Study Of Low Temperature Toughness On Welding Seam For X80 Level Steel Pipe

In recent years,under the belt and road policies of China,all countries have attached great importance to the construction and development of the oil and gas industry.The fourth line of Shanxi-Beijing project as a national strategic key project,the pipeline route area is mostly belongs to the alpine region,so the project require the use of X80 pipeline steel material by JCOE manufacturing steel pipe straight seam submerged arc welding process,and the impact to 45℃ and DWTT performance put forward special requirements.For example-45℃ impact weld average is not less than 40J,minimum value is not less than 30J;-45℃ weld DWTT test average shear area of not less than 75%,the minimum value is not less than 50%.Based on grade X80 Φ1219×27.5×12000 mm steel pipe weld as the research object,analyzes the performance of steel plate steel weld the influence law of low temperature toughness,compared the different welding materials,the influence of process parameters on the low temperature toughness of weld,to determine the optimal scope expanding rate achieve good low temperature toughness,lists the influence of different weld appearance of weld toughness at low temperature.In the end,a complete production process is formed to meet the project requirements.After the completion of the project,oil related experts invited our company to participate in the drafting of the low temperature toughness standard,and jointly contributed to the national key project.In this paper,X80 gradeΦ1219×27.5×12000 mm steel pipe weld as the research object,analyzed the influence of steel performance on the low temperature toughness of welded steel pipe,compared the influences of different welding consumables and process parameters on the low temperature toughness of the weld,determined the optimal rate of expansion rate range to obtain better low temperature toughness,listed the different weld morphology on the low temperature toughness of the weld.The final formation of a complete set of production technology,fully meet the fourth line of Shanxi-Beijing project requirements.After the project is completed,PetroChina related experts invited our company to participate in the fourth line of Shanxi-Beijing low temperature toughness standard drafting,together for the national key project.In this paper,through the study of factors affecting-45℃ weld toughness at low temperature the following valuable research results are obtained.For example:(1)Steel raw materials are studied to-45℃ impact performance influence on welding seam toughness at low temperature.Results show that the steel raw materials-45℃ average control over 320 J impact resistance,the minimum control in the 300 J,showed must be less than 0.9 at the same time,made from steel pipe,steel pipe weld low temperature toughness index is relatively stable and outstanding.(2)The effects of three kinds of high alloy welding wires H10Mn2-SJ101,H08C-SJ101 and H08D-SJ101H08C on the welding properties at low temperature were studied.The results show that H08C-SJ101 welding material with low temperature toughness index is stable and outstanding.(3)Studied the welding process parameters on the influence of the steel pipe weld low temperature toughness index,the results show that the welding line energy input within 50 to 52 KJ,outside welding line energy input 60-62 KJ,weld coarse grain zone in lath bainite is given priority to,with granular bainite and lath bainite lath is more slender,straight and clear,strip with high dislocation density,strength and toughness of weld is beneficial.The specific welding process parameters are as follows:before internal welding,the wire current is 1000 A,the voltage is 32 V,the middle wire current is 800 A,the voltage is 35 V,the back wire current is 600 A,the voltage is 39 V,and the welding speed is 0.8 m/min.Before external welding,wire 1000 A,voltage 32 V,medium wire 800 A,voltage 37 V,after wire 700 A,voltage 39 V,welding speed of 1.3 m/min.(4)Steel tube expanding rate was studied in weld-45℃ impact performance and the influence of drop weight tear performance,as the hole enlargement ratio increasing,the impact of drop weight tear and improve performance,but when the hole enlargement ratio is more than 0.9%after declining impact resistance,and drop weight tear data anomalies.The result of experimental data analysis shows that the best low temperature impact performance can be guaranteed and meet the project requirements only when the expansion rate is maintained between 0.6%and 0.9%.(5)The influence of welding seam on low temperature toughness index of weld was studied,and the optimal ratio of weld penetration,weld deviation and high technical index of weld residue were summarized,which effectively solved the problem of unstable welding quality in the production process.The results show that the deep penetration ratio of inner and outer welds should be kept between 0.85-0.9,the deviation of inner and outer welds should be kept within 1.5mm,the residual height of inner welds should be kept within 1.5-2 mm,and the residual height of outer welds should be controlled between 2.0-2.5 mm,so as to ensure the high acceptance rate of welds in batch production of steel tubes and the stability of low-temperature toughness index of welds.