What is the permissible level of shear stress in pump shafts used for double suction split case pumps for ANSI 410, 431, 316 materials?
Allowable stress levels, for static components, are usually related to the tensile stress of the material, per ASME rules. For cyclically loaded components, such as shafts, the endurance limits are applied, which produce values more conservative then for statically loaded members. For example, martensitic stainless steels, such as 400-series, often have a value of 7500psi allowable, but each manufacturer may have its own values and procedures. The importance of knowing the allowable shaft stress is obviously to determine if a shaft diameter is sufficiently large. However, other factors need to be considered. For example, for the types of pumps you mentioned, the impeller can be positioned on a shaft axially in variety of ways. Some designs have threaded shafts, with locknuts against the impeller hub. Others may have lock-rings, positioned in a shaft groove. Threaded shafts present additional stress concentration – and the shaft diameter must be sized even more conservatively to accommo
