Actually, because of some limitations blind use of WRC-107 may lead to a dangerous design. Sign of stresses are important in the stress combination. For overcoming this common problem, engineers must have knowledge about firstly all types of local stresses and secondly stress combination methods which have been introduced by ASME BPVC Section VIII Div 2.
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The outcome may lead to under design or overdesign If piping stress engineers or pressure vessel engineers who take care of nozzle loads, do not know how to treat all extracted local stresses properly. Depending on other applied loadings such as system weight, internal or external pressure, wind or earthquake, snow, thermal loads and etc., each type of mentioned local stresses should be combined with their relative stresses in a proper way. Each load creates some types of local stresses such as membrane or bending stresses in two directions: longitudinal and circumferential. WRC-107 supports 6 external loads in local stress calculation: Axial force, two lateral force, torsional moment and two bending moments as shown in figure 1.
For making a proper stress combination according to stress categories introduced in ASME BPVC Section VIII Div 2, an engineer should know the types of all local stresses and their causes. The local stresses are calculated by some geometric parameters which can be extracted by curves. The nozzle is assumed to be penetrated to a cylindrical or spherical shell.Īs shown in figure 1, local stresses are calculated at 8 points, named as, located on two levels, upper and lower plates. WRC-107 consists of many curves enabling engineers to calculate all types of local stresses caused by external loads exerting on a circular or rectangular nozzle on shell elements. Its limitations, scope and concepts of local stress cause are mentioned here. There are some important items that engineers who use these softwares should be aware. Some well-known softwares such as CAESAR II, PVElit and Compress use this method for nozzle loads checking.
This method was developed by Professor B.P.Bijlaard and firstly published by WRC in 1965.
Welding research council bulletin 107 which is globally known as WRC-107 introduces one of well-known and important methods for calculation of local stresses in junction of shell and nozzle.