CT6947 Hastelloy G3 Tube

Hastelloy G3 Tubes Description

Hastelloy G3 tubes (non‐welded or welded) demonstrate a thermomechanically processed γ‐austenitic microstructure. In non‐welded tubes the grain orientation aligns parallel to the tube axis. Non‐welded tubes develop a circumferential 〈110〉 texture through cold pilgering. This procedure increases hoop strength with yield values of at least 550 MPa axially and 600 MPa tangentially. Welded tubes show grain coarsening in the heat‐affected zone (HAZ), with grain sizes below 100 μm. Solution annealing at 1120°C mitigates this coarsening. The corrosion resistance derives from a Cr₂O₃/MoO₂/CuO passive film that repairs itself. Internal surface roughness is controlled to an Ra of ≤0.8 μm via abrasive flow machining. External electropolishing limits chromium depletion to under 0.2 μm.

Thermomechanical behaviour exhibits anisotropic thermal expansion. The axial coefficient is 13.9 μm/m·°C, and the radial value is 14.3 μm/m·°C over 20–400°C. Thermal conductivity is directional, at 10.5 W/m·K axially and 9.8 W/m·K radially measured at 100°C. Phase stability declines above 650°C. The σ‐phase precipitates at weld fusion lines following periods longer than 10 hours at 760°C, which reduces HAZ impact toughness by 25%. Hydraulic expansion induces work hardening with a dislocation density of approximately 1×10^14 m⁻². As a result, yield strength increases by 15–20% while elongation reduces to between 25% and 30%. Pressure integrity is maintained at 400°C. For a Ø25 mm × 2 mm tube the burst pressure exceeds 120 MPa, achieved by suppressing MC carbide coarsening (to less than 50 nm). Electrochemical impedance spectroscopy demonstrates a passive film resistance above 10^5 Ω·cm² in 40% sulfuric acid at 80°C. Residual stresses from forming are controlled below 20% of the yield strength by stress‐relief annealing.

Hastelloy G3 Tubes Applications

Hastelloy G3 tubes are used in severe environments where corrosion resistance and pressure integrity are essential. In chemical processing non‐welded tubes form heat exchanger bundles that handle concentrated sulphuric acid (up to 93% at 110°C) and phosphoric acid (up to 85% at 130°C). Copper‐enhanced passivation limits corrosion rates to below 0.03 mm per year. Welded tubes with a controlled HAZ microstructure are used for reactor dip pipes and distillation columns. These components are exposed to HCl/HF vapour mixtures. A molybdenum‐rich passive film containing more than 6.5% Mo provides resistance against pitting.

For oil and gas applications, cold‐drawn non‐welded tubes (Ø10–100 mm) function as downhole instrumentation conduits in sour wells. Service conditions include H₂S up to 3.5 bar and chloride concentrations up to 150 000 ppm at 150°C. These tubes resist sulphide stress cracking. In flue gas desulphurisation, U‐bend exchanger tubes are used with acidic chloride brines of pH 1.5–2.5 at 60–90°C. Repassivation kinetics prevent crevice corrosion under deposits.

Geothermal energy systems use thick‐walled tubes (wall thickness ≥5 mm) for brine injection lines. These tubes resist both silica scaling and CO₂‐induced corrosion at 250°C. In nuclear applications, tubes for spent fuel reprocessing handle nitric and nitrate solutions. In these cases, chromium oxide stabilisation preserves passivity under gamma irradiation. Thin‐walled variants (wall thickness 0.5–2 mm) are employed to produce catalyst carrier tubes in sulphuric acid regeneration plants. They withstand thermal cycling up to 600°C without recrystallisation.

The material exhibits directional thermal conductivity with an axial value of 10.5 W/m·K. This improves heat transfer efficiency. In addition, the internal surface finish (Ra ≤0.8 μm) reduces fouling. Burst pressure ratings above 120 MPa for a Ø25×2 mm tube ensure reliability in high‐pressure services. Orbital TIG welding obtains at least 90% joint efficiency using matching filler metals.

