15:01 Mar-13-2010 Abdulla Engineering, CORROSION DIV. SUPERINTENDENT SIRTE OIL COMPANY, Libya, Joined Jun 2004 7
Some times we have been asked to certify the welding activities when the welding inspector did not attend , based on using RT, is this possible, and what are the draw backs of not attending the welding operation, can we rely only on RT.
There is a big difference in accepting a weld based on RT and having a welding inspector witnessing the welding process.
Accepting a weld based on the inerpration of a radiograph only ensure that your weld is "defect free" or has "indications acceptable to code".
The witnesing of the welding by the welding inspector serve to ensure the welding procedure was followed. Some of the items the inspector would look for would be: the weld prep, the electrode used, temperature of the base metal for preheat (if needed), certification of the welder and so on. These any many more cannot be answered by looking at a radiograph.
What Mr Couture has said is correct and you can also add if the Welding Inspector had witnessed the Welding Test you would know that the named Welder had actually Welded the test piece, and not someone else.
Hello Abdulla, its my belief that many welds are produced without a welding inspector present, whether RT'ed afterwards or not. High integrity welds SHOULD be witnessed and measured for ROL = run out length, heat input etc but this does not always happen. If these are not controlled within the parameters of the approved welding procedure then control of the eventual mechanical strength of the joint is lost. This is not a situation detectable by NDT, which searches for discontinuities and not properties - that is why the weld PQR shows both the actual welding parameters used and the results of the necessary mechanical DESTRUCTIVE tests. The WPS will allow a controlled range of parameters based on the record of those parameters used to complete the joint.
As for "can we rely on RT", if the weld is unwitnessed and RT is the contractual requirement, that is all you will have. The controlling Code will to some degree stipulate quality requirements for the RT but these are minimal - density within limits and penetrameter appropriate hole/wire visibility. Acknowledging RT's capabilities are linked to defect morphology then you need to consult appropriate Probability of Detection tables for RT of various defect types to know if RT is the back-stop for any potential welding ills. The end user should stipulate and monitor production and inspection processes proportionate with the product criticality.