L245NCS/316L复合输气管道的焊接技术

Welding technology for L245NCS/316L bimetal gas line pipes

双金属复合管因其结构的特殊性及对力学性能和耐腐蚀性能的双重要求,使得其现场焊接施工遭遇诸多困难。为了保证高酸性气田开发集输过程中所用L245NCS/316L双金属复合管的焊接质量,针对其对接焊,采用了钨极氩弧焊打底、手工电弧焊填充盖面的方式,通过反复试验,优选了TGFA-309L(直径为2.2 mm)、ATS-F316L(直径为2.0 mm)、TGS-309MoL(直径为2.4mm)和CHE427(直径为3.2 mm)为焊接材料,确定了焊接工艺参数,对焊接接头进行了X射线探伤、力学性能试验、微观组织分析及晶间腐蚀倾向测试、失重腐蚀性能测试和抗Cl^-应力腐蚀性能测试,对抗Cl^-应力腐蚀试样腐蚀产物进行了XRD和SEM分析。结果表明:①焊接接头X射线探伤检测结果为Ⅱ级;②焊接接头各项力学性能指标均合格;③焊缝区微观组织主体为针状铁素体+粒状奥氏体+珠光体;④抗晶间腐蚀倾向测试与抗Cl^-应力腐蚀性能测试均未见裂纹,失重腐蚀测试气相和液相平均腐蚀速率分别为0.022 3 mm/a和0.068 1 mm/a;⑤Cl^-应力腐蚀试样XRD、SEM分析结果显示腐蚀产物膜的主要成分为FeS,是四方晶系晶体,呈堆砌状态,易穿透基体金属表面腐蚀产物膜,对基体金属会产生进一步的腐蚀。焊接接头各项性能指标表明,所拟定的焊接工艺方案对L245NCS/316L双金属复合管对接焊是可行的。

Bimetal pipes are structurally special with dual requirements on mechanical property and corrosion resistance, so their field welding is faced with multiple difficulties. For guaranteeing the welding quality of L245NCS/316L bimetal pipes which is used for the development, gathering and transportation of high sour gas, its butt welding is carried out by performing tungsten argon-arc welding for scratch coat and manual arc welding for screen. Based on trial and error, TGFA-309L （Ф2.2 mm）, ATS-F316L （Ф2.0 mm）, TGS-309MoL （Ф2.4 mm） and CHE427 （Ф3.2 mm） were selected as welding materials, and welding parameters were determined. Then, the welding joints were tested by means of X-ray flaw detection, mechanical performance test, microstructure analysis, intercrystalline corrosion tendency test, weight-loss corrosion performance test and Cl^- resistant stress corrosion performance test, and the corrosion product of Cl^-resistant stress corrosion specimen was analyzed by using XRD and SEM. The X-ray flaw detection result shows that the welding joints are of level II; that mechanical performance indicators of welding joints are all qualified; that the microstructure of weld zone is mainly acicular ferrite, granular austenite and pearlite; that no cracking is observed on the specimens of intercrystalline corrosion tendency test and Cl^- resistant stress corrosion test. The average corrosion rate of gas phase and liquid phase in weight-loss corrosion test is 0.022 3 mm/ a and 0.068 1 mm/a, respectively; and that the XRD and SEM test results of CI resistant stress corrosion specimen indicate that the main component of corrosion product film is FeS, which is the crystal of tetragonal system in the pattern of stacking and which can penetrate easily the corrosion product film on the surface of base metal to corrode the base metal. All performance indicators of the welding joints indicate that the proposed welding scheme is feasible for the butt welding of L245NB/316L bimetal pipe.