Hastelloy G3 Tubes Packaging

Products are packaged in customised cartons according to material dimensions. Small items are contained in PP boxes, while larger items are placed in custom wooden crates. Appropriate cushioning materials are used during packaging to ensure protection during transportation.

Packaging: Carton, Wooden Box, or Customized.

Please consult the packaging details provided for reference.

Manufacturing Process

1.       Testing Method

(1)    Chemical Composition Analysis. Techniques such as GDMS or XRF verify that purity requirements are met.

(2)    Mechanical Properties Testing. Tensile, yield and elongation tests assess material performance.

(3)    Dimensional Inspection. Measurements of thickness, width and length confirm specified tolerances.

(4)    Surface Quality Inspection. Visual and ultrasonic examinations detect scratches, cracks and inclusions.

(5)    Hardness Testing. This test determines material hardness and confirms uniformity and mechanical reliability.

Please refer to the testing procedures provided by SAM for further details.

Hastelloy G3 Tubes FAQs

Q1. How does the alloy maintain corrosion resistance in sulphuric acid environments above 60°C where standard stainless steels fail?

The alloy composition (Cr 22%, Mo 6.5%, Cu 2%) produces a Cr/Mo‐rich oxide layer that passivates the surface. This layer resists sulphuric acid concentrations up to 50% at 90°C. In contrast, 316L stainless steel experiences thinning in excess of 5 mm per year above 60°C because its chromium‐only film degrades.

Q2. Which chloride concentration and temperature limit avoid stress corrosion cracking in sour gas service?

Stress corrosion cracking is prevented in brines with chloride concentrations up to 150 000 ppm and H₂S partial pressures not exceeding 3.5 bar at 150°C. Exceeding these thresholds may cause molybdenum depletion at grain boundaries, a risk controlled by solution annealing at 1120°C.

Q3. Does cold working affect the corrosion performance in welded assemblies?

Cold worked sections with reductions greater than 15% exhibit a 20–30% lower critical pitting temperature in chloride environments. This occurs because dislocations introduce defects in the passive film. Post‐weld solution annealing at approximately 1100°C restores a homogeneous microstructure and ensures corrosion performance equivalent to that of the base metal.

Related Information

1.       Common Preparation Methods

Hastelloy G3 tubes are produced by distinct thermomechanical routes for non‐welded and welded variants. For non‐welded tubes, production begins with vacuum induction melting (VIM) of electrolytic nickel, chromium, molybdenum and copper in an argon atmosphere. The material undergoes vacuum arc remelting (VAR) to control interstitial elements (O≤30 ppm, N≤100 ppm). The homogenised ingot is held at 1200°C for 12 hours. It is then hot‐extruded at temperatures between 1150°C and 1200°C to form a hollow billet using a piercing mandrel.

The billet is cold pilgered in multiple passes with reductions of 15–25% per cycle. Intermediate solution annealing is performed at 1120°C for 1 hour per inch of thickness to restore the γ‐austenite microstructure. Final dimensions are achieved by cold drawing over polished mandrels with light reductions of 8–12%, introducing controlled work hardening while maintaining axial grain alignment.

Welded tubes are manufactured from continuously formed and TIG‐welded strips. These strips are solution annealed at 1120°C. In‐line induction heating between 1100°C and 1150°C normalises the weld seam, followed by rapid gas quenching to achieve corrosion resistance similar to that of the base metal.

Rapid cooling through the range of 650–900°C (in under 10 minutes) prevents σ‐phase precipitation. An isothermal hold at 850°C dissolves Laves phases. Internal surfaces are finished by abrasive flow machining to achieve an Ra of ≤0.8 μm. This step removes asperities that could initiate crevice corrosion. Electrochemical polishing then limits chromium depletion to below 0.2 μm.

Non‐destructive validation comprises eddy current testing (to detect flaws above 50 μm), ultrasonic immersion scanning (ensuring wall thickness tolerance within ±5%) and hydrostatic testing at 1.5× the design pressure. Corrosion performance is verified following ASTM G48 Method A. A critical pitting temperature of at least 85°C in 6% FeCl₃ confirms that the passive film integrity matches that of mill‐annealed plate specifications.