1 and 2 are 30 ksi [207 MPa] and 25 ksi [172 MPa] respectively.
Dimensional inspection and visual inspection: outside diameter, wall thickness, inside diameter, length, straightness, flat ends, finish and surface appearance.
Tensile test (ASTM E8) and hardness test (ASTM E18).
One or more non-destructive testing (NDT) may be specified: PMI, ultrasonic inspection (ASTM E213), eddy current inspection (ASTM E426/E571).
625 alloy pipe weight
The weight of Alloy 625 tube can be calculated using the following formula: W = ( D – t ) * t * 0.0246615 * F * L. W: Weight of the pipe, kg; D: Outer diameter of the pipe, mm; t: Pipe wall thickness, mm; F: Correction coefficient, 1.075; L: Pipe length, meters.
