Tensile as per ASME section 9

[fakhfakh]

For procedure qualification per ASME Section 9 and regarding the tensile acceptance criteria, why the code accepts 5% below the the minimum specified tensile strength of the base metal if the sample brakes out of the weld. Contrarely it tolerates not less than the minimum specified tensile strength if it breaks in the weld ?

 

[metengr]

If you mean this reference
(d) if the specimen breaks in the base metal outside of
the weld or weld interface, the test shall be accepted as
meeting the requirements, provided the strength is not more
than 5% below the minimum specified tensile strength of
the base metal.

This applies to either overmatched strength weld metal in relation to either of the base materials being joined or variability associated with the specified mechanical properties of the base material.

 

[fakhfakh]

Do you mean that the base metal is tolerated to have a tensile strength 5% below the minimum specified value ?

 

[Duwe6]

Only in this very specific instance: The testing of Reduced-Section tensile weld coupons, in accordance with Sect IX.

Reason being that you are testing the weld, not the base metal. If the base metal breaks before the weld, the weld is 'better' than the base metal, and the Welding Procedure was successful.

 

[fakhfakh]

I think that it may happens that the base metal sample has lower UTS than what is required as minimum, and the weld is stronger. The Code, in this case, allows that when the sample breakes out of the weld, lower strength by 5% is accepted.

May be this is the reason which is related to actual facts