Why Nickel Alloys for Heat Exchangers
Heat exchangers in aggressive environments demand materials that resist corrosion while maintaining thermal efficiency. Nickel alloys offer exceptional corrosion resistance, high-temperature strength, thermal stability, and resistance to stress corrosion cracking.
Nickel Alloy Grades for Heat Exchanger Tubes
| Alloy | UNS | Key Properties | Max Temp | PREN |
|---|---|---|---|---|
| Alloy 625 | N06625 | Excellent pitting resistance, high strength | 980C | 52 |
| Alloy 825 | N08825 | Resists H2SO4 and H3PO4, good SCC resistance | 540C | 27 |
| Alloy C-276 | N10276 | Superior localized corrosion resistance | 400C | 68 |
| Alloy 400 | N04400 | HF acid resistance, seawater service | 430C | -5 |
| Alloy 22 | N06022 | Better oxidizing media resistance than C-276 | 400C | 70 |
Heat Exchanger Tube Design Considerations
Standard dimensions follow TEMA and ASME requirements. Tubes per ASTM B163 (seamless), ASTM B704 (welded). Design must account for corrosion allowance (typically zero for nickel alloys), fouling factors, and thermal expansion.
Fabrication and Manufacturing
Tube Manufacturing: Seamless tubes by extrusion + cold drawing + annealing. Welded tubes from strip by GTAW/plasma welding.
Tube-to-Tubesheet Joining: Expanded (rolled) joints, welded and expanded, strength welded, or explosion welded.
Quality Control Requirements
- 100% eddy current testing (ECT)
- Hydrostatic or pneumatic test
- Intergranular corrosion test (ASTM G28)
- Pitting corrosion test (ASTM G48)
- Positive Material Identification (PMI)
Sourcing Nickel Alloy Tubes
CoreMetal Steel supplies nickel alloy heat exchanger tubes in Alloy 625, 825, C-276, 400, and 22 per ASTM B163/B704, with full documentation and NDT certification.
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