SMTS and Allowable Stress


Specified Minimum Tensile Strength (SMTS)

The ASME Code, Specified Minimum Tensile Strength or SMTS mean stress (Stress), the lowest that can make a material damaged or torn apart by tension ( The Tension), which is made from tensile tests ( Tensile Test,. ), also known as Ultimate Tensile Strength (UTS). 

SMTS

How to test and verified the SMTS of weldment: Tension Test Acceptance Criteria for Welding Procedure Qualification

Allowable Stress “S”; 

For ASME Code,   pressure vessel or pipe design, the code uses the Tensile stress of each material specified in the calculation.

Stress that the code specifies or allows is called Allowable Stress “S”, which is equal to the Specified Minimum Tensile Strength (SMTS) divided by the Safety Factor of that code.

Example: ASME 31.3 – S =3.0, ASME VIII, S = 3.5

Refer to: Allowable Stress in ASME VIII, B31.3, API 650, API 653

Allowable Stress ASME.png

Allowable Stress vs. Temperature; 

At higher temperatures, the metal material will become less stiff. Therefore, the ASME Code allows the use of Allowable Stress values in pipe designs or reduced pressure vessels in accordance with higher Design Temperature.

Allowable stress and Temperature ASME.png

 

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