Enter the allowable stress for the element material at hydrotest temperature. You can calculate this value in the ASME Code, Section II, Part D, Table 1A, 1b, and 3.
Operating temperature for most vessels is 40º F, 70º F, or 10º C.
The allowed hydrotest stress is typically 1.3 (1.5 for Pre-99 addenda) times the allowable stress for the vessel at ambient temperature. Under some circumstances you may choose to use an allowable hydrotest stress of 0.9 times the yield stress of the material at ambient temperature. This is especially helpful in the case of a tall vertical process tower where the hydrotest pressure is increased by the height of the water used for testing. Use of the higher hydrotest allowable stress may prevent the hydrotest case from controlling the thickness of the vessel.
If you select a material name or enter a valid material name in Material, the program looks into its database and determines the allowable stress for the material at ambient temperature, multiplies it by 1.3 (1.5 for Pre-99 addenda), and enters it into this field. The software also checks the value of 0.9 times the ambient yield stress. It then compares the two numbers and chooses the minimum of the two.