Corrosion cause analysis of welding seam in melamine device

The corrosion causes of Hastelloy welding seam in melamine device were analyzed by field emission scanning electron microscope(SEM), metallographic microscope, and X-ray diffractometer, providing a reference for the anti-corrosion of melamine device. The macroscopic analysis indicated that the most severely corroded area was the welding seam. The chemical composition test results showed that the composition met the requirements of C-276 Hastelloy. The metallographic structure test results indicated that the material structure was normal. The X-ray diffraction results showed that the corrosion products on the outer surface of welding seam were mainly NiO. The scanning electron microscope energy spectrum results indicated that the contents of Mo, Cr, and W in the most severely corroded welding seam were the lowest. Through comprehensive analysis, the results showed that the alloying contents of Mo, Cr, and W alloy elements in Hastelloy alloy welding seam were lower than those of the base material, which was the reason for the severe corrosion of welding seam. The alloy element Cr formed a dense passivation oxide film on the surface, and a low Cr content reduced the oxidation resistance of welding seam; a low Mo content reduced the reduction resistance of welding seam; a low W content reduced the high-temperature strength and corrosion resistance of welding seam. To improve the corrosion resistance of welding seam area, it was recommended to use welding wire with a higher corrosion resistance level than the base material for welding.