Study of features in weld root formation under double-sided synchronized arc welding of vertical joints of steel tanks

It is shown that increase in the welding productivity of vertical joints of storage tanks for oil and oil products can be achieved due to the double-sided synchronized formation of the X-shaped groove. To minimize various disturbances, including variation of gap size and root face dimension, computer engineering analysis is performed, which showed that the formation of root pass during welding with the movement of the electrode down (vertical down) with increased dimension of the root face leads to lack of penetration, but during groove filling with the movement of the electrodes up (vertical up) deep penetration is achieved given the considerable root face dimension. It is defined that during welding of 30 mm thickness plates with root face dimension range from 6 to 8 mm, it is necessary to ensure the root gap dimension range from 1.5 to 3 mm along the entire length of the seam. In this case, the remaining unfilled cross-sectional area of the groove is small, which makes it possible to fill it in during single pass under two-arc double-sided welding. There is area of double-sided synchronized welding modes in which the occurrence probability of typical defects during the formation of the weld root is minimal.

On the Influence of Back Pressure and Size on the Performance of Safety Valves

The paper presents the results of an extensive experimental research programme performed on safety valves in order to clarify the effects of back pressure and valve size on the flow capacity of a valve. As well known, back pressure strongly influences valve operating characteristics and can also reduce the discharge coefficient. This flow rate reduction can be related to the occurrence of a subsonic flow regime along the flow path and to insufficient disc lift. Last mentioned features can play a different role on different valve sizes because of the non exact geometrical scaling within the same valve size range. This happens because the requirements of typical application design standards, such as the API Standard 526, are such that the valve inlet, valve outlet and face to face dimension are not exactly scaled with respect to the orifice diameter. Moreover, face to face dimension can limit the body bowl volume leading to different device performances the same operational conditions. In order to clarify and evaluate the influence of the above mentioned parameters on the flow capacity of safety valves, many tests were carried on a single valve for different pressure ratios, disc lifts and for different valve outlet areas and body volumes representing different sizes derived from API Standard 526. Test results show significant differences on the flow capacity of safety valves under back pressure regime. This would suggest testing every valve size of the considered valve size range at different expansion ratios to confirm performance. Since this procedure leads to an excessive number of experimental tests, a sensitivity analysis on the influence of the most important geometrical parameters has been carried out. In order to minimize the number of experimental tests required for characterizing the flowing capacity of the whole valve size range, the paper proposes an experimental correlation for the prediction of the above mentioned non similarity effects.