When VT must be done on a UTed weld

[fabengr]

I have a conflict between a CWI and myself regarding when the VT must be done on a weld that will be UT tested.
My point is that section 6.11 (this is to the D1.1:2000 because it is on a nuclear project) says that the "Welds subject to nondestructive testing shall have been found acceptable by visual inspection in accordance with 6.9." means that the VT testing HAS to be done before the NDE can be started.
I am saying that the words "shall have been found" means the VT is done first.
The CWI is saying that the VT just has to be done before the weld can be completely accepted.
Comments?

 

[specialinspectormike]

The VT should be done first to eliminate any possible defects that need to be corrected before the UT test is performed. I.E. Surface Cracks, under fill, porosity, ETC. Over the years I've encountered a lot of lazy CWIs that will leave the VT to the UT guy if that guy happens to be a CWI also. This is problematic for a whole host of reasons including the unnecessary extension of inspection periods.
VT FIRST THEN NDT. PERIOD.

 

[metengr]

Typically, as long as VT is performed as well as NDT on completed welds it really makes no difference as to sequence. The Code obviously does not address specific sequence only what needs to be done. Keep in mind that VT would be last simply because if NDT finds a defect it may require weld repair and re-VT.

 

[DekDee]

fabengr,
IMHO you are correct.
Maybe just my interpretation but the way I read it is you must perform VT and then there are other NDT methods that can be performed "in addition" to VT.

Welds that are subject to MT and PT, in addition to visual inspection, shall……..

Welds that are subject to RT in addition to visual inspection,shall ……….

The acceptance criteria for welds subject to UT in addition to visual inspection shall
meet the following requirements:

Regards,
DD

 

[gtaw]

I suspect the intent is to perform VT before any additional NDE is performed. Like you, I believe the phrasing "shall have been" means the welds have been subjected to VT and found acceptable before further or additional NDE is performed.

I have worked with other welding standards that are more specific with regards to the need to pass VT before additional NDT is performed.

I believe the intent of most standards is that it is a waste of money to RT or UT a weld and declare it acceptable and then reject it visually because of undercut or excessive reinforcement, etc. Any repair required as a result of the NDE may also involve additional NDE to the original requirements. Calling the NDE technician back a second time increases cost.

However, there are times when it is more convenient and less expensive to perform the volumetric examination while the technician is on-hand rather than delay the volumetric examination only to reschedule the NDE technician for another visit at a later time. In my opinion, the primary concern is that both VT and the additional NDE be performed, the part is found acceptable by both VT, and by the additional NDE method. If it is more cost effective, perform the NDE first and perform the VT when it is convenient, so be it. Money does talk very loudly. Unfortunately, if we are the inspector (CWI or otherwise), not the Engineer, we are bound by the language of the welding standard. If the Engineer provides an exception to the requirements provided by the welding standard, the inspector can follow the Engineers direction.


Best regards - Al

 

[weldstan]

Why would you want to subject a weld to an expensive NDE if the weld could be rejected by VT mandating re-examination after repair? Economically speaking perform the VT and accept and then perform volumetric NDE.

 

[gtaw]

The cost of quality control is always an issue with a fabricator or a to the purchaser. Anything that can reduce cost and reduce the manufacturing time is worth considering. Generally, visual examination is the most cost effective method used to ensure the product meets the requirements of the contract documents, i.e., purchase order, code, project specifications, and drawings. As mentioned in a couple of posts, it is usually efficient and cost effective to perform the VT prior to additional NDE. However, what I've personally encountered has been contractors that attempted to use PT, MT, RT, or UT in lieu of VT. The opinion of the contractor's inspectors was that other nondestructive test methods replaced the need to perform VT.

RT, UT, PT, or MT cannot replace ongoing VT. Each test method, including VT, has limitations on what types of discontinuities can be located and properly assessed. I believe the various code bodies recognize the limitations of NDT and recognize the value of VT as being the most economical and timely method of locating and identifying deficiencies when they occur so that corrective measures can be to eliminate the unacceptable product from the production stream or to repair the deficiencies as they occur. this reduces cost by eliminating investing time and labor into a part or component that will not be acceptable. True, the discontinuity may be found (I did not say, "will be found")by another NDE method, but the cost of repair will be greater and the labor and time invested since the defect was introduced is lost, thus driving up cost.

As an example: Laminations along cut edges can often be detected visually. If the visual examination is not performed and the cut edge with the lamination is incorporated into the welded joint, it may be located and identified once the joint is welded if UT is specified and the technician uses compression waves (straight beam) to interrogate the joint along the edges of the welded joint. However, the cost of repair includes the time and labor of the original weld, removing the existing weld and adjacent base metal, and rewelding the joint. It RT is specified, the lamination will not be detected and the defective part will be shipped where it may fail while in service. An in-service failure can cost the company that produced the defective part, well, who knows how much the in service failure will cost in terms of injuries and associated damage.

A program of thorough on-going visual examination at all stages of the manufacturing process is much less expensive that performing NDE at the end of production when one considers the NDT method selected has the potential to miss critical subsurface defects. I used RT as an example, but the danger of a manufacturer or contractor substituting a different NDE method in place of VT is mitigated if the code requires VT be completed prior to the implementation of additional NTE methods. I believe it is the intent of AWS D1.1 that VT must be performed before other NDE methods are performed. Any deviation from the sequence specified would have to be approved by the Owner's Engineer. It is not a decision the contractor can make unilaterially.









Best regards - Al