There are numerous reasons a weld could fail UT. The indications from UT may be related to weld geometry, welding procedure, position, qualifications and experience of the welder, weather conditions if done in the field, electrode type and size, machine settings....on and on.
Common indications are slag inclusions within the weld, root problems (lack of fusion, root undercut, cracking, etc.), weld fusion along the prepared face, interpass cracks, interpass fusion, etc.
I will start by asking what you mean by NDT UT. I interpret it to mean Non Destructive Testing - Ultrasonic Testing. Is that what you mean? Some of us on this forum are not fully conversant with all of the testing methods available.
It might help if you explain to us how or in what respect the test failed. There must be more to the story than simply...the test failed.
Thank you so much for your replies, I'm still waiting for the actual report done by our NDT contractor. We were just told initially that it failed and we need to gouge out our joints. Yes its Ultrasonic Testing I apologize for confusion.
glenn0123....I'm not sure where in the world you are located, but in the US, the NDT company should have a quality program consistent with the requirements of the American Society for Nondestructive Testing (ASNT), SNT-TC-1A program. This provides for individual qualifications of the NDT personnel (typically minimum of Level II for testing without direct supervision), and the whole program supervised and administered by a person designated through National testing as a Level III.
Check to see that the person doing the testing is appropriately qualified, wherever you are located and by whatever organization is noted in your codes.
Air/Arc gouging is a common method of removing anomalous conditions before re-welding. Grinding is another common method.
Check also to make sure that your company is following its approved welding procedure (assuming you have such).
I assume these a complete joint penetration welds. Provided your welds met the visual inspection requirements, UT identifies discontinuities within the weld. Depending on the joint configuration, UT can identify incomplete fusion, cracks, slag, or other defects within these thickness of the weld. If these defects are frequent it is reasonable to request repair of all joints. If occasional problems are found localized repairs are most common. Cracks or inclusions are usually a symptom of other issues. Verify that the appropriate WPS is used correctly.
