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上海石化总厂引进的乙烯装置经二万多小时运行后,发现煤柴油裂解炉炉管开裂。经金相观察及电子探针定性、定量分析发现:炉管失效部位的横截面显著减薄。管子内璧存在着1～2毫米的内腐蚀层,其中含有多量的氧化铬,以网络状分布在晶界周围。在内腐蚀层晶粒边界还存在一些粗块状的硫化铬,在晶粒内存在粒状分布的硫化物。无论氧化或硫化都使晶界附近合金基体中产生明显的贫铬区,其含铬量要比晶粒心部低一倍左右。电子探针分析指出:在内腐蚀层前沿存在粒状的氧化铬,几乎未见到硫化物,由此推测该炉管的失效原因主要是以高温氧化为主,辅以硫蚀。
Shanghai Petrochemical Plant introduced more than 20,000 hours after the operation of ethylene plant, found cracking furnace tube cracking of coal-diesel oil. Metallographic observation and electron probe qualitative and quantitative analysis found that: the failure area of the tube cross section was significantly thinned. There are 1 to 2 mm inner tube corrosion layer, which contains a large amount of chromium oxide, network-like distribution around grain boundaries. There are also some coarse chrome sulfide in the inner erosion layer grain boundaries, and there are granular distribution of sulfide in the grains. No matter the oxidation or the sulfidation causes the obvious chromium-depleted zone in the alloy matrix near the grain boundary, the chromium content is about twice lower than that of the grain core. Electron probe analysis indicates that granular chromium oxide exists in the front of the inner corrosion layer, and almost no sulfides are observed. Therefore, it is speculated that the main cause of failure of the furnace tube is oxidation at high temperature, supplemented by sulfur erosion.