Weld Procedure Qualification: Acceptance Criteria (Tension Test) ASME Section IX QW-153.1 (d)

[auzie5]

ASME Section IX QW-153.1 (d) (p. 5 in 2011 edition) states:

"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."

Question: Why is it ok that the parent metal may have a lower tensile strength in this case?

For example, a stick of SA-106-B must have a minimum tensile strength of 70ksi. However, during a weld procedure qualification tensile test we notice that the parent metal is failing at 68ksi. Although the weld itself did not fail, this seems to be implying that the weld procedure we are testing is affecting the parent metal near to the weld (in this case lowering its tensile strength).

Why is this acceptable? I would imagine the goal of developing a weld procedure is to determine a set of parameters that not only achieves a weld and heat affected zone that are as strong as the parent metal, but also does not adversely affect the parent metal during the process.

 

[SJones]

The SMTS of A106 Grade B is 60,000 psi. Notwithstanding that misunderstanding, bear in mind that welding procedure qualification testing sometimes reveals nonconforming parent materials. Apart from that, the point of testing is to confirm that the complete weld zone has acceptable strength. There is a difference between acceptable strength and maintaining the exact as-supplied properties of the parent material.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

 

[auzie5]

Appreciate the comment. And thanks for pointing out my typo.

Thanks Steve.