石油化工腐蚀与防护
石油化工腐蝕與防護
석유화공부식여방호
PETROCHEMICAL CORROSION AND PROTECTION
2012年
5期
52-56
,共5页
失效分析%裂纹%试样
失效分析%裂紋%試樣
실효분석%렬문%시양
failure analysis%crack%sample
介绍了焦炭塔底部进料管线腐蚀开裂情况,对开裂部位进行了外观检查。弯头断裂失效部位发生在环焊缝附近区域,且沿周向开裂,裂纹平直,而裂纹扩展方向与焊接断面基本一致。对开裂部位弯头取样,进行化学组成及金相热应力分析和硬度测试,对腐蚀产物进行化学组成分析。根据生产工艺、介质组成和分析结果确定了失效的主要原因:随着装置原料劣质化,经过10 a运行后,管线高温硫腐蚀加剧,降低了管线的承载力;由于焊缝处存在异种钢的焊接,所使用的309不锈钢导热系数较321不锈钢略小,加之前者的外壁温度又低于后者,使309钢产生较大的轴向拉伸引力,导致焊缝处存在热应力、焊接残余拉应力,在高温硫腐蚀和异种钢焊接的共同作用下导致了焊缝开裂。
介紹瞭焦炭塔底部進料管線腐蝕開裂情況,對開裂部位進行瞭外觀檢查。彎頭斷裂失效部位髮生在環銲縫附近區域,且沿週嚮開裂,裂紋平直,而裂紋擴展方嚮與銲接斷麵基本一緻。對開裂部位彎頭取樣,進行化學組成及金相熱應力分析和硬度測試,對腐蝕產物進行化學組成分析。根據生產工藝、介質組成和分析結果確定瞭失效的主要原因:隨著裝置原料劣質化,經過10 a運行後,管線高溫硫腐蝕加劇,降低瞭管線的承載力;由于銲縫處存在異種鋼的銲接,所使用的309不鏽鋼導熱繫數較321不鏽鋼略小,加之前者的外壁溫度又低于後者,使309鋼產生較大的軸嚮拉伸引力,導緻銲縫處存在熱應力、銲接殘餘拉應力,在高溫硫腐蝕和異種鋼銲接的共同作用下導緻瞭銲縫開裂。
개소료초탄탑저부진료관선부식개렬정황,대개렬부위진행료외관검사。만두단렬실효부위발생재배한봉부근구역,차연주향개렬,렬문평직,이렬문확전방향여한접단면기본일치。대개렬부위만두취양,진행화학조성급금상열응력분석화경도측시,대부식산물진행화학조성분석。근거생산공예、개질조성화분석결과학정료실효적주요원인:수착장치원료렬질화,경과10 a운행후,관선고온류부식가극,강저료관선적승재력;유우한봉처존재이충강적한접,소사용적309불수강도열계수교321불수강략소,가지전자적외벽온도우저우후자,사309강산생교대적축향랍신인력,도치한봉처존재열응력、한접잔여랍응력,재고온류부식화이충강한접적공동작용하도치료한봉개렬。
The corrosion cracking of the bottom feed line of the coke drum was briefly described.The inspection found that the cracking failure occurred near the area of ring weld and promulgated circumferentially.The cracking was straight and flat,and promulgation direction was consistent with weld cross surface.By chemical composition analysis,thermal stress analysis and hardness testing of samples from elbow,the main causes of cracking were studied.The results showed that the high-temperature sulfur corrosion was the main culprit,which was resulted from processing of low-quality high-sulfur feedstock.After 10 years' operation,the pipeline bearing strength was reduced due to high-temperature sulfur corrosion.As different steels were welded,the heat conductivity coefficient of 309 stainless steel used was lower than that of 321 stainless steel and the temperature of external wall of 309 stainless steel was lower than that of 321 stainless steel,greater axial tensile stress was produced.The cracking propagation was accelerated under the combination effect of the thermal stress,welding residual tensile stress and the high-temperature sulfur corrosion,resulting in weld cracking.