Inconel-718-825-Boiler tubes

Inconel 718 is a nickel-chromium alloy strengthened by niobium and other elements; it offers very high strength and good creep and fatigue resistance at elevated temperatures. Inconel 825 is a nickel-iron-chromium alloy alloyed with molybdenum and copper for improved resistance to reducing acids and stress-corrosion cracking. In short: 718 = high strength at high temperature; 825 = superior corrosion resistance in aggressive environments.

Both alloys are used in high-temperature and corrosive environments. Typical uses include superheater and reheater tubing, heat exchangers, waste heat recovery systems, chemical process boilers, and offshore or marine boilers. Choose 718 where structural strength at high temperature is critical; choose 825 where corrosion resistance to chlorides, sulfuric or hydrochloric environments is required.

Inconel 718 retains significant tensile strength and creep resistance up to roughly 650–700°C (1200–1300°F) when properly heat-treated. Inconel 825 provides good strength and corrosion resistance up to moderately elevated temperatures (typically service up to ~600°C depending on environment). Always consult detailed design data for your specific operating temperature, pressure, and exposure.

High-level differences (representative):

• 718: Nickel-based with chromium, iron, niobium (columbium), molybdenum, and titanium/aluminum for precipitation hardening.
• 825: Nickel-iron-chromium base with molybdenum and copper additions for improved resistance to reducing acids and chloride stress-corrosion cracking.

For precise weight % ranges and limits, refer to the alloy specification or material certificate supplied with the tubes.

Common tube specifications include ASTM/ASME standards for nickel alloys and boiler tubing. Typical references are the applicable ASTM/ASME material and product standards for seamless and welded tubes. Confirm the exact standard required (for example, seamless vs welded, temper, tolerance class) when ordering or engineering.

Inconel tubes are available in a wide range of outside diameters (OD) and wall thicknesses (WT), from small-diameter precision tubes to larger pressure-tube sizes. Standard lengths and custom cut-to-length options are common. Suppliers typically publish a dimension chart — confirm OD, WT, length, end preparation and tolerance class when requesting a quote.

Tubes usually ship with Mill Test Certificate (MTC) / EN 10204 3.1 or equivalent, showing chemical analysis and mechanical test results. Other typical tests: PMI (positive material identification), NDT (eddy current, UT), dimensional inspection, and heat treatment records. Specify additional inspection or third-party test requirements at the time of order.

Both alloys are weldable using appropriate nickel-alloy filler metals and controlled procedures. Inconel 718 often requires careful pre/post weld heat treatment and following recommended PWHT to restore precipitation-hardening properties. Welding 825 is generally more forgiving but still benefits from qualified welding procedures to avoid sensitization and to ensure corrosion resistance.