摘要
煉油廠中的製程控制閥之前阻閥在操作中因發現流量不足而進行檢修。拆卸前阻閥（閥體形式為閘閥）後，發現閘閥內部閘板嚴重破損，有明顯裂紋。依據分析結果研判，閘閥發生破損的主因為硫化物應力腐蝕破裂（Sulfide Stress Corrosion Cracking, SSCC）。材料在濕硫化氫環境中發生硫化物應力腐蝕破裂必須滿足應力腐蝕的三個條件，即敏感材料、特定環境和拉伸應力。在閘閥內部之閘板其材質為410不銹鋼，具有高強度和高硬度之特點，量測其硬度值高達489HV，並且內部流體為濕硫化氫氣體，係屬於發生硫化物應力腐蝕破裂之特定環境，再加上閘板銲接時的殘留應力以及閥門啟閉時之工作應力等作用下，因而造成閘板發生嚴重破裂現象。因此，若使用本案中之410不銹鋼為閘板，閘板材料應進行熱處理，可有效地降低硫化物應力腐蝕破裂之可能性。並且亦建議雙閘板之製造形式採用鑄造成型，避免使用銲接方式製作之閘板，以降低銲接時之殘留應力。
並列摘要
The double-disc gate valve in a refinery was found that its flow rate is inadequate during operation. After disassembling the gate valve, there are some cracks on surface of the disc inside the gate valve. The analysis results indicated that the failure mechanism of the gate valve is sulfide stress corrosion cracking (SSCC). Generally, there are three conditions that it must meet when SSCC occurs, namely the sensitive material, the specific environment and tensile stress. The disc was made of 410 stainless steel and has the characteristics of high strength and high hardness (the measured hardness value is 489 HV). The internal fluid of the gate valve was wet H2S gas and this is one of the specific environments for the occurrence of SSCC. Moreover, tensile stress is from the residual stress of welding and the work stress during the valve opening and closing. Finally, a serious cracking phenomenon of the disc induced from the combined influence of tensile stress and a corrosive environment. If the disc is made of 410 stainless steel as this study case, postweld heat treatment (PWHT) will be an effective method for minimizing susceptibility to SSCC. It also recommend that the manufacture of the double gate plates can use casting to replace welding, and then the residual stress of welding could be reduced.