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对乙二醇装置零效蒸发器内壁开裂状况、性质和原因加以探讨。结果表明,裂纹基本属于弱氧化性介质条件下的晶间腐蚀开裂;介质中含有一定量的乙酸(CH3COOH)和少量甲酸(HCOOH),塔体材料抗晶间腐蚀性能不足,不适当的焊接工艺导致部分热影响区较长时间处于敏化温度(450~850℃)范围是引发塔体开裂的主要因素。防治途径包括:采用超低碳C≤0.02%、含有一定量Mo(2%~4%)或一定量δ铁素体(3%~10%)的奥氏体不锈钢制作壳体;严格执行小热输入、小摆动、窄焊道、低层间温度的焊接工艺;严格控制介质中杂质含量及pH值。
The cracking situation, properties and reasons of inner wall of ethylene glycol unit zero efficiency evaporator were discussed. The results show that the crack basically belongs to the intergranular corrosion cracking under the conditions of weak oxidizing medium. The medium contains a certain amount of acetic acid (CH3COOH) and a small amount of formic acid (HCOOH), and the tower body material has insufficient intergranular corrosion resistance. The improper welding process As a result, a part of the heat affected zone (HAZ) at the sensitization temperature (450-850 ° C) for a long time is the main factor causing cracking of the tower. Prevention and treatment include: the use of ultra-low carbon C ≤ 0.02%, containing a certain amount of Mo (2% ~ 4%) or a certain amount of ferrite (3% ~ 10%) of austenitic stainless steel shell; strict implementation of small Heat input, small swing, narrow bead, low temperature welding process; strict control of the medium impurity content and pH.