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Technical Discussions
Madhavan.S
Madhavan.S
04:28 Jun-04-2003
Radiographic Examination of Weld in Pipes

WELDING OF PIPES
The bevels for GTAW Root pass as per ASME B16.25 is Fig No-5 and Fig No-6 for thickness of pipes greater than 10 mm. The figures indicate a cylindrical surface of 5 mm in the inside and also a broken line indicating the transition from the welding groove to the body of the component. We have adopted a transition straight away in the inside instead of 5 mm straight machining. We have now come to know that the straight machining of 5 mm is preferable when compared to that of tapered transition for radiographic evaluation. But we have been adopting this transition in many jobs without experiencing any problem in evaluation of the welding. We request your views on this . In case you feel the transition is OK without straight machining, please provide your view points for justifying the same since our customer feels that straight machining of 5 mm is preferable.


    
 
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Doug Breeze
Director, Consultant; R&D
Inspection Software Limited, United Kingdom, Joined May 2000, 20

Doug Breeze

Director, Consultant; R&D
Inspection Software Limited,
United Kingdom,
Joined May 2000
20
06:00 Jun-06-2003
Re: Radiographic Examination of Weld in Pipes

The surface you describe is (or used to be!) called a counterbore. It has lots of benefits and few drawbacks, except for the machining costs...

1. Machining an identical counterbore on both joining pipes should prevent root-misalignment. This is leads to a more easily welded root-run, with less likelhood of root defects.

2. The counterbore provides uniform geometry on each side of the root so that radiography (and ultrasonic) inspection can more readily differentiate real defects from false geometric indications.

3. The counterbore reduces the included-angle at each root edge, and also distributes stresses adjacent to the root over a larger area thus minimising the risk of cracking and/or stress corrosion in this critical area.

Hope this helps.



    
 
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