Appearance of welding defects after galvanization 1

[demsha]

Hi All,

During Caisson shoe fabrication, it is normal practice to conduct UT inspection on full penetration welds.
No defects were identified at this stage. Subsequently, these shoes were sent through hot-dip galvanization process.
After galvanization, these shoes were again UT inspected. Then UT operator found indications inside welds. Then these areas were clearly marked and samples were removed from shoe. In the lab., these samples were metallographically analyzed. We found slag inclusions, porosity and lack of fusion on many shoe samples.


We use two UT operators from two different inspection agencies to conduct UT on black condition (prior to galvanizing). Both of them did not find any defect or defects were acceptable limits. Can anyone explain how these welding defects found after galvanization???

 

[gtaw]

There are UT operators and there are real UT technicians. Like people with driver's licenses, not all drivers are created equal, not all UT techs are created equal.

My recommendation is to specify and require the technicians be qualified and certified in accordance with ASNT CP-189. DO NOT accept qualification and certification to SNT-TC-1A!!!!!!!

You should also request copies of the following documentation from the vendor/contractor:
--Written Practice - defines how the technicians are qualified and certified (must be to CP-189)
--NDT Procedure - in your cast it will be for UT in accordance with the standard that is applicable to the work, i.e., for structural steel you should be using AWS D1.1 for example.
--Technician's qualifications: should list level of education, NDT training and test scores, and related work experience
--Technician's certification: should list the level of certification, expiration date, and signed by a ASNT ACCP Level III (again, not a Level III per SNT-TC-1A).

You should see an improvement in the consistency of test results before and after HDG. The defects you are detecting did not spring up as a result of the HDG operation. They can be attributed to incompetency.

Best regards - Al

 

[demsha]

Al, thanks for your input. I am sorry I misinterpreted as UT operator. Both of them are certified level 2 UT Inspectors.
One is Canadian CGSB Level 2 in UT with many years experience and other ASNT level 2 certified in UT.
Both of them are working in India checking these caisson shoes. I agreed with you that HDG could not cause porosity, LOF or slag inclusions to occur.
Could HDG process expanded those defects that were in the weld prior to galvanization? (UT in back stage passed because defects were within the acceptable limits).
Are there any published articles on this topic that I can read.

APPRECIATE YOUR SUPPORT

 

[Rich2001]

I have seen lamellar tearing like defects in thick carbon steel plates that occurred during HDG. I ran simulations using the 2-dim finite differences models (transient heat transfer) using the kettle temperature, various base metal temp and thicknesses. My conclusion is there are probably quite a few galvanized bridge bearing with lamellar defects. Why did I run the simulations? bearing were not inspected prior to installation, so I was working beneath a large bridge using a straight beam and finding tears 38 to 51mm deep, in the center sections of the bearing plates away from the edges and I became interested. BTW, the customer (state DOT) determined "use as is."

Richard

 

[Tmoose]

Hi Demsha,
Is the orientation of the steel plates correct for lamellar tearing to look like your defects/

 

[MintJulep]

Can anyone explain how these welding defects found after galvanization???

It seems that the question you should be asking is "Why were these welding defects not found by the inspection prior to galvanize?"

Are the inspectors any good? Really any good, not on paper good.

Is the equipment calibrated and in working order?

Is the inspection technique and procedure used capable of identifying the defects you are looking for?

Is there identification and traceability of samples? Maybe they are inspection that same good sample over and over, while the real production is busy making crap.

 

[gtaw]

Any NDT is only as good as the people performing the test.

It is not unusual for me to be hired to do a follow up UT inspection after some other lab has already inspected the same welds. The results can be discomforting. These are some of the issues I have recently encountered on structural steel projects:

1) Level II certified individual that only completed 2 days of 5 day Level I training class. Certified by his employer without any examinations. No excuse offered by the tech's employer.
2) Level II certified individual testing welds with a broken cable. He did not detect the problem because he did not calibrate the machine before conducting the test.
3) Level II certified individual calibrating the test instrument using the corner of a beam rather than the correct calibration standard. His excuse was the calibration standard is too heavy.
4) Level II certified individual did not bother to ask what acceptance criteria was applicable, i.e., static or cyclic.
5) Level II certified individual did not use the correct angle for shear wave test. He didn't have a copy of the welding code with him and he didn't have a written procedure.
6) Level II certified individual did not check for laminations before conducting shear wave test. He didn't think that it mattered.
7) Level II certified individual did not bother to recalibrate when changing from straight beam to angle beam testing. He felt recalibration was a waste of time.

UT is very reliable and very sensitive to the typical weld related discontinuities considered to be most detrimental. The catch is the testing must be conducted by properly motivated, trained, and disciplined individuals. In each of the case noted above the technicians were not tested as recommended by SNT-TC-1A by the laboratory that sent them to the job site. The laboratory's main concern was whether the technician owned a UT machine. Actions by a few end up giving all the good technicians a bad name.

The secret is to request the documents listed above. A laboratory that at least has the correct documentation understands what is required. The customer also needs to know what is required and needs to provide the NDT contractor with the correct information.

Best regards - Al

 

[demsha]

Thanks for all of you.

 

[Ron]

The defects found after HDG were there before the HDG...just not found by the NDT. Use different NDT person

 

[Goahead]

Depending on their size and orientation, slag inclusions, porosity and lack of fusion should be detectable also by radiographic inspection. Maybe it would be worth trying as an additional precaution.

http://www.welding-advisers.com/