Abstract：The residual carbon content on the inner surface of copper and copper alloy tube has an important influence on the performance and service life of the products. The sample surface was treated in the fresh concentrated nitric acid (1+1) for pickling, and then polished by mixture of nitric acid, phosphoric acid and glacial acetic acid. A passivation solution consisting of sulfuric acid, chromic anhydride, sodium chloride and pure water was used for passivation. After ultrasonic cleaning with trichloroethylene and cutting, the sample was tested by high frequency combustion infrared absorption method at the power of 1 100 W. Consequently, the determination method of residual carbon content on the inner surface of copper and copper alloy tube was established. The instrument was calibrated with certified reference material of ultra-low carbon steel at 2 200 W using tungsten-tin and pure iron as the flux. The calibration coefficient of the calibration curve was K = 1.012. Then, the pure iron and pure copper CRMs were used for verification. It was found that the error of the verification results was within ±0.000 2%. Red copper tube, cupronickel tubes and brass tube samples were determined for several times according to the experimental method. The standard deviations (SDs, n=6) were 0.95 mg/m2, 1.3 mg/m2 and 3.4 mg/m2, respectively. The absolute errors with the testing results according to national standard method (GB/T33817-2017) were 1.52 mg/m2, 2.49 mg/m2 and 2.44 mg/m2, respectively.
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