Not logged inAmerican Welding Society Forum
Forum AWS Website Help Search Login
Up Topic Welding Industry / ASME Codes / Which Ndt method is best for structural welded beams
- - By che simon Date 07-24-2015 11:21
Good day all. Please could you clarify my worries as to the best NDT methods for structural welding beams.
What is the advantage of ultrason to radiography if these two could be best?

Thanks

Simon
Parent - By TimGary (****) Date 07-24-2015 12:49
The best NDT method is competent visual inspection, both at fit-up and post weld.
UT and RT are for verifying internal soundness of welds.
The best choice between those two is dependant on circumstances such as joint geometry, access, availabilty and cost.
Each method has abilities to identify discontinuities the other has missed, so they are often used in tandem on highly critical joints.
Ultimately, the final definitions of which type and extent of NDT is to be performed is made by the project engineer and agreed to by all parties in contract documents.

Tim
Parent - By welderbrent (*****) Date 07-24-2015 23:16
Greetings Simon,

WELCOME TO THE AWS WELDING FORUM!!

To add to Tim's response, there is NO BEST NDT METHOD. 

They all have their advantages and disadvantages.  They all have limitations.  They all have practical application. 

As Tim mentioned, the best QC/QA system starts with trustworthy, knowledgeable, thorough Visual Inspection.  Even most codes specify that prior to other methods of NDT, VT will be performed first.  There are many reasons for this but I will refrain.  But what needs mentioning is that VT is also an NDT method, nothing is destroyed and it is the most complete method to be sure all code requirements are met.  UT cannot tell you if the preheat was right.  Can't tell you if the electrode was stored properly.  Can't tell you if the welder was properly qualified or that the welding was done within compliant parameters. 

Now, all other things being completed properly, from a cost, safety, accessibility to members, time, aspect you are normally going to be best off for structural applications with UT.  That does not mean RT does not have it's place and both have weaknesses and strengths.  

Personally, in this order for my work, VT, MT, and UT.  VT of the whole process.  MT of root passes on CJP's and of a percentage of surface passes and fillet welds. UT of CJP's and when applicable Lam scans. 

But, it is the EOR's job to choose how this is to be handled on their job to best meet the needs of the project.

Oh, and I am wondering why you are asking about structural RT vs UT in the ASME section?

He Is In Control, Have a Great Day,  Brent
Parent - By CWI555 (*****) Date 07-26-2015 03:51
Apples and oranges. One is better suited for planar flaws (cracks, lack of fusion etc), the other for voluminous (porosity, slag, etc).
Neither are a magic bullet nor are they replacement for weld program control.
For either to find anything, there must first be a flaw to find. While even the best can make mistakes, too many times people focus on the NDE rather than maintaining their welding program properly.

Beyond that, your engineers need to define what type of flaw is most agregious to your product form and proceed accordingly.
- By 803056 (*****) Date 07-26-2015 18:39 Edited 07-26-2015 18:43
There are some excellent arguments made and I agree with the comments.

RT requires access to both sides of the joint being tested. The film is placed on the far side, the X-ray tube or isotope place on the near side some distance from the surface being tested. That distance can be 24 to 36 inches or more. The discontinuity of interest has the highest probability of detection if it is parallel to the radiation beam. Keep in mind that the radiation is ionizing radiation which is harmful to anything that is alive. Humans can be shielded from the effects of the ionizing radiation by high density materials, i.e., concrete, water, etc., or distance. There are limits to the thickness of the test piece that can be interrogated. Essentially, RT produces a "shadowgraph", that is, the film can show you where it is, but not how deep it.

UT has no ill affects on the health of the operator or those individuals working nearby. That is a major plus for UT. Only one side of the joint needs to be accessible. Another plus for UT is that it can provide the inspector with more information (than RT) about discontinuities that are perpendicular to the ultrasonic sound beam. The angle of the sound can be adjusted by proper selection of the wedge angle (which produces a shear wave) to maximize the probability of detection. The inspector can determine the distance from the transducer to the discontinuity, the depth of the discontinuity, the length of the discontinuity, the orientation of the discontinuity, the character of the discontinuity, the sex of the discontinuity (oops, went a bridge too far with that last comment), but you get the idea. The drawback to UT is the weak link in the system, i.e., the operator. 

Best regards - Al
Up Topic Welding Industry / ASME Codes / Which Ndt method is best for structural welded beams

Powered by mwForum 2.29.2 © 1999-2013 Markus Wichitill