Incoloy 800H Heat Exchanger Tubes per API 660

API 660 (ISO 16812) is the design specification for shell-and-tube heat exchangers in refinery, petrochemical and general process service published by the American Petroleum Institute. It covers thermal-hydraulic design, mechanical design, tube-bundle construction, tubesheet design, vibration analysis, fabrication, inspection and testing. API 660 references TEMA Class R, B or C as the construction standard and ASME Section VIII Division 1 as the pressure-vessel code. Incoloy 800H (UNS N08810) and Incoloy 800HT (UNS N08811) are the specified tube and bundle material for high-temperature exchangers where the tube-side or shell-side operating envelope exceeds 540 deg C (1000 deg F): hydrogen-plant reformer effluent coolers, methanator feed-effluent exchangers, hydrotreater feed-effluent exchangers and waste-heat boiler tubes. TorqBolt supplies API 660 Incoloy 800H seamless tube, welded tube, forged tubesheet (SB-564) and buttweld + socketweld fittings with EN 10204 type 3.1 by default and type 3.2 on call-out.

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API 660 (current edition adopted by ISO 16812) defines the minimum requirements for design, fabrication, inspection and testing of shell-and-tube heat exchangers in refinery and petrochemical service. The scope covers thermal-hydraulic design (heat-transfer coefficient, pressure drop, fouling allowance), mechanical design (tubesheet thickness, shell wall, channel cover, expansion joints), tube-bundle construction (tube pattern, baffle spacing, tie-rod arrangement), vibration analysis (flow-induced vibration), fabrication (tube-to-tubesheet joints, baffle assembly), inspection (eddy-current, ultrasonic, hydrostatic test) and testing (performance test on call-out). The construction class is TEMA R, B or C per the purchase specification.

Incoloy 800H wins on API 660 exchangers when the operating envelope satisfies one or more of these conditions: tube-side or shell-side fluid above 540 deg C (1000 deg F) sustained; cycling thermal stress that fatigues 321 / 347 stainless steel; mild carburizing or oxidizing atmosphere where stainless-steel tube failures have been recorded; long-term creep envelope to 815 deg C (1500 deg F). Where corrosion is the controlling failure mode (chloride stress-corrosion, sulfuric or phosphoric acid), Incoloy 825 or Inconel 625 is the better choice. Where pure carburizing or nitriding is the controlling failure mode, Inconel 600 may be preferred.

API 660 tubesheets in high-temperature Incoloy 800H exchangers are typically forged solid SB-564 forgings with face-cladding only on the wet-corrosion side when bi-metallic construction is specified. Tube-to-tubesheet joint is strength-welded plus expanded: the tube end is first seal-welded to the tubesheet face by gas-tungsten arc with ERNiCr-3 (Inconel 82) filler, then hydraulically or roller-expanded into the tubesheet hole to develop the joint strength. The weld is liquid-penetrant tested per ASTM E165 and the expanded section is internally bored to confirm contact pressure. This joint is qualified for service pressure to 250 bar (3625 psi) and temperature to 815 deg C.

API 660 paragraph 7.7 requires flow-induced vibration (FIV) analysis on every bundle to confirm freedom from four failure modes: acoustic resonance (shell-side gas frequency match), fluid-elastic instability (cross-flow self-excitation), vortex shedding (single-tube Strouhal frequency match) and turbulent buffeting (random broadband excitation). The analysis uses TEMA Recommended Good Practice RGP-RCB-4.5 method or a more rigorous CFD approach. Critical frequencies are computed for each tube row and compared against allowable margins. The analysis report is delivered with the mechanical-design package before fabrication release.

API 660 paragraph 8 requires shell-side and tube-side hydrostatic test at 1.3 times maximum allowable working pressure adjusted for design-temperature allowable stress. Test water must be chloride-free (below 50 ppm Cl) to prevent stress-corrosion on the Incoloy 800H surfaces. Performance test (thermal-hydraulic verification against design) is supplied on call-out for the first-of-class exchanger in a battery; subsequent units are accepted on the qualified design alone.

Q. What is API 660 scope?
API 660 (ISO 16812) is the design specification for shell-and-tube heat exchangers in refinery, petrochemical and general process service. It covers thermal-hydraulic design, mechanical design, tube-bundle construction, tubesheet design, vibration analysis, fabrication, inspection and testing. API 660 references TEMA Class R, B or C as the construction standard and ASME Section VIII Division 1 as the pressure-vessel code.

Q. When is Incoloy 800H specified for API 660 heat exchanger tubes?
Incoloy 800H is specified for high-temperature exchangers where the tube-side or shell-side operating envelope is above 540 deg C (1000 deg F) and conventional 321 / 347 stainless steels fall short on sustained creep life. Typical service is hydrogen plant reformer effluent coolers, methanator feed-effluent exchangers, hydrotreater feed-effluent exchangers and waste-heat boiler tubes.

Q. Which TEMA class applies to Incoloy 800H exchangers?
TEMA Class R is the heaviest construction class and is the default for refinery and petrochemical service. TEMA Class B is the chemical-industry construction class. TEMA Class C is the general-purpose class. API 660 exchangers in Incoloy 800H for hydrogen-plant or reformer service are almost always TEMA Class R.

Q. How are Incoloy 800H tubes joined to the tubesheet?
Strength-welded plus expanded is the qualified joint for high-temperature service. The tube end is first seal-welded to the tubesheet face with GTAW using ERNiCr-3 (Inconel 82) filler, then hydraulically or roller expanded into the tubesheet hole to develop the joint strength. The weld is liquid-penetrant tested and the expanded section is internally bored for inspection.

Q. Does API 660 require vibration analysis on Incoloy 800H bundles?
Yes. API 660 paragraph 7.7 requires flow-induced vibration analysis on every bundle to confirm freedom from acoustic resonance, fluid-elastic instability, vortex shedding and turbulent buffeting. The analysis uses TEMA RGP-RCB-4.5 method or a more rigorous CFD approach. The analysis report is delivered with the mechanical-design package before fabrication release.