Abstract
Consideration is conducted on parameters controlling deformations of thick cylindrical vessels due to narrow-gap multi-pass welding of longitudinal joints. The change in inner diameter and the deformations in the vicinity of welds caused by longitudinal welding is measured for actual cylindrical vessels, 50-200 mm thick, 900-3000 mm in inner diameter. Experiments for thick plate specimens under the same narrow-gap welding process are also made.
In the multi-pass welding of thick plate, the deformation occurs after the manner of angular change as the root part of groove hardly moves. Therefore the amount of angular distortion is obtained by Δgw/h using the measured value of shrinkage Δgw at upper side of groove and plate thickness h. The above characteristics in deformation of multi-pass welds of both cylindrical vessel and plate specimen result in usefullness of the application of elastic theory based on dislocation model for estimating the deformation of cross-section of vessel due to longitudinal welds. According to the dislocation theory, change in inner diameter ΔDi is proportional to the inner diameter Di and is given by the equation
ΔDi=-Δgw/h·1/2π(1-1/2πsinθ)·Di(0°≤θ≤180°)
where the sign of ΔDi is defined as increase in Di is given as positive, and θ is the angle from the weld joint. The applicability of the above equation based on dislocation theory is confirmed by the present experiments. In the above equation, the term Δgw/h of angular distortion of thick cylindrical-vessel has a constant value regardless of inner diameter and plate thickness when plate thickness is larger than 50 mm. Accordingly, it is presumed that the change in inner diameter is controlled by only one parameter of inner diameter of vessel.
