FAQs For Inconel 625 Pipe

Q1: How to prevent oxidation or corrosion of Inconel 625 pipes in high-temperature environments?

A1:

Ø Limit service temperatures to ≤900°C.

Ø Apply anti-oxidation coatings (e.g., aluminide).

Ø Avoid prolonged exposure to sulfur or halogen-containing media.

Q2: What causes weld cracking or intergranular corrosion, and how to mitigate it?

A2:

Ø Cause: High heat input during welding leads to carbide precipitation.

Ø Solutions: Use low-heat-input TIG/laser welding, ERNiCrMo-3 filler, and post-weld solution annealing (1100–1150°C).

Q3: How to avoid cracking during cold working (e.g., bending)?

A3:

Ø Limit cold deformation to ≤20% per step.

Ø Anneal pipes at 980–1030°C before forming.

Ø Use high-performance lubricants (graphite/MoS₂-based).

Q4: How to address pitting or stress corrosion cracking (SCC) in chloride environments?

A4:

Ø Maintain Cl⁻ concentration <50 ppm.

Ø Implement cathodic protection or add corrosion inhibitors (e.g., molybdate).

Ø Clean pipes regularly to prevent Cl⁻ buildup.

Q5: How to minimize scaling or carbon buildup inside alloy 625 pipes?

A5:

Ø Use chemical cleaning (nitric + hydrofluoric acid mixtures).

Ø Optimize fluid velocity (>2 m/s).

Ø Apply ceramic coatings (e.g., Al₂O₃) on inner surfaces.

Q6: How to extend fatigue life under cyclic loading?

A6:

Ø Avoid sharp geometric transitions in design.

Ø Perform periodic NDT (ultrasonic/penetrant testing).

Ø Apply shot peening to critical areas.

Q7: Why does hydrogen embrittlement occur in hydrogen-rich environments?

A11:

Ø Cause: Hydrogen diffusion into the alloy matrix.

Ø Solutions: Avoid cathodic overprotection; use low-hydrogen welding processes.

Q8: Why does localized overheating occur during service, and how to resolve it?

A8:

Ø Cause: Uneven thermal distribution or flame impingement.

Ø Solutions: Redesign supports/insulation; avoid direct flame contact.

Q9: How to handle intermetallic phase precipitation during long-term aging?

A9:

Ø Control aging temperatures below 650°C.

Ø Perform solution annealing every 5–10 years (for critical applications).

Q10: How to repair surface scratches or minor corrosion damage?

A10:

Ø Polish affected areas mechanically.

Ø Re-passivate surfaces using nitric acid (20–50% concentration).

Q11: How to reduce costs while using Inconel 625 seamless pipes?

A7:

Ø Use composite pipes (carbon steel + Inconel 625 lining).

Ø Opt for cost-effective alternatives (e.g., NS336 alloy).

Ø Recycle qualified scrap material.

Q12: How to ensure dimensional stability during thermal cycling?

A12:

Ø Design expansion joints to accommodate thermal stress.

Ø Select optimized wall thickness based on ASME B31.3 guidelines.