The Study On The Key Factors Affecting In-Service Welding Quality For High Strength Pipelines

In recent years,high strength pipelines have been paved in our country.The length of pipelines is updating.Pipelines are developing in direction of larger diameter and higher strength,which puts forward more requirements on pipeline maintenance such as repair.In-service welding is an important repair technique,which is applied in replacing pipelines and valves,as well as adding branches.It has significant economic benefit.However,burnthrough and hydrogen induced cracking often occur in the construction,which affect in-service welding quality.Screening out key factors affecting quality by means of survey,then analyze foreign technical state,national and international standards comparsion,practice comparsion,as well as SYSWELD numerical simulation.These research aim at key factors.Specific conditions are described as follows.At first,key factors are classified as five kinds of skill points such as environmental requirements,pipe body,pre-welding treatment.These points are analyzed by virtue of foreign literature.After that,domestic and foreign standards or practice concerning 18 points are compared based on site actual.Then revision suggestions for standards are put forward.Finally,sleeve rapair numercial simulation is conducted to study different welding speeds,preheating temperatures and medium velocities influencing temperature field,stress field,hardness about welded joint.Selection suggestions for indexes of key factors and recommended practice are present for in-service welding based on above studies,which provides references for increasing the level of domestic in-service welding.