API 660 Short time tensile strength

[Peter113]

Dear All,
what is the meaning of short time tensile strength? This statement is indicated on mentioned Standard para. 7.8.9:

"Allowable stresses that have been established on the basis of short-time tensile strength shall not be used for the design of girth flanges, gasketed tubesheets and gasketed flat covers.
Note 2: In ASME Section II, the allowable stresses of some high-nickel alloys haven been established in this way"

Thanks in advance
Peter

 

[Christine74]

"Short-time tensile strength" means that no consideration is given to time-dependent material properties, such as stress-rupture and viscoelastic creep.

If you look through the materials listed in Sect. II part D you will notice that some materials, in particular the stainless grades, have two seperate listings with different allowable stresses, and the one with the higher allowable will reference General Note G5.

General Note G5 lets you use higher allowables under the assumption that some creep and deformation are acceptable. Clearly these higher allowables are not appropriate for gasketed joints.

-Christine