Allowable stress

The maximum stress a designer can assume that the parts will stand. Is always less than the minimum strength of the material. For example, the ASME Boiler and Pressure Vessel Code typically specifies an allowable stress that is one-quarter of the service temperature yield strength of the material. This introduces a four-to-one safety factor into the design process and is intended to compensate for uncertainties in estimates of strength, service loads, etc.