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本文通过试验、生产实践,尿素合成塔内挂片以及十余年来对实际使用的尿素合成塔衬里和内件腐蚀情况进行实地观察。从中发现18—12Mo板材,在尿素合成塔中腐蚀特点主要是晶间腐蚀和均匀腐蚀。而焊态的P5焊缝金属则以均匀腐蚀为主,看不到铁索体本身的选择性腐蚀。也发现物料冲刷腐蚀是不可忽视的。X—法或Huey法晶间腐蚀试验与尿素腐蚀性质根本不同。但对Cr—Ni—Mo型不锈耐酸材料而言,通常硝酸法晶界腐蚀试验腐蚀率低者,在尿素介质中也耐蚀。尿素用钢及焊缝金属之所以限制铁素体含量在于它有选择性腐蚀的特点。实践证明只有在低Cr、Ni型材料(象18—12Mo型)才出现。若选择高一档Cr、Ni含量又有Mo的焊材(象P5焊条)就不必限制铁素体含量。这样,既有高的耐蚀性,又有好的可焊性(热裂纹倾向小)。同时也可以看到提高了抗物料冲刷的耐蚀能力。采用316L钢板、匹配P5焊材作为尿素合成塔耐蚀材料。实践证明耐蚀性能优良。
This article through the test, the production practice, the coupon in the urea synthesis tower as well as more than ten years of actual use of urea synthesis liner lining and corrosion of the inner parts of the field observations. Found 18-12Mo plate, corrosion characteristics in the urea synthesis tower is mainly intergranular corrosion and uniform corrosion. The weld P5 weld metal is mainly based on uniform corrosion, tin can not see the selective corrosion of the body itself. Also found that material erosion erosion can not be ignored. X-method or Huey intergranular corrosion test and urea corrosion properties are fundamentally different. However, for Cr-Ni-Mo stainless acid-resistant materials, the corrosion rate of the nitric acid method in the grain boundary corrosion test is usually low and is also resistant to corrosion in the urea medium. The reason why urea and weld metal limit the ferrite content is that it has a selective corrosion characteristics. Practice has proved that only low Cr, Ni type material (like 18-12Mo type) appeared. If you choose a higher grade Cr, Ni content and Mo welding material (like P5 electrode) do not have to limit the ferrite content. In this way, both high corrosion resistance, but also good solderability (hot cracking tendency). At the same time, it can be seen that the anti-corrosion capability of anti-material erosion is improved. 316L steel, matching P5 welding consumables as a urea synthesis tower corrosion-resistant materials. Practice shows that corrosion resistance is excellent.