PetroStreet

It's been 06 months down the line with TOFD inspection on our heavy wall thickness weld joints.
Initially, at the start of the project, everthing was coming up too good, I mean good results due to good welding. Now, as we are near to our targets and undertaking welding jobs at GOLDEN joints, it has been observed that the welding defects are coming up more frequently. We are facing about 80% rejection in TOFD inspection which is quite strange for us.
Strange in a sense that the welders are same who are doing this job.
There can be many other reasons for that like:
1. At the closing of this job, welders are being pressurized to meet the target and do welding as quick as possible.
2. Welders are doing it intentionally at the closing to have some more bugs, some incentive.
3. Quality of electrodes and other consumables in the latest lot are doubtful.

Please share your views.

4- Closure joints may be more difficult to attain sound welding in complying essential WPS conditions (purging, preheating, interpass, postheating, etc) effectively.
5- Sample joints from TOFD rejection must be cross verified thru other means RT/PA to testify TOFD method statement / calibration.

Thanks for value addition.
Regarding point 5, should it be advisable to open up a debate of RT versus UT? Other UT technique like manual pulse-echo or phased array may be a better option.

I am interested in knowing the following:
1. Material being welded
2. Do your inspectors see the repairs themselves when grinding is done to kill repairs? Have they found what TOFD report asks for?
3. At which position in the weld, repairs are coming more frequent? Are these golden weld joints easily accessible for a welder to work?

Ben,
1. It's P11 and P22
2. Not till now. We are constituting this protocol straight away
3. 70% at the top or bottom of the weld. Will have to check the locations.

a. Focus on point 1 which you have mentioned.
b. Go yourself in the field and ask welders yourself as what they say about pressure by their supervisors.
c. Regarding point 2, I would not agree to much extent. How much weld joints are left and from how much period you are facing high repair?
d. Point 4 mentioned by Qaisar would be much more important if purging was mandatory. I have seen many problems at several project sites on SS golden welds. Purging is not an easy job in those cases. But this is not the case for your materials. However, pre-heating, post heating do matter for low alloys.
e. Verifying UT by RT would surely put you in trouble my friend. 100% sure. Heavy wall thickness joints would come up with fewer defects in RT and you would be questioned by many. Try pulse-echo manual UT.

I would make the following points considering you a a QC guy.
1. Make full analysis of what reports are saying. Complete your home work first then say anything. You must focus on the things I am mentioning below:
a) Opinion of your inspectors assigned on the welding job over the past few weeks / months. What they say about visual inspection they are performing.
b) Sit with TOFD guys and have a small meeting on understanding the defects. See where the defects are coming repeatedly.
c) Involve a level-III guy in UT, take his opinion. If already available, have his words on the results. There can be some variables.
Only after considering these points, make any comment.

arcpro,
Not much just few 20-25 weld joints are left and it's been one month now we are having high repair rate.
Thanks mechcolor for your valuable advise.

I would agree with the comments given by mechcolor. So right pointed out for the necessary home work you should do within your team to evaluate the actual reasons for recent high repair rate.
I would like to add few more points:

1. TOFD inspection largely depends on many factors like:
a. UT guy who is actually evaluation the results. See if the guy has been changed recently. What sensitivity he is being maintaining for interpretation of defects.
b. UT inspectors who are scanning the welds. Have they been changed. You must know that the surface preparation for carrying out UT inspection does come up with differences in scanning and that sometimes can change the results. Do discuss this also with UT guys at your site.

2. I do not consider that the welders would be doing this just to extend their stay at site for only 20-25 welds left now.

3. Re-evaluation of TOFD results may be carried out by another qualified UT guy would give you much more confidence in declaring the defects.

4. And most importantly as said by mechcolor, your inspectors would prove to be oxygen for you in these scenarios. Ask them how welding is going on in the field for the last one month.

I really appreciate the value addition by all of you.

The conclusion I am up to after thinking through and discussions with UT guys is as follows:
"From previous one month or so, my own QC inspectors are not looking after the job directly. Instead execution / construction guys are taking care of inspections themselves. This resulted in having poor control over welding job in the field resulting in high repair.

"On the other hand, a re-evaluation of TOFD scanning results revealed that there some allowable defects as per code case 181 but were declared rejected just due to keeping high sensitivity while evaluating scanning results. And yes as highlighted by ben, surface finish can also affect the results so sometimes a test scan is advisable to be made.

"So in short, we lack inspection controls which resulted in higher defect / reject rate and some UT results were given keeping higher sensitivity".

Once again thanks all for the help.