In-service Welding Of 20~# Pipeline Steel And Development Of Expert System

The burn-through experiment was studied through the static in-service welding experiments,according to the results,burn-through occured in 3mm thickness pipeline when the welding heat input and the pressure were small,3mm thickness pipeline had larger burn-through danger,the welding heat input should be controlled in 13.4kJ/cm or less to avoid burn-through during the in-service welding of 4mm thickness pipeline,however,burn-through didn't happened in 5.6mm thickness pipeline when the welding heat input and pressure were bigger,so the casing repair was not recommended when the thickness of pipelines was less than 4mm.The microstructure and hardness of single-pass welding joint were studied in different cooling condition,welding heat input and thickness of pipeline.The shape and quantity of ferrite of seam changed apparently with the difference of cooling condition,welding heat input and thickness of pipelines respectively,but the variation of GCHAZ microstructure appeared in the crisp microstructure,s form and quantity,the hardness of single-pass welding joint became higher and higher with the increase of flow velocity,the decrease of welding heat input and thickness of pipelines respectively.The acicular ferrite of the seam became tiny and bushy,more martensite microstructure appeared in GCHAZ,and the hardness of welding joint was higher especially in small thickness pipeline with high flow velocity and little welding heat input,however,the hardness of welding joint became lower apparently when the thickness was bigger,so the welding heat input should be increased properly to avoid hydrogen induced crack during the in-service welding of small thickness pipeline.Thickness of pipeline had much more effect on hardness of single-pass welding joint than flow velocity did through the orthogonal experiment of pipeline operating conditions in certain welding heat input.The microstructure and performance of multi-pass welding were studied in 4mm thickness pipeline with the flow velocity of 4m/s.The microstructure of welding joint was made better and the hardness reduced apparently by the influence of subsequent beads contrast to the microstructure and performance of single-pass welding.The dimple of welding joint's radical region through nick-break test was drew out,the seam had good plastic,so the technology of multi-pass welding with certain welding heat input is doable when the thickness of pipelines is not less than 4mm in the flow velocity of 0-4m/s.In order to reduce costs and avoid repetitiveness of in-service welding repair,the knowledge database and expert system of in-service welding were build by taking VB as development language,SQL Server 2000 as database tool,C/S as network structure,production rules representation as the main method to present knowledge and positive direction reasoning as the main system reasoning way.Through the system,we can not only inquire and browse WPS and PQR,but also design the technics of in-service welding,administrator can maintain and update the knowledge database of in-service welding regularly.Moreover,the system provided users with inquiry and browse of some staple welding expert knowledge.